High precision speckle and its preparation optimization and strain measurement method

Abstract

The application discloses a high-precision speckle and a preparation optimization and strain measurement method thereof, and the preparation and optimization method comprises the following steps: determining a speckle size matched with a sample, and selecting a nano-gold-water solution with the size; processing the sample to a sample size matched with the speckle size, and pre-treating the surface of the sample; obtaining a nano-gold-ethanol solution via the nano-gold-water solution; drop-coating the nano-gold-ethanol solution on the surface of the sample, and evaporating the ethanol solution; after the ethanol solution on the surface of the sample is evaporated, repeating the previous step until a proper speckle distribution density is obtained, and a high-precision speckle is prepared. Through the optimization method, the speckle image quality can be efficiently improved, and a high-precision material surface strain field distribution cloud picture is obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of digital image correlation method strain characterization, in particular to a high-precision speckle and a preparation optimization and strain measurement method thereof. BACKGROUND

[0002] Various forms of failure occur in the use process of engineering equipment and its components, among which fatigue fracture is one of the main forms of metal component fracture. Research on the mechanism of fatigue fracture of metal materials can greatly reduce the accident rate in actual production, improve material performance, and protect human life and property safety. When metal materials are subjected to tensile load, plastic deformation occurs near the crack tip and a plastic zone is formed. Research on the plastic deformation of the crack is of great significance to the study of damage and fracture of materials. Digital image correlation method has great potential in the characterization of strain field near the crack tip due to its non-contact and full-field measurement advantages.

[0003] Digital image correlation method is an image matching method based on gray features. The gray features on the surface of the sample are called speckle. In recent years, high-precision digital image correlation method has become a commonly used optical measurement method in the field of experimental mechanics. Accurate measurement of local strain of materials is very important to understand the role of microstructure in the material deformation process.

[0004] As an important carrier of object deformation information, the quality of speckle has a great influence on the accuracy of measurement results. Therefore, there is an urgent need for a high-quality speckle that meets the three conditions of contrast, randomness and anisotropy, and can accurately characterize the strain field near the fatigue crack tip. SUMMARY

[0005] The embodiment of the present application provides a high-precision speckle and a preparation optimization method, which overcomes the technical problems and defects of low speckle quality and precision in the prior art, and cannot accurately characterize the strain field near the fatigue crack tip. The digital image technology is used to realize further precision optimization.

[0006] Another object of the embodiment of the present application is to provide a high-precision speckle.

[0007] Still another object of the embodiment of the present application is to provide a strain measurement method based on the high-precision speckle.

[0008] In a first aspect, the embodiment of the present application provides a high-precision speckle preparation and optimization method, comprising the following steps:

[0009] Determine the size of the speckle suitable for the sample, and select a nanometer gold-water solution of the size;

[0010] Process the sample to a sample size suitable for the size of the speckle, and pretreat the surface of the sample.

[0011] Obtaining a gold nanoparticle-ethanol solution from the gold nanoparticle-water solution;

[0012] Dropping the gold nanoparticle-ethanol solution on the surface of the sample and evaporating the ethanol solution;

[0013] After the ethanol solution on the surface of the sample is evaporated, repeating the previous step until a proper speckle distribution density is obtained, thereby obtaining a high-precision speckle.

[0014] Optionally, in some embodiments of the present application, the method for determining the speckle size suitable for the sample is as follows:

[0015] Establishing a speckle distribution density formula In the formula:

[0016] ρ is the speckle distribution density;

[0017] n is the number of speckles contained in the subset;

[0018] d is the equivalent diameter of the speckle;

[0019] M is the magnification of the electron microscope photograph;

[0020] s is the length of the subset.

[0021] Optionally, in some embodiments of the present application, the method for obtaining the gold nanoparticle-ethanol solution is as follows: taking an appropriate amount of gold nanoparticle-water solution, centrifuging, removing the upper water solution, and adding anhydrous ethanol to the bottom precipitated gold nanoparticles.

[0022] Optionally, in some embodiments of the present application, the parameters of the centrifugation are

[0023] 6000-9000 r / min centrifugation for 2-8 min.

[0024] Optionally, in some embodiments of the present application, the volume of the injected alcohol solution is 1 / 4-1 / 2 of the volume of the replaced water solution.

[0025] Optionally, in some embodiments of the present application, the method further comprises a speckle optimization step, using an electron microscope to take pictures of the sample surface before / after loading, determining the electron microscope parameters; importing the sample surface pictures into digital image software, adjusting the subset parameters of the speckles, and further optimizing the speckle precision.

