A stress-strain synchronous measurement detection device and method

Abstract

The application discloses a kind of detection device and method of stress-strain synchronous measurement, belong to optical mechanics of measurement and material mechanics technical field.The application includes a piece of optical passive vibration isolation platform, optical system, loading system, digital holographic processing system and digital image correlation processing system are arranged on optical passive vibration isolation platform.Reference light and object light are sent in optical system.Fluorescence speckle image is collected using first CCD camera to carry out DIC analysis and obtain in-plane strain field;Meanwhile, the hologram formed by interference of object light and reference light carrying phase information of magnesium oxide sample is recorded using second CCD camera, and stress field is obtained by Fourier transform and deep learning network.The application realizes synchronous high-precision, non-contact, full-field measurement of ceramic material stress and strain, provides a new technical means for optical mechanics behavior discrimination, and can be applied to brittle material mechanical property test and microscopic deformation mechanism research.

Description

Technical Field

[0001] This invention relates to the fields of optical mechanics and materials mechanics, specifically to a detection device and method for simultaneous stress and strain measurement. Background Technology With advancements in technology and evolving industrial demands, the performance requirements for ceramic materials are continuously increasing, such as the pursuit of higher toughness. It is well known that the brittle nature of ceramics results in relatively low fracture toughness, making them prone to instantaneous fracture under stress. This affects product safety and reliability, especially under dynamic loads or extreme environmental conditions, where the risk of brittle fracture increases significantly. This weakness of ceramic materials has become a significant limiting factor in practical applications. To overcome this bottleneck, it is necessary to continuously explore methods to improve the toughness of ceramic materials, enhance the overall performance of functional ceramics, and enable them to play a vital role in a wider range of applications, thereby meeting the diverse material requirements of modern technological and industrial development.

[0002] Brittleness, an inherent characteristic of ceramic materials, means that they cannot undergo significant plastic deformation under external forces like metallic materials, but instead fracture directly. This behavior makes ceramics often unable to withstand sudden stresses under impact or tension, leading to structural failure. Brittle fracture typically occurs in micro-defects, pores, or stress concentration areas within the material. These micro-defects may arise during the material's production or processing, such as stress release during molding, sintering, or cooling. In many cases, these defects go unnoticed in actual use, so when subjected to stress exceeding the load-bearing limit, the ceramic will fracture instantaneously, causing serious consequences. Traditional theory holds that the brittleness of ceramic materials mainly stems from the lack of dislocation-mediated plasticity, meaning that stress concentration at the crack tip cannot dissipate energy through plastic deformation. Therefore, when the external load exceeds a certain threshold, the crack will propagate rapidly, leading to material failure.

[0003] Research on simultaneous stress-strain measurement of ceramic materials is not only of profound significance for improving the performance of existing ceramics, but also provides important basis for the design and development of new ceramic materials. With the continuous development of science and technology, the application scope of ceramic materials is constantly expanding, especially in fields with extremely high requirements for material performance, such as aerospace, medical devices, and the automotive industry, where research on simultaneous stress-strain measurement of ceramics is particularly important.

[0004] Therefore, simultaneous stress-strain measurement of ceramic materials not only has significant academic value but also practical application implications. By developing new measurement technologies and standards, the performance of ceramic materials can be rapidly and accurately evaluated, providing data support for their applications in various fields and promoting the development of materials science and its application in practical engineering.

[0005] Digital image correlation (DIC) technology calculates the in-plane displacement field of an object by tracking the correlation of speckle images on the material surface before and after deformation. This technique is insensitive to vibration, has a wide measurement range, and is very suitable for measuring large in-plane deformations. However, when measuring small displacements in materials such as ceramics, its accuracy for measuring out-of-plane displacements is relatively low, making it difficult to capture subtle deformations in the early stages of crack propagation in ceramics.

[0006] Digital holography generates holograms through the interference of object and reference beams, thereby reconstructing the phase changes of an object before and after deformation, and ultimately obtaining the stress field distribution, exhibiting extremely high measurement sensitivity. It has a natural advantage in measuring out-of-plane displacement and three-dimensional morphology. However, digital holography is extremely sensitive to environmental vibrations, and its phase unwrapping process is complex and computational stability is limited when dealing with large gradient displacements or complex in-plane deformations.

[0007] Currently, in the study of the mechanical properties of brittle materials such as magnesium oxide ceramics, obtaining the stress-strain evolution law is of great significance for revealing the failure mechanism. Traditional measurement methods usually rely on strain gauges or single optical methods, which have the following problems: contact measurement affects the properties of the sample itself; it is impossible to obtain full-field information; and it is difficult to achieve high-precision simultaneous measurement of stress and strain.

[0008] Digital holography can achieve phase information measurement with high precision; digital image correlation technology can acquire full-field displacement and strain distribution. However, both have limitations when used alone, so it is necessary to construct a stress-strain synchronous measurement method that combines the advantages of both technologies. Summary of the Invention

[0009] To overcome the above-mentioned technical problems, the present invention provides a detection device and method for synchronous measurement of stress and strain.

[0010] To achieve the above technical solution, in a first aspect, the present invention provides a detection device for synchronous measurement of stress and strain, comprising: an optical passive vibration isolation platform a, and an optical system b, a force loading system c, a digital image correlation processing system d, and a digital holographic processing system e installed on the optical passive vibration isolation platform a; Optical system b splits the emitted laser beam into object light and reference light; After the optical sample passes through the force loading system c to acquire a fluorescence speckle pattern, strain is detected by the digital image correlation processing system d. After the reference light interferes with the object light passing through the force loading system c, stress is detected using the digital holographic processing system e. The force loading system c contains a test object made of transparent ceramic material. By splitting the laser beam into object light and reference light, stress and strain can be detected simultaneously.

