Optimized measurement method of soft material strain field based on digital image correlation technique

Abstract

The application discloses a kind of soft material strain field optimization measurement method based on digital image correlation technology, the application realizes the application of digital image correlation technology in soft material mechanics field, introduces three data processing algorithms of data link, data transmission, data compensation on the basis of existing digital image correlation technology, solves the indirect contact problem, data loss problem and large deformation inadaptation problem of digital image correlation technology in soft material mechanics experimental measurement, establishes complete use method, provides new ideas and methods for the research of large deformation mechanics performance of hydrogel, shape memory polymer and other soft materials, makes up the deficiency of traditional soft material fracture toughness test method, with potential application value.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of indirect contact displacement field, strain field measurement method, specifically to a kind of soft material strain field optimization measurement method based on digital image correlation technology. BACKGROUND

[0002] In the research of soft material mechanical properties, the nonlinear deformation behavior of soft material, super-elastic behavior and various non-continuous deformation behavior, including fatigue characteristics, peeling characteristics, defect initiation, crack propagation and other mechanical behaviors, are important research directions. At present, the experimental measurement of various mechanical properties of soft material mainly relies on tensile testing machine or extensometer, and the load-displacement curve of soft material under different loading conditions is obtained by uniaxial tension, fatigue cycle loading, peeling and other methods. Further, the stress-strain curve is obtained by calculation, and the non-continuous deformation behavior of the material is analyzed based on the stress-strain curve. However, the traditional measurement method can only obtain the load and displacement of the specimen at the clamping position, and for the material inside, especially for the specimen with complex shape, internal defects, cracks and notches, various physical information inside the material far from the boundary, including local stress field, crack morphology and other information cannot be directly obtained.

[0003] Digital image correlation (Digital Image Correlation, DIC for short) technology is a measurement method for obtaining specimen surface displacement field and strain field through image processing, and is widely used in various research fields of material mechanics. Digital image correlation technology requires uniform arrangement of black and white speckle patterns on the surface of the specimen to be tested, and uses a camera to shoot the loading process of the specimen to be tested. Digital image correlation technology divides the captured image data into grids, and uses image correlation matching algorithm to correlate the gray-scale images in each grid, so as to calculate the displacement of the area corresponding to each grid. The correlation matching algorithm involved in digital image correlation technology is to introduce a correlation coefficient C(f(x i ,y i ),g(x′ i ,y′ i )) where f(x i ,y i ) is the gray-scale function of the area grid to be solved, g(x′ i ,y′ i) is the gray function of any region grid after deformation, and the digital image correlation technology finds the region of the grid after deformation that makes the correlation function reach the minimum value by comparing the correlation coefficient of the gray function of each grid after deformation with the gray function of the grid to be solved, and considers the position of the grid after deformation. Subsequently, the displacement and strain occurring are calculated according to the coordinates of the center point. The correlation coefficients commonly used by the digital image correlation technology mainly include two kinds, namely, the cross-correlation criterion and the sum of squares of differences criterion.

[0004] The upper limit of the accuracy of the digital image correlation technology as a displacement field measurement method based on image processing comes from the image accuracy and completeness. When the continuous deformation of the measured object reaches the limit, the material starts to appear damage and other non-continuous deformation. The site where the material damage occurs and the grid corresponding to the site will be invalid, causing the strain field information of the site to be lost. Therefore, the digital image correlation technology mainly has three defects in the field of soft material mechanics: indirect contact problem, data loss and large deformation inadaptation. The main performances of each defect are as follows:

[0005] 1) Indirect contact problem

[0006] The digital image correlation technology is an indirect contact optical measurement method, which needs to arrange a speckle pattern on the surface of the sample. When performing experiments on soft materials such as hydrogel, an appropriate paint must be found. For soft materials, especially for hydrogel and other soft materials with high water content, soft texture and easy to be affected by environmental factors such as temperature, humidity and external force, the selection of the paint for the speckle pattern has strict conditions, which must ensure that the paint is selected without affecting the mechanical properties of the soft material.