[0026] Optionally, in some embodiments of the present application, the contrast and brightness of the before / after taken sample surface pictures are consistent.

[0027] Optionally, in some embodiments of the present application, the picture resolution of the electron microscope is 2048x1536 pixels.

[0028] Optionally, in some embodiments of the present application, the subset of the speckle contains at least 3 × speckles.

[0029] Optionally, in some embodiments of the present application, the electron microscope parameters include picture magnification, contrast, brightness, and resolution.

[0030] In a second aspect, the embodiments of the present application also provide a high-precision speckle prepared according to the high-precision speckle preparation and optimization method.

[0031] In a third aspect, the embodiments of the present application also provide a strain measurement method of a high-precision speckle, characterized in that a digital image correlation (DIC) software is used to characterize the strain field change at the crack tip of a sample in a fatigue loading process with high precision; the method comprises the following steps:

[0032] determining the speckle size suitable for the sample, and selecting a nanogold-water solution with the size;

[0033] processing the sample to a sample size suitable for the speckle size, and pretreating the surface of the sample;

[0034] obtaining a nanogold-ethanol solution from the nanogold-water solution;

[0035] dropping the nanogold-ethanol solution on the surface of the sample, and evaporating the ethanol solution;

[0036] after the ethanol solution on the surface of the sample is evaporated, repeating the previous step until a proper speckle distribution density is obtained, thereby obtaining a high-precision speckle;

[0037] using an in-situ tensile test bench in an electron microscope cabin to perform a strain measurement test on the sample, and taking pictures of the same position of the sample under different loading cycles at the same magnification; using the in-situ tensile test bench in the electron microscope cabin to perform a fatigue test on the sample, and taking pictures of the crack tip of the sample under different loading cycles at the same magnification, at this time, attention is paid to keeping the field of view range of each picture the same,

[0038] a method for obtaining the displacement field and the strain field of the surface of the sample according to the speckle pattern.

[0039] The present application provides a preparation method for improving the speckle by optimization, and the image quality of the speckle can be efficiently improved by the optimization method, thereby obtaining a high-precision material surface strain field distribution cloud picture.

[0040] The application also provides a high-precision speckle, and the high-quality and high-precision speckle further improves the precision of the measurement result, and meanwhile meets three conditions of contrast, randomness and anisotropy.

[0041] The application further provides a high-precision speckle strain measurement method, which can be applied to fatigue tests and stress tests of various samples, has a wider application range and higher precision.

[0042] The application uses digital image correlation (DIC) software to accurately represent the strain field change at the crack tip of the sample in the fatigue loading process. BRIEF DESCRIPTION OF DRAWINGS

[0043] In order to more clearly illustrate the technical solutions in the embodiments of the application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without creative effort on the basis of these drawings.

[0044] Figure 1 The flowchart of the preparation and optimization method of the high-precision speckle of the application is shown in the figure.

[0045] Figure 2 The schematic diagram of the shape structure of the in-situ fatigue sample in the embodiment of the application is shown in the figure.

[0046] Figure 3 The speckle distribution diagram of the sample under the scanning electron microscope in the embodiment of the application is shown in the figure.

[0047] Figure 4 The crack tip morphology diagram of the sample before loading in the embodiment of the application is shown in the figure.

[0048] Figure 5 The strain distribution diagram of the crack tip of the sample in the embodiment of the application is shown in the figure. DETAILED DESCRIPTION

[0049] The technical solutions in the embodiments of the application will be described clearly and completely in combination with the drawings of the embodiments of the application. Obviously, the described embodiments are only some of the embodiments of the application, but not all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative effort fall within the scope of the application.

[0050] The embodiment of the present application provides a high-precision speckle and a preparation optimization and strain measurement method. The following will be described in detail. It should be noted that the description order of the following embodiments is not limited as the preferred order of the embodiments. In addition, in the description of the present application, the term "comprises" means "comprises but is not limited to". The terms first, second, third, etc. are only used as labels and do not impose numerical requirements or establish sequences. Various embodiments of the present application can exist in a range of forms; it should be understood that the description in a range of forms is only for the convenience and brevity, and should not be understood as a hard limit to the scope of the present application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single values in the range. For example, it should be considered that the range description from 3 to 6 has specifically disclosed sub-ranges, such as from 3 to 4, from 3 to 5, from 3 to 6, from 4 to 5, from 5 to 6, etc., and single numbers in the range, such as 3, 4, 5 and 6, which applies to any range. In addition, whenever a numerical range is indicated in this document, it refers to any cited number (fraction or integer) in the indicated range.

