Method for constructing CFRP laminated material simulation model based on DIC and synchrotron radiation

Abstract

The invention relates to a method for constructing a CFRP laminated material simulation model based on DIC and synchrotron radiation, belongs to the technical field of model simulation, and solves the problems that in the prior art, the CFRP fracture toughness cannot be accurately calculated, and the modeling parameters of a cohesion model are inaccurate. The method comprises the following steps: constructing a CFRP laminated material sample containing precracks, carrying out a three-section bending fracture loading test on the sample, calculating based on an I-type dynamic stress intensity factor to obtain a fracture toughness value, and introducing an integrated synchrotron radiation device to carry out an impact fracture test on the sample to obtain a high-resolution image. The final failure displacement is corrected based on the high-resolution image and the crack initiation time, and the initial damage displacement is corrected based on the fracture toughness value and the high-resolution image; and on the basis of the fracture toughness value and the corrected final failure displacement and initial damage displacement, constructing a finite element model of the CFRP laminated material sample containing the precracks. The accurate calculation method of the fracture toughness and the correction method of the cohesion 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 CFRP laminate material simulation model based on DIC and synchrotron radiation. Background Art

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

[0003] In the prior art, static loading and dynamic loading are commonly used methods to study the mechanical properties of CFRP. Static loading has the following disadvantages: insufficient mechanical performance, limited damage mechanism, and limited practical 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 practical applications. When studying the influence of CFRP matrix material properties or damage during loading based on dynamic loading, the fracture toughness of CFRP has an important influence on the simulation results. After a large number of CFRP simulation experimental studies, it is shown that under dynamic loading, there is a difference in the time scale between the propagation of one-dimensional stress waves and cracks, and the material has cracked 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 of CFRP interlayers. In addition, the prefabricated crack model in the CFRP finite element model usually uses a cohesive force model. When establishing a simulation model, if the parameters of the cohesive force model cannot be consistent with the actual CFRP material performance 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 under dynamic loading and a correction method for the cohesive force model parameters, 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, an embodiment of the present invention aims to provide a method for constructing a CFRP laminate material simulation model 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 embodiment of the present invention provides a method for constructing a CFRP laminate material simulation model based on DIC and synchrotron radiation, comprising: 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; A finite element model of the CFRP laminate sample containing prefabricated cracks is constructed based on the fracture toughness value and the corrected final failure displacement and initial damage displacement.

[0007] Based on the further improvement of the above method, after constructing the CFRP laminate material specimen, it is also necessary to verify whether the specimen size meets the plane strain condition.

[0008] Based on the further improvement of the above method, 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.

[0009] Based on a further improvement of the above method, 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.

[0010] Based on the further improvement of the above method, 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 moment of crack initiation, and E is the elastic modulus.

[0011] Based on the further improvement of the above method, the final failure displacement is corrected based on the high-resolution image and the crack initiation time, including: 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; An average moving speed is calculated 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.

[0012] Based on the further improvement of the above method, 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.

[0013] Based on the further improvement of the above method, the initial damage displacement is corrected based on the fracture toughness value and the high-resolution image, including: 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.

[0014] Based on the further improvement of the above method, when preparing the sample, a speckle with obvious black and white contrast is sprayed on the surface of the sample.

[0015] Based on the further improvement of the above method, the strain gauge uses a polyimide film substrate strain gauge.

[0016] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: 1. The present invention provides a method for constructing a simulation model of CFRP laminated materials based on DIC and synchrotron radiation, and calculating the interlaminar fracture toughness of CFRP laminated materials based on digital image correlation technology (DIC). Specifically, based on SHPB test images before and after the crack initiation time taken by a high-speed camera, the longitudinal displacement of the pixel point at the crack initiation time is obtained by the least squares method, and the fracture toughness at the crack initiation time is obtained based on the calculation formula of type I dynamic stress intensity factor and the calculation formula of fracture toughness. Compared with the calculation method of fracture toughness in traditional theory, the method proposed by the present invention can obtain the accurate opening displacement corresponding to the crack initiation time, thereby obtaining a more accurate fracture toughness value at the crack initiation time.

