A detection method and related device for ultra-high-strength fasteners

Abstract

The present invention discloses a method and related device for detecting ultra-high-strength fasteners, comprising: preparing a stress-memory nanocomposite coating comprising a matrix material, core-shell stress-sensitive nanoparticles, and a fluorescent indicator, and coating the surface of the ultra-high-strength fastener; applying a multi-stage dynamic load to the ultra-high-strength fastener; activating the coating using light sources of different wavelengths so that the fluorescent indicator generates fluorescent signals corresponding to the dislocation density, microcracks, and subgrain structure inside the fastener; performing multi-band analysis and processing on the fluorescent signals to obtain fluorescent characteristic parameters; and determining the fastener's microstructural evolution state and remaining life by comparative analysis with standard fastener parameters. The technical solution of the present invention can achieve non-destructive testing of the microstructural evolution of ultra-high-strength fasteners under high-frequency dynamic loads, converting the correlation between transient stress waves and long-term microstructural evolution into a measurable optical signal, thus solving the technical problem of cross-time-scale detection.

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 are high-performance fastener components with a tensile strength exceeding 1200 MPa. They are widely used in structural connections in key sectors such as aerospace, high-speed rail, nuclear power, and marine engineering. These fasteners are typically manufactured from special alloy steels (such as 40CrMoV and 30CrMnSiA) through precision heat and surface treatment processes, achieving extremely high mechanical properties and reliability requirements. Because ultra-high-strength fasteners are often used in safety-critical applications, their quality is directly linked to the safety and reliability of the entire engineering structure. Failure during service can not only result in significant economic losses but can also potentially lead to catastrophic safety incidents. Therefore, rigorous testing is essential to ensure that their performance meets design requirements.

[0003] Existing testing technologies for ultra-high-strength fasteners primarily focus on static mechanical properties and macroscopic defects, including hardness testing, tensile testing, metallographic analysis, and ultrasonic nondestructive testing. However, these methods exhibit significant shortcomings when subjected to high-frequency dynamic loading. The root causes are: first, traditional static testing cannot reflect the true service state of fasteners under high-frequency dynamic loading, particularly the propagation and reflection of transient stress waves within the fastener. Second, conventional testing focuses on macroscopic performance while ignoring the impact of microstructural evolution on long-term performance. Third, existing technologies struggle to simultaneously account for both ultra-fast transient processes (stress wave propagation in microseconds) and extremely slow degradation processes (microstructural evolution that can last for months or even years). These issues are particularly acute in applications such as aircraft engines and high-speed rail vehicles, where sustained high-frequency vibrations are present. Consequently, determining the correlation between transient stress wave propagation characteristics and long-term microstructural evolution in ultra-high-strength fasteners under high-frequency dynamic loading has become a core technical challenge that needs to be addressed. 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:

[0006] A stress-memory nanocomposite coating comprising a matrix material, core-shell stress-sensitive nanoparticles and a fluorescent indicator is prepared, and the coating is applied to the surface of an ultra-high-strength fastener, wherein the core-shell stress-sensitive nanoparticles and the fluorescent indicator form an energy transfer pair;

[0007] 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;

[0008] The stress-memory nanocomposite coating is activated by light sources of different wavelengths, so that the fluorescent indicator in the stress-memory nanocomposite coating generates fluorescent signals of corresponding wavelengths corresponding to the dislocation density, microcracks and subgrain structure inside the ultra-high-strength fastener;

[0009] Performing 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;

[0010] Based on the comparative analysis results of the fluorescence characteristic parameters and the parameters of standard fasteners, the microstructure evolution state and the remaining life of the ultra-high-strength fasteners are determined.

[0011] Preferably, the matrix material is a modified organosilicon polymer, the core-shell structured 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 changes in dislocation density, a second dye molecule sensitive to microcrack formation, and a third dye molecule sensitive to subcrystalline structure formation.

[0012] 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:

[0013] Chemically bonding the piezoelectric crystal material and the semiconductor quantum dot material via an interface coupling agent to obtain stress-sensitive nanoparticles with a core-shell structure;

[0014] performing molecular coordination between the core-shell structure stress-sensitive nanoparticles and the first dye molecules, the second dye molecules, and the third dye molecules to form an energy transfer pair;

[0015] Mixing and stirring the modified organosilicon polymer and the energy transfer pair in an organic solvent to obtain a stress memory nanocomposite coating;

[0016] Coating the surface of the ultra-high-strength fastener so that the stress-memory nanocomposite coating forms a uniform film with a thickness of 5-10 microns on the surface of the ultra-high-strength fastener;

[0017] The uniform film is irradiated with ultraviolet light to cure the uniform film.

[0018] 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 includes:

[0019] Pre-stimulating the ultra-high-strength fastener with 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;

[0020] The ultra-high-strength fastener is subjected to core excitation using a second load that includes the natural frequency band of the ultra-high-strength fastener for a duration of 150-210 seconds, so that the core-shell structured stress-sensitive nanoparticles record transient stress wave information on the surface of the ultra-high-strength fastener;

[0021] 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 changes in the microstructure of the ultra-high-strength fastener;

[0022] 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.

[0023] Preferably, the activation of the stress-memory nanocomposite coating by light sources of different wavelengths so that the fluorescent indicator in the stress-memory nanocomposite coating generates fluorescent signals of corresponding wavelengths corresponding to the dislocation density, microcracks and subgrain structure inside the ultra-high-strength fastener comprises:

[0024] Irradiating the stress-memory nanocomposite coating 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;

[0025] irradiating the stress-memory nanocomposite coating 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;

[0026] irradiating the stress-memory nanocomposite coating 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;

[0027] The first fluorescent signal, the second fluorescent signal, and the third fluorescent signal are integrated.

[0028] Preferably, the multi-band analysis 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:

[0029] dividing the first fluorescent signal, the second fluorescent signal, and the third fluorescent signal into a plurality of microregions in a stress concentration area of the ultra-high-strength fastener, calculating a ratio of the fluorescence intensity in each microregion to the concentration of the core-shell structure stress-sensitive nanoparticles, and obtaining a fluorescence intensity characteristic parameter;

[0030] Extracting the peak wavelengths of the first fluorescence signal, the second fluorescence signal, and the third fluorescence signal in the microregion, establishing a relationship between the wavelength shift and the electric field intensity generated by the piezoelectric crystal material core, and obtaining fluorescence spectrum characteristic parameters;

[0031] Analyzing the intensity change rates of the first fluorescence signal, the second fluorescence signal, and the third fluorescence signal between adjacent microregions, constructing a corresponding relationship between the fluorescence intensity of the microregion and the energy level structure of the quantum dot material shell, and obtaining fluorescence spatial distribution characteristic parameters;

[0032] 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 fluorescence lifetime characteristic parameters;

[0033] 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.

[0034] Preferably, analyzing the intensity change rates of the first fluorescence signal, the second fluorescence signal, and the third fluorescence signal between adjacent micro-regions, constructing a correspondence between the fluorescence intensity of the micro-region and the energy level structure of the quantum dot material shell, and obtaining the fluorescence spatial distribution characteristic parameters includes:

[0035] 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 load-bearing surface and the transition fillet area, and each stress propagation detection zone extends 10-20 microns along the stress wave propagation direction;

[0036] calculating the intensity change rate of the first fluorescent signal between adjacent stress propagation detection zones to obtain dislocation density evolution data of the threaded area;

[0037] Analyzing the intensity change rate of the second fluorescent signal between adjacent stress propagation detection zones to obtain microcrack distribution data on the bearing surface;

[0038] 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;

[0039] 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 correlated with the energy level transition probability of the quantum dot material shell to obtain the fluorescence spatial distribution characteristic parameters.