[0011] Specifically, the optical system b includes: a helium-neon laser 1, a first beam splitter 2; a first beam expander 3, a first spatial filter 4, a first collimating lens 5; a second beam splitter 9; a first total reflection mirror 11, an attenuator 12, a second beam expander 13, a second spatial filter 14, a second collimating lens 15, a second total reflection mirror 16, and a beam combiner 17. The force loading system c includes: an ultraviolet lamp 6, a transparent ceramic material test object 7, and a force loading test device 8; The digital image correlation processing system d includes: a first CCD camera 10 and a computer 19; The digital holographic processing system e includes: a second CCD camera 18 and a computer 19.

[0012] Specifically, in the optical system b, the laser emitted by the helium-neon laser 1 is split into object light and reference light after passing through the first beam splitter 2; The object beam passes sequentially through the first beam expander 3, the first spatial filter 4, and the first collimating lens 5 before entering the force loading system c; In the force loading system c, the force loading test device 8 is used to apply a load to the transparent ceramic material test object 7. The object light passes through the first collimating lens 5 and then through the transparent ceramic material test object 7. The ultraviolet lamp 6 is used to emit ultraviolet light to irradiate the fluorescent speckle on the surface of the transparent ceramic material test object 7. The object light carrying the fluorescent speckle information is transmitted to the first CCD camera 10 through the second beam splitter 9. The first CCD camera 10 is electrically connected to the computer 19. The computer 19 receives the fluorescent speckle image of the test sample 7 containing the deformation characteristics of the transparent ceramic material captured by the first CCD camera 10 and performs DIC analysis to obtain the strain field. The second beam splitter 9 splits the object beam into two optical paths: one with intensity balanced with the reference beam and carrying phase information of the transparent ceramic material test object 7, and the other carrying fluorescent speckle image information.

[0013] Specifically, in the optical system b, the laser emitted by the helium-neon laser 1 is split into object light and reference light after passing through the first beam splitter 2; The reference light passes sequentially through the first total reflection mirror 11, the attenuator 12 that adjusts the intensity of the reference light, the second beam expander 13, the second spatial filter 14, the second collimating lens 15, and the second total reflection mirror 16. Then, the object light in the second beam splitter 9 and the reference light in the second total reflection mirror 16 are interfered by the beam combiner 17 to generate alternating bright and dark fringes carrying the depth information of the transparent ceramic material sample 7. The fringes in the beam combiner 17 then enter the second CCD camera 18, which is electrically connected to the computer 19. The computer 19 captures the fringes containing the depth information of the magnesium oxide sample and decodes the interference fringes into phase. The spectrum is calculated using Fourier transform to obtain the stress field distribution. The attenuator 12 adjusts the intensity of the reference light to balance the intensity of the object light that is attenuated after passing through the transparent ceramic material of the test object 7; The first spatial filter 4, the first collimating lens 5, the second spatial filter 14, and the second collimating lens 15 cause the plane wave to diffract into a spherical wave and filter out the high-frequency part, and then collimate the optical path into a plane wave.

[0014] Secondly, the present invention provides a detection method for simultaneous stress-strain measurement, comprising the following steps: S1. Prepare for the experiment and deploy the optical system, force loading system, digital image correlation processing system, and digital holographic processing system on the optical passive vibration isolation platform a. S2. Based on the experimental environment built in S1, holograms and speckle images before and after deformation are acquired synchronously. S3. Perform phase reconstruction and phase unwrapping operations based on the acquired hologram; S4. Perform stress field calculation based on the phase change after the unpacking operation; S5. Calculate the displacement field using DIC analysis based on the acquired speckle images; S6. Calculate the strain field based on the displacement field.

[0015] Specifically, in step S2, the helium-neon laser 1 is first turned on, so that the emitted laser beam passes through the beam splitter 2 and is split into an object beam and a reference beam. The object beam passes through beam expander, filter and collimator in sequence, and then irradiates the transparent ceramic material test object 7 in the force loading system c. After passing through the second beam splitter 9, it is split into two paths. One path carries a fluorescence speckle image, which is acquired by the first CCD camera 10 for DIC analysis; the other path interferes with the reference beam at the beam combiner 17, and the second CCD camera 18 acquires the hologram. The method for acquiring the hologram is as follows: recording the holographic fringe pattern formed by the optical path difference caused by the deformation of the transparent ceramic material test object 7; before the force loading system c applies the load, the light intensity distribution of the hologram recorded by the interference between the reference light and the object light before the deformation of the transparent ceramic material test object 7 is as follows: After the force loading system c applies a load, the light intensity distribution of the hologram recorded by the interference between the reference light and the object light after the deformation of the transparent ceramic material test object (7) is as follows: In the formula, Indicates the initial hologram light intensity; Indicates the light intensity of the object before deformation; Indicates the intensity of the reference light; and These represent the conjugate rays of the object ray and the reference ray, respectively. This indicates the light intensity of the hologram after deformation; Indicates the light intensity of the object after deformation. This represents the conjugate of the object light after deformation.

[0016] Specifically, step S3 includes: reconstructing the complex amplitude of the object light field, expressed as follows: In the formula, The initial object optical recovery amplitude; Indicates the amplitude of the object light; Indicates the phase of the object beam before deformation; Represents the imaginary unit; The optically restored amplitude of the deformed object; Indicates the phase of the object beam after deformation; Performing an arctangent operation on the complex amplitude yields the corresponding enclosed phase, expressed as follows: In the formula, , These represent the enveloping phases of the initial object beam and the deformed object beam, respectively. express The imaginary part, express The real part; express The imaginary part, express The real part; use The convolutional neural network de-wrappes the phase distribution information of the sample to obtain the phase information of the sample. The relationship between the true phase and the wrapped phase is expressed as: In the formula, To unwrap the phase; For wrapping phase; Given integers, unwrap the wrapped phases of the initial object beam and the deformed object beam respectively to obtain the true phases of the initial object beam and the deformed object beam. , .

