A method for constructing a simulation model of CFRP laminates based on DIC and synchrotron radiation

Abstract

The present invention relates to a method for constructing a simulation model of a CFRP laminate based on DIC and synchrotron radiation, belonging to the technical field of model simulation, and solves the problems in the prior art that the fracture toughness of CFRP cannot be accurately calculated and the modeling parameters of the cohesive force model are inaccurate. A CFRP laminate specimen containing a prefabricated crack is constructed, and a three-point bending fracture loading test is carried out on the specimen. The fracture toughness value is calculated based on the type-I dynamic stress intensity factor. An integrated synchrotron radiation device is introduced to carry out an impact fracture test on the specimen to obtain high-resolution images. The final failure displacement is corrected based on the high-resolution images and the crack initiation time. The initial damage displacement is corrected based on the fracture toughness value and the high-resolution images. A finite element model of a CFRP laminate specimen containing a prefabricated crack is constructed based on the fracture toughness value and the corrected final failure displacement and initial damage displacement. An accurate calculation method for fracture toughness and a correction method for cohesive force model parameters are realized.

Description

Technical Field

[0001] The present invention relates to the technical field of model simulation, and in particular, to a method for constructing a simulation model of CFRP laminated material based on DIC and synchrotron radiation. Background Art

[0002] Carbon Fiber Reinforced Polymer (CFRP) is a composite material formed with carbon fiber or carbon fiber fabric as the reinforcement and resin, ceramic, metal, cement, carbonaceous or rubber, etc. as the matrix.

[0003] In the prior art, the methods commonly used to study the mechanical properties of CFRP are static loading and dynamic loading. Due to the following disadvantages of static loading: insufficient mechanical property performance, limitations of damage mechanisms, and limitations of actual application scenarios, these disadvantages have prompted researchers to turn to dynamic loading research in order to more realistically evaluate mechanical properties, reveal complex damage mechanisms, and improve the reliability of actual applications. When studying the influence of the properties of CFRP matrix materials or the damage situation during the loading process based on dynamic loading, the fracture toughness of CFRP has an important influence on the simulation results. Through a large number of simulation experiments on CFRP, it has been shown that under dynamic loading, there are differences in the time scale between one-dimensional stress waves and crack propagation, and the material has already cracked and damaged before reaching the peak of the dynamic load, resulting in the inability of traditional theoretical calculation methods (for example, calculation methods based on stress intensity factors, calculation methods based on energy release rates, etc.) to accurately describe the mechanical properties between CFRP layers. In addition, the prefabricated crack model in the CFRP finite element model usually selects the cohesive force model. When establishing the simulation model, if the parameters of this cohesive force model cannot be consistent with the actual CFRP material property parameters, it will also affect the accuracy of the simulation results.

[0004] Therefore, it is necessary to provide a calculation method for the fracture toughness of CFRP and a correction method for the parameters of the cohesive force model under dynamic loading, so as to establish an accurate CFRP finite element model to obtain accurate simulation results. Summary of the Invention

[0005] In view of the above analysis, the embodiments of the present invention aim to provide a method for constructing a simulation model of CFRP laminated material based on DIC and synchrotron radiation, so as to solve the problem of low model simulation accuracy caused by the inability to accurately calculate the fracture toughness of CFRP and inaccurate modeling parameters of the cohesive force model in the prior art.

[0006] The embodiments of the present invention provide a method for constructing a simulation model of CFRP laminated material based on DIC and synchrotron radiation, including:

[0007] Construct a CFRP laminate specimen containing a prefabricated crack, and paste a strain gauge near the tip of the prefabricated crack;

[0008] Conduct a three-point bending fracture loading test on the specimen using a Split Hopkinson Pressure Bar (SHPB), record the fracture process images of the specimen using a high-speed camera, and record the crack initiation time of the specimen using the strain gauge;

[0009] Process the fracture process images using DIC analysis software to obtain the opening displacement function at the crack tip, obtain the mode-I dynamic stress intensity factor at the crack tip of the specimen at the crack initiation moment based on the opening displacement function, and calculate the fracture toughness value based on this mode-I dynamic stress intensity factor;

[0010] Introduce an integrated synchrotron radiation device to conduct an impact fracture test on the specimen, and take high-resolution images of the fracture process of the specimen using a high-speed camera;

[0011] Correct the final failure displacement based on the high-resolution images and the crack initiation time, and correct the initial damage displacement based on the fracture toughness value and the high-resolution images;

[0012] Construct a finite element model of the CFRP laminate specimen containing a prefabricated crack based on the fracture toughness value and the corrected final failure displacement and initial damage displacement.