[0051] The weight / volume / mole of the related components mentioned in the embodiment of the present application can not only refer to the specific content of each component, but also represent the proportional relationship between the weight / volume / mole of each component, therefore, as long as the content of the related components in the embodiment of the present application is enlarged or reduced in proportion, it is within the scope disclosed in the embodiment of the present application. Specifically, mL in the embodiment of the present application can be converted into μL, mL, L, mm 3 Volume units known in the chemical field; mmol in the embodiment of the present application can be converted into μmol, mol and other molar units known in the chemical field.

[0052] In the first aspect, the embodiment provides a high-precision speckle preparation and optimization method. The embodiment can efficiently improve the speckle image quality and obtain a high-precision material surface strain field distribution cloud diagram through the optimization method. It involves the selection of nanometer gold speckle size, the preparation method of high-precision speckle and the optimization method. In the embodiment, the original speckle solvent used in the method is nanometer gold aqueous solution.

[0053] According to the drawings Figure 1 The high-precision speckle preparation and optimization method specifically includes the following steps:

[0054] S1: determining the speckle size suitable for the sample, and selecting nanometer gold-water solution of the size;

[0055] S2: process the sample to a sample size suitable for the speckle size, and pretreat the surface of the sample; in this embodiment, the pretreatment methods of the surface of the sample include, but are not limited to, surface polishing, etching cleaning, etc., and it should be noted that this embodiment is only a general example, and other equivalent surface pretreatment methods are also applicable.

[0056] S3: obtain a nano-gold-ethanol solution from the nano-gold-water solution;

[0057] S4: drop coat the nano-gold-ethanol solution on the surface of the sample, and evaporate the ethanol solution;

[0058] S5: after the ethanol solution on the surface of the sample is evaporated, repeat the previous step until a proper speckle distribution density is obtained, and a high-precision speckle is prepared.

[0059] In some embodiments, the method for determining the speckle size suitable for the sample is as follows:

[0060] Establish a speckle distribution density formula In the formula:

[0061] ρ is the speckle distribution density;

[0062] n is the number of speckles contained in the subset;

[0063] d is the equivalent diameter of the speckle;

[0064] M is the magnification of the electron microscope photograph;

[0065] s is the length of the subset.

[0066] In some embodiments, the method for obtaining the nano-gold-ethanol solution is as follows: take an appropriate amount of nano-gold-water solution, centrifuge, remove the upper water solution, and add anhydrous ethanol to the nano-gold precipitate at the bottom.

[0067] In some embodiments, the parameters of the centrifugation are 6000-9000 r / min for 2-8 min.

[0068] In some embodiments, the volume of the injected ethanol solution is 1 / 4-1 / 2 of the volume of the replaced water solution.

[0069] In some embodiments, it further includes a speckle optimization step,

[0070] S6: use an electron microscope to take pictures of the sample surface before and after loading, and determine the electron microscope parameters;

[0071] S7: import the sample surface picture into a digital image software, adjust the subset parameters of the speckles, and further optimize the speckle precision.

[0072] In some embodiments, the contrast and brightness of the front / back photographed pictures of the sample surface are consistent.

[0073] In some embodiments, the picture resolution of the electron microscope is 2048x1536 pixels.

[0074] In some embodiments, the subset of the speckles contains at least 3 × speckles.

[0075] In some embodiments, the electron microscope parameters include picture magnification, contrast, brightness and resolution.

[0076] In a second aspect, the embodiments also provide a high-precision speckle, which is prepared by the high-precision speckle preparation and optimization method according to any one of the above embodiments. The high-quality speckle further improves the accuracy of the measurement results, and at the same time meets the three conditions of contrast, randomness and anisotropy.

[0077] In a third aspect, the embodiments also provide an application of the high-precision speckle, which is used for fatigue test or stress or tensile or residual stress test. The high-precision speckle can be applied to fatigue test and stress test of various samples, and has a wider application range and higher precision.

[0078] It should be noted that only the fatigue test is explained in detail in this embodiment, and the steps of the stress test or other equivalent applications can be applied by conventional steps.

[0079] Embodiment 1

[0080] This embodiment takes a welded rotor of a steam turbine as an example, and the rotor material is 25Cr2Ni2MoV. A high-precision speckle preparation and optimization method is provided, which includes the following steps:

[0081] S1: Under 2000 times, the sample surface speckle spraying condition is inspected, the speckle size that meets the experimental requirements and is suitable for the sample is determined according to the speckle distribution density formula, and a nanometer gold-water solution of the size is selected. In this embodiment, nanometer gold with an equivalent diameter of 200 nm is selected.