[0017] Specifically, in step S4, a phase doubling factor t is introduced to increase the density of interference fringes, obtain richer detail information, and improve measurement sensitivity. The expression is as follows: in, , indicating the amount of phase change; Based on images or phase changes with increased interference fringe density Calculation for ceramic materials The stress field of a type-3 crack includes: According to the formulas for determining principal stresses in mechanics of materials, we have: According to the expression for the stress field near the crack tip in fracture mechanics: In the formula, and These represent the first and second principal stresses, respectively. and They represent direction and The normal stress component in the direction of direction; Represents the shear stress components; express Type stress intensity factor; Represents the radial distance at the crack tip in polar coordinates; This represents the angle at the crack tip in polar coordinates. Combining the above two equations, we can obtain the relationship between the principal stresses and the stress intensity factor: Since ceramic materials are optically insensitive, the interference fringes obtained from digital holograms are only related to the principal stresses. Therefore, another formula for calculating the stress intensity factor is: In the formula, The order of the interference fringes. The material stripe value, This represents the thickness of the object before deformation.

[0018] This allows us to obtain a direct expression for the principal stresses and the material fringes: Specifically, step S5 includes: based on the speckle images of the transparent ceramic material test object 7 before and after deformation in S2, firstly, a square reference image sub-region is selected on the image before deformation and its center point is found. Then find the center point of the sub-region on the deformed image. center point direction and The displacement component in the direction is expressed as and Then, a correlation function is defined to measure the similarity between two sub-regions of the image before and after deformation, expressed as: In the formula, The coordinates in the sub-region of the image before deformation are The grayscale of a point; The corresponding point in the deformed image sub-region grayscale; Coordinates of corresponding points in the image sub-regions before and after deformation and Through shape functions and vectors of undetermined parameters Connecting them: in, and Representing points respectively exist direction and The displacement function in the direction is expressed using first-order shape functions: In the formula, and It is a point To the center of the reference image sub-region distance, , , and This represents the displacement gradient of a sub-region of the image.

[0019] Specifically, step S6 includes: The similarity between image sub-regions before and after object deformation is calculated using the standardized covariance cross-correlation function (DVC). The DVC is used to maximize the standardized covariance cross-correlation function. The expression for the standardized covariance cross-correlation function is as follows: The similarity between image subregions before and after object deformation is calculated using the normalized least squares distance correlation function. The normalized least squares distance correlation function is maximized using DIC. The expression for the normalized least squares distance correlation function is as follows: In the formula, The coordinates in the reference image sub-region are The grayscale of the dot, The corresponding point in the target image sub-region grayscale, , These are the average gray levels of the reference image sub-region and the target image sub-region, respectively. This indicates the range parameter for the summation of the relevant functions; The DIC calculation results are used to match the sub-regions before and after deformation to obtain the full-field displacement distribution. Then, the strain field is calculated through fitting or difference: First, displacement data of a continuous region within a preset range is extracted around the selected measurement point. Next, the displacement plane of this region is fitted using the least squares method, and a local coordinate system centered on the measurement point is established. Finally, the displacement components of all measurement points on the specimen surface are transformed to the local coordinate system, and the differences between different displacement components are calculated. , as well as Strain components.

[0020] The beneficial effects of this invention are: (1) Full-field coupling measurement: This invention effectively solves the dimensional limitations of traditional single optical measurement methods by organically combining digital holography and digital image correlation technology. Digital image correlation technology has significant advantages in acquiring in-plane displacement and strain fields on the surface of magnesium oxide samples, while digital holography provides accurate and complete stress information through phase information. The fusion of the two enables the simultaneous acquisition of the complete deformation field of the sample in a single experiment, and achieves synchronous decoupling of stress and strain through a specific algorithm, providing detailed data support for the comprehensive evaluation of the mechanical behavior of ceramic materials.

[0021] (2) High dynamic measurement range: This invention utilizes the excellent tolerance of DIC technology to large gradient displacements to ensure that the measurement does not fail when the material enters plastic deformation or microcracks appear. At the same time, it leverages the high sensitivity of digital holography to wavelength-level deformation to capture micro-stress concentration and micro-deformation of ceramics in the early stage of fracture. This measurement mechanism greatly expands the dynamic measurement range of the system, enabling it to monitor both macroscopic mechanical response and microscopic failure mechanisms.

[0022] (3) Real-time monitoring: The digital holographic processing system can capture the holographic image of the sample in real time, and the digital image correlation processing system can also capture the deformation image information of the fluorescent speckle on the sample surface in real time. Therefore, it can monitor the stress shape change of the transparent ceramic sample in real time and monitor the entire process of the transparent ceramic material fracture under load. (4) Synchronous measurement: During the same loading process, the two systems can simultaneously acquire a hologram containing the phase information of the sample and an image containing the fluorescent speckle information of the sample surface. Through processing, the stress field and strain field of the sample under load deformation can be obtained simultaneously, thereby realizing the synchronous measurement of stress and strain.