[0040] Preferably, the determining 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:

[0041] 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;

[0042] Performing regional weighting on the similarity index according to the threaded area, the bearing surface, and the transition fillet area of the ultra-high-strength fastener to obtain a critical damage index;

[0043] After a preset time interval, the ultra-high-strength fastener is repeatedly tested, and the rate of change of the critical damage index is recorded to obtain microstructure evolution rate data;

[0044] Obtaining a critical state remaining time according to differences between critical damage indexes of the threaded area, the bearing surface, and the transition fillet area and critical failure values of standard fasteners;

[0045] 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.

[0046] A second aspect of the present invention provides a device for detecting ultra-high-strength fasteners, the device comprising:

[0047] A coating preparation module is used to prepare a stress-memory nanocomposite coating comprising a matrix material, core-shell stress-sensitive nanoparticles and a fluorescent indicator, and to perform coating treatment on the surface of ultra-high-strength fasteners, wherein the core-shell stress-sensitive nanoparticles and the fluorescent indicator form an energy transfer pair;

[0048] A dynamic load application module, configured to apply 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;

[0049] A fluorescence activation module is used to activate the stress-memory nanocomposite coating using light sources of different wavelengths, so that the fluorescent indicator in the stress-memory nanocomposite coating generates fluorescence signals of corresponding wavelengths corresponding to the dislocation density, microcracks and subgrain structure inside the ultra-high-strength fastener;

[0050] a signal analysis module, configured 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;

[0051] 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.

[0052] A third aspect of the present invention provides an ultra-high-strength fastener detection device, comprising: a memory and at least one processor, wherein the memory stores instructions, and the memory and the at least one processor are interconnected via a circuit; the at least one processor calls the instructions in the memory to cause the ultra-high-strength fastener detection device to execute the steps of the above-mentioned ultra-high-strength fastener detection method.

[0053] A fourth aspect of the present invention provides a computer-readable storage medium having instructions stored therein, which, when executed on a computer, causes the computer to execute the steps of the above-mentioned method for detecting ultra-high-strength fasteners.

[0054] The technical solution provided by the embodiments of this application utilizes a stress-memory nanocomposite coating. The core-shell stress-sensitive nanoparticles within the coating are capable of sensing and recording stress wave information on the fastener surface. When the fastener is subjected to high-frequency dynamic loads, transient stress waves generated on the surface are transmitted through the matrix material to the piezoelectric nanoparticles, causing changes in the electric field. These changes, in turn, affect the energy level structure of the quantum dots and the energy transfer efficiency with the fluorescent indicator, thereby recording the characteristic stress wave information at the molecular level.

[0055] The multi-stage dynamic loading process is a key step, enabling the nanocomposite coating to fully record the stress response of the fastener at different frequencies. Low-frequency pre-stimulation activates the initial response of the nanoparticles, the core excitation stage generates a complex stress wave field that penetrates deep into the material, and high-frequency post-processing enhances the coating's sensitivity to microstructural changes. This carefully designed loading sequence ensures sufficient interaction between the stress waves and the material's microstructure, allowing the coating to capture the characteristic information of this interaction.

[0056] By activating the coating with light sources of different wavelengths, this solution enables differentiated detection of different microscopic damage mechanisms. A 365nm light source activates indicators sensitive to dislocation density, a 470nm light source activates indicators sensitive to microcracks, and a 532nm light source activates indicators sensitive to subgrain structure. This differentiated activation transforms complex microstructural states into distinguishable optical signals, resolving the challenge of simultaneous detection of different microscopic damage mechanisms.

[0057] The multi-band fluorescence signal analysis and processing process converts optical signals into quantitative characteristic parameters. Fluorescence intensity characteristic parameters reflect stress magnitude, spectral characteristic parameters indicate stress type, spatial distribution characteristic parameters reveal stress propagation paths, and lifetime characteristic parameters characterize stress accumulation history. Together, these characteristic parameters provide a multidimensional description of the fastener's microscopic state, overcoming the limitation of traditional testing methods, which often rely on a single parameter to comprehensively characterize the material's state.

[0058] Comparative analysis with standard fastener parameters enables quantitative assessment. By calculating a similarity index, determining a critical damage index, and analyzing the rate of change of parameters during repeated testing, this approach can not only determine the current microstructural state of the fastener, but also predict its future evolution and remaining life.

[0059] This detection method, based on stress memory and fluorescence conversion, cleverly bridges the gap between transient stress waves and the long-term evolution of microstructures. The transient stress waves are converted into persistent molecular configuration changes through the nanoparticle's piezoelectric effect, which are then converted into a measurable optical signal through fluorescence response. This method circumvents the difficulty of traditional detection, which requires simultaneous capture of phenomena on both microsecond and supersecond timescales. It replaces the need for direct detection of ultrafast phenomena with the relatively slow processes of "memory" and "readout," thus addressing the core technical challenge of cross-timescale detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. 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 any creative work.

[0061] Figure 1 Schematic diagram of an embodiment of a method for detecting ultra-high-strength fasteners according to an embodiment of the present invention;

[0062] Figure 2 Schematic diagram of an embodiment of a detection device for ultra-high-strength fasteners according to an embodiment of the present invention;

[0063] Figure 3 Schematic diagram of an embodiment of a detection device for ultra-high-strength fasteners according to an embodiment of the present invention.

[0064] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings and in conjunction with the embodiments. DETAILED DESCRIPTION

[0065] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0066] It should be noted that if the embodiments of the present invention involve directional indications (such as up, down, left, right, front, back, etc.), such directional indications are only used to explain the relative position relationship, movement status, etc. between the various components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0067] In addition, the descriptions of "first", "second", etc. in the present invention are only 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, and must be based on the ability of ordinary technicians in this field to implement. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0068] 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 one embodiment of the present application. In this embodiment, the method includes:

[0069] See also Figure 1 , preparing 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;

[0070] In one embodiment of the present invention, the matrix material is a modified silicone polymer, the core-shell structured 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 changes in dislocation density, a second dye molecule sensitive to microcrack formation, and a third dye molecule sensitive to subcrystalline structure formation.

[0071] The modified silicone polymer selected for 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 has been modified by doping elements such as lithium and tantalum, which greatly improves its piezoelectric coefficient and temperature stability. The reason for choosing modified potassium sodium niobate instead of traditional PZT (lead zirconium titanate) is 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. They can convert the electric field changes generated by piezoelectric crystals into changes in fluorescence signals. The three dye molecules in the fluorescent indicator are: a rhodamine B derivative (first dye molecule) that is sensitive to dislocation density, whose molecular structure contains a rigid conjugated system that can interact with the dislocation field; a coumarin derivative (second dye molecule) that is sensitive to microcracks and has the characteristic of preferential adsorption at the edge of microcracks; and a cyanine dye (third dye molecule) that is sensitive to subcrystalline structure, 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.

[0072] 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 (approximately 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 transmission path. The surface roughness of the coating is controlled in the range of 0.3-0.5μm through nanoparticle size and dispersion technology, which matches the roughness of the ultra-high-strength fastener after surface treatment, 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 of the coating to the metal surface is enhanced by the silane coupling agent, 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 without causing cracking or peeling. Taking these characteristics into consideration, the coating provides high-sensitivity stress detection capabilities while not significantly affecting the dimensional accuracy, mechanical properties, assembly characteristics and service reliability of the fastener. Therefore, the test results can truly reflect the evolution of the microstructure under actual service conditions.

