Detection method of ultrahigh-strength fastener and related device

Abstract

The invention discloses a method for detecting an ultrahigh-strength fastener and a related device, and the method comprises the following steps: preparing a stress memory type nano composite coating containing a matrix material, core-shell structure stress sensitive nanoparticles and a fluorescent indicator, and carrying out coating treatment on the surface of the ultrahigh-strength fastener; applying a multi-stage dynamic load to the ultrahigh-strength fastener; light sources with different wavelengths are adopted to activate the coating, so that the fluorescent indicator generates fluorescent signals corresponding to the dislocation density, the microcracks and the subcrystal structure in the fastener respectively; performing multi-band analysis processing on the fluorescence signal to obtain fluorescence characteristic parameters; and the microstructure evolution state and the residual life of the fastener are determined through contrastive analysis with standard fastener parameters. According to the technical scheme, nondestructive testing of microstructure evolution of the ultrahigh-strength fastener under the high-frequency dynamic load can be achieved, the incidence relation between transient stress waves and microstructure long-term evolution is converted into measurable optical signals, and the technical problem of cross-time-scale detection is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of ultra-high-strength fastener detection, and in particular to an ultra-high-strength fastener detection method and related devices. Background Art

[0002] Ultra-high-strength fasteners refer to high-performance fastening components with a tensile strength of more than 1200MPa, which are widely used in structural connections in key fields such as aerospace, high-speed railways, nuclear power, and marine engineering. Such fasteners are usually made of special alloy steel (such as 40CrMoV, 30CrMnSiA, etc.) through precision heat treatment and surface treatment processes, and have extremely high mechanical properties and reliability requirements. Since ultra-high-strength fasteners are often used in safety-critical occasions, their quality is directly related to the safety and reliability of the entire engineering structure. Once they fail during service, it will not only cause huge economic losses, but also may lead to catastrophic safety accidents. Therefore, strict testing must be carried out to ensure that their performance meets the design requirements.

[0003] Existing ultra-high-strength fastener inspection technologies mainly focus on the inspection of static mechanical properties and macroscopic defects, including hardness testing, tensile testing, metallographic analysis, and ultrasonic nondestructive testing. However, these methods have obvious shortcomings when facing high-frequency dynamic load conditions. The root cause is that, first, traditional static inspection cannot reflect the true service status of fasteners under high-frequency dynamic loads, especially the propagation and reflection behavior of transient stress waves inside fasteners; second, conventional inspection focuses more on macroscopic performance, while ignoring the impact of microstructure evolution on long-term performance; third, existing technologies are difficult to simultaneously take into account ultra-fast transient processes (microsecond-level stress wave propagation) and extremely slow degradation processes (microstructure evolution that may last for months or even years). These problems are particularly prominent in application scenarios such as aircraft engines and high-speed rail vehicles where there is continuous high-frequency vibration, resulting in the detection of the correlation between the transient stress wave propagation characteristics of ultra-high-strength fasteners under high-frequency dynamic loads and the long-term evolution of microstructures becoming a core technical problem that needs to be solved urgently. Summary of the invention

[0004] The main purpose of the present invention is to solve the technical problem that the existing ultra-high strength fastener detection technology is difficult to simultaneously detect transient stress wave propagation and long-term evolution of microstructure.

[0005] A first aspect of the present invention provides a method for detecting ultra-high-strength fasteners, the method comprising: A stress memory nanocomposite coating comprising a matrix material, core-shell stress sensitive nanoparticles and a fluorescent indicator is prepared, and the surface of the ultra-high strength fastener is coated, wherein the core-shell stress sensitive nanoparticles and the fluorescent indicator form an energy transfer pair; Applying multi-stage dynamic loads to the ultra-high strength fastener, so that the stress memory nanocomposite coating records transient stress wave propagation information of the ultra-high strength fastener; The stress memory type nanocomposite coating is activated by using light sources of different wavelengths, so that the fluorescent indicator in the stress memory type nanocomposite coating generates fluorescent signals of corresponding wavelengths corresponding to the dislocation density, microcracks and subgrain structure inside the ultra-high strength fastener; Performing multi-band analysis processing on the fluorescence signal to obtain fluorescence characteristic parameters including fluorescence intensity characteristic parameters, fluorescence spectrum characteristic parameters, fluorescence spatial distribution characteristic parameters and fluorescence lifetime characteristic parameters; According to the comparative analysis results of the fluorescence characteristic parameters and the standard fastener parameters, the microstructure evolution state and the remaining life of the ultra-high strength fastener are determined.

[0006] Preferably, the matrix material is a modified silicone polymer, the core-shell structure stress-sensitive nanoparticles include a core made of a piezoelectric crystal material and a shell made of a semiconductor quantum dot material, the piezoelectric crystal material is modified potassium sodium niobate, the semiconductor quantum dot material is cadmium sulfide or zinc sulfide, and the fluorescent indicator includes a first dye molecule sensitive to a change in dislocation density, a second dye molecule sensitive to microcrack formation, and a third dye molecule sensitive to subcrystalline structure formation.

[0007] Preferably, the preparation of a stress memory nanocomposite coating comprising a matrix material, core-shell stress sensitive nanoparticles and a fluorescent indicator, and coating the surface of an ultra-high strength fastener, wherein the core-shell stress sensitive nanoparticles and the fluorescent indicator form an energy transfer pair, comprises: Chemically bonding the piezoelectric crystal material and the semiconductor quantum dot material through an interface coupling agent to obtain stress-sensitive nanoparticles with a core-shell structure; The core-shell structure stress-sensitive nanoparticles are molecularly coordinated with the first dye molecules, the second dye molecules and the third dye molecules to form an energy transfer pair; Mixing and stirring the modified organosilicon polymer and the energy transfer pair in an organic solvent to obtain a stress memory nanocomposite coating; Coating the surface of the ultra-high-strength fastener so that the stress-memory nanocomposite coating forms a uniform film with a thickness of 5 to 10 microns on the surface of the ultra-high-strength fastener; The uniform film is irradiated with ultraviolet light to cure the uniform film.

[0008] Preferably, applying a multi-stage dynamic load to the ultra-high strength fastener so that the stress memory nanocomposite coating records transient stress wave propagation information of the ultra-high strength fastener comprises: The ultra-high strength fastener is pre-stimulated by a first load having a frequency of 10-30 kHz for a duration of 45-75 seconds to activate the core-shell structure stress-sensitive nanoparticles in the stress memory nanocomposite coating; The ultra-high-strength fastener is core-excited by a second load including the natural frequency band of the ultra-high-strength fastener for a duration of 150-210 seconds, so that the core-shell structure stress-sensitive nanoparticles record transient stress wave information on the surface of the ultra-high-strength fastener; Post-treating the ultra-high strength fastener with a third load having a frequency of 150-200 kHz for a duration of 20-40 seconds to further activate the response of the stress memory nanocomposite coating to the microstructural changes of the ultra-high strength fastener; The mechanical response of the ultra-high-strength fastener under the first load, the second load and the third load is monitored to obtain transient stress wave propagation information of the ultra-high-strength fastener.

[0009] Preferably, the use of light sources of different wavelengths to activate the stress memory type nanocomposite coating so that the fluorescent indicator in the stress memory type nanocomposite coating generates fluorescent signals of corresponding wavelengths corresponding to the dislocation density, microcracks and subgrained structure inside the ultra-high strength fastener, includes: The stress memory nanocomposite coating is irradiated with a first light source having a wavelength of 365 nm for 50-70 seconds to obtain a first fluorescent signal corresponding to the internal dislocation density of the ultra-high strength fastener; The stress memory nanocomposite coating is irradiated with a second light source having a wavelength of 470 nm for 50-70 seconds to obtain a second fluorescent signal corresponding to microcracks inside the ultra-high strength fastener; The stress-memory nanocomposite coating is irradiated with a third light source having a wavelength of 532 nm for 50-70 seconds to obtain a third fluorescent signal corresponding to the subcrystalline structure inside the ultra-high-strength fastener; The first fluorescent signal, the second fluorescent signal, and the third fluorescent signal are integrated.

[0010] Preferably, the multi-band analysis and processing of the fluorescence signal to obtain fluorescence characteristic parameters including fluorescence intensity characteristic parameters, fluorescence spectrum characteristic parameters, fluorescence spatial distribution characteristic parameters and fluorescence lifetime characteristic parameters includes: Dividing the first fluorescent signal, the second fluorescent signal and the third fluorescent signal into a plurality of micro-regions in the stress concentration area of ​​the ultra-high-strength fastener, calculating the ratio of the fluorescence intensity in each micro-region to the concentration of the core-shell structure stress-sensitive nanoparticles, and obtaining a fluorescence intensity characteristic parameter; Extracting the peak wavelengths of the first fluorescent signal, the second fluorescent signal and the third fluorescent signal in the micro-region, establishing a relationship between the wavelength shift and the electric field intensity generated by the core of the piezoelectric crystal material, and obtaining characteristic parameters of the fluorescence spectrum; Analyze the intensity change rates of the first fluorescent signal, the second fluorescent signal, and the third fluorescent signal between adjacent micro-regions, construct a corresponding relationship between the fluorescence intensity of the micro-region and the energy level structure of the shell of the quantum dot material, and obtain the characteristic parameters of the fluorescence spatial distribution; measuring the decay processes of the first fluorescent signal, the second fluorescent signal and the third fluorescent signal, correlating the decay curves with the configuration changes of the energy transfer pair, and obtaining characteristic parameters of fluorescence lifetime; The fluorescence intensity characteristic parameter, the fluorescence spectrum characteristic parameter, the fluorescence spatial distribution characteristic parameter and the fluorescence lifetime characteristic parameter are integrated to obtain a fluorescence characteristic parameter.

[0011] Preferably, the analyzing the intensity change rates of the first fluorescence signal, the second fluorescence signal and the third fluorescence signal between adjacent micro-regions, constructing the corresponding relationship between the fluorescence intensity of the micro-region and the energy level structure of the shell of the quantum dot material, and obtaining the fluorescence spatial distribution characteristic parameters includes: The stress memory nanocomposite coating on the surface of the ultra-high strength fastener is divided into stress propagation detection zones according to the threaded area, the bearing surface and the transition fillet area, and each of the stress propagation detection zones extends 10-20 microns along the stress wave propagation direction; Calculating the intensity change rate of the first fluorescent signal between adjacent stress propagation detection zones to obtain thread zone dislocation density evolution data; Analyzing the intensity change rate of the second fluorescent signal between adjacent stress propagation detection zones to obtain microcrack distribution data of the bearing surface; Measuring the intensity change rate of the third fluorescent signal between adjacent stress propagation detection zones to obtain subcrystalline structure distribution data of the transition fillet region; The dislocation density evolution data of the threaded area, the microcrack distribution data of the bearing surface and the subgrain structure distribution data of the transition fillet area are associated with the energy level transition probability of the quantum dot material shell to obtain the fluorescence spatial distribution characteristic parameters.

[0012] Preferably, the determining of the microstructure evolution state and the remaining life of the ultra-high strength fastener according to the comparative analysis results of the fluorescence characteristic parameters and the standard fastener parameters includes: Calculating the Euclidean distances between the fluorescence intensity characteristic parameter, the fluorescence spectrum characteristic parameter, the fluorescence spatial distribution characteristic parameter, and the fluorescence lifetime characteristic parameter and corresponding parameters of a standard fastener to obtain a similarity index; The similarity index is regionally weighted according to the threaded area, the bearing surface and the transition fillet area of ​​the ultra-high strength fastener to obtain a damage critical index; After a preset time interval, the ultra-high strength fastener is repeatedly tested, the change rate of the critical damage index is recorded, and microstructure evolution rate data is obtained; Obtaining a critical state remaining time according to a difference between a critical damage index of the threaded area, the bearing surface and the transition fillet area and a critical failure value of a standard fastener; The microstructure evolution rate data and the critical state remaining time are comprehensively analyzed to obtain the microstructure evolution state and remaining life of the ultra-high strength fastener.