[0023] (5) Non-invasive: The present invention adopts a completely non-contact optical measurement scheme, which avoids the initial damage and stress interference caused to the brittle ceramic surface by the addition of sensors. By optimizing the optical path design and introducing common path interference, the device enhances the ability to suppress environmental vibration and air disturbance while ensuring high resolution, thus ensuring the authenticity and reliability of the mechanical parameters of ceramic materials. Attached Figure Description

[0024] Figure 1 This is the optical path diagram of the device of the present invention; Figure 2 This is a photograph of a magnesium oxide ceramic sample. Figure 3 The present invention prepares blue fluorescent speckles on magnesium oxide samples and selects analytical regions for DIC analysis to obtain strain; Figure 4 This is a schematic diagram of the image sub-regions before and after deformation in the DIC principle of this invention embodiment; wherein, Figure 4 (a) is the image before deformation; Figure 4 (b) is the image after deformation; Figure 5 This is a schematic diagram of holographic stripe pattern calculation in an embodiment of the present invention; Figure 6 This is a digital hologram in this embodiment of the invention carrying amplitude and phase information of a magnesium oxide sample under different loads, which can be further calculated and analyzed for stress characteristics; wherein, Figure 6 (a) is a schematic diagram of the digital hologram in the first state. Figure 6 (b) is a schematic diagram of the digital hologram in the second state. Figure 6 (c) is a schematic diagram of the digital hologram in the third state; Figure 7 This is a phase change diagram of the interference between the object beam and the reference beam of the magnesium oxide sample obtained in an embodiment of the present invention. The stress distribution characteristics can be analyzed based on these phase changes; wherein, Figure 7 (a) is a schematic diagram of the phase change in the first state. Figure 7 (b) is a schematic diagram of the phase change in the second state. Figure 7 (c) is a schematic diagram of the phase change in the third state; Explanation of reference numerals in the attached figures: 1-Laser; 2-First beam splitter; 3-First beam expander; 4-First spatial filter; 5-First collimating lens; 6-Ultraviolet lamp; 7-Magnesium oxide sample; 8-Force loading test device; 9-Second beam splitter; 10-First CCD camera; 11-First total reflection mirror; 12-Attenuator; 13-Second beam expander; 14-Second spatial filter; 15-Second collimating lens; 16-Second total reflection mirror; 17-Beam combiner; 18-Second CCD camera; 19-Computer. Detailed Implementation

[0025] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0026] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0027] See Figure 1 A detection device for synchronous measurement of stress and strain includes: an optical passive vibration isolation platform a, an optical system b, a force loading system c, a digital image correlation processing system d, and a digital holographic processing system e mounted on the optical passive vibration isolation platform a; the optical system b splits the emitted laser light into an object beam and a reference beam; the object beam passes through the force loading system c to acquire a fluorescence speckle pattern, and then the strain field is obtained by DIC analysis through the digital image correlation processing system d; the reference beam interferes with the object beam carrying object information after passing through the force loading system c, forming alternating bright and dark interference fringes due to the phase difference; the digital holographic processing system e decodes the fringes into phase, and the spectrum is calculated using Fourier transform to obtain the stress field distribution.

[0028] Furthermore, the optical system b includes: a helium-neon laser 1 for generating laser light; a first beam splitter 2 for splitting the laser beam into an object beam and a reference beam; a first beam expander 3 for diffracting the object beam; a first spatial filter 4 for high-frequency filtering of the expanded object beam; a first collimating lens 5 for collimating the expanded and filtered spherical waves; a second beam splitter 9 for splitting the object beam; a first total reflection mirror 11 for reflecting the reference beam to form a circuit; an attenuator 12 for adjusting the intensity of the reference beam; a second beam expander 13 for diffracting the reference beam; a second spatial filter 14 for high-frequency filtering of the expanded reference beam; a second collimating lens 15 for collimating the expanded and filtered spherical waves; a second total reflection mirror 16 for reflecting the reference beam to form a circuit; and a beam combiner 17 for generating interference between the object beam and the reference beam.

[0029] Furthermore, the force loading system c includes: an ultraviolet lamp 6 for activating the fluorescent speckle on the sample surface, a transparent ceramic material test object 7, and a force loading test device 8; In this invention, the transparent ceramic material to be tested is a magnesium oxide sample, see [link to relevant documentation]. Figure 2 .

[0030] Furthermore, the digital image correlation processing system d includes: a first CCD camera 10 and a computer 19.

[0031] Furthermore, the digital holographic processing system e includes: a second CCD camera 18 and a computer 19.

[0032] To illustrate the optical path diagram of the device in detail, the following is a detailed explanation: First, for the object beam: the laser emitted by the helium-neon laser 1 in optical system b is split into object beam and reference beam after passing through the first beam splitter 2. The object beam then passes through the first beam expander 3, the first spatial filter 4, and the first collimating lens 5 before entering the force loading system c. In the force loading system c, the force loading test device 8 is used to apply a load to the transparent ceramic material test object 7. The object beam passes through the first collimating lens 5 and then through the transparent ceramic material test object 7. The placement of the ultraviolet lamp 6 does not affect the optical path between the first collimating lens 5 and the transparent ceramic material test object 7, and the emitted ultraviolet light illuminates the fluorescent speckle on the surface of the transparent ceramic material test object 7. Afterward, the object beam carrying the fluorescent speckle information is passed through the first... The beam splitter 9 transmits the signal to the first CCD camera 10, which is electrically connected to the computer 19. The computer 19 receives the fluorescent speckle image of the transparent ceramic material test object 7 captured by the first CCD camera 10, which contains the deformation characteristics of the sample, and performs DIC analysis to obtain the strain field. The second beam splitter 9 splits the object beam into one optical path with balanced intensity and phase of the reference light and carrying phase information of the transparent ceramic material test object 7, and another optical path carrying fluorescent speckle image information. The object beam passes through the transparent ceramic material test object 7, i.e., the magnesium oxide sample, under loading. Random speckles are prepared on the sample surface using the stamping method, and the fluorescent speckles on the sample surface are activated by an ultraviolet lamp.