[0007] 2) Data loss

[0008] The measurement principle of the digital image correlation technology is to calculate the similarity between the sub-regions of two images to obtain the strain of the center point. In soft material experiments, local fracture, large deformation and other mechanical behaviors often occur, which causes the speckle pattern in the region to be squeezed and deformed, loses the digital features of the image, and leads to the loss of local point data or too large local error.

[0009] 3) Large deformation inadaptation

[0010] The identification basis of the digital image correlation technology is the speckle pattern on the surface of the sample. For large deformation soft materials, the deformation rate can sometimes reach 500%, 1000% or even higher. High deformation rate means that the quality of the speckle pattern on the surface of the test sample decreases, and the surface image will lose digital features and cause data loss, which leads to inevitable decline in image recognition accuracy.

[0011] Due to the existence of the above three problems, the digital image correlation technology cannot be directly applied in the field of soft material mechanics experiment measurement. SUMMARY

[0012] In order to solve the problems of the digital image correlation technology in the field of soft material mechanics, the application provides a soft material strain field optimization measurement method based on the digital image correlation technology, so that the digital image correlation technology can be well applied in the field of soft material mechanics, and the surface displacement field and strain field data of the soft material can be accurately measured and calculated.

[0013] In order to achieve the above object, the application adopts the following technical scheme:

[0014] The soft material strain field optimization measurement method based on the digital image correlation technology has the following specific steps:

[0015] Step 1: first, according to the specific physical and chemical properties of the measured soft material sample, select the appropriate speckle paint, and then arrange the speckle pattern according to the equipment requirements of the digital image correlation technology used;

[0016] Step 2: design the experimental process according to the experimental needs, and perform a pre-experiment to determine the experimental range, select the segmented interval according to the deformation degree of the measured soft material sample measured by the pre-experiment, and take 10% strain or 20% strain as the segmentation point;

[0017] Step 3: according to the segmented interval determined in step 2, perform a formal test, and supplement the speckle on the surface of the soft material sample after each segment ends; the supplemental paint needs to be supplemented to the accuracy requirement of the digital image correlation technology equipment; after each segment experiment ends, export the initial data file and the last time data file of each segment through the digital image correlation technology equipment, and name them in time sequence to ensure that all data files are arranged in time sequence;

[0018] Step 4: import the initial data and the last time data of each segmented interval into the data processing computer, and calculate the full-field displacement and strain data by using the data linking algorithm, the data compensation algorithm and the data transmission algorithm.

[0019] As described in step 1, according to the specific physical and chemical properties of the measured soft material sample, the appropriate speckle paint is selected, and the selection method of the speckle paint is: for the material with high strength and no water absorption, select the spray paint, carbon powder or eye shadow powder; for the material with weak strength and good hydrophilicity, and the surface has adhesion, use eye shadow powder or carbon powder solid particles.

[0020] The data compensation algorithm in step 4 has the following specific contents:

[0021] The data compensation algorithm is an improved algorithm for the data loss problem of digital image correlation technology. In the observation process, the digital image correlation technology may lose the digital features of the image due to excessive local deformation of the tested sample, resulting in the loss of part of the data. In addition, due to the segmented measurement, each segment needs to be manually divided and calculated, and the calculation area of each segment is different, resulting in the loss of part of the image data and the corresponding data points at the boundary in the data linking process. The lost data points have three parts: the data points that cannot be identified due to the loss of local pattern features in the calculation process of the digital image correlation technology, the data points that need to be cleared and revalued due to the excessive error, and the points that are not successfully matched in the data linking process.

[0022] To solve the data loss problem, the method of interpolation after segmentation is used to fill the data by referring to the idea of finite element. That is, by predefining the interpolation function

[0023]

[0024] wherein

[0025] represents the coordinate point coordinate that needs to be interpolated;

[0026] independent variable is a function, which represents the interpolation result.