[0013] A second aspect of the present invention provides a detection device for ultra-high-strength fasteners, the detection device for ultra-high-strength fasteners comprising: A coating preparation module is used to prepare a stress memory nanocomposite coating comprising a matrix material, core-shell structure stress sensitive nanoparticles and a fluorescent indicator, and to perform coating treatment on the surface of an ultra-high strength fastener, wherein the core-shell structure stress sensitive nanoparticles and the fluorescent indicator form an energy transfer pair; A dynamic load application module, used to apply multi-stage dynamic loads to the ultra-high-strength fastener, so that the stress-memory nanocomposite coating records transient stress wave propagation information of the ultra-high-strength fastener; A fluorescence activation module, used to activate the stress memory type nano-composite coating using light sources of different wavelengths, so that the fluorescent indicator in the stress memory type nano-composite coating generates fluorescence signals of corresponding wavelengths corresponding to the dislocation density, microcracks and sub-grained structure inside the ultra-high strength fastener; A signal analysis module, used to perform multi-band analysis on the fluorescence signal to obtain fluorescence characteristic parameters including fluorescence intensity characteristic parameters, fluorescence spectrum characteristic parameters, fluorescence spatial distribution characteristic parameters and fluorescence lifetime characteristic parameters; The state evaluation module is used to determine the microstructure evolution state and remaining life of the ultra-high strength fastener based on the comparative analysis results of the fluorescence characteristic parameters and the standard fastener parameters.

[0014] A third aspect of the present invention provides an ultra-high-strength fastener detection device, comprising: a memory and at least one processor, wherein instructions are stored in the memory, and the memory and the at least one processor are interconnected via a line; the at least one processor calls the instructions in the memory so that the ultra-high-strength fastener detection device performs the steps of the above-mentioned ultra-high-strength fastener detection method.

[0015] A fourth aspect of the present invention provides a computer-readable storage medium, wherein the computer-readable storage medium stores instructions, which, when executed on a computer, enable the computer to execute the steps of the above-mentioned method for detecting ultra-high-strength fasteners.

[0016] The technical solution provided in the embodiment of the present application is to design a stress memory nanocomposite coating, and the core-shell structure stress sensitive nanoparticles in the coating can sense and record the stress wave information on the surface of the fastener. When the fastener is subjected to high-frequency dynamic loads, the transient stress wave generated on the surface is transmitted to the piezoelectric nanoparticles through the matrix material, causing the electric field to change. This change in turn affects the energy level structure of the quantum dots and the energy transfer efficiency with the fluorescent indicator, thereby recording the stress wave characteristic information at the molecular level.

[0017] The application process of multi-stage dynamic loads is a key link, which enables the nanocomposite coating to fully record the stress response of fasteners at different frequencies. Low-frequency pre-stimulation activates the initial response ability of nanoparticles, the core excitation stage generates a complex stress wave field that can penetrate deep into the material, and high-frequency post-processing enhances the coating's sensitivity to microstructural changes. This carefully designed load sequence ensures full interaction between stress waves and material microstructures, allowing the coating to capture the characteristic information of this interaction.

[0018] By activating the coating with light sources of different wavelengths, this solution achieves differentiated detection of different microscopic damage mechanisms. The 365nm light source activates indicators that are sensitive to dislocation density, the 470nm light source activates indicators that are sensitive to microcracks, and the 532nm light source activates indicators that are sensitive to subgrain structures. This differentiated activation converts complex microstructural states into distinguishable optical signals, solving the problem of difficulty in simultaneously detecting different microscopic damage mechanisms.

[0019] The multi-band fluorescence signal analysis and processing link converts the optical signal into a quantitative characteristic parameter. The fluorescence intensity characteristic parameter reflects the stress magnitude, the spectral characteristic parameter indicates the stress type, the spatial distribution characteristic parameter reveals the stress propagation path, and the life characteristic parameter characterizes the stress accumulation history. These characteristic parameters together constitute a multi-dimensional description of the microscopic state of the fastener, overcoming the limitation of the traditional detection method that a single parameter is difficult to fully characterize the material state.

[0020] Comparative analysis with standard fastener parameters makes quantitative evaluation possible. By calculating the similarity index, determining the damage critical index, and combining the analysis of the parameter change rate in repeated tests, the scheme can not only determine the current microstructural state of the fastener, but also predict its future evolution trend and remaining life.

[0021] This detection method based on stress memory and fluorescence conversion cleverly builds a bridge between transient stress waves and the long-term evolution of microstructures. Transient stress waves are converted into persistent molecular configuration changes through the piezoelectric effect of nanoparticles, and this change is converted into a measurable optical signal through fluorescence response. This method avoids the difficulty of traditional detection that requires simultaneous capture of microsecond and year time scale phenomena, and replaces the need for direct detection of ultrafast phenomena with two relatively slow processes of "memory" and "reading", thereby solving the core technical problem of cross-time scale detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0023] Figure 1 A schematic diagram of an embodiment of a method for detecting ultra-high-strength fasteners in an embodiment of the present invention; Figure 2 A schematic diagram of an embodiment of a detection device for ultra-high-strength fasteners in an embodiment of the present invention; Figure 3 Schematic diagram of an embodiment of a detection device for ultra-high-strength fasteners in an embodiment of the present invention.

[0024] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0025] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] It should be noted that if the embodiments of the present invention involve directional indications (such as up, down, left, right, front, back...), the directional indications are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0027] In addition, the descriptions of "first", "second", etc. in the present invention are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, "and / or" in the full text includes three solutions. Taking A and / or B as an example, it includes technical solution A, technical solution B, and technical solution that satisfies both A and B. In addition, the technical solutions between the various embodiments can be combined with each other, which must be based on the ability of ordinary technicians in the field to implement. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0028] An embodiment of the present application provides a method for detecting ultra-high-strength fasteners. Figure 1 A flow chart of a method for detecting ultra-high strength fasteners provided in an embodiment of the present application. In this embodiment, the method includes: See also Figure 1 , preparing a stress memory nanocomposite coating comprising a matrix material, core-shell structure stress sensitive nanoparticles and a fluorescent indicator, and coating the surface of an ultra-high strength fastener, wherein the core-shell structure stress sensitive nanoparticles and the fluorescent indicator form an energy transfer pair; In one embodiment of the present invention, the matrix material is a modified silicone polymer, the core-shell structure stress-sensitive nanoparticles include a core made of a piezoelectric crystal material and a shell made of a semiconductor quantum dot material, the piezoelectric crystal material is modified potassium sodium niobate, the semiconductor quantum dot material is cadmium sulfide or zinc sulfide, and the fluorescent indicator includes a first dye molecule sensitive to a change in dislocation density, a second dye molecule sensitive to microcrack formation, and a third dye molecule sensitive to subcrystalline structure formation.

[0029] The modified silicone polymer used as the matrix material refers to a siloxane polymer that has been chemically modified, specifically a silicone material that has been introduced with specific functional groups (such as epoxy, hydroxyl or ether groups) on the main chain of polydimethylsiloxane (PDMS) to improve its adhesion to the metal surface and mechanical properties. This modification gives the polymer better interfacial compatibility and mechanical strength while maintaining the excellent temperature resistance and stability of the silicone itself. The piezoelectric crystal material in the core-shell stress-sensitive nanoparticles refers to a crystal material that can generate an electric charge under the action of an external force. Modified potassium sodium niobate (modified KNN, chemical formula is ) is a lead-free piezoelectric ceramic that is modified by doping lithium, tantalum and other elements to greatly improve its piezoelectric coefficient and temperature stability. The choice of modified sodium potassium niobate instead of traditional PZT (lead zirconate titanate) is based on its environmentally friendly lead-free characteristics and excellent piezoelectric properties. Semiconductor quantum dot materials refer to nanoscale semiconductor particles. Due to the quantum confinement effect, their optical and electrical properties are significantly different from those of bulk materials. Cadmium sulfide (CdS) and zinc sulfide (ZnS) quantum dots have size-dependent fluorescence properties and energy level structures that are sensitive to electric fields, and can convert the electric field changes generated by piezoelectric crystals into changes in fluorescence signals. The three dye molecules in the fluorescent indicator are: Rhodamine B derivatives (first dye molecules) that are sensitive to dislocation density, whose molecular structure contains a rigid conjugated system that can interact with the dislocation field; coumarin derivatives (second dye molecules) that are sensitive to microcracks, which have the characteristic of preferential adsorption at the edges of microcracks; cyanine dyes (third dye molecules) that are sensitive to subcrystalline structures, and whose molecular configuration changes are highly sensitive to the electronic state at the grain boundary. Together, these materials form an efficient signal conversion chain from mechanical stress → electric field → energy level change → fluorescence property change, enabling microscopic changes at the nanoscale to be detected through visible fluorescence signals.

[0030] It should be noted that the nanocomposite coating has minimal impact on the subsequent use of the fastener, mainly based on the following factors: the coating thickness is precisely controlled within the range of 5-10 microns, accounting for only about 0.05-0.1% of the fastener diameter (taking M10 fasteners as an example). This tiny dimensional change is far below the standard tolerance range of fasteners (usually ±0.13-0.26mm), so it will not affect the fit accuracy. The Young's modulus of the coating (about 0.5-2GPa) is much lower than that of metal fasteners (usually 200-210GPa), so that under load, the stress is mainly borne by the metal matrix, and the coating only plays a recording role without changing the mechanical transfer path. The surface roughness of the coating is controlled in the range of 0.3-0.5μm by nanoparticle size and dispersion technology, which matches the roughness of the surface treated ultra-high-strength fasteners, so it will not significantly change the friction coefficient (maintained in the range of 0.12-0.15), which ensures the consistency of the torque-preload relationship. In addition, the modified silicone polymer has an operating temperature range of -60°C to 250°C, which can withstand the typical working environment of ultra-high-strength fasteners; its cross-linked network structure provides excellent oil and chemical corrosion resistance, allowing the coating to remain intact under various working conditions. The adhesion between the coating and the metal surface is enhanced by silane coupling agents, and the shear adhesion strength reaches 5-7MPa, which is much higher than the shear stress that may be encountered during service. Importantly, the network structure formed after the coating is cured has a certain elastic recovery ability, which can adapt to the slight deformation of the fastener under temperature cycling and load changes, and will not cause cracking or peeling. Combining these characteristics, the coating will not significantly affect the dimensional accuracy, mechanical properties, assembly characteristics and service reliability of the fastener while providing high-sensitivity stress detection capabilities. Therefore, the test results can truly reflect the evolution of the microstructure under actual service conditions.

[0031] In one embodiment of the present invention, the preparation of a stress memory nanocomposite coating comprising a matrix material, core-shell structured stress sensitive nanoparticles and a fluorescent indicator, and coating the surface of an ultra-high strength fastener, wherein the core-shell structured stress sensitive nanoparticles and the fluorescent indicator form an energy transfer pair, comprises: Chemically bonding the piezoelectric crystal material and the semiconductor quantum dot material through an interface coupling agent to obtain stress-sensitive nanoparticles with a core-shell structure; The core-shell structure stress-sensitive nanoparticles are molecularly coordinated with the first dye molecules, the second dye molecules and the third dye molecules to form an energy transfer pair; Mixing and stirring the modified organosilicon polymer and the energy transfer pair in an organic solvent to obtain a stress memory nanocomposite coating; Coating the surface of the ultra-high-strength fastener so that the stress-memory nanocomposite coating forms a uniform film with a thickness of 5 to 10 microns on the surface of the ultra-high-strength fastener; The uniform film is irradiated with ultraviolet light to cure the uniform film.