[0033] Secondly, regarding the reference light: the laser emitted by the helium-neon laser 1 in optical system b is split into an object beam and a reference beam after passing through the first beam splitter 2. The reference beam sequentially passes through the first total reflection mirror 11, the attenuator 12 for adjusting the intensity of the reference beam, the second beam expander 13, the second spatial filter 14, the second collimating lens 15, and the second total reflection mirror 16. Then, the object beam in the second beam splitter 9 and the reference beam in the second total reflection mirror 16 are interfered by the beam combiner 17 to generate alternating bright and dark fringes carrying the depth information of the magnesium oxide sample. The fringes enter the second CCD camera 18, which is electrically connected to the computer 19. The computer 19 captures the fringes containing the depth information of the magnesium oxide sample and decodes the interference fringes into phase. The spectrum is calculated using Fourier transform to obtain the stress field distribution. The attenuator 12, which adjusts the intensity of the reference light, adjusts the intensity of the reference light to balance the intensity of the object light, which is attenuated after passing through the sample. The second total reflection mirror 16 diffracts the plane wave into a spherical wave, filters out the high-frequency part, and then collimates the light path into a plane wave.

[0034] In addition, to ensure the final analysis effect, the first beam expander 3, the first spatial filter 4, the first collimating lens 5, the transparent ceramic material test object 7, the second beam splitter 9 used to split the object beam, and the beam combiner 17 in the optical path are located on the same optical axis.

[0035] A detection method for simultaneous stress-strain measurement, comprising the following steps: S1. Experimental preparation and system setup; The process includes setting up and adjusting the optical path components, including adjusting the force loading test device 8 to a suitable position to avoid blocking the optical path; preparing fluorescent speckles on the surface of the transparent ceramic material test object 7 using the stamp transfer method; placing the transparent ceramic material test object 7 in the loading area and fixing it so that it cannot be easily shaken; turning on the ultraviolet lamp 6, turning on the first CCD camera 10 and the second CCD camera 18 and adjusting the parameters respectively to make the image clear; S2. Synchronously acquire holograms and speckle images before and after deformation; Turn on the helium-neon laser 1 so that the emitted laser beam passes through the beam splitter 2 and is split into object beam and reference beam; For the reference beam, the complex amplitude distribution of the reference beam before the object deforms is as follows: In the formula, Indicates the reference optical recovery amplitude. Indicates the amplitude of the reference light. Indicates the phase of the reference light before deformation; Represents the imaginary unit; For the object light at the initial moment, the complex amplitude distribution before the object changes, as captured by the second CCD camera 18 in its first image acquisition, is as follows: In the formula, The initial object optical complex amplitude, Indicates the amplitude of the object light. Indicates the phase of the object beam before deformation; The intensity distribution of the hologram recorded by the interference between the reference light and the object light before the object deforms is as follows: In the formula, Indicates the initial hologram light intensity; and These represent the conjugate rays of the object ray and the reference ray, respectively. Indicates the light intensity of the object before deformation; Indicates the intensity of the reference light; and It represents the interference information between the object beam and the reference beam.

[0036] The object beam is diffracted and expanded sequentially by the first beam expander 3, the first spatial filter 4 filters the high frequency, the first collimating lens 5 converts the expanded and filtered spherical wave back into a plane wave and collimates it, the ultraviolet lamp 6 is turned on and activates the fluorescent speckle on the sample surface, the force loading test device 8 applies a load to the transparent ceramic material test object 7, and then the beam is split by the second beam splitter 9. One beam carrying the fluorescent speckle image information is captured by the first CCD camera 10, and the other beam carrying the sample phase information is captured by the second CCD camera 18. For the reference light that does not carry sample information, after being reflected by the first total reflection mirror 11, the intensity of the passing beam is adjusted by the attenuator 12 to keep the intensity the same as the object light. Then, it passes through the second beam expander 13 and the spatial filter 14 in sequence, so that the plane wave becomes a spherical wave. Then, the high-frequency stray light is filtered out. Then, it passes through the second collimating mirror 15 to make the spherical wave back into a plane wave and collimate it. Then, it passes through the refracted light path of the second total reflection mirror 16. Finally, it is combined with the object light at the beam combiner 17. At this time, the reference light and the object light interfere with each other to obtain the holographic fringe pattern after the ceramic material sample is deformed.

[0037] When the second CCD camera 18 acquires the image for the second time, that is, when acquiring the hologram after the object is deformed, the reference light remains unchanged. Assuming that the intensity of the object light after the object is deformed remains unchanged, and only the phase changes, then the complex amplitude distribution of the object light after the object is deformed is: In the formula, The optically recovered amplitude of the deformed object. Indicates the amplitude of the object light. This indicates the phase of the object beam after deformation.

[0038] The intensity distribution of the hologram recorded at this time, due to the interference between the reference light and the object light after the object is deformed, is as follows: In the formula: This represents the light intensity of the deformed hologram. Indicates the light intensity of the object after deformation. Indicates the intensity of the reference light. and This represents the interference information between the object beam and the reference beam, where , These represent the conjugate rays of the object ray and the reference ray, respectively.