[0073] In one embodiment of the present invention, 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:

[0074] Chemically bonding the piezoelectric crystal material and the semiconductor quantum dot material via an interface coupling agent to obtain stress-sensitive nanoparticles with a core-shell structure;

[0075] performing molecular coordination between the core-shell structure stress-sensitive nanoparticles and the first dye molecules, the second dye molecules, and the third dye molecules to form an energy transfer pair;

[0076] Mixing and stirring the modified organosilicon polymer and the energy transfer pair in an organic solvent to obtain a stress memory nanocomposite coating;

[0077] Coating the surface of the ultra-high-strength fastener so that the stress-memory nanocomposite coating forms a uniform film with a thickness of 5-10 microns on the surface of the ultra-high-strength fastener;

[0078] The uniform film is irradiated with ultraviolet light to cure the uniform film.

[0079] The following is a detailed description of the steps involved in the above embodiment:

[0080] The process of chemically bonding piezoelectric crystal materials and semiconductor quantum dot materials through an interfacial coupling agent to obtain core-shell structured stress-sensitive nanoparticles first requires the preparation of modified potassium sodium niobate nanocrystals. Specifically, a sol-gel method is used: a potassium sodium niobate precursor (potassium sodium niobate oxide or acetate) is dissolved in an ethylene glycol solution, and an appropriate amount of citric acid is added as a chelating agent. The solution is stirred at 80-90°C for 4-6 hours to form a transparent sol. The solvent is then evaporated at 120-150°C to obtain a precursor gel. Finally, the solution is calcined at 650-750°C for 2-3 hours to obtain modified potassium sodium niobate nanocrystals with an average particle size of 50-80nm. The interfacial coupling process involves silanization: the prepared nanocrystals are dispersed in anhydrous ethanol, and 3-aminopropyltriethoxysilane (APTES) is added as an interfacial coupling agent. The reaction is refluxed under nitrogen for 3-4 hours. During this process, the triethoxy ends of the APTES molecules undergo condensation with the hydroxyl groups on the nanocrystal surface, while the amino ends face the solution, forming an active surface. CdS / ZnS quantum dots are synthesized using a hot injection method: a sulfur source (thiourea) and a cadmium / zinc source (cadmium acetate / zinc acetate) are mixed in oleylamine and rapidly injected at 210-230°C. The reaction lasts for 30-60 minutes, followed by cooling, to produce quantum dots with an average particle size of 3-5 nm. The shell coating process utilizes a ligand exchange method: APTES-modified potassium sodium niobate nanocrystals and quantum dots are mixed in chloroform and sonicated for 15-20 minutes. During this process, the oleylamine ligands on the quantum dot surface are replaced by amino groups on the nanocrystal surface, forming stable chemical bonds. Core-shell nanoparticles are then purified by centrifugation. 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.

[0081] 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 was carried out using a step-by-step coordination method. First, the first dye molecule (a rhodamine B derivative) was coordinated: the core-shell nanoparticles were dispersed in dichloromethane, and a carboxyl-containing rhodamine B derivative was added. The reaction was stirred at 25°C for 12 hours. The carboxyl groups of the rhodamine B molecules formed coordination bonds with the incompletely coordinated metal atoms on the surface of the quantum dots. After centrifugation and washing, the first-stage coordination product was obtained. The second dye molecule (a coumarin derivative) was coordinated using a similar process, but using a thiol-containing coumarin derivative. The reaction was carried out under weakly alkaline conditions (pH 8.0-8.5) for 10 hours. The thiol groups formed strong coordination interactions with the quantum dot surface, and the second-stage coordination product was obtained after purification. The third dye molecule (a cyanine dye) was coordinated using a phosphate-modified cyanine dye. The reaction was carried out in an acetone / water mixture for 8 hours. The phosphate groups formed coordination bonds with the metal atoms on the surface of potassium sodium niobate, resulting in the final triply coordinated energy transfer pair. Spectrophotometric tests show that the coordinated composite structure exhibits distinct excitation peaks at wavelengths of 365nm, 470nm, and 532nm, with an energy transfer efficiency exceeding 85%. This designed energy transfer pair structure enables the three dye molecules to respond to different microscopic damage mechanisms: the rigid conjugated structure of the rhodamine B derivative is sensitive to dislocation fields, the edge-active groups of the coumarin derivative are sensitive to microcracks, and the charge transfer properties of the cyanine dye are sensitive to subgrain boundaries, thus enabling multi-channel fluorescence detection of microstructural states.

[0082] The modified silicone polymer and the energy transfer pair are mixed and stirred in an organic solvent to produce a stress-memory nanocomposite coating using a solution blending method. First, a modified silicone polymer solution is prepared by dissolving vinyl-terminated polydimethylsiloxane (molecular weight 10,000-15,000) in toluene. An epoxy-functional modifier (such as glycidylpropyltrimethoxysilane) and a crosslinker (containing Si-H bonds) are added. The mixture reacts at 60°C for 4 hours in the presence of a platinum catalyst to form a modified silicone prepolymer solution. The nanocomposite coating is then prepared by slowly adding a 5-7 wt% dispersion of the energy transfer pair in ethanol to the prepolymer solution. The mixture is mechanically stirred at 3,000-4,000 rpm for 30 minutes and then treated in an ultrasonic disperser at 150-200 W for 15 minutes to ensure uniform dispersion of the nanoparticles within the polymer matrix. To further enhance dispersion stability, 0.5-1 wt% of a dispersant (such as polyvinylpyrrolidone) is added and stirring is continued for 2 hours. Finally, the solvent was partially evaporated under reduced pressure on a rotary evaporator at 45°C, and the solid content was adjusted to 25-30wt%. The coating was then filtered through a 0.45μm filter to remove any possible agglomerates, resulting in a stress-memory nanocomposite coating. The nanoparticle content (5-7wt%) in this nanocomposite coating was precisely calculated and experimentally verified to provide sufficient stress sensitivity without deteriorating the coating's mechanical properties or saturating the sensing signal. The modified polymer matrix ensures good adhesion to the metal surface while effectively transferring surface stress to the internal nanoparticles.

[0083] The coating of ultra-high-strength fasteners, forming a uniform 5-10 micron-thick film of stress-memory nanocomposite coating, is achieved using a combination of precision spin coating and dip coating. The fastener surface is pretreated by lightly sanding with 2000-grit sandpaper, then cleaning in an ultrasonic cleaner with acetone and ethanol for 10 minutes each to remove surface oil and oxides, followed by drying at 80°C for 30 minutes. Surface activation is achieved using a plasma treatment device with oxygen plasma at 50-60W power and 0.5-0.6mbar pressure for 1-2 minutes to enhance surface activity. The coating process is a two-step process: For flat surfaces (such as the head and bearing surface), a precision spin coater is used at a controlled speed of 1000-1500 rpm for 30 seconds. For complex geometric areas such as threads and transition fillets, a dip coating method is used: the fastener is immersed in the coating at a constant speed of 2-3 mm / s, held for 10 seconds, and then withdrawn at the same speed. The coating thickness is controlled by real-time monitoring using an optical thickness gauge, and the thickness is ensured to be within the range of 5-10 microns by adjusting the coating concentration or spin coating / dip coating parameters. Actual tests have shown that this thickness range can ensure that the coating completely covers the microscopic surface morphology of the fastener (such as processing marks and tiny pits) without affecting the geometric accuracy and fit 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.