[0027] The interpolation method function used is

[0028] Unknown coefficient vector of polynomial product

[0029] The incomplete scattered data obtained by the digital image correlation technology is segmented, and a finite number of units are obtained after segmentation. The interpolation data field is calculated in each unit by the interpolation method, that is, the interpolation data field is obtained The lost data point coordinates are substituted into the interpolation function, and the lost data point is found in the segmented unit and is valued.

[0030] The data linking algorithm in step 4 has the following specific content:

[0031] First, the data of the last photo of a segment is derived, including the coordinates (x, y) and the displacement (u, v). The data represents the displacement (u, v) of the data point with coordinates (x, y) in the reference photo of the segment. Then the new coordinate point position (x′, y′) of the data point moved to is obtained, which is (x+u, y+v).

[0032] The reference photo data of the next segment of data is assigned: since (x, y) is the lens pixel grid coordinates of the digital image correlation technology high-speed camera in the initial state, (x, y) are all integers; however, (u, v) represents the displacement of a certain calculation area, which is not an integer, so the new coordinate point (x', y') is a vector composed of two small arrays, and there is no corresponding lens pixel grid point corresponding to it, but the new coordinate point (x', y') will inevitably fall into a four-pixel region composed of four pixel points ([x'], [y']), ([x'] + 1, [y']), ([x'], [y'] + 1), ([x'] + 1, [y'] + 1), where [] is the floor operator, the strain value and displacement value of the new coordinate point (x', y') are assigned to the surrounding four points, and then all the initial state data points are assigned to the deformed blank data points, and the multiple assigned points are averaged, that is, the data linking between the two segments of data is completed.

[0033] The data transmission algorithm in step 4 has the following specific content:

[0034] The displacement and strain calculated by the digital image correlation technology each time a picture is imported are the displacement and strain calculated by taking one of the pictures in the segment as the reference picture relative to the first picture in the segment. Considering that the strain calculated by the digital image correlation technology is engineering strain, the true strain under each picture in each segment is obtained by calculation using geometric relationships; according to the mathematical definition of engineering strain, the digital image correlation technology calculates the strain value of each segment of data relative to the first reference picture in the segment:

[0035]

[0036]

[0037]

[0038] In the formula:

[0039] ε1, ε2, ε3 are the strain fields of the tested sample at time 1, time 2, and time 3 calculated by the digital image correlation technology; l0, l1, l2, l3 are transition variables in the mathematical definition of strain;

[0040] By multiplying, the strain value of each point in the picture P corresponding to time k relative to the initial state is obtained: k

[0041]

[0042] In the formula: ε k is the picture P corresponding to time k​k the true strain of each point relative to the initial state; are respectively the strain of the test sample at k-1, k-2 and 1 calculated by digital image correlation technology; l k , l k-1 , l k-2 , l k-3 is a transition variable in the mathematical definition of strain;

[0043] The displacement data and strain data of each scattered data set are transmitted through the geometric relationship, and then the strain values of the test sample at all times during the entire experiment are obtained.

[0044] Compared with the prior art, the present application has the following advantages:

[0045] 1) The device requires simple operation, and only one data processing computer is needed to realize the upgrading and optimization of the digital image correlation technology.

[0046] 2) The present application develops data linking, data transmission and data compensation algorithms, and a complete experimental process on the basis of the existing digital image correlation technology. The data compensation algorithm solves the data loss problem of the digital image correlation technology in the field of soft material mechanics, and the data linking, data transmission and segmented experiment overcome the problem of large deformation inadaptation of the digital image correlation technology in the field of soft material mechanics, providing new experimental method support for the research of non-continuous mechanical behavior of soft material mechanics, such as fracture and large deformation. BRIEF DESCRIPTION OF DRAWINGS

[0047] Figure 1 The present application is a method flowchart.

[0048] Figure 2 The present application is a hardware system schematic diagram. Wherein 1 is a stretcher, 2 is a digital image correlation technology high-speed camera, 3 is a data processing computer, and 4 is a test sample.

[0049] Figure 3 The size of the hydrogel material selected in the embodiment is shown in the schematic diagram.