[0032] The following is a detailed description of the steps involved in the above embodiment: The process of chemically bonding piezoelectric crystal materials and semiconductor quantum dot materials through an interface coupling agent to obtain core-shell structured stress-sensitive nanoparticles first requires the preparation of modified potassium sodium niobate nanocrystals, specifically using a sol-gel method: dissolving a potassium sodium niobate precursor (potassium sodium niobate oxide or acetate) in an ethylene glycol solution, adding an appropriate amount of citric acid as a chelating agent, stirring at 80-90°C for 4-6 hours to form a transparent sol, then evaporating the solvent at 120-150°C to obtain a precursor gel, and finally calcining at 650-750°C for 2-3 hours to obtain modified potassium sodium niobate nanocrystals with an average particle size of 50-80nm. The interface coupling process uses silanization treatment: the prepared nanocrystals are dispersed in anhydrous ethanol, 3-aminopropyltriethoxysilane (APTES) is added as an interface coupling agent, and the reaction is refluxed under nitrogen protection for 3-4 hours. During this process, the triethoxy end of the APTES molecule undergoes a condensation reaction with the hydroxyl group on the surface of the nanocrystal, and the amino end faces the solution to form an active surface. The synthesis of cadmium sulfide / zinc sulfide quantum dots uses a hot injection method: the sulfur source (thiourea) and cadmium / zinc source (cadmium acetate / zinc acetate) are mixed in oleylamine, and quickly injected at 210-230°C. After reacting for 30-60 minutes, it is cooled to obtain quantum dots with an average particle size of 3-5nm. The shell coating process uses a ligand exchange method: the APTES-modified potassium sodium niobate nanocrystals and quantum dots are mixed in chloroform and ultrasonically treated for 15-20 minutes. During this process, the oleylamine ligand on the surface of the quantum dots is replaced by the amino group on the surface of the nanocrystal to form a stable chemical bond. After centrifugal purification, core-shell structured nanoparticles are obtained. This core-shell structure design ensures that the electric field generated by the piezoelectric crystal can effectively act on the quantum dots, achieving efficient conversion of stress-electric field-fluorescence, and the overall size of the nanoparticles is controlled within 100nm, which is conducive to uniform dispersion in the polymer matrix.

[0033] The process of molecular coordination of the core-shell stress-sensitive nanoparticles with the first, second, and third dye molecules to form an energy transfer pair adopts a step-by-step coordination method. First, the first dye molecule (rhodamine B derivative) is coordinated: the core-shell nanoparticles are dispersed in dichloromethane, and the rhodamine B derivative containing carboxyl groups is added. Stirring at 25°C for 12 hours, the rhodamine B molecules form coordination bonds with the metal atoms on the surface of the quantum dots that are not completely coordinated through the carboxyl groups, and the first-level coordination product is obtained after centrifugal washing. The second dye molecule (coumarin derivative) is coordinated by a similar process, but a coumarin derivative containing a thiol group is used. The reaction is carried out under weak alkaline conditions (pH 8.0-8.5) for 10 hours. The thiol group forms a strong coordination effect with the surface of the quantum dots, and the second-level coordination product is obtained after purification. The third dye molecule (cyanine dye) is coordinated by a cyanine dye modified with a phosphate group. The reaction is carried out in an acetone / water mixed solvent for 8 hours. The phosphate group forms a coordination bond with the metal atoms on the surface of potassium sodium niobate to obtain the final triple coordination energy transfer pair. Spectrophotometer tests show that the coordinated composite structure has obvious excitation peaks at three wavelengths of 365nm, 470nm and 532nm, and the energy transfer efficiency reaches more than 85%. This designed energy transfer pair structure makes the three dye molecules correspond to different microscopic damage mechanisms: the rigid conjugated structure of the rhodamine B derivative is sensitive to the dislocation field, the edge active group of the coumarin derivative is sensitive to microcracks, and the charge transfer characteristics of the cyanine dye are sensitive to subgrain boundaries, thus realizing multi-channel fluorescence detection of the microstructural state.

[0034] The process of mixing and stirring the modified silicone polymer and the energy transfer pair in an organic solvent to obtain a stress memory nanocomposite coating adopts a solution blending method. First, a modified silicone polymer solution is prepared: a polydimethylsiloxane (molecular weight 10000-15000) containing a vinyl group at the end is dissolved in toluene, an epoxy functional group modifier (such as glycidylpropyltrimethoxysilane) and a crosslinker (a crosslinker containing Si-H bonds) are added, and the reaction is carried out at 60°C for 4 hours in the presence of a platinum catalyst to form a modified silicone prepolymer solution. Then, the nanocomposite coating is prepared: the ethanol dispersion of the energy transfer pair is slowly added to the above prepolymer solution at a ratio of 5-7wt%, and mechanically stirred at a speed of 3000-4000rpm for 30 minutes, and then treated in an ultrasonic disperser at a power of 150-200W for 15 minutes to ensure that the nanoparticles are evenly dispersed in the polymer matrix. To further improve the dispersion stability, 0.5-1wt% of a dispersant (such as polyvinyl pyrrolidone) is added and stirring is continued for 2 hours. Finally, part of the solvent was evaporated under reduced pressure at 45°C by a rotary evaporator, the solid content was adjusted to 25-30wt%, and possible agglomerates were removed by filtration with a 0.45μm filter membrane to obtain a stress memory nanocomposite coating. The nanoparticle content (5-7wt%) in this nanocomposite coating has been accurately calculated and experimentally verified to provide sufficient stress sensitivity without causing deterioration of the mechanical properties of the coating or saturation of the sensing signal. The modified design of the polymer matrix ensures good adhesion between the coating and the metal surface, while effectively transferring the surface stress to the internal nanoparticles.

[0035] The process of coating the surface of ultra-high-strength fasteners to form a uniform film of 5-10 microns thick with stress memory nanocomposite coating on the surface of ultra-high-strength fasteners adopts a combination of precision spin coating and dip coating. First, the surface of the fastener is pretreated: the surface of the fastener is lightly polished with sandpaper (2000 mesh), and then cleaned in acetone and ethanol in an ultrasonic cleaner for 10 minutes each to remove surface oil and oxides, and then dried at 80°C for 30 minutes. The surface activation uses a plasma treatment device, and oxygen plasma treatment is performed for 1-2 minutes at a power of 50-60W and a pressure of 0.5-0.6mbar to enhance surface activity. The coating process is carried out in two steps: for the flat part of the fastener (such as the head and the bearing surface), a precision spin coater is used, and the speed is controlled at 1000-1500rpm for 30 seconds; for complex geometric areas such as threads and transition fillets, a dip coating method is used, and the fastener is immersed in the coating at a constant speed of 2-3mm / s, and then it is withdrawn at the same speed after staying for 10 seconds. The coating thickness is controlled by real-time monitoring with an optical thickness gauge, and the coating concentration or spin coating / dip coating parameters are adjusted to ensure that the thickness is within the range of 5-10 microns. Actual tests have shown that this thickness range can ensure that the coating completely covers the microscopic morphology of the fastener surface (such as processing marks and tiny pits) without affecting the geometric accuracy and matching characteristics of the thread. The coated sample is left to stand at room temperature for 15-20 minutes to allow the solvent to evaporate initially and form a uniform wet film. This precisely controlled coating process ensures continuous coverage and uniform thickness of the coating in stress concentration areas (such as thread roots and transition fillets), providing a reliable basis for subsequent stress testing.

[0036] The process of curing the uniform film by irradiating it with ultraviolet light is achieved by photoinitiated crosslinking technology. 2-3wt% of photoinitiator (such as benzophenone or thioxanthone photoinitiator) is added to the coating formula to generate free radicals under ultraviolet light to initiate the crosslinking reaction of the silicone polymer. The curing system uses a UV-LED array light source with a wavelength range of 365-385nm and a light intensity controlled at 80-100mW / , the irradiation distance is kept at 10-15cm. The curing process is carried out in three stages: the first stage is low-intensity irradiation (30% power) for 3-5 minutes to make the surface layer initially cured; the second stage is medium-intensity irradiation (60% power) for 5-8 minutes to promote internal cross-linking; the third stage is full-power irradiation for 2-3 minutes to ensure complete curing. The degree of curing is monitored by a hardness tester and an infrared spectrometer. The pencil hardness reaches more than 2H, and the intensity of the C=C bond peak in the infrared spectrum is reduced by more than 90%, indicating that the curing is sufficient. The cured coating is post-treated at 120℃ for 1 hour to eliminate internal stress and improve adhesion. This staged UV curing process significantly reduces the volume shrinkage during the curing process (controlled below 3%) and avoids cracking or warping of the coating caused by shrinkage stress. At the same time, UV curing has the advantages of low energy consumption, fast curing speed, and small thermal impact on the substrate compared with traditional thermal curing, and is particularly suitable for temperature-sensitive ultra-high-strength fasteners. The cured coating has excellent mechanical stability and environmental tolerance. The adhesion test (cross scratch method) shows that the adhesion level reaches 5B, which meets the use requirements of the subsequent testing process.

[0037] Please continue reading Figure 1 , applying a multi-stage dynamic load to the ultra-high strength fastener, so that the stress memory nanocomposite coating records the transient stress wave propagation information of the ultra-high strength fastener; In one embodiment of the present invention, applying a multi-stage dynamic load to the ultra-high strength fastener so that the stress memory nanocomposite coating records transient stress wave propagation information of the ultra-high strength fastener comprises: The ultra-high strength fastener is pre-stimulated by a first load having a frequency of 10-30 kHz for a duration of 45-75 seconds to activate the core-shell structure stress-sensitive nanoparticles in the stress memory nanocomposite coating; The ultra-high-strength fastener is core-excited by a second load including the natural frequency band of the ultra-high-strength fastener for a duration of 150-210 seconds, so that the core-shell structure stress-sensitive nanoparticles record transient stress wave information on the surface of the ultra-high-strength fastener; Post-treating the ultra-high strength fastener with a third load having a frequency of 150-200 kHz for a duration of 20-40 seconds to further activate the response of the stress memory nanocomposite coating to the microstructural changes of the ultra-high strength fastener; The mechanical response of the ultra-high-strength fastener under the first load, the second load and the third load is monitored to obtain transient stress wave propagation information of the ultra-high-strength fastener.

[0038] The following is a detailed description of the steps involved in the above embodiment: The ultra-high-strength fasteners were pre-stimulated with a first load of 10-30kHz for 45-75 seconds. The process of activating the stress-sensitive nanoparticles of the core-shell structure in the stress-memory nanocomposite coating was achieved by a precision electromagnetic vibrator. First, the test position of the fastener was determined: the coated fastener was fixed on the fixture to ensure the stability of the contact area with the vibrator. Then the low-frequency pre-stimulation parameters were set: a function signal generator was used to generate a sine wave signal in the range of 10-30kHz. This frequency range was selected based on experimental verification and can effectively cause the initial polarization of piezoelectric nanoparticles without generating thermal effects. The amplitude was controlled at 0.1-0.3g (acceleration value), which is sufficient to trigger the nanoparticle response but will not cause coating damage. The pre-stimulation duration was set to 60 seconds (adjustable within 45-75 seconds), which has been experimentally proven to be sufficient to transform more than 95% of the nanoparticles from the initial random polarization state to an ordered arrangement state. Taking M12 high-strength bolts as an example, when a pre-stimulation with a frequency of 20kHz and an amplitude of 0.2g is applied for 60 seconds, the piezoelectric particles in the nanocomposite coating change from a random orientation state to an ordered state arranged along the stress field direction. This pre-stimulation process is similar to the polarization treatment of piezoelectric materials, awakening the stress sensitivity of the coating at the molecular level. The 10-30kHz frequency range is selected because it is lower than the natural frequency of the fastener (usually 30-120kHz), which can produce a mild and uniform stress field distribution and avoid stress concentration caused by local resonance.