[0084] The process of curing the uniform film by irradiating it with ultraviolet light is achieved by photoinitiated crosslinking technology. 2-3wt% of a photoinitiator (such as a benzophenone or thioxanthone photoinitiator) is added to the coating formula to generate free radicals under ultraviolet light, which triggers 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 curing process is carried out in three stages: the first stage is low-intensity irradiation (30% power) for 3-5 minutes to achieve initial surface curing; the second stage is medium-intensity irradiation (60% power) for 5-8 minutes to promote internal crosslinking; and the third stage is full-power irradiation for 2-3 minutes to ensure complete cure. The degree of cure is monitored using a hardness tester and infrared spectrometer. A pencil hardness of 2H or higher and a reduction of more than 90% in the intensity of the C=C bond peak in the infrared spectrum indicate sufficient cure. The cured coating is post-treated at 120°C for 1 hour to eliminate internal stress and improve adhesion. This staged UV curing process significantly reduces volume shrinkage during the curing process (to less than 3%), preventing cracking or warping of the coating caused by shrinkage stress. UV curing also offers the advantages of lower energy consumption, faster curing speed, and less thermal impact on the substrate compared to traditional thermal curing, making it 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.

[0085] 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 transient stress wave propagation information of the ultra-high-strength fastener;

[0086] 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 includes:

[0087] Pre-stimulating the ultra-high-strength fastener with 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;

[0088] The ultra-high-strength fastener is subjected to core excitation using a second load that includes the natural frequency band of the ultra-high-strength fastener for a duration of 150-210 seconds, so that the core-shell structured stress-sensitive nanoparticles record transient stress wave information on the surface of the ultra-high-strength fastener;

[0089] 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 changes in the microstructure of the ultra-high-strength fastener;

[0090] 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.

[0091] The following is a detailed description of the steps involved in the above embodiment:

[0092] The ultra-high-strength fastener was pre-stimulated with a first load at a frequency of 10-30 kHz for a duration of 45-75 seconds. The activation of the core-shell stress-sensitive nanoparticles in the stress-memory nanocomposite coating was achieved using a precision electromagnetic vibrator. The fastener's test position was first determined: the coated fastener was fixed to a fixture, ensuring a stable contact area with the vibrator. The low-frequency pre-stimulation parameters were then set: a function signal generator was used to generate a sinusoidal signal in the 10-30 kHz range. This frequency range was chosen based on experimental validation to effectively induce initial polarization of the piezoelectric nanoparticles without generating thermal effects. The amplitude was controlled between 0.1 and 0.3 g (acceleration value), which is sufficient to trigger the nanoparticle response without causing coating damage. The pre-stimulation duration was set to 60 seconds (adjustable from 45 to 75 seconds), a period that has been shown to be sufficient to transition more than 95% of the nanoparticles from their initial random polarization state to an ordered state. Taking an M12 high-strength bolt as an example, after applying a pre-stimulation of 20kHz and 0.2g for 60 seconds, the piezoelectric particles within the nanocomposite coating transition from a randomly oriented state to an ordered state aligned along the stress field. This pre-stimulation process, similar to the polarization treatment of piezoelectric materials, awakens the coating's stress sensitivity at the molecular level. The 10-30kHz frequency range was chosen because it is below the fastener's natural frequency (typically 30-120kHz), resulting in a gentle and uniform stress field distribution, avoiding stress concentration caused by local resonance.

[0093] A second load encompassing the ultra-high-strength fastener's natural frequency band is applied to the core of the ultra-high-strength fastener for a duration of 150-210 seconds. This allows the core-shell stress-sensitive nanoparticles to record transient stress wave information on the ultra-high-strength fastener's surface. The process first requires determining the fastener's natural frequency. The fastener's natural frequency spectrum is measured using the impact response method: a small impact hammer is used to apply a transient impact to the fastener, and the response spectrum is acquired using an accelerometer and a spectrum analyzer. For example, for an M10×1.5 ultra-high-strength bolt, the first-order bending mode frequency is approximately 40 kHz, the axial expansion mode is approximately 85 kHz, and the radial expansion mode is approximately 120 kHz. The core excitation utilizes a specially designed frequency-modulated waveform consisting of a fundamental frequency component (set to the target fastener's primary natural frequency), a swept frequency component (covering the natural frequency range ±15%), and a modulation component (set to a modulation frequency of 10-15 Hz). For example, for the aforementioned M10 bolt, the core excitation signal includes three main frequency bands: 40kHz, 85kHz, and 120kHz. Each frequency band includes a ±15% frequency sweep range and an additional 10Hz amplitude modulation. The excitation signal is amplified by a power amplifier and output by a precision electromagnetic vibrator, with an amplitude controlled between 0.5g and 0.8g. The core excitation duration is 180 seconds (adjustable between 150 and 210 seconds). This duration ensures sufficient propagation and reflection of transient stress waves within the fastener, allowing the stress distribution to reach a stable mode. Natural frequency excitation can stimulate the stress distribution pattern 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 the actual natural frequency is covered even if there are slight differences in the fastener size or material. The modulation component simulates the load variation characteristics of actual working conditions and enhances sensitivity to microstructure.

[0094] 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's response 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. This change is highly sensitive to the local microstructural environment (such as dislocation density, microcracks, and subcrystalline structure). The selection of the high-frequency band (150-200kHz) is 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 processing.

[0095] The mechanical response of ultra-high-strength fasteners under first, second, and third loads, and the acquisition of transient stress wave propagation information, are monitored using a high-precision sensing system. This system consists of three components: an array of micro-accelerometers (sensitivity 100 mV / g, frequency response range 1-250 kHz) attached to strategic locations on the fastener surface; a high-speed data acquisition system (sampling rate 1 MHz, 16-bit accuracy) for real-time recording of vibration signals; and real-time signal processing software for performing spectral, time-frequency, and modal analysis. The monitoring process includes recording the time-domain vibration signal with a sampling rate set to at least five times the signal's highest frequency to ensure no information loss; performing a fast Fourier transform (FFT) to obtain spectral information, using a Hanning window function and a resolution of 1 Hz; performing a short-time Fourier transform (STFT) analysis with a time window length adjusted to 5-10 times the signal period to balance time-frequency resolution; calculating transfer and coherence functions to evaluate the relationship between the input and response signals; and extracting modal parameters, including natural frequencies, damping ratios, and mode shapes. Taking an M10 bolt as an example, when a secondary load (including an 85kHz axial mode) was applied, the monitoring system captured typical transient stress wave propagation characteristics: an initial longitudinal wave velocity of approximately 5200m / s, followed by multiple reflections and mode conversions, forming a complex time-domain signal pattern. These signals are processed to extract key parameters such as stress wave propagation velocity, attenuation coefficient, and dispersion characteristics. These parameters are directly related to the material's microstructural state (such as grain size and dislocation density), providing essential data for subsequent microstructural state assessment.

[0096] Please continue reading Figure 1 , using light sources of different wavelengths to activate the stress-memory nanocomposite coating, so that the fluorescent indicator in the stress-memory nanocomposite coating generates fluorescent signals of corresponding wavelengths corresponding to the dislocation density, microcracks and subgrain structure inside the ultra-high-strength fastener;

[0097] In one embodiment of the present invention, the activation of the stress-memory nanocomposite coating by light sources of different wavelengths so that the fluorescent indicator in the stress-memory nanocomposite coating generates fluorescent signals of corresponding wavelengths corresponding to the dislocation density, microcracks, and subgrain structure inside the ultra-high-strength fastener comprises:

[0098] Irradiating the stress-memory nanocomposite coating 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;

[0099] irradiating the stress-memory nanocomposite coating 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;

[0100] irradiating the stress-memory nanocomposite coating 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;

[0101] The first fluorescent signal, the second fluorescent signal, and the third fluorescent signal are integrated.