[0050] Figure 4a There is still an area not covered by paint at the center position of the test sample, which needs further paint supplement. Figure 4b The solid particle paint is uniformly arranged on the surface of the test sample, forming a uniform and random speckle pattern on the surface of the test sample.

[0051] Figure 5 The present application is a schematic diagram of the principle of data linking in the algorithm part.

[0052] Figure 6 The flowchart of the data linking, data compensation and data transmission algorithm designed for the present application in the data processing process.

[0053] Figure 7 The displacement field false color maps of a piece of hydrogel tested sample measured and calculated by using the present application at the 10th photo, the 50th photo, the 100th photo and the 140th photo, wherein, figure a is the 10th photo, i.e. the displacement field false color map at 10 seconds of loading; figure b is the 50th photo, i.e. the displacement field false color map at 50 seconds of loading; figure c is the 100th photo, i.e. the displacement field false color map at 100 seconds of loading; figure d is the 140th photo, i.e. the displacement field false color map at 140 seconds of loading. DETAILED DESCRIPTION

[0054] The present application will be further described in detail below in combination with the drawings and specific embodiments.

[0055] On the basis of the existing digital image correlation technology, the present application designs an optimized experimental method, including inventing a new experimental process for the original digital image correlation technology in the experimental process, and writing a set of calculation code by using MATLAB.

[0056] The experimental method part of the present application is: by means of segmented measurement, the deformation problem and the complex deformation problem of the soft material mechanical property experiment are divided into multiple small intervals, the deformation field is measured and calculated in each small interval independently by using the digital image correlation technology equipment, and the starting data and the final data of each small interval are reserved.

[0057] As shown in Figure 1 , the specific embodiment of the experimental method part is:

[0058] Step 1: first, according to the specific physical and chemical properties of the soft material sample to be measured, select the appropriate speckle paint. For water-containing materials such as hydrogel, which have high water content and low strength, solid particles such as eye shadow powder and carbon powder can be used; for materials such as silica gel, which have low water content and high strength, paint, watercolor and other spray dyes or carbon powder or eye shadow powder can be used. Then arrange the speckle pattern according to the requirements of the digital image correlation technology equipment. The speckle pattern as shown in Figure 4a has many blanks in the center of the tested sample, which needs to be further supplemented with paint to cover the blank positions. The well-arranged speckle pattern as shown in Figure 4b uniformly arranges the solid particle paint on the surface of the tested sample, forming a uniform and random speckle pattern on the surface of the tested sample, which meets the accuracy requirements of the digital image correlation technology.

[0059] Step 2: design the experimental process according to the experiment and the specific physical and chemical properties of the tested sample, and perform a pre-experiment to determine the approximate experimental range, and select the appropriate segmentation interval according to the deformation degree. Generally, 10% strain or 20% strain is taken as the segmentation point.

[0060] Step 3: according to the segmentation interval determined in step 2, the test is carried out, and the surface of the soft material sample is supplemented with speckle spraying at the end of each segment. The coating needs to be supplemented to the accuracy requirement of the digital image correlation technology equipment; after each segment experiment, the initial data file and the last time data file of each segment are exported through the digital image correlation technology equipment, and are named in time sequence, so that all data files can be arranged in time sequence.

[0061] Step 4: the initial data and the last time data of each segment are transmitted into the data processing computer, and the full-field displacement and strain data are calculated by using data linking, data compensation and data transmission algorithm. As shown in the formula, the specific process is as follows: Figure 6

[0062] The main content of the software part of the application is: after obtaining the deformation displacement field data in each small interval, the code written by MATLAB is used to process the data, so as to obtain the deformation field data of the tested sample. The software part is composed of three parts: data linking, data compensation and data transmission.

[0063] 1) Data linking

[0064] Since the application selects a group measurement method, each group of data can only represent the deformation data of the tested sample in a certain stage. Considering the continuity of the deformation of the tested sample, the continuity of the geometry can be used to link the measured displacement and strain data of each group, so as to obtain the full-field displacement and strain data of the tested sample.