[0082] In this step, the speckle distribution density formula used is: In the formula,

[0083] ρ is the speckle distribution density;

[0084] n is the number of speckles contained in the subset;

[0085] d is the equivalent diameter of the speckle;

[0086] M is the magnification of the electron microscope photograph;

[0087] s is the subset edge length.

[0088] S2: refer to the attached Figure 2 The sample is processed to a sample size that matches the speckle size and meets the experimental requirements, and the surface of the sample is pretreated, including polishing the surface of the sample in advance and etching and cleaning the polished sample surface with an acidic or alkaline solution. The above two polishing or etching and cleaning methods can be repeatedly or separately applied, or other equivalent surface pretreatment methods are also applicable. In this embodiment, the compact tension sample with a pre-existing crack is processed into a bone-shaped sample, and the surface of the sample is polished and etched and cleaned.

[0089] S3: Obtain a nano-gold-ethanol solution from the nano-gold-water solution. In some embodiments, the method of obtaining a nano-gold-ethanol solution is as follows: take an appropriate amount of nano-gold-water solution, centrifuge, remove the upper water solution, and add anhydrous ethanol to the nano-gold precipitate at the bottom.

[0090] In this embodiment, an appropriate amount of nano-gold-water solution is injected into a centrifuge tube and placed in a centrifuge at a speed of 6000 r / min for 2 min. The water solution separated at the top of the centrifuge tube is removed with a pipette, and anhydrous ethanol is added to the nano-gold precipitate at the bottom of the centrifuge tube. In this embodiment, the volume of the injected ethanol solution is 1 / 4 of the volume of the water solution displaced.

[0091] S4: Drop the nano-gold-ethanol solution on the surface of the sample and evaporate the ethanol solution. The sample is placed on a constant temperature heating platform for heating and incubation. The nano-gold ethanol solution is taken with a dropper and dropped on the observation surface of the sample. The heating temperature is 80°C, and the incubation time is 30s.

[0092] S5: refer to the attached Figure 3 After the ethanol solution on the surface of the sample is evaporated, S4 is repeated, and the speckle distribution density is observed under an electron microscope until a proper and satisfactory speckle distribution density is obtained.

[0093] In this embodiment, the speckle can be further optimized as follows:

[0094] S6: refer to the attached Figure 4 The sample surface before / after loading is photographed using an electron microscope to determine the electron microscope parameters. It should be noted that in this embodiment, the electron microscope parameters include the magnification, contrast, brightness, and resolution of the picture in this step. The contrast and brightness of the before / after photographed sample surface pictures are consistent, and the picture resolution of the electron microscope is 2048x1536 pixels. In this embodiment, the morphology of the sample crack tip before loading is photographed using an electron microscope to determine the picture magnification, contrast, brightness, and resolution. The figure serves as a reference image for strain characterization.

[0095] S7: importing the sample surface picture into digital image software, adjusting the subset parameters of the speckle, in the embodiment, at least 3 × speckles are contained in the subset of the speckle, and the speckle precision is further optimized.

[0096] Based on the above steps, a high-precision speckle can be obtained in the embodiment, and the high-quality and high-precision speckle further improves the precision of the measurement result, and at the same time, the contrast, randomness and anisotropy conditions are met.

[0097] Based on the obtained high-precision speckle, the embodiment can further provide an application of the high-precision speckle, and the high-precision speckle is used for fatigue test or stress test. The high-precision speckle can be applied to fatigue test and stress test of various samples, and has a wider application range and higher precision.

[0098] The embodiment takes fatigue test as an example:

[0099] S8: using an in-situ tensile test bench in an electron microscope cabin to perform fatigue test on the sample, and shooting pictures of the same position of the sample under different loading cycles at the same magnification; using the in-situ tensile test bench in the electron microscope cabin to perform fatigue test on the sample, and shooting pictures of the crack tip of the sample under different loading cycles at the same magnification, at this time, it is noted that the field of view range of each picture is the same;

[0100] S9: referring to the attached Figure 5 , high-precision characterization of strain field change at the crack tip of the sample in the fatigue loading process is performed by using digital image correlation (DIC) software. The digital image correlation (DIC) has the characteristics of high measurement precision, multi-scale measurement and non-contact, and gradually becomes one of the measurement methods for displacement and strain in the material deformation process. DIC is a method of preparing speckles on the surface of the sample, shooting speckle pictures of the sample before and after applying external force load, and obtaining the displacement field and strain field of the sample surface by related operation according to the speckle picture. In the embodiment, the digital image correlation (DIC) software is used to high-precision characterize the strain field change at the crack tip of the sample in the fatigue loading process.