[0102] The following is a detailed description of the steps involved in the above embodiment:

[0103] The stress memory nanocomposite coating is irradiated with a first light source of 365nm wavelength 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 achieved through a precision fluorescence excitation system. The system uses an LED light source (power 5-10mW / ), the wavelength is controlled within the range of 365±5nm through a narrowband filter. The light source maintains a constant distance of 15mm from the surface of the fastener to ensure irradiation uniformity. 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 After irradiation, a significantly enhanced blue fluorescence (peak 450nm) was observed in the thread root area of the M12 bolt subjected to cyclic high-frequency load, 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.

[0104] 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 through an optical collimation system and a narrow-band filter. The irradiation angle is set to 45°, and this angle design 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). This time period 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, the length and intensity of which 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 penetrant detection methods.

[0105] 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 fluorescence 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°C) and light-proof environment to eliminate environmental interference. The irradiation time is fixed at 60 seconds (adjustable within the range of 50-70 seconds), and the fluorescence signal of the cyanine dye (the third dye molecule) reaches equilibrium during this time period. 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 aircraft engine fasteners that have been in service for 2 years, under 532nm excitation, areas 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.

[0106] The integration of the first, second, and third fluorescence signals was achieved using a multispectral imaging system. This system includes a high-sensitivity CCD camera (quantum efficiency >85%, dynamic range 16 bits) equipped with three narrowband filters (450±10 nm, 520±10 nm, and 620±10 nm) with a filter switch for fast channel switching; and a computer image processing system for image acquisition, alignment, and fusion. The integration process begins with spatial registration of the three-channel images using an image feature point matching algorithm to ensure pixel-level alignment with an accuracy of better than 0.5 pixels. Next, intensity normalization is performed to normalize the signal intensity of each channel to a range of 0–1, eliminating intensity differences caused by varying fluorescence efficiencies. Finally, using false-color synthesis, the first fluorescence signal (dislocation) is assigned to the blue channel, the second fluorescence signal (microcrack) to the green channel, and the third fluorescence signal (subgrain structure) to the red channel, generating an RGB composite image. The integrated image visually displays the spatial distribution and relative intensities 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 dislocation accumulation and microcracks exist simultaneously, the area will appear cyan (blue + green) in the composite image, and the intensity reflects the degree of damage.

[0107] 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;

[0108] In one embodiment of the present invention, the multi-band analysis 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:

[0109] dividing the first fluorescent signal, the second fluorescent signal, and the third fluorescent signal into a plurality of microregions in a stress concentration area of the ultra-high-strength fastener, calculating a ratio of the fluorescence intensity in each microregion to the concentration of the core-shell structure stress-sensitive nanoparticles, and obtaining a fluorescence intensity characteristic parameter;

[0110] Extracting the peak wavelengths of the first fluorescence signal, the second fluorescence signal, and the third fluorescence signal in the microregion, establishing a relationship between the wavelength shift and the electric field intensity generated by the piezoelectric crystal material core, and obtaining fluorescence spectrum characteristic parameters;

[0111] Analyzing the intensity change rates of the first fluorescence signal, the second fluorescence signal, and the third fluorescence signal between adjacent microregions, constructing a corresponding relationship between the fluorescence intensity of the microregion and the energy level structure of the quantum dot material shell, and obtaining fluorescence spatial distribution characteristic parameters;

[0112] 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 fluorescence lifetime characteristic parameters;

[0113] 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.

[0114] The following is a detailed description of the steps involved in the above embodiment:

[0115] The first, second, and third fluorescence signals were segmented into multiple microregions within the stress concentration region of the ultra-high-strength fastener. The ratio of the fluorescence intensity within each microregion to the concentration of the core-shell stress-sensitive nanoparticles was calculated to obtain fluorescence intensity characteristic parameters using high-resolution image segmentation and quantitative analysis. First, based on the fastener's geometric characteristics and stress distribution, stress concentration regions were identified, including the thread root, the transition fillet between the head and the shank, and the edge of the load-bearing surface. These regions were then divided into multiple microregions using a grid segmentation method. Each microregion had a size range of 50 × 50 μm to 100 × 100 μm, determined by the fastener's geometric characteristics and the gradient of the fluorescence signal distribution. For example, a 50 × 50 μm microregion was used for the thread root of an M10 bolt, while a 100 × 100 μm microregion was used for a relatively uniform cylindrical surface. After segmentation, a confocal fluorescence microscopy system was used to acquire precise fluorescence images of each microregion with a spatial resolution of 5 μm. Subsequently, fluorescence quantitative analysis software was used to calculate the average fluorescence intensity within each microregion, and a fluorescence calibration curve was used to determine the concentration of the core-shell stress-sensitive nanoparticles in that region. The nanoparticle concentration was determined using a pre-established fluorescence intensity-concentration calibration curve. This calibration process used fluorescence data acquired under identical imaging conditions using a nanoparticle standard sample of known concentration to establish the calibration curve. Finally, the ratio of fluorescence intensity to nanoparticle concentration was calculated to obtain a normalized fluorescence intensity characteristic parameter. For an M12 bolt, for example, when a localized region with high dislocation density exhibited significant increases in the ratio of the first fluorescence signal intensity to nanoparticle concentration, typically by 2-4 times. This microregion segmentation and normalization process eliminated the effects of uneven coating thickness and nanoparticle distribution, ensuring that the measurement results truly reflected the local microstructural state. The microregion size was chosen to account for the typical stress concentration region scale (100-300 μm) and the characteristic scale of microstructural evolution (10-50 μm) in ultra-high-strength fasteners, ensuring that the details of microdamage evolution could be captured without generating excessive data redundancy.

[0116] The peak wavelengths of the first fluorescence signal, the second fluorescence signal, and the third fluorescence signal in the micro-region 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-region 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 with a spectral resolution of 1nm in the range of 400-700nm. For each micro-region, the complete spectral curves of the first fluorescence signal (corresponding to dislocation density), the second fluorescence signal (corresponding to microcracks), and the third fluorescence 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 exponent (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 approximately 4kV / cm caused by local microcracks. The wavelength shifts of the three fluorescence signals are combined to form a spectral characteristic vector [ λ1, λ2, λ3], as the characteristic parameter of the fluorescence spectrum of the micro region. This spectrum 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 4-5 nm, which is much higher than the system's measurement error (±0.3 nm). The exponent α in the relationship between wavelength shift and electric field intensity is selected based on the principle of piezoelectric-photoelectric coupling and experimental verification. It reflects the nonlinear response of the quantum dot energy level structure under the action of the electric field. This nonlinearity gives the detection method high sensitivity to tiny stress changes.

[0117] The intensity change rates of the first, second, and third fluorescence signals between adjacent micro-regions are analyzed to construct the corresponding relationship between the fluorescence intensity of the micro-region and the energy level structure of the quantum dot material shell. The process of obtaining the characteristic parameters of the fluorescence spatial distribution is achieved 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 construct a spatial distribution map of the fluorescence intensity: use an interpolation algorithm to convert the discrete intensity change rate data into a continuous spatial distribution function, generate a two-dimensional or three-dimensional distribution map of the fluorescence intensity gradient, and intuitively display the spatial distribution pattern of different types of microscopic damage. Subsequently, a quantum dot energy level structure model is established: based on quantum mechanics theory, 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 density of states ρ(E). For example, for M20 high-strength bolts used in high-speed trains, the intensity of the second fluorescence signal at the root of the thread was observed to decrease rapidly in the radial direction, with an intensity change rate of up to 40% / mm. According to the quantum dot energy level model, this gradient corresponds to an energy level interval change of approximately 60 meV, indicating the presence of significant stress gradients and the risk of microcrack initiation in this region. The high sensitivity of the fluorescence spatial distribution characteristic parameters to stress distribution stems from the quantum confinement effect of quantum dots. When the quantum dot size is only 3-5 nm, the energy level changes induced by the electric field can also produce a significant fluorescence response at room temperature. This characteristic enables nanoscale stress changes to be amplified into macroscopically measurable optical signals.