[0013] Based on a further improvement of the above method, after constructing the CFRP laminate specimen, it is also necessary to verify whether the specimen size meets the plane strain condition.

[0014] Based on a further improvement of the above method, the plane strain condition includes:

[0015] ,

[0016] ,

[0017] where H is the specimen height, B is the specimen width, and a is the length of the prefabricated crack.

[0018] Based on a further improvement of the above method, the obtaining of the mode-I dynamic stress intensity factor at the crack tip of the specimen at the crack initiation moment based on the opening displacement function includes:

[0019] Obtain two frames of fracture process images that are closest to the crack initiation moment captured by the high-speed camera as the first fracture process image and the second fracture process image;

[0020] Select a series of equally spaced pixel points on the first fracture process image and the second fracture process image, and obtain the distance of each pixel point from the crack tip in the first fracture process image and the second fracture process image. Calculate the opening displacement of each pixel point at different shooting times based on the opening displacement function, the distance of each pixel point from the crack tip, and the shooting times of the first fracture process image and the second fracture process image. Substitute the opening displacement corresponding to each pixel point and the distance from the crack tip into the mode I dynamic stress intensity factor calculation equation to obtain the mode I dynamic stress intensity factor of each pixel point at different shooting times. Fit the shooting times and the mode I dynamic stress intensity factor corresponding to each shooting time based on the least squares method to obtain the time-intensity factor fitting equation;

[0021] Set the time to the initiation time, and substitute it into the time-intensity factor fitting equation to obtain the mode I dynamic stress intensity factor at the initiation time.

[0022] Based on a further improvement of the above method, calculating the fracture toughness value based on the mode I dynamic stress intensity factor includes:

[0023] ,

[0024] ,

[0025] wherein, is the initiation time, is the mode I dynamic stress intensity factor at the initiation time, is the fracture toughness value at the initiation time, and E is the elastic modulus.

[0026] Based on a further improvement of the above method, correcting the final failure displacement based on the high-resolution image and the initiation time includes:

[0027] Obtain two frames of high-resolution images with the shooting times closest to the initiation time of the high-speed camera as the third fracture process image and the fourth fracture process image;

[0028] Calculate the opening displacement values of the material at the film tip position in the third fracture process image and the fourth fracture process image, and take the larger opening displacement value as the final failure displacement;

[0029] Select any point on the crack in the third fracture process image as a reference point, obtain the position of the reference point in the fourth fracture process image, obtain the displacement of the reference point based on the position change of the reference point in the third fracture process image and the fourth fracture process image, and calculate the first moving speed based on the displacement;

[0030] The average crack opening velocity is calculated based on the longitudinal displacement information at the crack tip, and it is used as the second moving velocity;

[0031] The average moving velocity is calculated based on the first moving velocity and the second moving velocity;

[0032] Based on the crack initiation time, the time corresponding to the third fracture process image, the time corresponding to the fourth fracture process image, and the average moving velocity, the final failure displacement is corrected.

[0033] Based on a further improvement of the above method, the correction of the final failure displacement based on the crack initiation time, the time corresponding to the third fracture process image, the time corresponding to the fourth fracture process image, and the average moving velocity includes:

[0034] ,

[0035] ,

[0036] where, is the corrected final failure displacement, is the final failure displacement, is the correction amount of the final failure displacement, is the average moving velocity, is the time corresponding to the third fracture process image, is the crack initiation time, is the time corresponding to the fourth fracture process image.

[0037] Based on a further improvement of the above method, the correction of the initial damage displacement based on the fracture toughness value and the high-resolution image includes:

[0038] The measured load peak is calculated based on the longitudinal displacement information at the crack tip , and the theoretical load peak is calculated based on the fracture toughness value and the corrected final failure displacement ;

[0039] Based on the measured load peak and the theoretical load peak the initial damage displacement is corrected:

[0040] ,

[0041] ,

[0042] ,

[0043] where, is the corrected initial damage displacement, is the initial damage displacement, and E is the elastic modulus. is the correction amount of the initial damage displacement.