[0065] Firstly, the last time data of a group of experimental images, i.e. the last photo, is exported by using the digital image correlation technology equipment, including coordinates (x, y), displacement (u, v), which represents the displacement (u, v) of the data point with coordinates (x, y) in the reference photo of this segment. Then the new coordinate point (x', y')=(x+u, y+v) of the data point can be obtained.

[0066] Then the data in the reference photo of the next segment data is assigned value. Since (x', y ′ ​) is generally a vector composed of two small arrays, which cannot be directly determined for a certain lens pixel point, but it must fall into a four-pixel region composed of four pixel points ([x'], [y']), ([x'] + 1, [y']), ([x'], [y'] + 1), ([x'] + 1, [y'] + 1) (where [] is the down rounding symbol), as shown in Figure 5 The strain value of the point (x', y') can be used to assign values to the surrounding four points, and then all the points are traversed, and the average value of multiple assignments is obtained, that is, the data linkage between the two data segments can be completed.

[0067] It must be pointed out that the "data linkage" algorithm designed by the present application not only completes the linkage between different groups of data, but also performs certain smoothing processing on the data. Such smoothing processing can effectively remove error data for actual soft material mechanics experiment measurement.

[0068] 2) Data compensation

[0069] Data compensation is an improved algorithm for the data loss problem of digital image correlation technology. During the observation process, the digital image correlation technology may lose the digital features of the surface image of the tested sample due to excessive local deformation, resulting in incorrect reading of displacement data. In addition, a part of the data may have low reliability and increased error due to the decrease in local speckle quality. In addition, due to the segmented measurement, each segment needs to be manually divided and calculated, and the calculation areas of each segment may differ slightly, resulting in the loss of a part of the data points at the boundary during the data linkage process.

[0070] In view of the above data loss problem, the present application adopts the idea of "first subdivision and then interpolation" to fill the data. That is, by presetting an interpolation function

[0071]

[0072] wherein

[0073] represents the coordinates of the coordinate point to be interpolated;

[0074] the independent variable is a function representing the interpolation result;

[0075] the selected interpolation method function

[0076] the unknown coefficient vector of the polynomial product;

[0077] The incomplete scattered data calculated according to the digital image correlation technique is geometrically divided, and a finite number of division units are obtained, and an interpolation data field is calculated in each unit by an interpolation method to obtain The coordinates of the data points to be filled in are calculated again Import, and find the corresponding division unit and assign values.

[0078] 3) Data transmission

[0079] The displacement and strain calculated by the digital image correlation technique for each imported picture are the displacement and strain calculated by taking one picture in the picture as a reference picture relative to the first reference picture in the picture. According to the mathematical definition of engineering strain, the strain value of each piece of data relative to the first reference picture in the piece is calculated:

[0080]

[0081]

[0082]

[0083] In the formula:

[0084] The strain fields of the tested sample at time 1, time 2, and time 3 calculated by the digital image correlation technique are respectively; l0, l1, l2, and l3 are transition variables in the mathematical definition formula of strain.

[0085] The picture P corresponding to time k is obtained by multiplying: k The strain value of each point in the picture relative to the initial state is:

[0086]

[0087] In the formula: ε k The true strain of each point in the picture P corresponding to time k relative to the initial state is: k The strain fields of the tested sample at time k-1, time k-2, and time 1 calculated by the digital image correlation technique are respectively; l k , l k-1 , l k-2 , l k-3 are transition variables in the mathematical definition formula of strain

[0088] Thus, the displacement data and strain data in each scattered data set are linked through geometric relationships, and the strain values of the tested sample at all times during the entire experiment are obtained.