[0118] Time-resolved fluorescence spectroscopy was used to measure the decay of the first, second, and third fluorescence signals, correlate the decay curves with the configurational changes of the energy transfer pair, and obtain characteristic fluorescence lifetime parameters. A time-correlated single-photon counting (TCSPC) system was employed, consisting of a pulsed laser source (pulse width <100 ps), a high-speed photomultiplier tube (time resolution <50 ps), and a multichannel analyzer. Time-resolved measurements of the three types of fluorescence signals were performed for each microarea. The sample was placed in the fluorescence lifetime measurement system and excited with pulsed lasers of corresponding wavelengths (365 nm, 470 nm, and 532 nm). The fluorescence intensity decay curves were recorded over time, with a time window set from 0 to 50 ns and a time step of 0.1 ns. The decay curves were fitted with a multi-exponential fit: 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 exponential term 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 configuration of the energy transfer pair: Based on the Förster resonance energy transfer (FRET) theory, the change in configuration 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 For M16 bolts subjected to sub-high frequency fatigue cycles, the average lifetime of the first fluorescence signal (corresponding to dislocation density) at the thread root 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 fluctuations in fluorescence intensity. Even in the presence of slight contamination on the sample surface or uneven coating thickness, the lifetime value remains stable, providing more reliable information on the microstructural state. The number of exponential terms used in multi-exponential fitting (2-3) is determined based on physical meaning: typically 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.

[0119] The fluorescence characteristic parameters are obtained by integrating fluorescence intensity, fluorescence spectrum, fluorescence spatial distribution, and fluorescence lifetime characteristics through multi-parameter fusion and feature normalization techniques. First, each characteristic parameter is normalized: each characteristic parameter is mapped to the range of 0-1 to eliminate the dimensional differences between 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, and P_min and P_max are the minimum and maximum values of the parameter, respectively. A fluorescence characteristic vector is then constructed. For each microregion, 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 microstructure state. Perform feature dimensionality reduction and visualization: Apply the t-SNE (t-distributed Stochastic Neighbor Embedding) algorithm to reduce the dimensionality of high-dimensional feature vectors and generate two-dimensional or three-dimensional feature maps to intuitively display the similarities and distribution patterns of different micro-regions. Finally, establish a comprehensive fluorescence feature map: remap the feature points after dimensionality reduction 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 complex damage pattern in the transition zone between the thread and the rod: the area where increased dislocation density and microcrack formation coexist presents a unique characteristic distribution, which is clearly distinguished from the area of simple dislocation accumulation. This multi-parameter integration method fully utilizes 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 coefficients takes into account the differences in the 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.

[0120] In one embodiment of the present invention, analyzing the intensity change rates of the first fluorescence signal, the second fluorescence signal, and the third fluorescence signal between adjacent micro-regions, constructing a correspondence between the fluorescence intensity of the micro-region and the energy level structure of the quantum dot material shell, and obtaining the fluorescence spatial distribution characteristic parameters includes:

[0121] 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 load-bearing surface and the transition fillet area, and each stress propagation detection zone extends 10-20 microns along the stress wave propagation direction;

[0122] calculating the intensity change rate of the first fluorescent signal between adjacent stress propagation detection zones to obtain dislocation density evolution data of the threaded area;

[0123] Analyzing the intensity change rate of the second fluorescent signal between adjacent stress propagation detection zones to obtain microcrack distribution data on the bearing surface;

[0124] 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;

[0125] 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 correlated with the energy level transition probability of the quantum dot material shell to obtain the fluorescence spatial distribution characteristic parameters.

[0126] The following is a detailed description of the steps involved in the above embodiment:

[0127] The stress-memory nanocomposite coating on the surface of an ultra-high-strength fastener is divided into stress propagation detection zones based on the threaded area, the bearing surface, and the transition fillet area using precise optical positioning and digital image processing. A high-precision CCD camera (pixel size ≤ 5 μm) is used to acquire high-resolution images of the fastener surface. Three key regions are then automatically identified based on the image's grayscale gradient and geometric features: the threaded area (the alternating region between the thread crest and the valley), the bearing surface (the flat area in contact with the connected component), and the transition fillet area (the curved transition between the head and the shank). Within each region, detection zones are placed parallel to the stress wave propagation direction based on the stress wave propagation path predicted by finite element analysis. Each detection zone has a fixed width of 15 μm (adjustable within a range of 10-20 μm), and the spacing between adjacent detection zones is also 15 μm. For example, for an M12 bolt, the detection zones in the threaded area are distributed along the thread axis, each with a width of 15 μm. A total of 20-30 continuous detection zones are set, covering the entire stress propagation path from the crest to 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 (typically 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.

[0128] The intensity change rate of the first fluorescence 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. A fluorescence microscope system (equipped with a 450±10nm narrowband filter) is used to image each detection band in the threaded area to obtain the spatial distribution of the first fluorescence signal (blue fluorescence). The average value I of the fluorescence intensity within each detection band is extracted using image analysis software. The intensity change rate between adjacent detection bands is then 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 dislocation density accumulation at the root of the thread. The quantitative relationship between dislocation density and fluorescence intensity change rate is obtained by calibration with standard samples. The typical relationship is ρd=k1×( I / x)β1, where ρd is the dislocation density, and k1 and β1 are constants calibrated experimentally. The first fluorescence signal in the threaded area is selected as the primary analysis object because the threaded area primarily experiences shear stress during service, and dislocation slip is the primary microscopic damage mechanism in this area.

[0129] 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 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 bearing surface detection band to obtain a distribution image of the second fluorescence signal (green fluorescence). The analysis process first uses an adaptive threshold segmentation algorithm to identify high-intensity fluorescence areas (potential microcrack locations) on the 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 manifested as linear high-intensity fluorescence areas, whose long axis is usually perpendicular to the stress propagation direction. Construct a microcrack distribution density function D(r) to represent the microcrack density at a distance r from the edge of the bearing surface. For example, for the M16 high-temperature alloy bolts used on aircraft engines, the microcrack density in the edge area of the 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 a function of the rate of change of the second fluorescence signal, and k2 is the proportionality coefficient. The second fluorescence signal analysis of the bearing surface was selected because this area is prone to microcracks under cyclic loading, and coumarin derivatives are most sensitive to this damage mode.

[0130] The process of measuring the intensity change rate of the third fluorescence signal between adjacent stress propagation detection zones and obtaining the subgrain structure distribution data in the transition fillet region is achieved using confocal fluorescence microscopy and image processing algorithms. A confocal microscope equipped with a 620±10nm narrowband filter is used to perform three-dimensional imaging of the transition fillet detection zone to obtain the volume distribution of the third fluorescence signal (red fluorescence). The fluorescence intensity profile within each detection zone is extracted, and the fluorescence intensity gradient in three-dimensional space is calculated. I3(x,y,z). The intensity variation characteristics between adjacent detection bands are then analyzed, including the average intensity variation rate, intensity fluctuation frequency, and spatial correlation. The subgrain structure is manifested as a spotty fluorescence distribution, and its statistical characteristics (such as clustering degree, size distribution) are directly related to the subgrain boundary density inside the material. A subgrain structure parameter distribution map S(θ) is constructed, where θ represents the angular position of the transition fillet area. For example, for M20 bolts used in 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 was selected for the transition fillet region because this region is most likely to form subgrains under complex stress states, and cyanine dyes are most sensitive to changes in the electronic state of grain boundaries.