[0039] S3. Phase reconstruction and phase unwrapping extraction; From the above derivation of S1~S2, it can be seen that after the ceramic material is deformed under load, the amplitude remains unchanged, only the phase changes. Therefore, the complex amplitude of the reconstructed object light field is: By performing an arctangent calculation on the complex amplitude of the sample, the corresponding sample envelopment phase can be obtained: In the formula, , These represent the enveloping phases of the initial object beam and the deformed object beam, respectively. express The imaginary part, express The real part; express The imaginary part, express The real part; use A convolutional neural network de-wrappes the encapsulated phase information to obtain the phase information of the sample. The relationship between the true phase and the encapsulated phase is as follows: To unwrap the phase; For wrapping phase; Given integers, unwrap the wrapped phases of the initial object beam and the deformed object beam respectively to obtain the true phases of the initial object beam and the deformed object beam. , The goal of unpacking is to find the integer. Make phase continuous.

[0040] S4. Stress field calculation; The two object light fields before and after the sample deformation interfere with each other, and the interference intensity is: The phase changes of the two object light fields before and after the sample deformation are as follows: As can be seen from the formula for calculating interference intensity, only when the interference intensity is at different locations... A bright fringe is formed only when the phase difference is 2π. Increasing the density of interference fringes is an effective way to obtain richer details from the interference fringe image.

[0041] By introducing a phase multiplication factor t, the phase change can be reduced from 2π to 2π / t, thereby effectively increasing the density of interference fringes in the field of view; at this time, the interference intensity can be expressed as: According to the above formula, if a laser irradiates a uniform and smooth sample surface, the amplitude at each point on the sample will remain constant. In this case, the laser can be used to... Set to a constant; under this condition, the intensity of the interference fringes is determined only by the phase change. The determination, and its distribution exhibiting a cosine function variation pattern, in space At locations where values ​​are equal, the light intensity remains consistent, ultimately resulting in an intensity distribution map exhibiting alternating bright and dark fringes. This can be analyzed by examining the interference fringes or phase changes in the image. This allows us to obtain the stress variation characteristics of the sample. Since ceramic materials are brittle and prone to cracking and fracture during loading, the stress intensity factor can also be used to analyze the stress field intensity near the crack tip. The following is for... Derivation of the stress field near the tip of a type-3 crack: According to the formulas for determining principal stresses in mechanics of materials, we have: According to the expression for the stress field near the crack tip in fracture mechanics: In the formula, and These represent the first and second principal stresses, respectively. and They represent direction and The normal stress component in the direction of direction; Represents the shear stress components; express Type stress intensity factor; This represents the radial distance at the crack tip in polar coordinates; Representing the angle at the crack tip in polar coordinates, such as Figure 5 As shown.

[0042] Combining the above two equations, we can obtain the relationship between the principal stresses and the stress intensity factor: Since ceramic materials are optically insensitive, the interference fringes obtained from digital holograms are only related to the principal stresses, leading to another formula for calculating the stress intensity factor: In the formula, The order of the interference fringes. The material stripe value, This represents the thickness of the object before deformation. Let be the polar coordinates of any point on the interference fringe from the crack tip.

[0043] We can obtain a direct expression for the principal stress and the material fringes: S5 and DIC analysis are used to obtain the displacement field; The object beam is split by the second beam splitter 9. One beam, carrying fluorescence speckle image information, is captured by the first CCD camera 10 and analyzed by the computer 19 using DIC (Digital Image Processing). DIC processes digital images of the object's surface before and after deformation; its basic principle is as follows: Figure 4 As shown, the image at the initial moment is generally referred to as the image before deformation or the reference image, while other acquired images are called the image after deformation or the target image. That is, a pixel of size [value missing] is taken from the reference image. See the square reference image sub-region. Figure 3 And take its center point For a given point, the correlation coefficient with the reference image sub-region is calculated using a specific search method according to a pre-set correlation function within the deformed image. This process identifies the maximum or minimum correlation coefficient between the point and the reference image sub-region. The center point of the target image sub-region direction and The displacement component in the direction is and .

[0044] To analyze the correlation between image sub-regions before and after object deformation, a correlation function needs to be defined: In the formula, The coordinates in the reference image sub-region are The grayscale of the dot, The corresponding point in the target image sub-region grayscale, It is a description and A function that is similar to something to some extent.

[0045] Coordinates of corresponding points in the image sub-regions before and after deformation and It can be achieved through shape functions and vectors of undetermined parameters. Connecting them: in, and Representing points respectively exist direction and Displacement function in the direction; Suppose that the target image sub-region undergoes translation, rigid body rotation, shearing, stretching, or a combination of deformations relative to the reference image sub-region. This can be expressed using a first-order shape function: In the formula, and It is a point To the center of the reference image sub-region distance, , , , This represents the displacement gradient of a sub-region of the image.

[0046] S6. Strain field calculation; The similarity between image sub-regions before and after object deformation is determined by a correlation function, commonly the standardized covariance cross-correlation function: In the formula, The coordinates in the reference image sub-region are The grayscale of the dot, The corresponding point in the target image sub-region grayscale, , These are the average gray levels of the reference image sub-region and the target image sub-region, respectively. For the vector of parameters to be determined, This indicates the range parameter for the summation of the relevant functions; And the normalized least square distance correlation function: The core of DIC calculation lies in achieving accurate matching by maximizing the cross-correlation function of image sub-regions before and after deformation, or minimizing their least squared distance function.

[0047] By precisely matching the reference image sub-region before deformation with the target sub-region after deformation, the full-field displacement distribution is obtained. Then, the strain field is further calculated through fitting or differencing: First, displacement data of a continuous region within a preset range is extracted around the selected measurement point. Next, the displacement plane of this region is fitted using the least squares method, and a local coordinate system centered on the measurement point is established. Finally, the displacement components of all measurement points on the sample surface are transformed to this local coordinate system, and the differences between different displacement components are calculated. , as well as Iso-strain components.

[0048] The stress and strain of the magnesium oxide sample can be calculated simultaneously using the above steps.