[0089] Example 1​

[0090] This embodiment 1 is the measurement effect of the present application for PAAm hydrogel material under continuous deformation condition in pure shear test. In this embodiment, as shown in Figure 2 The hardware part includes a soft material tensile machine 1, a digital image correlation technology high-speed camera 2, a data processing computer 3 and a tested sample 4. The cutting frequency of the digital image correlation technology high-speed camera 2 is 1 frame per second, the tensile rate of the tensile machine 1 is 10 mm / min, the size of the cut hydrogel tested sample is 50 mm x 30 mm, the size of the acrylic splint used is 50 mm x 10 mm, and the effective size left is 50 mm x 10 mm, as shown in Figure 3 Due to the characteristics of PAAm gel, black eye shadow powder (black round dots) is selected as the coating in this example. To ensure uniformity, the eye shadow powder is evenly scattered on a flat and clean glass plate, and then the cut PAAm gel sample is gently placed on it. The eye shadow powder is fixed on the surface by the adhesion of the PAAm gel itself, and then the acrylic splint is fixed and placed on the tensile machine for testing. In this experiment, the experimental interruption points (time) are set at 50 seconds, 100 seconds and 140 seconds. When the experiment is interrupted, a small amount of eye shadow powder is collected on a clean white paper in front of the tested sample, and an ear bulb is used to gently blow air on the eye shadow powder on the white paper, so that the eye shadow powder on the white paper is carried to the surface of the tested sample by the airflow, and the dot arrangement is completed. Then, the tensile force and displacement values of the tensile machine sensor are reset to zero and the experiment begins.

[0091] After the experiment is completed and the experimental data is obtained, the data is processed using MATLAB software according to the aforementioned method. The data processing results of this example are shown in Figure 7

[0092] Among them, Fig. a is the 10th photo, i.e. the displacement field false color map at 10 seconds; Fig. b is the 50th photo, i.e. the displacement field false color map at 50 seconds; Fig. c is the 100th photo, i.e. the displacement field false color map at 100 seconds; Fig. d is the 140th photo, i.e. the displacement field false color map at 140 seconds. From the figures, it can be seen that the data loss and large deformation incompatibility problem of digital image correlation technology has been solved. After processing by the present application, there are no missing points and outliers in the displacement data field, and the overall data shows good continuity and uniformity, which is consistent with the continuity assumption of continuum mechanics and also consistent with the simulation results of finite element, proving the feasibility of the data compensation algorithm; secondly, Figs. b, c and d are experimental results of segmented experiments, which are successfully linked with the displacement data field of Fig. a through data transmission and data linking algorithm, and the surface displacement data field of the tested sample at this time is obtained, proving the feasibility and stability of the data linking and data transmission algorithm.​

Claims

1. A method for optimizing the measurement of strain field in soft materials based on digital image correlation technology, characterized in that: The specific steps of this method are as follows: Step 1: First, select a suitable speckle coating based on the specific physicochemical properties of the soft material sample being tested, and then arrange the speckle pattern according to the equipment requirements of the digital image correlation technology used. Step 2: Design the experimental process according to the experimental requirements, and conduct a preliminary experiment to determine the experimental range. Select the segment interval based on the degree of deformation of the soft material sample measured in the preliminary experiment, with the occurrence of 10% strain or 20% strain as the segment point. Step 3: Conduct the formal test according to the segmented intervals determined in Step 2. After each segment, apply additional speckle coating to the surface of the soft material sample. The additional coating needs to be applied up to the accuracy requirements of the digital image correlation technology equipment. After each segment of the experiment, export the initial data file and the final time data file of each segment through the digital image correlation technology equipment, and name them in chronological order to ensure that all data files are arranged in chronological order. Step 4: Input the initial data and the last time data of each segment interval into the data processing computer, and use the data linking algorithm, data compensation algorithm and data transfer algorithm to calculate the full field displacement and strain data.

2. The soft material strain field optimization measurement method based on digital image correlation technology according to claim 1, characterized in that: As described in step 1, a suitable speckle coating is selected based on the specific physicochemical properties of the soft material sample being tested. The selection method for speckle coating is as follows: for materials with high self-strength and non-absorbent properties, spray paint, toner, or eyeshadow powder is selected; for materials with low self-strength, good hydrophilicity, and sticky surface, eyeshadow powder or toner solid particles are used.