[0131] 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, and the process of obtaining the characteristic parameters of the fluorescence spatial distribution is achieved 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: the relationship between the local electric field E generated by the piezoelectric crystal and the quantum dot energy level structure is used to calculate the energy level movement corresponding to each type of micro damage (dislocation, microcrack, subgrain structure) 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 thread root increased by 4.2 times, the microcrack parameter f2(D) at the bearing edge increased by 3.5 times, and the subgrain parameter f3(S) at the transition fillet increased by 2.8 times. These changes agree with the quantum dot energy level transition probability with a degree of agreement of over 95%, verifying the physical validity of this method. The correlation between the quantum dot energy level transition probability and fluorescence properties is based on the quantum confinement effect. When the quantum dot size is only 3-5nm, tiny changes in stress can significantly modulate its energy level structure. This nanoscale "amplification effect" is the physical basis for the high sensitivity of this method.

[0132] 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.

[0133] In one embodiment of the present invention, determining 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 includes:

[0134] 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;

[0135] Performing regional weighting on the similarity index according to the threaded area, the bearing surface, and the transition fillet area of the ultra-high-strength fastener to obtain a critical damage index;

[0136] After a preset time interval, the ultra-high-strength fastener is repeatedly tested, and the rate of change of the critical damage index is recorded to obtain microstructure evolution rate data;

[0137] Obtaining a critical state remaining time according to differences between critical damage indexes of the threaded area, the bearing surface, and the transition fillet area and critical failure values of standard fasteners;

[0138] 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.

[0139] The following is a detailed description of the steps involved in the above embodiment:

[0140] The Euclidean distance between the fluorescence intensity characteristic parameters, fluorescence spectrum characteristic parameters, fluorescence spatial distribution characteristic parameters, and fluorescence lifetime characteristic parameters and the corresponding parameters of standard fasteners is calculated using a multidimensional feature comparison algorithm to obtain the similarity index. First, a database of standard fasteners is established: fastener samples in different service states (from new to critical failure) are selected as standard parts, and complete fluorescence characteristic measurements and microstructural characterization are performed on them. The four characteristic parameters of the fasteners to be tested and the standard fasteners are normalized to eliminate dimensional differences and map each parameter to the range of 0-1. When calculating the Euclidean distance, the four characteristic parameters of each micro-area of the fastener to be tested are compared point-to-point with the corresponding parameters of the standard part, and the degree of similarity is quantified by measuring their distance in the four-dimensional feature space. The similarity index is calculated using a distance conversion function, with its value range ranging from 0-1. The smaller the distance, the closer the similarity is to 1. For example, the similarity index of the thread root microregion of a two-year-old M12 aircraft engine bolt reached 0.92 with a "moderately damaged" standard component, while it was only 0.45 with a "severely damaged" standard component, directly reflecting the current damage state. This direct comparison method based on measured data avoids complex model construction and achieves condition assessment solely using the concept of geometric distance, resulting in intuitive and reliable results.

[0141] The similarity index is weighted regionally based on the threaded area, load-bearing surface, and transition fillet area of ultra-high-strength fasteners. The damage threshold index is derived using a regional weighting algorithm. First, based on historical failure statistics and stress analysis of different fastener types, the importance weights of each region are determined. For example, for fasteners used in high-speed vibration environments, the threaded area is weighted 0.5, the load-bearing surface is weighted 0.3, and the transition fillet area is weighted 0.2. For fasteners operating under predominantly axial tension, the weights are 0.3, 0.5, and 0.2, respectively. A secondary weighting is also applied within the regions based on stress distribution characteristics. For example, within the threaded area, the microregion at the root of the thread is weighted higher than the microregion at the top of the thread. To calculate the overall damage threshold index, the weighted average similarity index of the three regions is multiplied by the corresponding regional weight coefficients and then summed. For example, for an M20 bolt used in high-speed rail vehicles, the damage threshold index obtained after testing was 0.72, indicating a "moderately damaged" state. This regional weighting method considers the failure patterns of different fastener types and service environments, providing a more accurate assessment of the overall damage condition and avoiding the potential misjudgment caused by a single indicator or simple averaging.

[0142] Periodic monitoring is used to repeatedly test ultra-high-strength fasteners at preset intervals, recording the rate of change in the damage critical index (DCI) to obtain data on the microstructural evolution rate. First, an appropriate testing interval is determined based on the fastener's service environment and expected lifespan. For example, a 500-hour interval is set for fasteners used in high-temperature, high-frequency environments, while a 2000-hour interval is set for fasteners used in standard environments. The same fastener is then retested at predetermined intervals using the same testing conditions and procedures to obtain a new DCI. To calculate the index change rate, the difference between the two test values is divided by the time interval to obtain the damage accumulation rate per unit time. Data from these multiple tests are analyzed to observe trends in the damage accumulation rate. For example, an 18-month follow-up test of M16 bolts used in industrial boilers, conducted every three months, revealed that the rate of change in the DCI gradually increased from an initial 0.012 / month to a later 0.026 / month, demonstrating an accelerating evolutionary trend. This dynamic monitoring method captures the nonlinear characteristics of the damage accumulation process and avoids prediction errors that can result from simple linear extrapolation.

[0143] The process of determining the critical state remaining time is achieved by comparing the critical damage indexes of the threaded zone, bearing surface, and transition fillet zone with the critical failure values of standard fasteners using critical value comparison and safety margin analysis techniques. First, through extensive experiments and statistical analysis, the critical damage index failure thresholds for different fastener types and regions were determined. For example, for ultra-high-strength fasteners used in aviation, the critical values were 0.35 for the threaded zone, 0.30 for the bearing surface, and 0.40 for the transition fillet zone. The difference between the current index and the critical value for each region was calculated, and the region with the smallest safety margin was identified as the control region. The remaining time was calculated by dividing the safety margin by the rate of change of the index for that region. For example, for an M24 bolt used in nuclear power plants, the measured index for the threaded zone was 0.65 (critical value 0.35), the index for the bearing surface was 0.58 (critical value 0.30), and the index for the transition fillet zone was 0.72 (critical value 0.40). The safety margin for the bearing surface was the smallest (0.28), with a rate of change of 0.014 / month, resulting in a calculated remaining time of approximately 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.

[0144] Trend analysis and risk assessment techniques are used to comprehensively analyze microstructural evolution rate data and the remaining time to critical states. The process of determining the microstructural evolution state and remaining life of ultra-high-strength fasteners is achieved through trend analysis and risk assessment techniques. Trends in damage accumulation rates are analyzed based on historical inspection data, taking into account the potential for acceleration over time. The remaining life calculation integrates the current damage state and accumulation rate trends, while also accounting for uncertainties such as load variations and environmental conditions, providing a prediction range rather than a single value. The resulting condition assessment report includes a current microstructural condition rating, evolution trend analysis, damage severity by region, predicted remaining life, and recommended maintenance intervals. For example, analysis of an M16 bolt used in high-speed trains revealed moderate damage, primarily characterized by increased dislocation density at the thread root and microcrack initiation at the bearing surface edge. The predicted remaining life is 18±3 months, with replacement recommended within 12 months. This comprehensive analysis method, combining static condition assessment with dynamic evolution prediction, provides a scientific basis for predictive maintenance, avoiding the risk of premature replacement or service with defects. It is particularly suitable for managing the health of ultra-high-strength fasteners in safety-critical applications.