[0101] It should be noted that only fatigue test is explained in detail in the embodiment, and the steps of stress test or other equivalent applications can be applied by conventional steps.

[0102] Embodiment 2

[0103] The embodiment provides a high-precision speckle preparation and optimization method. Compared with the embodiment 1, the equivalent diameter of the gold nanoparticles is 100 nm in the embodiment, and the difference includes:

[0104] S3: obtaining a nano-gold-ethanol solution from the nano-gold-water solution; in some embodiments, the method of obtaining a nano-gold-ethanol solution is as follows: taking an appropriate amount of nano-gold-water solution, centrifugal separation, removing the upper water solution, and adding anhydrous ethanol to the nano-gold precipitated at the bottom.

[0105] In this embodiment, an appropriate amount of nano-gold-water solution is injected into a centrifuge tube, placed in a centrifuge, centrifuged at a speed of 6500 r / min for 8 min, the separated water solution at the top of the centrifuge tube is removed with a pipette, and anhydrous ethanol is added to the nano-gold precipitated at the bottom of the centrifuge tube. In this embodiment, the volume of the injected ethanol solution is 1 / 4 of the volume of the water solution replaced.

[0106] S4: drop coating the nano-gold-ethanol solution on the surface of the sample, and evaporating the ethanol solution; placing the sample on a constant temperature heating platform for heating and incubation, using a dropper to suck the nano-gold ethanol solution and drop coating it on the observation surface of the sample; the heating temperature is 80℃, and the incubation time is 1 min; since the sample surface is small and the anhydrous ethanol is drop coated, the evaporation speed is very fast, and a high temperature is not needed, therefore, as an alternative, the sample heating in this place can be replaced by cold strong wind blowing the sample surface or using an electric hair dryer to blow the sample surface to reach the heating temperature.

[0107] In this embodiment, the speckle can be further optimized, and the specific steps are as follows:

[0108] S6: taking pictures of the sample surface before / after loading using an electron microscope to determine the electron microscope parameters; it should be noted that in this embodiment, the electron microscope parameters include the magnification, contrast, brightness and resolution of the pictures in this step; the contrast and brightness of the pictures of the sample surface before / after taking are consistent, and the picture resolution of the electron microscope is 2048x1536 pixels. This data is mainly related to the values in the speckle distribution density formula, and in this embodiment, 138 is taken as an example, which is the ratio of the picture size to the picture resolution during scanning, and in other embodiments, the corresponding values in the speckle distribution density formula can be changed by selecting the resolution.

[0109] S7: importing the sample surface pictures into digital image software to adjust the subset parameters of the speckles, in this embodiment, the subset of the speckles at least contains 4 × 4 speckles, and the speckle accuracy is further optimized.

[0110] Based on the above steps, a high-precision speckle can be obtained in this embodiment, and the high-quality and high-precision speckle further improves the accuracy of the measurement results, and at the same time meets the three conditions of contrast, randomness and anisotropy.

[0111] Based on the obtained high-precision speckle, the fatigue test can be further carried out based on the same test method in Embodiment 1.

[0112] Embodiment 3

[0113] The embodiment provides a high-precision speckle preparation and optimization method. In comparison with Embodiment 1, the equivalent diameter of the gold nanoparticles is 50 nm in the embodiment, and the difference between the steps comprises the following steps.

[0114] S3: obtaining a gold nanoparticle-ethanol solution from the gold nanoparticle-water solution; in some embodiments, the method for obtaining the gold nanoparticle-ethanol solution is as follows: taking an appropriate amount of the gold nanoparticle-water solution, centrifuging, removing the upper water solution, and adding anhydrous ethanol to the bottom precipitated gold nanoparticles.

[0115] In the embodiment, an appropriate amount of gold nanoparticle-water solution is injected into a centrifuge tube, and placed in a centrifuge at a speed of 7000 r / min for 5 min. The water solution separated from the top of the centrifuge tube is removed by a pipette, and anhydrous ethanol is added to the precipitated gold nanoparticles at the bottom of the centrifuge tube. In the embodiment, the volume of the injected ethanol solution is 1 / 3 of the volume of the removed water solution.

[0116] S4: dropping the gold nanoparticle-ethanol solution on the surface of the sample and evaporating the ethanol solution; placing the sample on a constant temperature heating table for heating and incubation, using a dropper to suck the gold nanoparticle-ethanol solution and drop it on the observation surface of the sample; the heating temperature is 90°C, and the incubation time is 1 min.