3. The soft material strain field optimization measurement method based on digital image correlation technology according to claim 1, characterized in that: The data compensation algorithm described in step 4 is as follows: Data compensation algorithms are improved algorithms designed to address the data loss problem in digital image correlation technology. During the observation process, digital image correlation technology may lose some data due to excessive local deformation of the test sample, resulting in the loss of digital features of the image. Additionally, some data may have reduced reliability and excessive error due to the deterioration of local speckle quality. In addition, due to segmented measurement, the calculation area needs to be manually redefined each time the segment is divided. The calculation areas of each segment will be different, which will cause some image data and its corresponding data points to be lost at the boundary during the data linking process. There are three parts of the lost data points: data points that cannot be identified during the calculation of digital image correlation technology due to excessive deformation of the surface of the test sample, resulting in the loss of local pattern features; data points that need to be cleared and reassigned due to excessive error and low confidence level; and points that were not successfully matched during the data linking process. To address the data loss problem, drawing inspiration from the finite element method, a method of first partitioning and then interpolating is used to fill in the data; that is, by using a pre-defined interpolation function. in This represents the coordinates of the points that need to be interpolated. Independent variable The function represents the interpolation result; The interpolation method function used; The vector of unknown coefficients of a polynomial product; The incomplete scattered data obtained from digital image correlation techniques is partitioned into a finite number of cells. Within each cell, an interpolated data field is calculated using interpolation methods, thus obtaining the interpolated data field. Then retrieve the coordinates of the lost data points Substitute the values ​​into the subdivision cell containing the missing data points and assign them values.

4. The soft material strain field optimization measurement method based on digital image correlation technology according to claim 1, characterized in that: The data linking algorithm described in step 4 is as follows: First, export all the data of the last photo in a certain segment, including coordinates (x,y) and displacement (u,v). This data represents the displacement (u,v) of the data point with coordinates (x,y) in the reference photo segment. Then, we can obtain the new coordinate position (x′,y′) = (x+u,y+v) that the data point has moved to. Assign values ​​to the reference image data for the next data segment: Since (x, y) are the lens pixel grid coordinates of the high-speed camera in the initial state of digital image correlation technology, (x, y) are all integers; however, (u, v) represents the displacement of a certain calculation area, which is not an integer. Therefore, the new coordinate point (x′, y′) is a vector composed of two decimals. There is no directly corresponding lens pixel grid point, but the new coordinate point (x′, y′) will inevitably fall into a four-pixel region composed of four pixels ([x′], [y′]), ([x′]+1, [y′]), ([x′], [y′]+1), ([x′]+1, [y′]+1), where [] is the rounding down operator. Assign values ​​to the four surrounding points with the strain and displacement values ​​of the new coordinate point (x′, y′). Then, iterate through all the data points in the initial state and assign values ​​to the deformed blank data points. Take the average value of the multiple assigned points to complete the data link between the two data segments.

5. The soft material strain field optimization measurement method based on digital image correlation technology according to claim 1, characterized in that: The data transmission algorithm described in step 4 is as follows: Digital image correlation (DIC) technology calculates displacement and strain for each imported image segment by using a specific image within that segment as a reference image (the first image in the segment). Considering that the strain calculated by DIC is engineering strain, geometric relationships are used to calculate the actual strain for each image segment. Based on the mathematical definition of engineering strain, DIC calculates the strain value for each data segment relative to the first reference image in that segment. In the formula: It is the strain field of the test sample at time 1, time 2, and time 3 calculated by digital image correlation technology; l0, l1, l2, and l3 are the transition variables in the mathematical definition of strain; By multiplying the results, we can obtain the photograph P corresponding to a certain time k. k Strain values ​​at various points relative to the initial state: Where: ε k Photograph P corresponding to time k k The actual strain at each point relative to the initial state; These are the strains of the test sample at times k-1, k-2, and 1, calculated using digital image correlation techniques; k , l k-1 , l k-2 , l k-3 It is the transition variable in the mathematical definition of strain; Displacement and strain data from various distributed datasets are transferred through geometric relationships to obtain the strain values ​​of the test sample at all moments throughout the entire experiment.

Images