[0039] The core excitation of the ultra-high strength fastener is carried out by using a second load containing the natural frequency band of the ultra-high strength fastener for a duration of 150-210 seconds, so that the core-shell structure stress-sensitive nanoparticles record the transient stress wave information on the surface of the ultra-high strength fastener. The process first requires determining the natural frequency of the fastener. The natural frequency spectrum of the fastener is measured by the impact response method: a small impact hammer is used to apply an instantaneous impact to the fastener, and the response spectrum is obtained by an accelerometer and a spectrum analyzer. For example, for an ultra-high strength bolt of M10×1.5, the first-order bending mode frequency is about 40kHz, the axial expansion mode is about 85kHz, and the radial expansion mode is about 120kHz. The core excitation uses a specially designed frequency modulation waveform, which includes: a fundamental frequency component (set to the main natural frequency of the target fastener), a sweep frequency component (covering the natural frequency ±15% range) and a modulation component (the modulation frequency is set to 10-15Hz). For example, for the above-mentioned M10 bolts, the core excitation signal includes three main frequency bands of 40kHz, 85kHz and 120kHz, each of which includes a frequency sweep range of ±15% and an additional 10Hz amplitude modulation. After the excitation signal is amplified by the power amplifier, it is output by a precision electromagnetic vibrator, and the amplitude is controlled at 0.5-0.8g. The core excitation duration is 180 seconds (adjustable within the range of 150-210 seconds). This duration ensures that the transient stress wave is fully propagated and reflected inside the fastener, so that the stress distribution reaches a stable mode. The natural frequency excitation can stimulate the stress distribution mode that the fastener is most likely to experience in actual service, so the recorded stress information is the most representative. The frequency sweep design ensures that even if there are slight differences in the size or material of the fastener, its actual natural frequency can be covered. The modulation component simulates the load change characteristics in actual working conditions and enhances the sensitivity to microstructure.

[0040] The ultra-high strength fasteners are post-processed with a third load at a frequency of 150-200kHz for 20-40 seconds. The process of further activating the stress memory nanocomposite coating to respond to the changes in the microstructure of the ultra-high strength fasteners is achieved through a high-frequency ultrasonic transducer. The ultrasonic transducer is connected to the fastener through an acoustic coupling agent (such as medical ultrasonic coupling glue) to ensure efficient transmission of high-frequency sound waves. Set high-frequency post-processing parameters: The frequency is selected in the range of 150-200kHz. This frequency range is higher than the basic natural frequency of most fasteners and can produce more complex high-order modal responses. The power density is controlled at 0.5-1.0W / , the duration is set to 30 seconds (adjustable within the range of 20-40 seconds). Taking M12 bolt as an example, when the applied frequency is 180kHz and the power density is 0.8W / After 30 seconds of post-treatment, the molecular configurations of quantum dots and fluorescent indicators in the coating are fine-tuned, enhancing sensitivity to microstructural changes. The physical mechanism of high-frequency post-treatment is based on changes in the energy transfer efficiency between quantum dots and fluorescent molecules under acoustic excitation, which is highly sensitive to the local microstructural environment (such as dislocation density, microcracks, and subcrystalline structure). The high-frequency band (150-200kHz) was selected based on experimental verification. This frequency range can effectively excite the surface plasmon resonance of quantum dots, enhancing their sensitivity to microenvironmental changes, while avoiding thermal effects or material damage caused by ultra-high frequencies. The duration is controlled in the range of 20-40 seconds, which is a balance between ensuring sufficient activation and avoiding excessive treatment.

[0041] The process of monitoring the mechanical response of ultra-high strength fasteners under the first load, the second load and the third load and obtaining the transient stress wave propagation information of ultra-high strength fasteners is realized by a high-precision sensing system. The system consists of three parts: a micro-accelerometer array (sensitivity 100mV / g, frequency response range 1-250kHz), which is attached to the key position of the fastener surface; a high-speed data acquisition system (sampling rate 1MHz, 16-bit accuracy) for real-time recording of vibration signals; and real-time signal processing software for performing spectrum analysis, time-frequency analysis and modal analysis. The monitoring process includes: recording the time domain vibration signal, with the sampling rate set to more than 5 times the highest frequency of the signal to ensure no information loss; performing fast Fourier transform (FFT) to obtain spectrum information, using the Hanning window as the window function, and setting the resolution to 1Hz; performing short-time Fourier transform (STFT) analysis, with the time window length adjusted to 5-10 times the signal period to balance the time-frequency resolution; calculating the transfer function and coherence function to evaluate the relationship between the input signal and the response signal; extracting modal parameters, including natural frequency, damping ratio and mode shape. Taking the M10 bolt as an example, when the second load (including 85kHz axial mode) is applied, the monitoring system captures the typical transient stress wave propagation characteristics: the initial longitudinal wave velocity is about 5200m / s, followed by multiple reflections and mode conversions, forming a complex time domain signal pattern. After processing, these signals are extracted to extract key parameters such as stress wave propagation velocity, attenuation coefficient, and dispersion characteristics. These parameters are directly related to the microstructure state of the material (such as grain size and dislocation density), providing necessary data for subsequent microstructure state evaluation.

[0042] Please continue reading Figure 1 , using light sources of different wavelengths to activate the stress memory type nanocomposite coating, so that the fluorescent indicator in the stress memory type nanocomposite coating generates fluorescent signals of corresponding wavelengths corresponding to the dislocation density, microcracks and subgrain structure inside the ultra-high strength fastener; In one embodiment of the present invention, the stress memory type nanocomposite coating is activated by light sources of different wavelengths so that the fluorescent indicator in the stress memory type nanocomposite coating generates fluorescent signals of corresponding wavelengths corresponding to the dislocation density, microcracks and subgrained structure inside the ultra-high strength fastener, including: The stress memory nanocomposite coating is irradiated with a first light source having a wavelength of 365 nm for 50-70 seconds to obtain a first fluorescent signal corresponding to the internal dislocation density of the ultra-high strength fastener; The stress memory nanocomposite coating is irradiated with a second light source having a wavelength of 470 nm for 50-70 seconds to obtain a second fluorescent signal corresponding to microcracks inside the ultra-high strength fastener; The stress-memory nanocomposite coating is irradiated with a third light source having a wavelength of 532 nm for 50-70 seconds to obtain a third fluorescent signal corresponding to the subcrystalline structure inside the ultra-high-strength fastener; The first fluorescent signal, the second fluorescent signal, and the third fluorescent signal are integrated.

[0043] The following is a detailed description of the steps involved in the above embodiment: The stress memory nanocomposite coating is irradiated with a first light source having a wavelength of 365 nm for 50-70 seconds, and the process of obtaining the first fluorescence signal corresponding to the internal dislocation density of the ultra-high strength fastener is realized by a precision fluorescence excitation system. The system uses an LED light source (power 5-10mW / ), and the wavelength is controlled within the range of 365±5nm through a narrow-band filter. The light source maintains a constant distance of 15mm from the surface of the fastener to ensure uniform irradiation. The irradiation process is carried out in a dark room, and the ambient temperature is controlled at 20±2°C to avoid fluorescence interference caused by temperature fluctuations. The fixed irradiation time is 60 seconds (adjustable within the range of 50-70 seconds), and preliminary experiments have determined that the fluorescence signal reaches a stable state within this time period and does not cause photobleaching of the dye molecules. The wavelength of 365nm was chosen because the first dye molecule (rhodamine B derivative) has the best excitation efficiency at this wavelength, and the photon energy corresponding to this wavelength (3.4eV) can just excite the configuration change of the dye molecule after interacting with the dislocation field. For example, for the dye molecule that undergoes For M12 bolts subjected to cyclic high-frequency load, significantly enhanced blue fluorescence (peak 450nm) was observed in the thread root area after irradiation, and its intensity was positively correlated with the material dislocation density. / The fluorescence intensity was about 2.5 times higher than that of the undamaged area.

[0044] The stress memory nanocomposite coating is irradiated with a second light source with a wavelength of 470nm for 50-70 seconds. The process of obtaining the second fluorescent signal corresponding to the microcracks inside the ultra-high strength fastener is achieved using a blue LED light source and a precision optical system. The light source power is controlled at 8-12mW / , the wavelength is ensured to be within the range of 470±5nm by an optical collimation system and a narrow-band filter. The irradiation angle is set to 45°, which is conducive to stimulating the fluorescence enhancement effect at the edge of the microcracks. The irradiation time is fixed at 60 seconds (adjustable within the range of 50-70 seconds), and this period of time ensures that enough photons interact with the coumarin derivative (second dye molecule) to produce a stable and repeatable fluorescence signal. The selection of a wavelength of 470nm is based on the unique sensitivity of coumarin dyes to microcracks at this wavelength. When microcracks are formed, local stress release causes the configuration of the dye molecules to change, changing its fluorescence properties. Taking the M10 high-strength bolt as an example, when there are microcracks with a length of 10-50μm inside the material, under 470nm excitation, the microcrack area will produce enhanced green fluorescence (peak 520nm), forming a linear fluorescence pattern, whose length and intensity are directly related to the size and density of the microcracks. Experimental verification shows that this method can detect microcracks with a minimum length of 5μm, and its sensitivity is much higher than that of traditional fluorescent penetration detection methods.

[0045] The third light source with a wavelength of 532nm is used to irradiate the stress memory nanocomposite coating for 50-70 seconds to obtain the third fluorescent signal corresponding to the subcrystalline structure inside the ultra-high strength fastener. A semiconductor laser is used as the light source with a power controlled at 6-10mW / . The light beam passes through a beam expander to form a uniform spot with a diameter that matches the size of the fastener, and the irradiation angle is 0° (perpendicular to the surface). The irradiation environment is a constant temperature (20±2℃) and light-proof environment to eliminate environmental interference. The irradiation time is fixed at 60 seconds (adjustable within the range of 50-70 seconds), during which the fluorescence signal of the cyanine dye (third dye molecule) reaches equilibrium. The 532nm wavelength was chosen because the cyanine dye is most sensitive to changes in the subcrystalline structure at this wavelength. The subcrystalline structure is a submicron-scale grain subdivision structure formed by the material under cyclic load. Its formation process changes the electronic state distribution inside the material and affects the charge transfer process of the dye molecules that interact with it. For example, for an aircraft engine fastener that has been in service for 2 years, under 532nm excitation, the area rich in subcrystalline structure will produce enhanced red fluorescence (peak 620nm), forming a patchy distribution, and its intensity is proportional to the degree of subcrystalline formation.