[0117] In the embodiment, the speckle can be further optimized, and the specific steps are as follows:

[0118] S6: using an electron microscope to shoot the pictures of the sample surface before and after loading, and determining the electron microscope parameters; it should be noted that the electron microscope parameters in the embodiment include the picture magnification, contrast, brightness and resolution in the step; the contrast and brightness of the pictures of the sample surface before and after shooting are consistent, and the picture resolution of the electron microscope is 2048x1536 pixels.

[0119] S7: importing the sample surface pictures into a digital image software, and adjusting the subset parameters of the speckles; in the embodiment, the subset of the speckles at least contains 5 × 5 speckles, and the speckle precision is further optimized.

[0120] Based on the above steps, a high-precision speckle can be obtained in the embodiment. The high-quality speckle further improves the precision of the measurement result, and at the same time meets the three conditions of contrast, randomness and anisotropy.

[0121] Based on the obtained high-precision speckle, the fatigue test can be further carried out based on the same test method in Embodiment 1 using the high-precision speckle obtained in the embodiment.

[0122] Embodiment 4

[0123] The embodiment provides a high-precision speckle preparation and optimization method. In the embodiment, gold nanoparticles with an equivalent diameter of 100 nm are selected, and the difference between the embodiment and Embodiment 1 is that the steps include:

[0124] S3: obtaining a gold nanoparticle-ethanol solution from the gold nanoparticle-water solution; in some embodiments, the method for obtaining the gold nanoparticle-ethanol solution is as follows: taking an appropriate amount of gold nanoparticle-water solution, centrifuging, removing the upper water solution, and adding anhydrous ethanol to the bottom precipitated gold nanoparticles.

[0125] In the embodiment, an appropriate amount of gold nanoparticle-water solution is injected into a centrifuge tube, placed in a centrifuge, centrifuged at a speed of 7000 r / min for 4 min, the separated water solution on the top of the centrifuge tube is removed by a pipette, and anhydrous ethanol is added to the precipitated gold nanoparticles at the bottom of the centrifuge tube. In the embodiment, the volume of the injected ethanol solution is 1 / 2 of the volume of the water solution replaced;

[0126] S4: dropping the gold nanoparticle-ethanol solution on the surface of the sample and evaporating the ethanol solution; placing the sample on a constant temperature heating table for heating and incubation, using a dropper to suck the gold nanoparticle-ethanol solution and drop it on the observation surface of the sample; the heating temperature is 85°C, and the incubation time is 45s;

[0127] In the embodiment, the speckle can be further optimized, and the specific steps are as follows:

[0128] S6: using an electron microscope to shoot the pictures of the sample surface before and after loading to determine the electron microscope parameters; it should be noted that in the embodiment, the electron microscope parameters include the picture magnification, contrast, brightness and resolution in the step; the contrast and brightness of the pictures of the sample surface before and after shooting are consistent, and the picture resolution of the electron microscope is 2048x1536 pixels.

[0129] S7: importing the sample surface pictures into a digital image software to adjust the subset parameters of the speckle; in the embodiment, the subset of the speckle contains at least 5 × 5 speckles, and the speckle precision is further optimized.

[0130] Based on the above steps, a high-precision speckle can be obtained in the embodiment, and the high-quality speckle further improves the precision of the measurement result, and at the same time meets the three conditions of contrast, randomness and anisotropy.

[0131] Based on the obtained high-precision speckle, the fatigue test can be further carried out based on the same test method in Embodiment 1.

[0132] Embodiment 5

[0133] The embodiment provides a high-precision speckle preparation and optimization method. In the embodiment, the equivalent diameter of the gold nanoparticles is 100 nm. The difference between the embodiment and Embodiment 1 is that the steps include the following steps.

[0134] S3: obtaining a gold nanoparticle-ethanol solution from the gold nanoparticle-water solution; in some embodiments, the method for obtaining the gold nanoparticle-ethanol solution is as follows: taking an appropriate amount of the gold nanoparticle-water solution, centrifuging, removing the upper water solution, and adding anhydrous ethanol to the bottom precipitated gold nanoparticles.

[0135] In the embodiment, an appropriate amount of gold nanoparticle-water solution is injected into a centrifuge tube, and placed in a centrifuge at a speed of 8000 r / min for 2 min. The water solution separated from the top of the centrifuge tube is removed by a pipette gun, and anhydrous ethanol is added to the precipitated gold nanoparticles at the bottom of the centrifuge tube. In the embodiment, the volume of the injected ethanol solution is 1 / 2 of the volume of the removed water solution.

[0136] S4: dropping the gold nanoparticle-ethanol solution on the surface of the sample and evaporating the ethanol solution; placing the sample on a constant temperature heating table for heating and incubation, using a dropper to suck the gold nanoparticle-ethanol solution and drop it on the observation surface of the sample; the heating temperature is 88°C, and the incubation time is 25 s.