[0049] See the results of the digital holograms during the experiment. Figure 6 middle Figure 6 (a) Figure 6 (b) and Figure 6 (c) shows a digital hologram of the amplitude and phase information of a magnesium oxide sample under different loads in different states.

[0050] Figure 7 The next step in the reconstruction process involves performing a Discrete Fourier Transform (DFT) on the digital hologram to obtain its spectrum. Then, an Inverse Fourier Transform (IFT) is performed to convert the frequency domain information back to the spatial domain, thus obtaining the complex amplitude of the reconstructed object beam field. This complex amplitude contains both the amplitude and phase information of the object beam, comprehensively revealing the optical properties of the sample under different loading conditions, and further analyzing stress characteristics. For specific results, see [link to relevant documentation]. Figure 7 (a) Figure 7 (b) and Figure 7 (c).

[0051] The specific embodiments of the present invention have been described in detail above with reference to examples. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A detection device for simultaneous stress and strain measurement, characterized in that, The device includes: an optical passive vibration isolation platform a, an optical system b, a force loading system c, a digital image correlation processing system d, and a digital holographic processing system e mounted on the optical passive vibration isolation platform a; Optical system b splits the emitted laser beam into object light and reference light; After the optical sample passes through the force loading system c to acquire a fluorescence speckle pattern, strain is detected by the digital image correlation processing system d. After the reference light interferes with the object light passing through the force loading system c, stress is detected using the digital holographic processing system e. The force loading system c contains a test object made of transparent ceramic material; By splitting the laser beam into object light and reference light, stress and strain can be detected simultaneously.

2. The detection device for synchronous stress-strain measurement according to claim 1, characterized in that: The optical system b includes: a helium-neon laser (1), a first beam splitter (2); a first beam expander (3), a first spatial filter (4), a first collimating lens (5); a second beam splitter (9); a first total reflection mirror (11), an attenuator (12), a second beam expander (13), a second spatial filter (14), a second collimating lens (15), a second total reflection mirror (16), and a beam combiner (17). The force loading system c includes: an ultraviolet lamp (6), a transparent ceramic material test object (7), and a force loading test device (8); The digital image correlation processing system d includes: a first CCD camera (10) and a computer (19); The digital holographic processing system e includes: a second CCD camera (18) and a computer (19).

3. The detection device for synchronous measurement of stress and strain according to claim 2, characterized in that: The laser emitted by the helium-neon laser (1) in the optical system b is split into object light and reference light after passing through the first beam splitter (2); The object light passes through the first beam expander (3), the first spatial filter (4), and the first collimating lens (5) in sequence before entering the force loading system c; In the force loading system c, the force loading test device (8) is used to apply a load to the transparent ceramic material test object (7). The object light passes through the transparent ceramic material test object (7) after passing through the first collimating lens (5). The ultraviolet lamp (6) is used to emit ultraviolet light to irradiate the fluorescent speckle on the surface of the transparent ceramic material test object (7). The object light carrying the fluorescent speckle information is transmitted to the first CCD camera (10) through the second beam splitter (9). The first CCD camera (10) and the computer (19) are electrically connected. The computer (19) receives the fluorescent speckle image of the test sample (7) containing the deformation characteristics of the transparent ceramic material captured by the first CCD camera (10) and performs DIC analysis to obtain the strain field. The second beam splitter (9) splits the object beam into a light path whose intensity is balanced with the reference light and carries the phase information of the transparent ceramic material test object (7) and a light path carrying the fluorescent speckle image information.

4. The detection device for synchronous measurement of stress and strain according to claim 3, characterized in that: The laser emitted by the helium-neon laser (1) in the optical system b is split into object light and reference light after passing through the first beam splitter (2); The reference light passes sequentially through the first total reflection mirror (11), the attenuator (12) that adjusts the intensity of the reference light, the second beam expander (13), the second spatial filter (14), the second collimating lens (15), and the second total reflection mirror (16). Then, the object light in the second beam splitter (9) and the reference light in the second total reflection mirror (16) are interfered by the beam combiner (17) to generate alternating bright and dark fringes carrying the depth information of the transparent ceramic material test object (7). The fringes in the beam combiner (17) then enter the second CCD camera (18). The second CCD camera (18) is electrically connected to the computer (19). The computer (19) captures the fringes containing the depth information of the magnesium oxide sample and decodes the interference fringes into phase. The spectrum is calculated using Fourier transform to obtain the stress field distribution. The attenuator (12) adjusts the intensity of the reference light to balance the intensity of the light that is attenuated after passing through the transparent ceramic material of the test object (7); The first spatial filter (4), the first collimating lens (5), the second spatial filter (14), and the second collimating lens (15) cause the plane wave to diffract into a spherical wave and filter out the high-frequency part, and then collimate the optical path into a plane wave.

5. A detection method for simultaneous stress-strain measurement, characterized in that, The method is implemented using the apparatus of any one of claims 1 to 4, and includes the following steps: S1. Prepare for the experiment and deploy the optical system, force loading system, digital image correlation processing system, and digital holographic processing system on the optical passive vibration isolation platform a. S2. Based on the experimental environment built in S1, holograms and speckle images before and after deformation are acquired synchronously. S3. Perform phase reconstruction and phase unwrapping operations based on the acquired hologram; S4. Perform stress field calculation based on the phase change after the unpacking operation; S5. Calculate the displacement field using DIC analysis based on the acquired speckle images; S6. Calculate the strain field based on the displacement field.