[0044] Based on a further improvement of the above method, when making the specimen, speckles with obvious black and white contrast are sprayed on the surface of the specimen.

[0045] Based on a further improvement of the above method, the strain gauge selects a polyimide film-based strain gauge.

[0046] Compared with the prior art, the present invention can at least achieve one of the following beneficial effects:

[0047] 1. The present invention provides a method for constructing a simulation model of CFRP laminates based on DIC and synchrotron radiation. The interlaminar fracture toughness of CFRP laminates is calculated based on digital image correlation technology (DIC). Specifically, based on the SHPB test images before and after the crack initiation time captured by a high-speed camera, the longitudinal displacement of the pixel points at the crack initiation moment is obtained by using the least square method. Based on the calculation formula of the mode I dynamic stress intensity factor and the calculation formula of the fracture toughness, the fracture toughness at the crack initiation moment is obtained. Compared with the traditional calculation method of fracture toughness in the theory, the method proposed by the present invention can obtain the opening displacement corresponding to the accurate crack initiation moment, so as to obtain a more accurate fracture toughness value at the crack initiation moment.

[0048] 2. The present invention provides a method for constructing a simulation model of CFRP laminates based on DIC and synchrotron radiation. A synchrotron radiation device is introduced to obtain high-resolution fracture process images, and the constitutive model parameters are directly observed through the ultrafast X-ray phase contrast imaging and high time and high spatial resolution of the synchrotron accelerator. Specifically, the final failure displacement is corrected based on the high-resolution image and the crack initiation time, the initial damage displacement is corrected based on the fracture toughness value and the high-resolution image, and the cohesive force model is combined with the material characteristic parameters related to the strain rate effect, so as to establish an accurate simulation model of CFRP laminates, which can more accurately describe the interlaminar fracture damage evolution of CFRP laminates under dynamic loading.

[0049] In the present invention, the above technical solutions can also be combined with each other to realize more preferred combination schemes. Other features and advantages of the present invention will be described in the subsequent specification, and some advantages can be made obvious from the specification, or understood by implementing the present invention. The objectives and other advantages of the present invention can be realized and obtained from the content specifically pointed out in the specification and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] The accompanying drawings are only for the purpose of showing specific embodiments and are not considered as limiting the present invention. Throughout the drawings, the same reference signs denote the same components;

[0051] FIG. 1 is an exemplary diagram of a method for constructing a simulation model of a CFRP laminate based on DIC and synchrotron radiation in an embodiment of the present invention;

[0052] Figure 2 is an exemplary diagram of a CFRP laminate specimen prepared in an embodiment of the present invention;

[0053] Figure 3 is an exemplary diagram of an integrated DIC and SHPB device in an embodiment of the present invention;

[0054] Figure 4 is a comparative exemplary diagram of test results and theoretical numerical calculation results under different loading test conditions in an embodiment of the present invention. Detailed Embodiments

[0055] The preferred embodiments of the present invention will be specifically described below with reference to the accompanying drawings. The accompanying drawings form a part of this application and are used together with the embodiments of the present invention to explain the principles of the present invention, and are not used to limit the scope of the present invention.

[0056] The Split Hopkinson Pressure Bar (SHPB) impact test is an important experimental technique for studying the dynamic mechanical properties of materials at high strain rates. Based on the one-dimensional stress wave theory, the impact energy is transmitted to the specimen through an elastic bar (usually a metal bar). The specimen is subjected to high strain rate loading in a very short time, thereby realizing the dynamic compression performance test. The test device mainly includes: mainly composed of a gas gun, a bullet (impact bar), an incident bar, a transmission bar, a damper, and a data acquisition system, etc.

[0057] The DIC analysis system, namely the digital image correlation system, is an optical measurement system used to measure the surface deformation of an object. By tracking the images of the object surface, it realizes the measurement of the three-dimensional coordinates, displacement, and strain of the object during the deformation process. Its basic principle is as follows: The region of interest in the pre-deformation image is divided into grids, and each sub-region is regarded as a rigid motion. Then, for each sub-region, through a certain search method, relevant calculations are carried out according to a pre-defined correlation function to find the region in the post-deformation image with the maximum cross-correlation coefficient with this sub-region, that is, the position of this sub-region after deformation, and then the displacement of this sub-region is obtained. By calculating all sub-regions, the full-field deformation information can be obtained. It includes: an image acquisition device, usually a CCD camera or a high-speed camera, used to capture the digital images of the object surface before and after deformation; an illumination light source. In order to form a clear speckle pattern on the object surface, a suitable illumination light source is required, such as a fiber optic gooseneck light, etc., to provide uniform illumination; an image acquisition card, used to convert the analog image signal collected by the camera into a digital signal and transmit it to the computer for processing; a computer, installed with corresponding DIC analysis software, used to perform relevant calculations and data analysis on the collected digital images to obtain information such as the displacement and strain of the object surface.