[0137] In the embodiment, the speckle can be further optimized, and the specific steps are as follows:

[0138] S6: using an electron microscope to shoot the pictures of the sample surface before and after loading, and determining the electron microscope parameters; it should be noted that the electron microscope parameters in the embodiment include the picture magnification, contrast, brightness and resolution in the step; the contrast and brightness of the pictures of the sample surface before and after shooting are consistent, and the picture resolution of the electron microscope is 2048x1536 pixels.

[0139] S7: importing the sample surface pictures into a digital image software, and adjusting the subset parameters of the speckles; in the embodiment, the subset of the speckles at least contains 4 × four speckles, and the speckle precision is further optimized.

[0140] Based on the above steps, a high-precision speckle can be obtained in the embodiment. The high-quality speckle further improves the precision of the measurement result, and at the same time meets the three conditions of contrast, randomness and anisotropy.

[0141] Based on the obtained high-precision speckle, the same test method as in Embodiment 1 can be further used to perform a fatigue test on the high-precision speckle obtained in this embodiment.

[0142] Embodiment 6

[0143] This embodiment provides a high-precision speckle preparation and optimization method, which is different from Embodiment 1 in the following steps:

[0144] S3: Obtain a gold nanoparticle-ethanol solution from the gold nanoparticle-water solution; in some embodiments, the method for obtaining the gold nanoparticle-ethanol solution is as follows: take an appropriate amount of gold nanoparticle-water solution, centrifuge, remove the upper water solution, and add anhydrous ethanol to the bottom precipitated gold nanoparticles.

[0145] In this embodiment, an appropriate amount of gold nanoparticle-water solution is injected into a centrifuge tube and placed in a centrifuge at a speed of 9000 r / min for 6 min. The water solution separated from the top of the centrifuge tube is removed with a pipette, and anhydrous ethanol is added to the precipitated gold nanoparticles at the bottom of the centrifuge tube. In this embodiment, the volume of the injected ethanol solution is 1 / 2 of the volume of the water solution removed;

[0146] S4: Drop the gold nanoparticle-ethanol solution on the surface of the sample and evaporate the ethanol solution; place the sample on a constant temperature heating platform for heating and incubation, use a dropper to suck the gold nanoparticle-ethanol solution and drop it on the observation surface of the sample; the heating temperature is 82°C, and the incubation time is 1 min;

[0147] In this embodiment, the speckle can be further optimized, and the specific steps are as follows:

[0148] S6: Use an electron microscope to take pictures of the sample surface before and after loading to determine the electron microscope parameters; it should be noted that in this embodiment, the electron microscope parameters include the magnification, contrast, brightness, and resolution of the pictures in this step; ensure that the contrast and brightness of the before / after taken sample surface pictures are consistent, and the picture resolution of the electron microscope is 2048x1536 pixels.

[0149] S7: Import the sample surface pictures into a digital image software and adjust the subset parameters of the speckle; in this embodiment, the subset of the speckle contains at least 3 × 3 speckles, and the speckle precision is further optimized.

[0150] Based on the above steps, a high-precision speckle can be obtained in this embodiment. The high-quality and high-precision speckle further improves the precision of the measurement results, and at the same time meets the three conditions of contrast, randomness, and anisotropy.

[0151] Based on the obtained high-precision speckle, the fatigue test can be further carried out based on the same test method in Embodiment 1.

[0152] In a third aspect, the embodiment provides a strain measurement method of high-precision speckle, characterized in that the digital image correlation method (DIC) software is used to characterize the strain field change at the crack tip of the sample in the fatigue loading process with high precision; the method comprises the following steps:

[0153] The speckle size suitable for the sample is determined, and the nanogold-water solution with the size is selected;

[0154] The sample is processed to the sample size suitable for the speckle size, and the surface of the sample is pretreated;

[0155] The nanogold-ethanol solution is obtained from the nanogold-water solution;

[0156] The nanogold-ethanol solution is drop-coated on the surface of the sample, and the ethanol solution is evaporated;

[0157] After the ethanol solution on the surface of the sample is evaporated, the previous step is repeated until the appropriate speckle distribution density is obtained, and the high-precision speckle is prepared;

[0158] The strain measurement test of the sample is carried out in the electron microscope cabin using the in-situ tensile test bench, and the pictures of the same position of the sample under the same magnification and different loading cycles are taken; the fatigue test of the sample is carried out in the electron microscope cabin using the in-situ tensile test bench, and the pictures of the crack tip of the sample under the same magnification and different loading cycles are taken, at this time, it is noted that the field of view range of each picture is the same,

[0159] The method for obtaining the displacement field and the strain field of the surface of the sample according to the speckle diagram.