6. The detection method for synchronous stress-strain measurement according to claim 5, characterized in that, Step S2 first turns on the helium-neon laser (1), so that the emitted laser passes through the beam splitter (2) and is split into an object beam and a reference beam. The object beam passes through the beam expander, filter and collimator in sequence, and then irradiates the transparent ceramic material test object (7) in the force loading system c. After passing through the second beam splitter (9), it is split into two paths. One path carries a fluorescent speckle image, which is collected by the first CCD camera (10) for DIC analysis; the other path interferes with the reference beam at the beam combiner (17) and is used by the second CCD camera (18) to collect a hologram. The method for acquiring the hologram is as follows: recording the holographic fringe pattern formed by the optical path difference caused by the deformation of the transparent ceramic material test object (7); before the force loading system c applies the load, the light intensity distribution of the hologram recorded by the interference between the reference light and the object light before the deformation of the transparent ceramic material test object (7) is as follows: After the force loading system c applies a load, the light intensity distribution of the hologram recorded by the interference between the reference light and the object light after the deformation of the transparent ceramic material test object (7) is as follows: In the formula, Indicates the initial hologram light intensity; Indicates the light intensity of the object before deformation; Indicates the intensity of the reference light; and These represent the conjugate rays of the object ray and the reference ray, respectively. This indicates the light intensity of the hologram after deformation; Indicates the light intensity of the object after deformation. This represents the conjugate of the object light after deformation.

7. The detection method for synchronous stress-strain measurement according to claim 6, characterized in that, Step S3 includes: reconstructing the complex amplitude of the object light field, expressed as follows: In the formula, The initial object optical recovery amplitude; Indicates the amplitude of the object light; Indicates the phase of the object beam before deformation; Represents the imaginary unit; The optically restored amplitude of the deformed object; Indicates the phase of the object beam after deformation; Performing an arctangent operation on the complex amplitude yields the corresponding enclosed phase, expressed as follows: In the formula, , These represent the enveloping phases of the initial object beam and the deformed object beam, respectively. express The imaginary part, express The real part; express The imaginary part, express The real part; use The convolutional neural network de-wrappes the encapsulated phase distribution information to obtain the true phase information of the sample object light. The relationship between the true phase and the encapsulated phase is expressed as: In the formula, To unwrap the phase; For wrapping phase; Given integers, unwrap the wrapped phases of the initial object beam and the deformed object beam respectively to obtain the true phases of the initial object beam and the deformed object beam. , .

8. The detection method for synchronous stress-strain measurement according to claim 7, characterized in that, In step S4, a phase doubling factor t is introduced to increase the density of interference fringes, obtain richer detail information, and improve measurement sensitivity. The expression is as follows: in, , representing the amount of phase change; Based on images or phase changes with increased interference fringe density Calculation for ceramic materials The stress field of a type-3 crack includes: According to the formulas for determining principal stresses in mechanics of materials, we have: According to the expression for the stress field near the crack tip in fracture mechanics: In the formula, and These represent the first and second principal stresses, respectively. and They represent direction and The normal stress component in the direction of direction; Represents the shear stress components; express Type stress intensity factor; This represents the radial distance at the crack tip in polar coordinates; This represents the angle at the crack tip in polar coordinates. Combining the above two equations, we can obtain the relationship between the principal stresses and the stress intensity factor: Since ceramic materials are optically insensitive, the interference fringes obtained from digital holograms are only related to the principal stresses. Therefore, another formula for calculating the stress intensity factor is: In the formula, The order of the interference fringes. The material stripe value, This represents the thickness of the object before deformation. This allows us to obtain a direct expression for the principal stresses and the material fringes:

9. The detection method for synchronous stress-strain measurement according to claim 8, characterized in that, The steps of S5 include: based on the speckle images of the transparent ceramic material test object (7) before and after deformation in S2, firstly, a square reference image sub-region is selected on the image before deformation and its center point is found. Then find the center point of the sub-region on the deformed image. center point direction and The displacement component in the direction is expressed as and Then, a correlation function is defined to measure the similarity between two sub-regions of the image before and after deformation, expressed as: In the formula, The coordinates in the sub-region of the image before deformation are The grayscale of a dot; The corresponding point in the deformed image sub-region grayscale; Coordinates of corresponding points in the image sub-regions before and after deformation and Through shape functions and vectors of undetermined parameters Connecting them: in, and Representing points respectively exist direction and The displacement function in the direction is expressed using first-order shape functions: In the formula, and It is a point To the center of the reference image sub-region distance, , , and This represents the displacement gradient of a sub-region of the image.

10. The detection method for synchronous stress-strain measurement according to claim 9, characterized in that, Step S6 includes: The similarity between image sub-regions before and after object deformation is calculated using the standardized covariance cross-correlation function (DVC). The DVC is used to maximize the standardized covariance cross-correlation function. The expression for the standardized covariance cross-correlation function is as follows: The similarity between image subregions before and after object deformation is calculated using the normalized least squares distance correlation function. The normalized least squares distance correlation function is maximized using DIC. The expression for the normalized least squares distance correlation function is as follows: In the formula, The coordinates in the reference image sub-region are The grayscale of the dot, The corresponding point in the target image sub-region grayscale, , These are the average gray levels of the reference image sub-region and the target image sub-region, respectively. This indicates the range parameter for the summation of the relevant functions; The DIC calculation results are used to match the sub-regions before and after deformation to obtain the full-field displacement distribution. Then, the strain field is calculated through fitting or difference: First, displacement data of a continuous region within a preset range is extracted around the selected measurement point. Next, the displacement plane of this region is fitted using the least squares method, and a local coordinate system centered on the measurement point is established. Finally, the displacement components of all measurement points on the specimen surface are transformed to the local coordinate system, and the differences between different displacement components are calculated. , as well as Strain components.

Images