[0058] A specific embodiment of the present invention discloses a method for constructing a simulation model of CFRP laminates based on DIC and synchrotron radiation, as Figure 1 shown, which is characterized by including:

[0059] S1: Construct a CFRP laminate specimen containing a prefabricated crack, and paste a strain gauge near the tip of the prefabricated crack.

[0060] According to the standard, design and prepare a CFRP laminate specimen, the lay-up sequence of which is , insert a polytetrafluoroethylene material with a micron-scale thickness into the central layer of the specimen as the prefabricated crack, as Figure 2 shown.

[0061] Exemplarily, to prepare the laminate sample, first design the pressing mold based on the specimen size, and prepare the impregnated matrix. The unidirectional fiber is obtained through the filament winding device built in the processing workshop. Then use the matrix to wet the unidirectional fiber cloth to obtain CFRP prepreg; next, stack the prepreg blanks in a predetermined lay-up sequence, and place polytetrafluoroethylene at the edge of the mold when laying to the central layer, with the length of the prefabricated crack being 3 mm, and then symmetrically lay the other side; after the lay-up is completed, keep it at and 70 Kpa environment for 2 hours; finally, according to the standard, the specimen should meet the plane strain condition, and the laminate is made by processing with a surface milling machine For the test sample, the plane strain conditions are as follows:

[0062] ,

[0063] ,

[0064] where H is the height of the specimen, B is the width of the specimen, and a is the length of the prefabricated crack.

[0065] It is understandable that polytetrafluoroethylene is placed at the edge to better maintain pressure and form, and prevent serious dislocation.

[0066] Before the dynamic fracture experiment, the surface of the specimen ( plane) is sprayed with white paint, and after air drying, black dot speckles are sprayed. A high-speed camera is used to take images of the current random speckles as the reference image for subsequent calculation of the opening displacement function. A resistance strain gauge is pasted near the tip of the prefabricated crack on the other side of the specimen to test effective strain information. The strain gauge selected is a polyimide film-based strain gauge of the model. The paste position is wiped clean with alcohol, and after air drying, type patch glue is dropped, and the strain gauge is pressed firmly on the surface of the specimen. Then the leads of the strain gauge are welded and pins are added. After completion, the resistance value of the strain gauge is measured again, and it can meet the requirement within the error range.

[0067] Preferably, a multimeter is used to measure the resistance value of the strain gauge. The resistance value of the strain gauge is , and considering the instrument error of the multimeter, the measurement within this range is acceptable.

[0068] S2: Use a split Hopkinson bar SHPB to conduct a three-point bending fracture loading test on the specimen, use a high-speed camera to record the fracture process images of the specimen, and use the strain gauge to record the crack initiation time of the specimen.

[0069] For the Hopkinson bar (SHPB) impact test, a bullet, an incident bar, a transmission bar, and each strain bridge box SDY2301 need to be installed. The ultra-dynamic strain gauge, data acquisition system, high-speed photography device, etc. need to be debugged. After installing each component, it is necessary to check whether the positions of each component are correct, whether the functions are normal, etc. After verification, DIC and SHPB are integrated to conduct an impact fracture test on the specimen. By releasing compressed air in the sealed air chamber, the bullet impacts the end of the incident bar at a certain speed to generate an elastic stress wave. The test device carried in the present invention is as shown in the appendix Figure 3 .

[0070] S3: Use DIC analysis software to process the fracture process images to obtain the crack tip opening displacement function. Based on the crack tip opening displacement function, obtain the mode I dynamic stress intensity factor at the crack tip of the specimen at the crack initiation moment, and calculate the fracture toughness value based on this mode I dynamic stress intensity factor.