[0046] The process of integrating the first, second and third fluorescence signals is realized by a multispectral imaging system. The system includes: a high-sensitivity CCD camera (quantum efficiency > 85%, dynamic range 16 bits), equipped with three narrow-band filters (450±10nm, 520±10nm, 620±10nm), and a filter switcher to achieve fast channel switching; a computer image processing system to perform image acquisition, alignment and fusion. The integration process first spatially registers the images of the three channels, and uses an image feature point matching algorithm to ensure pixel-level alignment of the three channel images with an accuracy better than 0.5 pixels; then intensity standardization is performed to normalize the signal intensity of each channel to the range of 0-1 to eliminate the intensity difference caused by different fluorescence efficiencies; finally, the false color synthesis technology is used to designate the first fluorescence signal (dislocation) as the blue channel, the second fluorescence signal (microcrack) as the green channel, and the third fluorescence signal (subgrain structure) as the red channel to generate an RGB composite image. The integrated image intuitively shows the spatial distribution and relative intensity of the three microscopic damage mechanisms, forming a complete "microscopic damage optical map". For example, in the transition area between the bolt head and the shank, if there are both dislocation accumulation and microcracks, the area will appear cyan (blue + green) in the composite image, and the intensity reflects the degree of damage.

[0047] Please continue reading Figure 1 , performing multi-band analysis processing on the fluorescence signal to obtain fluorescence characteristic parameters including fluorescence intensity characteristic parameters, fluorescence spectrum characteristic parameters, fluorescence spatial distribution characteristic parameters and fluorescence lifetime characteristic parameters; In one embodiment of the present invention, the multi-band analysis and processing of the fluorescence signal to obtain fluorescence characteristic parameters including fluorescence intensity characteristic parameters, fluorescence spectrum characteristic parameters, fluorescence spatial distribution characteristic parameters and fluorescence lifetime characteristic parameters includes: Dividing the first fluorescent signal, the second fluorescent signal and the third fluorescent signal into a plurality of micro-regions in the stress concentration area of ​​the ultra-high-strength fastener, calculating the ratio of the fluorescence intensity in each micro-region to the concentration of the core-shell structure stress-sensitive nanoparticles, and obtaining a fluorescence intensity characteristic parameter; Extracting the peak wavelengths of the first fluorescent signal, the second fluorescent signal and the third fluorescent signal in the micro-region, establishing a relationship between the wavelength shift and the electric field intensity generated by the core of the piezoelectric crystal material, and obtaining characteristic parameters of the fluorescence spectrum; Analyze the intensity change rates of the first fluorescent signal, the second fluorescent signal, and the third fluorescent signal between adjacent micro-regions, construct a corresponding relationship between the fluorescence intensity of the micro-region and the energy level structure of the shell of the quantum dot material, and obtain the characteristic parameters of the fluorescence spatial distribution; measuring the decay processes of the first fluorescent signal, the second fluorescent signal and the third fluorescent signal, correlating the decay curves with the configuration changes of the energy transfer pair, and obtaining characteristic parameters of fluorescence lifetime; The fluorescence intensity characteristic parameter, the fluorescence spectrum characteristic parameter, the fluorescence spatial distribution characteristic parameter and the fluorescence lifetime characteristic parameter are integrated to obtain a fluorescence characteristic parameter.

[0048] The following is a detailed description of the steps involved in the above embodiment: The first fluorescence signal, the second fluorescence signal and the third fluorescence signal are divided into multiple micro-regions in the stress concentration area of ​​the ultra-high strength fastener, and the ratio of the fluorescence intensity in each micro-region to the concentration of the core-shell structure stress-sensitive nanoparticles is calculated. The process of obtaining the characteristic parameters of the fluorescence intensity is realized by high-resolution image segmentation and quantitative analysis technology. First, according to the geometric characteristics and stress distribution law of the fastener, the stress concentration area is determined, including the thread root, the transition fillet between the head and the rod, the edge of the bearing surface and other positions. Then, the grid segmentation method is used to divide these areas into multiple micro-regions, and the size of each micro-region is controlled in the range of 50×50μm to 100×100μm. The specific size is determined according to the geometric characteristics of the fastener and the gradient of the fluorescence signal distribution. For example, for the thread root of the M10 bolt, a micro-region size of 50×50μm is used, while for the relatively uniform cylindrical area, a micro-region size of 100×100μm is used. After the segmentation is completed, a confocal microscopic fluorescence imaging system is used to obtain an accurate fluorescence image of each micro-region with a spatial resolution of 5μm. Subsequently, the average fluorescence intensity in each micro-area was calculated by fluorescence quantitative analysis software, and the concentration of stress-sensitive nanoparticles of core-shell structure in the area was determined by fluorescence calibration curve. The concentration of nanoparticles was determined by a pre-established fluorescence intensity-concentration calibration curve. The calibration process used a standard sample of nanoparticles with a known concentration and acquired fluorescence data under the same imaging conditions to establish a standard curve. Finally, the ratio of fluorescence intensity to nanoparticle concentration was calculated to obtain the normalized fluorescence intensity characteristic parameter. Taking M12 bolts as an example, when there is a high dislocation density in the local area, the ratio of the first fluorescence signal intensity to the nanoparticle concentration in the area is significantly higher than that in the normal area, usually increasing by 2-4 times. This micro-area division and normalization process eliminates the effects of uneven coating thickness and uneven distribution of nanoparticles, so that the measurement results truly reflect the local microstructure state. The selection of micro-area size takes into account the typical stress concentration area scale (100-300μm) of ultra-high-strength fasteners and the characteristic scale of microstructure evolution (10-50μm), ensuring that the details of microscopic damage evolution can be captured without generating too much data redundancy.

[0049] The peak wavelengths of the first fluorescent signal, the second fluorescent signal, and the third fluorescent signal in the micro-area are extracted, and the relationship between the wavelength displacement and the electric field intensity generated by the core of the piezoelectric crystal material is established. The process of obtaining the characteristic parameters of the fluorescence spectrum is achieved using hyperspectral imaging and spectral analysis technology. Each micro-area is scanned using a spectral fluorescence imaging system, which consists of a monochromator, a high-sensitivity CCD detector, and a computer-controlled scanning platform. It can obtain complete fluorescence spectrum information in the range of 400-700nm with a spectral resolution of 1nm. For each micro-area, the complete spectral curves of the first fluorescent signal (corresponding to dislocation density), the second fluorescent signal (corresponding to microcracks), and the third fluorescent signal (corresponding to subcrystalline structure) are obtained. The peak wavelength λmax of each spectrum is determined by the Gaussian fitting method, and the offset from the peak wavelength λ0 in the reference state (stress-free) is calculated. λ=λmax-λ0. Wavelength shift There is a relationship between λ and the electric field strength E generated by the core of the piezoelectric crystal material λ=k× , where k is the proportionality coefficient and α is the characteristic index (usually in the range of 1.2-1.8). These parameters are determined by standard field strength calibration experiments. For example, for the bolt thread area, when subjected to high-frequency dynamic load, the peak wavelength of the second fluorescence signal shifts from 520nm to 526nm. This 6nm wavelength shift corresponds to an equivalent electric field strength of about 4kV / cm caused by local microcracks. The wavelength shifts of the three fluorescence signals are combined to form a spectral feature vector [ λ1, λ2, λ3], as the characteristic parameter of the fluorescence spectrum of the micro-region. This spectral parameter is extremely sensitive to the change of the material microstructure. For example, when the dislocation density changes from / Increase to / When the wavelength of the first fluorescence signal is shifted by 4-5nm, it is much higher than the measurement error of the system (±0.3nm). The selection of the exponent α in the relationship between wavelength shift and electric field intensity is based on the piezoelectric-photoelectric coupling principle and experimental verification, reflecting the nonlinear response characteristics of the quantum dot energy level structure under the action of the electric field. This nonlinear characteristic gives the detection method high sensitivity to tiny stress changes.

[0050] The intensity change rates of the first fluorescence signal, the second fluorescence signal, and the third fluorescence signal between adjacent micro-regions are analyzed, and the corresponding relationship between the fluorescence intensity of the micro-region and the energy level structure of the quantum dot material shell is constructed. The process of obtaining the characteristic parameters of the fluorescence spatial distribution is realized by using spatial gradient analysis and quantum energy level modeling technology. First, the fluorescence intensity gradient between adjacent micro-regions is calculated: for any two adjacent micro-regions i and j, the intensity change rates of the three types of fluorescence signals are calculated. I / d=(Ii-Ij) / dij, where Ii and Ij are the fluorescence intensities of the two micro-regions, and dij is the distance between the centers of the two micro-regions. Then, a spatial distribution map of the fluorescence intensity is constructed: an interpolation algorithm is used to convert discrete intensity change rate data into a continuous spatial distribution function, generating a two-dimensional or three-dimensional distribution map of the fluorescence intensity gradient, which intuitively displays the spatial distribution pattern of different types of microscopic damage. Subsequently, a quantum dot energy level structure model is established: based on the theory of quantum mechanics, a theoretical model is constructed to describe the changes in the energy level structure of cadmium sulfide / zinc sulfide quantum dots under different stress fields, taking into account quantum confinement effects, piezoelectric polarization effects, and stress-induced lattice deformation. By numerically solving the Schrödinger equation, a quantitative relationship between stress field intensity, quantum dot energy level spacing, and fluorescence intensity is established. Finally, the measured fluorescence intensity gradient is compared with the theoretical model to calculate the energy level structure parameters of each micro-region, including the energy level spacing. E, quantum efficiency η and state density ρ(E). For example, for M20 high-strength bolts for high-speed trains, the intensity of the second fluorescence signal was observed to decrease rapidly in the radial direction at the root of the thread, and the intensity change rate reached 40% / mm. According to the quantum dot energy level model, this gradient corresponds to an energy level interval change of about 60meV, indicating that there is a significant stress gradient and microcrack initiation risk in this area. The high sensitivity of the fluorescence spatial distribution characteristic parameters to stress distribution is due to the quantum confinement effect of quantum dots. When the size of quantum dots is only 3-5nm, the energy level change induced by the electric field can also produce a significant fluorescence response at room temperature. This feature enables the stress change at the nanoscale to be amplified into a macroscopically measurable optical signal.

[0051] The decay process of the first fluorescence signal, the second fluorescence signal and the third fluorescence signal is measured, and the decay curve is associated with the configuration change of the energy transfer pair. The process of obtaining the characteristic parameters of the fluorescence lifetime is realized by time-resolved fluorescence spectroscopy. A time-correlated single photon counting system (TCSPC) is used, which consists of a pulsed laser light source (pulse width <100ps), a high-speed photomultiplier tube (time resolution <50ps) and a multi-channel analyzer. The three types of fluorescence signals in each micro-area are measured by time resolution: the sample is placed in the fluorescence lifetime measurement system, and the sample is excited by a pulsed laser of the corresponding wavelength (365nm, 470nm, 532nm). The decay curve of the fluorescence intensity over time is recorded, and the time window is set to 0-50ns, and the time step is 0.1ns. The decay curve is fitted with multiple exponentials: I(t)=∑Ai·exp(-t / τi), where I(t) is the fluorescence intensity at time t, Ai is the initial intensity of the i-th component, and τi is the corresponding fluorescence lifetime. Usually, the fluorescence decay curve can be well fitted by 2-3 exponential terms, each of which corresponds to a specific fluorescent molecular configuration or energy transfer path. Calculate the average fluorescence lifetime and lifetime distribution: Calculate the intensity-weighted average lifetime τavg=∑Ai·τi / ∑Ai and the lifetime distribution function P(τ) based on the fitting parameters. Establish the relationship between the lifetime parameters and the energy transfer pair configuration: Based on the Förster resonance energy transfer (FRET) theory, the configuration change causes the distance and orientation between the energy donor (quantum dot) and the acceptor (dye molecule) to change, which directly affects the energy transfer efficiency and fluorescence lifetime. For example, for the acceptor The average lifetime of the first fluorescence signal (corresponding to dislocation density) at the root of the thread of an M16 bolt subjected to a sub-high frequency fatigue cycle was shortened from an initial 8.2 ns to 5.7 ns, indicating an increase in energy transfer efficiency due to dislocation accumulation. The advantage of fluorescence lifetime measurement is that it is insensitive to fluorescence intensity fluctuations. Even in the presence of slight contamination on the sample surface or uneven coating thickness, the lifetime value can remain stable, providing more reliable information on the state of the microstructure. The number of exponential terms (2-3) used in multi-exponential fitting is determined based on physical meaning: usually the first term corresponds to direct radiative transitions, the second term corresponds to energy transfer through the FRET mechanism, and the third term (if present) reflects more complex non-radiative processes.