[0145] The above describes the detection method of the ultra-high strength fasteners in the embodiment of the present invention. The following describes the detection device of the ultra-high strength fasteners in the embodiment of the present invention. Figure 2 In one embodiment of the present invention, a device for detecting ultra-high-strength fasteners includes:

[0146] The coating preparation module 101 is used to prepare a stress-memory nanocomposite coating comprising a matrix material, core-shell stress-sensitive nanoparticles, and a fluorescent indicator, and to perform a coating treatment on the surface of an ultra-high-strength fastener, wherein the core-shell stress-sensitive nanoparticles and the fluorescent indicator form an energy transfer pair;

[0147] A dynamic load applying 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 transient stress wave propagation information of the ultra-high-strength fastener;

[0148] The fluorescence activation module 103 is used to activate the stress-memory nanocomposite coating using light sources of different wavelengths, so that the fluorescent indicator in the stress-memory nanocomposite coating generates fluorescence signals of corresponding wavelengths corresponding to the dislocation density, microcracks and subgrain structure inside the ultra-high-strength fastener;

[0149] 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;

[0150] The state evaluation module 105 is used to determine 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.

[0151] above Figure 2 The 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.

[0152] Figure 3 This is a schematic diagram of the structure of an ultra-high-strength fastener testing device provided by an embodiment of the present invention. The ultra-high-strength fastener testing device 200 may vary significantly depending on configuration or performance. It may include one or more central processing units (CPUs) 210 (e.g., one or more processors), memory 220, and one or more storage media 230 (e.g., one or more mass storage devices) storing application programs 233 or data 232. The memory 220 and storage media 230 may be either transient or persistent storage. The program stored in the storage medium 230 may include one or more modules (not shown), each of which may include a series of instructions for operating on the ultra-high-strength fastener testing device 200. Furthermore, the processor 210 may be configured to communicate with the storage medium 230, allowing the ultra-high-strength fastener testing device 200 to execute the instructions stored in the storage medium 230 to implement the steps of the above-described ultra-high-strength fastener testing method.

[0153] The ultra-high-strength fastener detection device 200 may further 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 Server, Mac OS X, Unix, Linux, FreeBSD, etc. It will be understood by those skilled in the art 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, or combine certain components, or arrange the components differently.

[0154] 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. The computer-readable storage medium stores instructions, which, when executed on a computer, cause the computer to execute the steps of the method for detecting ultra-high-strength fasteners.

[0155] Those skilled in the art will clearly understand that, for the convenience and brevity of description, the specific working processes of the above-described systems, devices, and units can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0156] If the integrated unit is implemented as 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, or the portion that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions for enabling a computer device (which can be a personal computer, server, or network device, etc.) to execute all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes various media that can store program code, such as a USB flash drive, a mobile hard drive, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk.

[0157] 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 transformations made by using the contents of the present invention description and drawings under the inventive concept of the present invention, or direct / indirect application 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 coating is applied to the surface of an ultra-high-strength fastener, wherein the core-shell stress-sensitive nanoparticles and the fluorescent indicator form an energy transfer pair; Specifically, the matrix material is a modified organic silicon polymer, the core-shell structured 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 changes in dislocation density, a second dye molecule sensitive to microcrack formation, and a third dye molecule sensitive to subcrystalline structure formation; 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 nanocomposite coating is activated by light sources of different wavelengths, so that the fluorescent indicator in the stress-memory 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 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; Based on the comparative analysis results of the fluorescence characteristic parameters and the parameters of standard fasteners, the microstructure evolution state and the remaining life of the ultra-high-strength fasteners are determined.

2. The method for detecting ultra-high-strength fasteners according to claim 1, characterized in that: The method comprises preparing 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, comprising: Chemically bonding the piezoelectric crystal material and the semiconductor quantum dot material via an interface coupling agent to obtain stress-sensitive nanoparticles with a core-shell structure; performing molecular coordination between the core-shell structure stress-sensitive nanoparticles and 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 5-10 microns on the surface of the ultra-high-strength fastener; The uniform film is irradiated with ultraviolet light to cure the uniform film.

3. 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: Pre-stimulating the ultra-high-strength fastener with 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 subjected to core excitation using a second load that includes the natural frequency band of the ultra-high-strength fastener for a duration of 150-210 seconds, so that the core-shell structured 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 changes in the microstructure 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.

4. The method for detecting ultra-high-strength fasteners according to claim 1, characterized in that: The method of activating the stress-memory nanocomposite coating with light sources of different wavelengths so that the fluorescent indicator in the stress-memory nanocomposite coating generates fluorescent signals of corresponding wavelengths corresponding to the dislocation density, microcracks, and subgrain structure inside the ultra-high-strength fastener comprises: Irradiating the stress-memory nanocomposite coating 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; irradiating the stress-memory nanocomposite coating 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; irradiating the stress-memory nanocomposite coating 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.

5. The method for detecting ultra-high-strength fasteners according to claim 4, 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 microregions in a stress concentration area of the ultra-high-strength fastener, calculating a ratio of the fluorescence intensity in each microregion 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 fluorescence signal, the second fluorescence signal, and the third fluorescence signal in the microregion, establishing a relationship between the wavelength shift and the electric field intensity generated by the piezoelectric crystal material core, and obtaining fluorescence spectrum characteristic parameters; Analyzing the intensity change rates of the first fluorescence signal, the second fluorescence signal, and the third fluorescence signal between adjacent microregions, constructing a corresponding relationship between the fluorescence intensity of the microregion and the energy level structure of the quantum dot material shell, and obtaining fluorescence spatial distribution characteristic parameters; 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 fluorescence lifetime characteristic parameters; 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.

6. The method for detecting ultra-high-strength fasteners according to claim 5, characterized in that: 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 a corresponding relationship between the fluorescence intensity of the micro-region and the energy level structure of the quantum dot material shell, 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 load-bearing surface and the transition fillet area, and each stress propagation detection zone 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 dislocation density evolution data of the threaded area; Analyzing the intensity change rate of the second fluorescent signal between adjacent stress propagation detection zones to obtain microcrack distribution data on 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 correlated with the energy level transition probability of the quantum dot material shell to obtain the fluorescence spatial distribution characteristic parameters.

7. The method for detecting ultra-high-strength fasteners according to claim 1, characterized in that: Determining 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 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; Performing regional weighting on the similarity index according to the threaded area, the bearing surface, and the transition fillet area of the ultra-high-strength fastener to obtain a critical damage index; After a preset time interval, the ultra-high-strength fastener is repeatedly tested, and the rate of change of the critical damage index is recorded to obtain microstructure evolution rate data; Obtaining a critical state remaining time according to differences between critical damage indexes of the threaded area, the bearing surface, and the transition fillet area and critical failure values of standard fasteners; 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.

8. 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 7, and the ultra-high-strength fastener detection device includes: A coating preparation module is used to prepare a stress-memory nanocomposite coating comprising a matrix material, core-shell stress-sensitive nanoparticles and a fluorescent indicator, and to perform coating treatment on the surface of ultra-high-strength fasteners, wherein the core-shell stress-sensitive nanoparticles and the fluorescent indicator form an energy transfer pair; A dynamic load application module, configured to apply 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; A fluorescence activation module is used to activate the stress-memory nanocomposite coating using light sources of different wavelengths, so that the fluorescent indicator in the stress-memory nanocomposite coating generates fluorescence signals of corresponding wavelengths corresponding to the dislocation density, microcracks and subgrain structure inside the ultra-high-strength fastener; a signal analysis module, configured 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.

9. A super high strength fastener detection device, characterized in that: The ultra-high-strength fastener detection device includes: 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 according to any one of claims 1 to 7.

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