[0071] Using DIC analysis software to process the fracture process images to obtain the crack tip opening displacement function specifically includes:

[0072] Divide the reference image into multiple sub-regions. The speckle patterns within each sub-region will be searched and matched in the deformed image, and according to the expected maximum displacement, set the search range of each sub-region in the deformed image. Within the search range of each sub-region, calculate the correlation function of the sub-region (e.g., Normalized Cross-Correlation (NCC)) between the reference image and the deformed image (each fracture process image captured). The position corresponding to the maximum value of the correlation function can be used as the best matching position of the sub-region before and after deformation, and calculate the displacement of the sub-region. Based on the displacements of the sub-regions at each best matching position, construct the full-field displacement field to describe the deformation of the object surface. Finally, the crack tip opening displacement function can be obtained by analyzing and calculating the full-field displacement. , NCC))), and the position corresponding to the maximum value of the correlation function can be used as the best matching position of the sub-region before and after deformation, and calculate the displacement of the sub-region. Based on the displacements of the sub-regions at each best matching position, construct the full-field displacement field to describe the deformation of the object surface. Finally, the crack tip opening displacement function can be obtained by analyzing and calculating the full-field displacement. . In addition, select the extreme points in the specimen strain signal as the crack initiation time.

[0073] The obtaining of the mode I dynamic stress intensity factor at the crack tip of the specimen at the crack initiation moment based on the crack tip opening displacement includes:

[0074] A1: Obtain two fracture process images with the shooting moments closest to the crack initiation moment of the high-speed camera as the first fracture process image and the second fracture process image.

[0075] It can be understood that it is generally very difficult for the shooting moment of the high-speed camera to coincide exactly with the crack initiation time. Therefore, the present invention selects two fracture process images before and after the crack initiation moment as the basis for subsequent calculation of the mode I dynamic stress intensity factor.

[0076] A2: Select a series of equally spaced pixel points on the first fracture process image and the second fracture process image, and obtain the distance of each pixel point from the crack tip in the first fracture process image and the second fracture process image. Calculate the opening displacement of each pixel point at different shooting times based on the opening displacement function, the distance of each pixel point from the crack tip, and the shooting times of the first fracture process image and the second fracture process image. Substitute the opening displacement corresponding to each pixel point and the distance from the crack tip into the mode-I dynamic stress intensity factor calculation equation to obtain the mode-I dynamic stress intensity factor of each pixel point at different shooting times. Fit the shooting times and the mode-I dynamic stress intensity factor corresponding to each shooting time based on the least squares method to obtain the time-intensity factor fitting equation;

[0077] The mode-I dynamic stress intensity factor calculation equation is:

[0078] ,

[0079] where, is the distance from the crack tip, is the shooting time, is the shear modulus, is the specimen Poisson's ratio, is the opening displacement function.

[0080] A3: Set the time to the crack initiation time, and substitute it into the time-intensity factor fitting equation to obtain the mode-I dynamic stress intensity factor at the crack initiation time.

[0081] The calculation of the fracture toughness value based on the mode-I dynamic stress intensity factor includes:

[0082] ,

[0083] ,

[0084] where, is the crack initiation time, is the mode-I dynamic stress intensity factor at the crack initiation time, is the fracture toughness value at the crack initiation time, and E is the elastic modulus.

[0085] S4: Introduce an integrated synchrotron radiation device to conduct an impact fracture test on the specimen, and use a high-speed camera to capture high-resolution images of the specimen fracture process.

[0086] On the basis of the existing integrated DIC and SHPB devices, an integrated synchrotron device is introduced. The synchrotron radiation centerline station transmits a strong X-ray beam to the sample position. The slow shutter and the fast shutter are synchronized with the camera, SHPB, and oscilloscope to minimize the thermal load of the sample caused by the incident X-rays. The thickness is of a single crystal scintillator is used to convert X-rays into visible light. Then, an impact fracture test is carried out on the specimen and recorded by a high-speed camera, so as to obtain high-resolution process images of the specimen fracture.

[0087] Understandably, under dynamic loading, during the fracture process of the composite material, there is a difference in the time scale between the high-speed propagation of cracks and the propagation of stress waves. Therefore, it is necessary to perform multi-scale analysis of the fracture process of the specimen in terms of time and space in order to deeply understand the fracture mechanism of the specimen. However, conventional testing methods (SHPB) cannot determine the time sequence of the damage of the matrix and fibers, and it is easy to introduce interference factors such as instrument errors at low resolution. Therefore, synchrotron radiation is used for high-resolution detection, so as to provide more accurate guidance for the subsequent correction of the final failure displacement and the initial damage displacement.