[0052] The process of integrating fluorescence intensity characteristic parameters, fluorescence spectrum characteristic parameters, fluorescence spatial distribution characteristic parameters and fluorescence lifetime characteristic parameters to obtain fluorescence characteristic parameters is realized through multi-parameter fusion and feature normalization technology. First, each type of characteristic parameter is normalized: each characteristic parameter is mapped to the range of 0-1 to eliminate the dimensional differences of different physical quantities. Specifically, the Min-Max normalization method P_norm=(P-P_min) / (P_max-P_min) is used, where P is the original parameter value, P_min and P_max are the minimum and maximum values ​​of the parameter, respectively. Then, the fluorescence characteristic vector is constructed: for each micro-region, the normalized characteristic parameters are combined into a characteristic vector F=[w1·I_norm,w2·λ_norm,w3·G_norm,w4·τ_norm], where w1-w4 are the weight coefficients of each characteristic parameter, determined by principal component analysis (PCA) to maximize the sensitivity of the characteristic vector to changes in microscopic tissue state. Perform feature dimension reduction and visualization: Apply the t-SNE (t-distributed Stochastic Neighbor Embedding) algorithm to reduce the dimension of high-dimensional feature vectors, generate two-dimensional or three-dimensional feature maps, and intuitively display the similarities and distribution patterns of different micro-regions. Finally, establish a comprehensive fluorescence feature map: remap the reduced feature points to the fastener geometric model to generate a color-coded feature map, with different colors representing different microstructural states. For example, for the M12 high-temperature alloy bolts used in aircraft engines, the fluorescence feature map after integrating the feature parameters clearly shows the composite damage mode in the transition zone between the thread and the rod: the area where the dislocation density increases and the microcrack formation coexists presents a unique feature distribution, which is clearly distinguished from the area of ​​simple dislocation accumulation. This multi-parameter integration method makes full use of the sensitivity of different types of fluorescence feature parameters to different aspects of the microstructure, greatly improving the comprehensiveness and accuracy of detection. The determination of the characteristic parameter weight coefficient takes into account the differences in sensitivity of each parameter to different types of microdamage: for dislocation density changes, the fluorescence lifetime characteristic parameter (w4) has the highest weight; for microcrack formation, the spatial distribution characteristic parameter (w3) has the largest weight; for subgrain structure, the spectral characteristic parameter (w2) is the most sensitive.

[0053] In one embodiment of the present invention, the analysis of the intensity change rates of the first fluorescence signal, the second fluorescence signal, and the third fluorescence signal between adjacent micro-regions, the construction of the corresponding relationship between the fluorescence intensity of the micro-region and the energy level structure of the shell of the quantum dot material, and the acquisition of the fluorescence spatial distribution characteristic parameters include: The stress memory nanocomposite coating on the surface of the ultra-high strength fastener is divided into stress propagation detection zones according to the threaded area, the bearing surface and the transition fillet area, and each of the stress propagation detection zones extends 10-20 microns along the stress wave propagation direction; Calculating the intensity change rate of the first fluorescent signal between adjacent stress propagation detection zones to obtain thread zone dislocation density evolution data; Analyzing the intensity change rate of the second fluorescent signal between adjacent stress propagation detection zones to obtain microcrack distribution data of the bearing surface; Measuring the intensity change rate of the third fluorescent signal between adjacent stress propagation detection zones to obtain subcrystalline structure distribution data of the transition fillet region; The dislocation density evolution data of the threaded area, the microcrack distribution data of the bearing surface and the subgrain structure distribution data of the transition fillet area are associated with the energy level transition probability of the quantum dot material shell to obtain the fluorescence spatial distribution characteristic parameters.

[0054] The following is a detailed description of the steps involved in the above embodiment: The process of dividing the stress memory nanocomposite coating on the surface of ultra-high strength fasteners into stress propagation detection zones according to the threaded area, the bearing surface and the transition fillet area is achieved through precise optical positioning and digital image processing technology. First, a high-precision CCD camera (pixel size ≤ 5μm) is used to obtain a high-resolution image of the fastener surface. Then, based on the grayscale gradient and geometric features of the image, three key areas are automatically identified: the threaded area (the alternating area between the thread teeth and the valley), the bearing surface (the plane area in contact with the connected parts) and the transition fillet area (the transition arc area between the head and the rod). In each area, a detection zone parallel to the stress wave propagation direction is set according to the stress wave propagation path predicted by finite element analysis. The width of each detection zone is fixed at 15 microns (adjustable within the range of 10-20 microns), and the spacing between adjacent detection zones is also 15 microns. For example, for an M12 bolt, the detection zones set in the threaded area are distributed along the axial direction of the thread, each detection zone is 15 microns wide, and a total of 20-30 continuous detection zones are set to cover the complete stress propagation path of the thread from the top of the thread to the bottom of the valley. The selection of a detection band width of 10-20 microns is based on a comprehensive consideration of the stress wave wavelength of ultra-high-strength fasteners (usually 30-100 microns) and the characteristic size of microstructure evolution (5-15 microns). This scale can capture subtle changes in stress gradients while ensuring a sufficient signal-to-noise ratio.

[0055] The intensity change rate of the first fluorescent signal between adjacent stress propagation detection bands is calculated to obtain the dislocation density evolution data of the threaded area using fluorescence quantitative analysis technology. Each detection band in the threaded area is imaged using a fluorescence microscope system (equipped with a 450±10nm narrow-band filter) to obtain the spatial distribution of the first fluorescent signal (blue fluorescence). The average value I of the fluorescence intensity in each detection band is extracted using image analysis software. Then the intensity change rate between adjacent detection bands is calculated. I / x=(I(n+1)-In) / d, where In and I(n+1) are the average fluorescence intensities of the nth and n+1th detection bands, and d is the distance between the centers of the two detection bands (usually 30 microns). Based on the rate of change data, a spatial distribution curve of the dislocation density in the threaded area is constructed. For example, for an M10 fastener subjected to 106 high-frequency load cycles, the rate of change of the first fluorescence intensity at the root of the thread reaches 35% / 30μm, while that at the top of the thread is only 5% / 30μm. This significant difference directly reflects the higher accumulation of dislocation density at the root of the thread. The quantitative relationship between dislocation density and the rate of change of fluorescence intensity is obtained by calibration with standard samples, and the typical relationship is ρd=k1×( I / x)β1, where ρd is the dislocation density, k1 and β1 are constants calibrated by the experiment. The first fluorescence signal is selected as the main analysis object in the threaded area because the threaded area mainly experiences shear stress during service, and dislocation slip is the main microscopic damage mechanism in this area.

[0056] The process of analyzing the intensity change rate of the second fluorescent signal between adjacent stress propagation detection bands and obtaining the microcrack distribution data of the load-bearing surface is achieved through high-resolution fluorescence imaging and image analysis technology. A fluorescence microscope system equipped with a 520±10nm narrow-band filter is used to image the load-bearing surface detection band to obtain a distribution image of the second fluorescent signal (green fluorescence). The analysis process first uses an adaptive threshold segmentation algorithm to identify high-intensity fluorescent areas (potential microcrack locations) on the load-bearing surface. Then, along the stress propagation direction, the changes in fluorescence morphological parameters between each pair of adjacent detection bands are analyzed, including the intensity change rate, fluorescence shape factor (aspect ratio), and directionality. The microcrack characteristics are reflected in linear high-intensity fluorescent areas, whose long axes are usually perpendicular to the stress propagation direction. Construct a microcrack distribution density function D(r), which represents the microcrack density at a distance r from the edge of the load-bearing surface. For example, for the M16 high-temperature alloy bolts used on aircraft engines, the microcrack density in the edge area of ​​the load-bearing surface reaches 2.8 / , while the central area is only 0.3 / This distribution directly reflects the uneven stress distribution on the bearing surface. The relationship between the microcrack density and the spatial distribution of the second fluorescent signal is expressed as D=k2×G( I2), where G( I2) is the function of the rate of change of the second fluorescence signal, and k2 is the proportionality coefficient. The second fluorescence signal analysis is selected for the bearing surface because this area is prone to form microcracks under cyclic loading, and coumarin derivatives are most sensitive to this damage mode.

[0057] The process of measuring the intensity change rate of the third fluorescent signal between adjacent stress propagation detection bands and obtaining the subgrain structure distribution data of the transition fillet area is realized by using confocal fluorescence microscopy technology and image processing algorithms. A confocal microscope equipped with a 620±10nm narrow-band filter is used to perform three-dimensional imaging of the transition fillet area detection band to obtain the volume distribution of the third fluorescent signal (red fluorescence). The fluorescence intensity profile within each detection band is extracted to calculate the fluorescence intensity gradient in three-dimensional space. I3(x,y,z). Then the intensity variation characteristics between adjacent detection bands are analyzed, including the average intensity change rate, intensity fluctuation frequency and spatial correlation. The subgrain structure is manifested as a spot-like fluorescence distribution, and its statistical characteristics (such as clustering degree and size distribution) are directly related to the subgrain boundary density inside the material. Construct a subgrain structure parameter distribution map S(θ), where θ represents the angular position of the transition fillet area. For example, for M20 bolts for high-speed trains, the subgrain structure parameters at the θ=45° position (at the maximum shear stress) are 3.7 times higher than those at the θ=0° position, indicating that significant microstructural reorganization has occurred in this area. The relationship between the subgrain structure parameters and the third fluorescence signal characteristics is S=k3×[ I3]γ, where k3 and γ are experimental calibration parameters. The third fluorescence signal analysis is selected in the transition fillet region because this region is most likely to form a subcrystalline structure under complex stress conditions, and cyanine dyes are most sensitive to changes in the electronic state of grain boundaries.

[0058] The dislocation density evolution data of the threaded area, the microcrack distribution data of the bearing surface, and the subgrained structure distribution data of the transition fillet area are associated with the energy level transition probability of the quantum dot material shell, and the process of obtaining the characteristic parameters of the fluorescence spatial distribution is realized through quantum spectroscopy model and data fusion technology. First, a quantum dot energy level transition model is established: based on density functional theory (DFT) and quantum mechanics calculations, a theoretical model of the energy level structure and transition probability of cadmium sulfide / zinc sulfide quantum dots under different stress fields is established. Then the stress-energy level response function is calculated: using the relationship between the local electric field E generated by the piezoelectric crystal and the quantum dot energy level structure, the energy level movement corresponding to each type of microscopic damage (dislocation, microcrack, subgrained structure) is calculated. E and transition probability changes P. Correlation data and theoretical model: Fit the measured fluorescence intensity change rate of the three regions with the theoretically calculated transition probability change to establish a quantitative mapping relationship between fluorescence characteristics and microstructure parameters. Finally, construct the fluorescence spatial distribution characteristic parameter vector F=[w1·f1(ρd),w2·f2(D),w3·f3(S)], where f1, f2, f3 are mapping functions, and w1, w2, w3 are weight coefficients. For example, the bolts of an aircraft engine are After sub-high frequency vibration, the dislocation density parameter f1(ρd) at the root of the thread increased by 4.2 times, the microcrack parameter f2(D) at the edge of the bearing surface increased by 3.5 times, and the subgrain parameter f3(S) at the transition fillet increased by 2.8 times. These changes are consistent with the energy level transition probability changes of quantum dots by more than 95%, verifying the physical validity of this method. The correlation between the energy level transition probability of quantum dots and the fluorescence properties is based on the quantum confinement effect. When the size of quantum dots is only 3-5nm, small stress changes can significantly modulate their energy level structure. This nanoscale "amplification effect" is the physical basis for the high sensitivity of this method.