[0160] The high-precision speckle and the preparation and optimization and strain measurement method thereof provided by the embodiment of the application are described in detail above, and the principles and implementation manners of the application are described by applying specific examples; the above embodiment is only used to help understand the method and the core idea thereof; at the same time, for those skilled in the art, according to the idea of the application, the specific implementation manner and application range will be changed, and the above description should not be understood as a limitation of the application.

Claims

1. A method for preparing high-precision speckle patterns, characterized in that, Includes the following steps: Determine the speckle size suitable for the sample, and select a nano-gold-water solution of the specified size; The sample is processed to a size that matches the speckle size, and the surface of the sample is pretreated. A gold nanoparticle-ethanol solution was obtained via the aforementioned gold nanoparticle-water solution; A nano-gold-ethanol solution was drop-coated onto the surface of the sample, and the ethanol solution was evaporated. After the ethanol solution on the surface of the sample evaporates, repeat the previous step until an appropriate speckle distribution density is obtained, thus preparing a high-precision speckle pattern. The method for determining the speckle size suitable for the sample is as follows: Establish the formula for speckle distribution density In the formula: ρ The density of speckle distribution; n is the number of speckle patterns contained in the subset; d is the equivalent diameter of the speckle pattern; M is the magnification of the electron microscope image; s is the side length of the subset.

2. The high-precision speckle pattern preparation method according to claim 1, characterized in that, The method for obtaining a nano-gold-ethanol solution is as follows: Take an appropriate amount of nano-gold aqueous solution, centrifuge to separate, remove the upper aqueous solution, and add anhydrous ethanol to the nano-gold precipitate at the bottom.

3. The high-precision speckle pattern preparation method according to claim 2, characterized in that: The centrifugation parameters are: centrifugation at a speed of 6000-9000 r / min for 2-8 min; and / or the volume of anhydrous ethanol solution added is 1 / 4 to 1 / 2 of the volume of the displaced aqueous solution.

4. The high-precision speckle preparation and optimization method according to claim 1, characterized in that: It also includes a speckle optimization step. Use an electron microscope to take images of the sample surface before and after loading to determine the electron microscope parameters; The sample surface image was imported into digital image processing software, and the subset parameters of the speckle pattern were adjusted to further optimize the speckle accuracy.

5. The high-precision speckle pattern preparation method according to claim 4, characterized in that: The contrast and brightness of the sample surface images taken before and after are consistent; and / or the electron microscope images have a resolution of 2048×1536 pixels; and / or the electron microscope parameters include image magnification, contrast, brightness, and resolution.

6. The high-precision speckle pattern preparation method according to claim 5, characterized in that: The subset of speckle contains at least 3 × Three speckled spots.

7. A high-precision speckle pattern, characterized in that: The speckle pattern prepared by the high-precision speckle preparation method according to any one of claims 1-6.

8. A high-precision strain measurement method for speckle patterns, characterized in that, The strain field changes at the crack tip of the specimen during fatigue loading were characterized with high precision using digital image correlation (DIC) software; the process included the following steps: Determine the speckle size suitable for the sample, and select a nano-gold-water solution of the specified size; The sample is processed to a size that matches the speckle size, and the surface of the sample is pretreated. A gold nanoparticle-ethanol solution was obtained via the aforementioned gold nanoparticle-water solution; A nano-gold-ethanol solution was drop-coated onto the surface of the sample, and the ethanol solution was evaporated. After the ethanol solution on the surface of the sample evaporates, repeat the previous step until an appropriate speckle distribution density is obtained, thus preparing a high-precision speckle pattern. Strain measurements were performed on the specimens using an in-situ tensile testing machine in the electron microscope chamber. Images of the same location on the specimens were taken at the same magnification but under different loading cycles. Fatigue tests were also performed on the specimens using the same in-situ tensile testing machine in the electron microscope chamber. Images of the crack tips on the specimens were taken at the same magnification but under different loading cycles. Care was taken to ensure that the field of view was the same for each image. A method for obtaining the displacement and strain fields of the sample surface by performing relevant calculations based on speckle diagrams; The method for determining the speckle size suitable for the sample is as follows: Establish the formula for speckle distribution density In the formula: ρ is the speckle distribution density; n is the number of speckle patterns contained in the subset; d is the equivalent diameter of the speckle pattern; M is the magnification of the electron microscope image; s is the side length of the subset.

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