[0088] S5: Correct the final failure displacement based on the high-resolution image and the crack initiation time, and correct the initial damage displacement based on the fracture toughness value and the high-resolution image.

[0089] The correction of the final failure displacement based on the high-resolution image and the crack initiation time includes:

[0090] B1: Obtain two frames of high-resolution images with the shooting moments of the high-speed camera closest to the crack initiation moment as the third fracture process image and the fourth fracture process image.

[0091] As mentioned above, it is generally difficult for the shooting moment of the high-speed camera to coincide exactly with the crack initiation time. Therefore, the present invention selects two high-resolution images before and after the crack initiation moment as the basis for subsequent correction of the final failure displacement.

[0092] B2: Calculate the opening displacement values of the materials at the film tip positions in the third fracture process image and the fourth fracture process image, and take the larger opening displacement value as the final failure displacement.

[0093] As described above, the method for obtaining the opening displacement by the DIC analysis software. Based on this method, obtain the opening displacement values of the materials at the film tip positions in the third fracture process image and the fourth fracture process image, and take the larger of the third fracture process image and the fourth fracture process image as the final failure displacement value (i.e., the failure displacement boundary value).

[0094] B3: Select any point on the crack in the third fracture process image as a reference point, obtain the position of this reference point in the fourth fracture process image, obtain the displacement of this reference point based on the position change of this reference point in the third fracture process image and the fourth fracture process image, and calculate the first moving speed based on this displacement.

[0095] Among them, the shooting times of the third fracture process image and the fourth fracture process image are known. Based on the position change of the same point in the third fracture process image and the fourth fracture process, the displacement of this point can be calculated. Furthermore, based on the displacement and the change value of the shooting time, the moving speed of this reference point can be obtained.

[0096] B4: Calculate the average crack opening speed based on the longitudinal displacement information of the crack tip, and use it as the second moving speed.

[0097] Among them, the shooting times of the third fracture process image and the fourth fracture process image are known. Calculate the opening displacement values in the third fracture process image and the fourth fracture process image based on the DIC analysis software. Furthermore, based on the change amount of the opening displacement value and the change value of the shooting time, the average crack opening speed can be obtained.

[0098] B5: Calculate the average moving speed based on the first moving speed and the second moving speed.

[0099] B6: Realize the correction of the final failure displacement based on the crack initiation time, the time corresponding to the third fracture process image, the time corresponding to the fourth fracture process image, and the average moving speed, including:

[0100] ,

[0101] ,

[0102] Among them, is the corrected final failure displacement, is the final failure displacement, is the correction amount of the final failure displacement, is the average moving speed, is the time corresponding to the third fracture process image, is the crack initiation time, is the time corresponding to the fourth fracture process image.

[0103] The correction of the initial damage displacement based on the fracture toughness value and the high-resolution image includes:

[0104] C1: Calculate the measured load peak value based on the longitudinal displacement information of the crack tip , the theoretical load peak is calculated based on the fracture toughness value and the corrected final failure displacement .

[0105] Specifically, using DIC analysis software, the collected images are processed to calculate the longitudinal strain values of each point on the surface of the specimen. The strain distribution can be obtained by comparing the displacements of the speckles in the images before and after deformation and combining relevant algorithms. Record the corresponding load values and the calculated longitudinal strain values, plot the load-strain curve, and on the load-strain curve, find the maximum load corresponding to the strain value, which is the measured load peak. In the present invention, the prefabricated crack adopts a bilinear configuration of the cohesive constitutive model. After determining the fracture toughness and the final failure displacement, using the physical meaning of the area enclosed by the constitutive curve and the abscissa, the theoretical load peak can be calculated using the following formula:

[0106] ,

[0107] is the fracture toughness value, is the final failure displacement.

[0108] C2: Based on the measured load peak and the theoretical load peak correct the initial damage displacement:

[0109] ,

[0110] ,

[0111] ,

[0112] Among them, is the corrected initial damage displacement, is the initial damage displacement, E is the elastic modulus, is the correction amount of the initial damage displacement. Among them, the initial damage displacement refers to the damage displacement value of the prefabricated crack at the moment of crack initiation.