[0059] Please continue reading Figure 1 According to the comparative analysis results of the fluorescence characteristic parameters and the standard fastener parameters, the microstructure evolution state and the remaining life of the ultra-high strength fastener are determined.

[0060] In one embodiment of the present invention, the determination of the microstructure evolution state and the remaining life of the ultra-high strength fastener based on the comparative analysis results of the fluorescence characteristic parameters and the standard fastener parameters includes: Calculating the Euclidean distances between the fluorescence intensity characteristic parameter, the fluorescence spectrum characteristic parameter, the fluorescence spatial distribution characteristic parameter, and the fluorescence lifetime characteristic parameter and corresponding parameters of a standard fastener to obtain a similarity index; The similarity index is regionally weighted according to the threaded area, the bearing surface and the transition fillet area of ​​the ultra-high strength fastener to obtain a damage critical index; After a preset time interval, the ultra-high strength fastener is repeatedly tested, the change rate of the critical damage index is recorded, and microstructure evolution rate data is obtained; Obtaining a critical state remaining time according to a difference between a critical damage index of the threaded area, the bearing surface and the transition fillet area and a critical failure value of a standard fastener; The microstructure evolution rate data and the critical state remaining time are comprehensively analyzed to obtain the microstructure evolution state and remaining life of the ultra-high strength fastener.

[0061] The following is a detailed description of the steps involved in the above embodiment: The Euclidean distance between the characteristic parameters of fluorescence intensity, fluorescence spectrum, fluorescence spatial distribution and fluorescence lifetime and the corresponding parameters of standard fasteners is calculated, and the process of obtaining the similarity index is realized by a multidimensional feature comparison algorithm. First, a standard fastener database is established: fastener samples with different service conditions (from brand new to critical failure) are selected as standard parts, and complete fluorescence feature measurements and microstructure characterization are performed on them. The four types of characteristic parameters of the fasteners to be tested and the standard fasteners are normalized to eliminate the dimension difference, so that each parameter is mapped to the 0-1 interval. When calculating the Euclidean distance, the four types of characteristic parameters of each micro-area of ​​the fastener to be tested are compared point-to-point with the corresponding parameters of the standard parts, and the degree of similarity is quantified by measuring their distance in the four-dimensional feature space. The similarity index is calculated by the distance conversion function, so that its value range is 0-1. The smaller the distance, the closer the similarity is to 1. For example, for an M12 aircraft engine bolt that has been in service for two years, the similarity index of the micro-area at the root of the thread is as high as 0.92 with the "moderately damaged" standard part, while it is only 0.45 with the "severely damaged" standard part, which directly reflects the current damage state. This method based on direct comparison of measured data avoids the construction of complex models and only uses the concept of geometric distance to achieve state assessment. The results are intuitive and reliable.

[0062] The similarity index is weighted according to the threaded area, bearing surface and transition fillet area of ​​the ultra-high-strength fastener, and the process of obtaining the critical damage index is implemented by a partition weighting algorithm. First, the importance weight of each area is determined based on the historical failure statistics and stress analysis of different types of fasteners. For example, for fasteners used in high-speed vibration environments, the weight of the threaded area is 0.5, the weight of the bearing surface is 0.3, and the weight of the transition fillet area is 0.2; while for working conditions dominated by axial tension, the weights are 0.3, 0.5, and 0.2 respectively. The region is also weighted twice according to the stress distribution characteristics. For example, in the threaded area, the micro-area weight of the thread root is higher than that of the tooth top. When the overall critical damage index is finally calculated, the weighted average similarity index of the three regions is multiplied by the corresponding regional weight coefficient and then summed. For example, for the M20 bolts used in high-speed rail vehicles, the critical damage index obtained after detection is 0.72, indicating that it is in a "moderately damaged" state. This regional weighting method takes into account the failure laws of different fastener types and service environments, more accurately evaluates the overall damage status, and avoids the misjudgment that may be caused by a single indicator or simple average.

[0063] After a preset time interval, the ultra-high strength fasteners are repeatedly tested, the change rate of the damage critical index is recorded, and the process of obtaining the microstructure evolution rate data is achieved through periodic monitoring. First, the appropriate test interval is determined according to the service environment and expected life of the fastener, such as 500 hours for fasteners used in high temperature and high frequency environments and 2000 hours for fasteners used in ordinary environments. According to the same test conditions and procedures, the same fastener is re-tested at a predetermined period to obtain a new damage critical index. When calculating the index change rate, the index difference between the two tests is divided by the time interval to obtain the damage accumulation rate per unit time. The multiple test data are analyzed to observe the trend change of the damage accumulation rate. For example, the M16 bolts used in industrial boilers were tracked for 18 months, and the test was conducted every 3 months. It was found that the change rate of the damage critical index gradually increased from the initial 0.012 / month to the later 0.026 / month, showing an accelerated evolution trend. This dynamic monitoring method captures the nonlinear characteristics of the damage accumulation process and avoids the prediction error that may be caused by simple linear extrapolation.

[0064] According to the difference between the critical damage index of the threaded area, the bearing surface and the transition fillet area and the critical value of failure of the standard fastener, the process of obtaining the critical state remaining time is realized by using the critical value comparison and safety margin analysis technology. First, through a large number of experiments and statistical analysis, the failure thresholds of the critical damage index of different types of fasteners in different areas are determined. For example, the critical value of the threaded area of ​​ultra-high strength fasteners for aviation is 0.35, the bearing surface is 0.30, and the transition fillet area is 0.40. The difference between the current index and the critical value of each area is calculated, and the area with the smallest safety margin is determined as the control area. The remaining time is calculated by dividing the safety margin by the index change rate of the area. For example, for the M24 bolts used in nuclear power plants, the threaded area index is measured to be 0.65 (critical value 0.35), the bearing surface index is 0.58 (critical value 0.30), and the transition fillet area index is 0.72 (critical value 0.40). The bearing surface safety margin is the smallest (0.28), and its change rate is 0.014 / month. The remaining time is calculated to be about 20 months. This critical area-based calculation method follows the "short board effect" principle to ensure that the evaluation results are sufficiently safe and conservative.

[0065] The process of comprehensively analyzing the microstructure evolution rate data and the critical state remaining time to obtain the microstructure evolution state and remaining life of ultra-high strength fasteners is realized through trend analysis and risk assessment technology. The change trend of the damage accumulation rate is analyzed based on historical detection data, taking into account the characteristics that the rate may accelerate over time. When calculating the remaining life, the current damage state and the accumulation rate trend are combined, and uncertain factors such as load changes and environmental conditions are considered at the same time, and a prediction interval is given instead of a single value. Finally, a state assessment report is generated, which includes the current state rating of the microstructure, evolution trend analysis, damage degree of each area, predicted remaining life and recommended maintenance cycle. For example, the analysis of M16 bolts for high-speed trains shows that the current state is moderately damaged, with the main characteristics of increased dislocation density at the root of the thread and initiation of microcracks at the edge of the bearing surface. The predicted remaining life is 18±3 months, and it is recommended to replace it within 12 months. This comprehensive analysis method combines static state assessment and dynamic evolution prediction, provides a scientific basis for predictive maintenance, avoids the risk of premature replacement or service with illness, and is particularly suitable for the health management of ultra-high strength fasteners in safety-critical fields.

[0066] The above describes the detection method of the ultra-high strength fastener in the embodiment of the present invention. The following describes the detection device of the ultra-high strength fastener in the embodiment of the present invention. Figure 2 , an embodiment of the detection device of ultra-high strength fasteners in the embodiment of the present invention includes: The coating preparation module 101 is used to prepare a stress memory nanocomposite coating comprising a matrix material, core-shell structure stress sensitive nanoparticles and a fluorescent indicator, and to perform coating treatment on the surface of the ultra-high strength fastener, wherein the core-shell structure stress sensitive nanoparticles and the fluorescent indicator form an energy transfer pair; A dynamic load application module 102 is used to apply a multi-stage dynamic load to the ultra-high strength fastener, so that the stress memory nanocomposite coating records the transient stress wave propagation information of the ultra-high strength fastener; The fluorescence activation module 103 is used to activate the stress memory type nano-composite coating using light sources of different wavelengths, so that the fluorescent indicator in the stress memory type nano-composite coating generates fluorescence signals of corresponding wavelengths corresponding to the dislocation density, microcracks and sub-grained structure inside the ultra-high strength fastener; The signal analysis module 104 is used to perform multi-band analysis on the fluorescence signal to obtain fluorescence characteristic parameters including fluorescence intensity characteristic parameters, fluorescence spectrum characteristic parameters, fluorescence spatial distribution characteristic parameters and fluorescence lifetime characteristic parameters; The state evaluation module 105 is used to determine the microstructure evolution state and remaining life of the ultra-high strength fastener based on the comparative analysis results of the fluorescence characteristic parameters and the standard fastener parameters.

[0067] above Figure 2The detection device for medium and ultra-high strength fasteners in the embodiment of the present invention is described in detail from the perspective of modular functional entities. The detection device for ultra-high strength fasteners in the embodiment of the present invention is described in detail from the perspective of hardware processing.

[0068] Figure 3 2 is a schematic diagram of the structure of a detection device for ultra-high-strength fasteners provided by an embodiment of the present invention. The detection device 200 for ultra-high-strength fasteners may have relatively large differences due to different configurations or performances, and may include one or more processors (central processing units, CPU) 210 (for example, one or more processors) and a memory 220, and one or more storage media 230 (for example, one or more mass storage device terminals) storing application programs 233 or data 232. Among them, the memory 220 and the storage medium 230 may be temporary storage or permanent storage. The program stored in the storage medium 230 may include one or more modules (not shown in the figure), and each module may include a series of instruction operations in the detection device 200 for ultra-high-strength fasteners. Furthermore, the processor 210 may be configured to communicate with the storage medium 230, and execute a series of instruction operations in the storage medium 230 on the detection device 200 for ultra-high-strength fasteners to implement the steps of the above-mentioned detection method for ultra-high-strength fasteners.

[0069] The ultra-high-strength fastener detection device 200 may also include one or more power supplies 240, one or more wired or wireless network interfaces 250, one or more input and output interfaces 260, and / or one or more operating systems 231, such as Windows Serve, Mac OS X, Unix, Linux, FreeBSD, etc. Those skilled in the art will appreciate that Figure 3 The structure of the ultra-high-strength fastener detection device shown does not constitute a limitation on the ultra-high-strength fastener detection device provided by the present invention, and may include more or fewer components than shown in the figure, or a combination of certain components, or a different arrangement of components.

[0070] The present invention also provides a computer-readable storage medium, which may be a non-volatile computer-readable storage medium or a volatile computer-readable storage medium. Instructions are stored in the computer-readable storage medium. When the instructions are executed on a computer, the computer executes the steps of the method for detecting ultra-high-strength fasteners.