[0113] S6: Based on the fracture toughness value, the corrected final failure displacement and the initial damage displacement, construct a finite element model of the CFRP laminate specimen containing a prefabricated crack.

[0114] Use commercial finite element software to establish the geometric models of the CFRP specimen and the SHPB loading device, set the ply angle of the specimen, set the prefabricated crack as a cohesive element, and assign the corrected final failure displacement and the initial damage displacement, thereby establishing a finite element model of the CFRP laminate specimen that can accurately describe the mechanical properties.

[0115] Furthermore, in order to verify the effectiveness of the correction method proposed by the present invention, the present invention sets up two groups of tests. Among them, the loading air pressures are set to 0.05 Mpa and 0.08 MPa respectively. According to the actual test loading state, a loading pulse is given to the incident bar. After the numerical calculation is completed, the load-displacement curve of the specimen is extracted. For the two bullet loading test conditions, the numerical calculation results are compared with the test results as Figure 4 , and it is found that in the case of dynamic impact, the established simulation model can capture the nonlinear characteristics in the initial stage of loading, and can reasonably predict the load peak and the overall shape of the curve, verifying the effectiveness and correctness of the cohesive model parameter correction method.

[0116] Compared with the prior art, a method for constructing a CFRP laminate simulation model based on DIC and synchrotron radiation provided in this embodiment calculates the interlaminar fracture toughness of CFRP laminates based on digital image correlation technology DIC. Specifically, based on the SHPB test images before and after the crack initiation time captured by a high-speed camera, the longitudinal displacement of the pixel points at the crack initiation moment is obtained by using the least square method. Based on the calculation formula of the mode I dynamic stress intensity factor and the calculation formula of the fracture toughness, the fracture toughness at the crack initiation moment is obtained. Compared with the traditional method for calculating the fracture toughness in the theory, the method proposed by the present invention can obtain the opening displacement value corresponding to the accurate crack initiation moment, so as to obtain a more accurate fracture toughness value at the crack initiation moment; introducing a synchrotron radiation device to obtain high-resolution fracture process images, and directly observing the constitutive model parameters through the ultrafast X-ray phase contrast imaging of the synchrotron accelerator and high time and high space resolution. Specifically, based on the high-resolution images and the crack initiation time, the final failure displacement is corrected, and based on the fracture toughness value and the high-resolution images, the initial damage displacement is corrected, and the material characteristic parameters related to the strain rate effect of the cohesive model are combined, so as to establish an accurate CFRP laminate simulation model, which can more accurately describe the interlaminar fracture damage evolution of CFRP laminates under dynamic loading.

[0117] Those skilled in the art can understand that all or part of the processes of implementing the above method embodiments can be completed by instructing relevant hardware through a computer program, and the program can be stored in a computer-readable storage medium. Among them, the computer-readable storage medium is a disk, an optical disk, a read-only memory or a random access memory, etc.

[0118] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention.

Claims

1. A method for constructing a CFRP laminate material simulation model based on DIC and synchrotron radiation, characterized in that: include: constructing a CFRP laminate sample including a prefabricated crack, and pasting a strain gauge near the tip of the prefabricated crack; A split Hopkinson bar SHPB is used to perform a three-stage bending fracture loading test on the sample, a high-speed camera is used to record the fracture process image of the sample, and the strain gauge is used to record the crack initiation time of the sample; The fracture process image is processed by DIC analysis software to obtain an opening displacement function of a crack tip, a mode I dynamic stress intensity factor of the crack tip of the sample at the time of crack initiation is obtained based on the opening displacement function, and a fracture toughness value is calculated based on the mode I dynamic stress intensity factor; An integrated synchrotron radiation device is introduced to carry out an impact fracture test on the sample, and a high-speed camera is used to take a high-resolution image of the fracture process of the sample; Correcting the final failure displacement based on the high-resolution image and the crack initiation time, and correcting the initial damage displacement based on the fracture toughness value and the high-resolution image; Constructing a finite element model of a CFRP laminate sample containing prefabricated cracks based on the fracture toughness value and the corrected final failure displacement and initial damage displacement; The fracture toughness value is calculated based on the type I dynamic stress intensity factor, including: ， ， in, For the moment of cracking, is the I-mode dynamic stress intensity factor at the crack initiation moment, is the fracture toughness value at the crack initiation moment, E is the elastic modulus, is the Poisson's ratio of the sample.

2. The method for constructing a CFRP laminate material simulation model based on DIC and synchrotron radiation according to claim 1, characterized in that: After constructing the CFRP laminate specimen, it is also necessary to verify whether the specimen size satisfies the plane strain condition.

3. The method for constructing a CFRP laminate material simulation model based on DIC and synchrotron radiation according to claim 2, characterized in that: The plane strain condition includes: ， ， Where H is the specimen height, B is the specimen width, and a is the length of the prefabricated crack.

4. The method for constructing a CFRP laminate material simulation model based on DIC and synchrotron radiation according to claim 1, characterized in that: The method of obtaining the mode I dynamic stress intensity factor of the crack tip of the sample at the crack initiation moment based on the opening displacement function includes: Acquire two frames of fracture process images whose shooting time of the high-speed camera is closest to the fracture initiation time as the first fracture process image and the second fracture process image; A series of equally spaced pixel points are selected on the first fracture process image and the second fracture process image, and the distance of each pixel point from the crack tip in the first fracture process image and the second fracture process image is obtained. The opening displacement of each pixel point at different shooting times is calculated based on the opening displacement function, the distance of each pixel point from the crack tip, and the shooting time of the first fracture process image and the second fracture process image. The opening displacement and the distance from the crack tip corresponding to each pixel point are substituted into the calculation equation of the type I dynamic stress intensity factor to obtain the type I dynamic stress intensity factor of each pixel point at different shooting times. The time-intensity factor fitting equation is obtained by fitting each shooting time and the type I dynamic stress intensity factor corresponding to the shooting time based on the least squares method; The time is set as the crack initiation time, and it is substituted into the time-intensity factor fitting equation to obtain the type I dynamic stress intensity factor at the crack initiation time.

5. The method for constructing a CFRP laminate material simulation model based on DIC and synchrotron radiation according to claim 1, characterized in that: The correcting the final failure displacement based on the high-resolution image and the crack initiation time includes: Acquire two frames of high-resolution images whose shooting time of the high-speed camera is closest to the crack initiation time as the third fracture process image and the fourth fracture process image; Calculating the opening displacement value of the material at the tip position of the film in the third fracture process image and the fourth fracture process image, and taking the larger opening displacement value as the final failure displacement; Selecting any point on the crack in the third fracture process image as a reference point, obtaining a position of the reference point in the fourth fracture process image, obtaining a displacement of the reference point based on a position change of the reference point in the third fracture process image and the fourth fracture process image, and calculating a first moving speed based on the displacement; The average crack opening speed is calculated based on the longitudinal displacement information of the crack tip and is used as the second moving speed; Calculate an average moving speed based on the first moving speed and the second moving speed; The final failure displacement is corrected based on the crack initiation moment, the moment corresponding to the third fracture process image, the moment corresponding to the fourth fracture process image, and the average moving speed.

6. The method for constructing a CFRP laminate material simulation model based on DIC and synchrotron radiation according to claim 5, characterized in that: The correction of the final failure displacement based on the crack initiation moment, the moment corresponding to the third fracture process image, the moment corresponding to the fourth fracture process image and the average moving speed includes: ， ， in, is the corrected final failure displacement, is the final failure displacement, is the correction amount of the final failure displacement, is the average moving speed, is the time corresponding to the third fracture process image, For the moment of cracking, is the moment corresponding to the fourth fracture process image.

7. The method for constructing a CFRP laminate material simulation model based on DIC and synchrotron radiation according to claim 6, characterized in that: The correcting the initial damage displacement based on the fracture toughness value and the high-resolution image comprises: The measured load peak value is calculated based on the longitudinal displacement information of the crack tip. , the theoretical load peak value is calculated based on the fracture toughness value and the corrected final failure displacement ; Based on the measured peak load and theoretical load peak Correct the initial damage displacement: ， ， , in, is the corrected initial damage displacement, is the initial damage displacement, E is the elastic modulus, is the correction amount of the initial damage displacement.

8. The method for constructing a CFRP laminate material simulation model based on DIC and synchrotron radiation according to claim 1, characterized in that: When preparing the sample, a speckle with obvious black and white contrast is sprayed on the surface of the sample.

9. The method for constructing a CFRP laminate material simulation model based on DIC and synchrotron radiation according to claim 1, characterized in that: The strain gauge is a polyimide film substrate strain gauge.

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