[0071] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working process of the above-described system, device, or unit can refer to the corresponding process in the aforementioned method embodiment and will not be repeated here.

[0072] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention is essentially or the part that contributes to the prior art or the whole or part of the technical solution can be embodied in the form of a software product. The computer software product is stored in a storage medium, including several instructions to enable a computer device (which can be a personal computer, server, or network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM), random access memory (RAM), disk or optical disk and other media that can store program code.

[0073] The above description is only a preferred embodiment of the present invention, and does not limit the patent scope of the present invention. All equivalent structural changes made by using the contents of the present invention specification and drawings under the inventive concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A method for detecting ultra-high strength fasteners, characterized in that: include: A stress memory nanocomposite coating comprising a matrix material, core-shell stress sensitive nanoparticles and a fluorescent indicator is prepared, and the surface of the ultra-high strength fastener is coated, wherein the core-shell stress sensitive nanoparticles and the fluorescent indicator form an energy transfer pair; Applying multi-stage dynamic loads to the ultra-high strength fastener, so that the stress memory nanocomposite coating records transient stress wave propagation information of the ultra-high strength fastener; The stress memory type nanocomposite coating is activated by using light sources of different wavelengths, so that the fluorescent indicator in the stress memory type nanocomposite coating generates fluorescent signals of corresponding wavelengths corresponding to the dislocation density, microcracks and subgrain structure inside the ultra-high strength fastener; Performing multi-band analysis processing on the fluorescence signal to obtain fluorescence characteristic parameters including fluorescence intensity characteristic parameters, fluorescence spectrum characteristic parameters, fluorescence spatial distribution characteristic parameters and fluorescence lifetime characteristic parameters; According to the comparative analysis results of the fluorescence characteristic parameters and the standard fastener parameters, the microstructure evolution state and the remaining life of the ultra-high strength fastener are determined.

2. The method for detecting ultra-high strength fasteners according to claim 1, characterized in that: The matrix material is a modified organic silicon polymer, the core-shell structure stress-sensitive nanoparticles include a core made of a piezoelectric crystal material and a shell made of a semiconductor quantum dot material, the piezoelectric crystal material is modified potassium sodium niobate, the semiconductor quantum dot material is cadmium sulfide or zinc sulfide, and the fluorescent indicator includes a first dye molecule sensitive to a change in dislocation density, a second dye molecule sensitive to microcrack formation, and a third dye molecule sensitive to subcrystalline structure formation.

3. The method for detecting ultra-high strength fasteners according to claim 2, characterized in that: The method comprises preparing a stress memory nanocomposite coating comprising a matrix material, core-shell structure stress sensitive nanoparticles and a fluorescent indicator, and coating the surface of an ultra-high strength fastener, wherein the core-shell structure stress sensitive nanoparticles and the fluorescent indicator form an energy transfer pair, comprising: Chemically bonding the piezoelectric crystal material and the semiconductor quantum dot material through an interface coupling agent to obtain stress-sensitive nanoparticles with a core-shell structure; The core-shell structure stress-sensitive nanoparticles are molecularly coordinated with the first dye molecules, the second dye molecules and the third dye molecules to form an energy transfer pair; Mixing and stirring the modified organosilicon polymer and the energy transfer pair in an organic solvent to obtain a stress memory nanocomposite coating; Coating the surface of the ultra-high-strength fastener so that the stress-memory nanocomposite coating forms a uniform film with a thickness of 5 to 10 microns on the surface of the ultra-high-strength fastener; The uniform film is irradiated with ultraviolet light to cure the uniform film.

4. The method for detecting ultra-high strength fasteners according to claim 1, characterized in that: The step of applying a multi-stage dynamic load to the ultra-high strength fastener so that the stress memory nanocomposite coating records transient stress wave propagation information of the ultra-high strength fastener comprises: The ultra-high strength fastener is pre-stimulated by a first load having a frequency of 10-30 kHz for a duration of 45-75 seconds to activate the core-shell structure stress-sensitive nanoparticles in the stress memory nanocomposite coating; The ultra-high-strength fastener is core-excited by a second load including the natural frequency band of the ultra-high-strength fastener for a duration of 150-210 seconds, so that the core-shell structure stress-sensitive nanoparticles record transient stress wave information on the surface of the ultra-high-strength fastener; Post-treating the ultra-high strength fastener with a third load having a frequency of 150-200 kHz for a duration of 20-40 seconds to further activate the response of the stress memory nanocomposite coating to the microstructural changes of the ultra-high strength fastener; The mechanical response of the ultra-high-strength fastener under the first load, the second load and the third load is monitored to obtain transient stress wave propagation information of the ultra-high-strength fastener.

5. The method for detecting ultra-high strength fasteners according to claim 1, characterized in that: The method of activating the stress memory type nanocomposite coating by using light sources of different wavelengths so that the fluorescent indicator in the stress memory type nanocomposite coating generates fluorescent signals of corresponding wavelengths corresponding to the dislocation density, microcracks and subgrained structure inside the ultra-high strength fastener, comprises: The stress memory nanocomposite coating is irradiated with a first light source having a wavelength of 365 nm for 50-70 seconds to obtain a first fluorescent signal corresponding to the internal dislocation density of the ultra-high strength fastener; The stress memory nanocomposite coating is irradiated with a second light source having a wavelength of 470 nm for 50-70 seconds to obtain a second fluorescent signal corresponding to microcracks inside the ultra-high strength fastener; The stress-memory nanocomposite coating is irradiated with a third light source having a wavelength of 532 nm for 50-70 seconds to obtain a third fluorescent signal corresponding to the subcrystalline structure inside the ultra-high-strength fastener; The first fluorescent signal, the second fluorescent signal, and the third fluorescent signal are integrated.

6. The method for detecting ultra-high strength fasteners according to claim 5, characterized in that: The multi-band analysis and processing of the fluorescence signal to obtain fluorescence characteristic parameters including fluorescence intensity characteristic parameters, fluorescence spectrum characteristic parameters, fluorescence spatial distribution characteristic parameters and fluorescence lifetime characteristic parameters includes: Dividing the first fluorescent signal, the second fluorescent signal and the third fluorescent signal into a plurality of micro-regions in the stress concentration area of ​​the ultra-high-strength fastener, calculating the ratio of the fluorescence intensity in each micro-region to the concentration of the core-shell structure stress-sensitive nanoparticles, and obtaining a fluorescence intensity characteristic parameter; Extracting the peak wavelengths of the first fluorescent signal, the second fluorescent signal and the third fluorescent signal in the micro-region, establishing a relationship between the wavelength shift and the electric field intensity generated by the core of the piezoelectric crystal material, and obtaining characteristic parameters of the fluorescence spectrum; Analyze the intensity change rates of the first fluorescent signal, the second fluorescent signal, and the third fluorescent signal between adjacent micro-regions, construct a corresponding relationship between the fluorescence intensity of the micro-region and the energy level structure of the shell of the quantum dot material, and obtain the characteristic parameters of the fluorescence spatial distribution; measuring the decay processes of the first fluorescent signal, the second fluorescent signal and the third fluorescent signal, correlating the decay curves with the configuration changes of the energy transfer pair, and obtaining characteristic parameters of fluorescence lifetime; The fluorescence intensity characteristic parameter, the fluorescence spectrum characteristic parameter, the fluorescence spatial distribution characteristic parameter and the fluorescence lifetime characteristic parameter are integrated to obtain a fluorescence characteristic parameter.

7. The method for detecting ultra-high strength fasteners according to claim 6, characterized in that: The analyzing the intensity change rates of the first fluorescent signal, the second fluorescent signal, and the third fluorescent signal between adjacent micro-regions, constructing the corresponding relationship between the fluorescence intensity of the micro-region and the energy level structure of the shell of the quantum dot material, and obtaining the characteristic parameters of the fluorescence spatial distribution includes: The stress memory nanocomposite coating on the surface of the ultra-high strength fastener is divided into stress propagation detection zones according to the threaded area, the bearing surface and the transition fillet area, and each of the stress propagation detection zones extends 10-20 microns along the stress wave propagation direction; Calculating the intensity change rate of the first fluorescent signal between adjacent stress propagation detection zones to obtain thread zone dislocation density evolution data; Analyzing the intensity change rate of the second fluorescent signal between adjacent stress propagation detection zones to obtain microcrack distribution data of the bearing surface; Measuring the intensity change rate of the third fluorescent signal between adjacent stress propagation detection zones to obtain subcrystalline structure distribution data of the transition fillet region; The dislocation density evolution data of the threaded area, the microcrack distribution data of the bearing surface and the subgrain structure distribution data of the transition fillet area are associated with the energy level transition probability of the quantum dot material shell to obtain the fluorescence spatial distribution characteristic parameters.

8. The method for detecting ultra-high strength fasteners according to claim 1, characterized in that: The method of determining the microstructure evolution state and the remaining life of the ultra-high strength fastener based on the comparative analysis results of the fluorescence characteristic parameters and the standard fastener parameters includes: Calculating the Euclidean distances between the fluorescence intensity characteristic parameter, the fluorescence spectrum characteristic parameter, the fluorescence spatial distribution characteristic parameter, and the fluorescence lifetime characteristic parameter and corresponding parameters of a standard fastener to obtain a similarity index; The similarity index is regionally weighted according to the threaded area, the bearing surface and the transition fillet area of ​​the ultra-high strength fastener to obtain a damage critical index; After a preset time interval, the ultra-high strength fastener is repeatedly tested, the change rate of the critical damage index is recorded, and microstructure evolution rate data is obtained; Obtaining a critical state remaining time according to a difference between a critical damage index of the threaded area, the bearing surface and the transition fillet area and a critical failure value of a standard fastener; The microstructure evolution rate data and the critical state remaining time are comprehensively analyzed to obtain the microstructure evolution state and remaining life of the ultra-high strength fastener.

9. A detection device for ultra-high strength fasteners, characterized in that: The ultra-high-strength fastener detection device adopts the ultra-high-strength fastener detection method according to any one of claims 1 to 8, and the ultra-high-strength fastener detection device comprises: A coating preparation module is used to prepare a stress memory nanocomposite coating comprising a matrix material, core-shell structure stress sensitive nanoparticles and a fluorescent indicator, and to perform coating treatment on the surface of an ultra-high strength fastener, wherein the core-shell structure stress sensitive nanoparticles and the fluorescent indicator form an energy transfer pair; A dynamic load application module, used to apply multi-stage dynamic loads to the ultra-high-strength fastener, so that the stress-memory nanocomposite coating records transient stress wave propagation information of the ultra-high-strength fastener; A fluorescence activation module, used to activate the stress memory type nano-composite coating using light sources of different wavelengths, so that the fluorescent indicator in the stress memory type nano-composite coating generates fluorescence signals of corresponding wavelengths corresponding to the dislocation density, microcracks and sub-grained structure inside the ultra-high strength fastener; A signal analysis module, used to perform multi-band analysis on the fluorescence signal to obtain fluorescence characteristic parameters including fluorescence intensity characteristic parameters, fluorescence spectrum characteristic parameters, fluorescence spatial distribution characteristic parameters and fluorescence lifetime characteristic parameters; The state evaluation module is used to determine the microstructure evolution state and remaining life of the ultra-high strength fastener based on the comparative analysis results of the fluorescence characteristic parameters and the standard fastener parameters.

10. A super high strength fastener detection device, characterized in that: The ultra-high-strength fastener detection device comprises: a memory and at least one processor, wherein the memory stores instructions; The at least one processor calls the instructions in the memory to enable the ultra-high-strength fastener detection device to perform the steps of the ultra-high-strength fastener detection method as described in any one of claims 1-8.

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