[0017] 2. The present invention provides a method for constructing a simulation model of CFRP laminated materials based on DIC and synchrotron radiation, introducing a synchrotron radiation device to obtain a high-resolution image of the fracture process, and directly observing the constitutive model parameters through ultrafast X-ray phase contrast imaging of the synchrotron accelerator and high time and high spatial resolution. Specifically, the final failure displacement is corrected based on the high-resolution image and the crack initiation time, and the initial damage displacement is corrected based on the fracture toughness value and the high-resolution image. The cohesive force model is combined with the material characteristic parameters related to the strain rate effect, thereby establishing an accurate simulation model of CFRP laminated materials, which can more accurately describe the interlaminar fracture damage evolution of CFRP laminated materials under dynamic loading.

[0018] In the present invention, the above-mentioned technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can become obvious from the description, or can be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The accompanying drawings are only used for the purpose of illustrating specific embodiments and are not to be considered as limiting the present invention. In the entire drawings, the same reference symbols represent the same components; FIG1 is an exemplary diagram of a method for constructing a CFRP laminate material simulation model based on DIC and synchrotron radiation in an embodiment of the present invention; Figure 2 is an example diagram of a CFRP laminate material sample prepared in an embodiment of the present invention; Figure 3 is an exemplary diagram of an integrated DIC and SHPB device in an embodiment of the present invention; Figure 4 It is an example diagram comparing the test results and the theoretical numerical calculation results under different loading test conditions in the embodiment of the present invention. DETAILED DESCRIPTION

[0020] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0021] The Split Hopkinson Pressure Bar (SHPB) impact test is an important experimental technique used to study the dynamic mechanical properties of materials under high strain rates. Based on the one-dimensional stress wave theory, the impact energy is transferred to the specimen through an elastic rod (usually a metal rod). The specimen is loaded with a high strain rate in a very short time, thereby realizing dynamic compression performance testing. The test device mainly includes: mainly composed of an air gun, a bullet (impact rod), an incident rod, a transmission rod, a damper and a data acquisition system.

[0022] The DIC analysis system, or digital image correlation system, is an optical measurement system used to measure the deformation of the surface of an object. By tracking the image of the surface of the object, it can measure the three-dimensional coordinates, displacement and strain of the object during the deformation process. Its basic principle is: the area of ​​interest in the image before deformation is gridded, and each sub-area is treated as a rigid motion. Then, for each sub-area, a certain search method is used to perform correlation calculations according to a pre-defined correlation function, and the area with the maximum mutual correlation coefficient with the sub-area is found in the deformed image, that is, the position of the sub-area after deformation, and then the displacement of the sub-area is obtained. By calculating all sub-areas, the deformation information of the entire field can be obtained. It includes: image acquisition equipment, usually a CCD camera or a high-speed camera, used to capture digital images of the object surface before and after deformation; lighting source, in order to form a clear speckle pattern on the object surface, a suitable lighting source is required, such as a fiber optic gooseneck light, to provide uniform illumination; an image acquisition card, used to convert the analog image signals collected by the camera into digital signals and transmit them to a computer for processing; a computer, equipped with corresponding DIC analysis software, used to perform relevant calculations and data analysis on the collected digital images to obtain information such as displacement and strain on the object surface.

[0023] A specific embodiment of the present invention discloses a method for constructing a CFRP laminate material simulation model based on DIC and synchrotron radiation, such as Figure 1 As shown, it is characterized by comprising: S1: construct a CFRP laminate sample containing a prefabricated crack, and paste a strain gauge near the tip of the prefabricated crack.

[0024] according to The CFRP laminate specimens were designed and prepared in the standard way, and the ply layup order was , insert a micron-thick polytetrafluoroethylene material into the central layer of the specimen as a prefabricated crack, such as Figure 2 shown.

[0025] For example, to prepare a laminated sample, first design the sample based on the sample size. The pressing mold is used to prepare the prepreg matrix. The unidirectional fiber is obtained by the filament winding device built in the processing workshop. Then the matrix is ​​used to wet the unidirectional fiber cloth to obtain the CFRP prepreg; the prepreg blanks are then stacked in a predetermined layer order, and polytetrafluoroethylene is placed on the edge of the mold when the central layer is laid, and the pre-crack length is 3mm, and then the other side is laid symmetrically; after the plying is completed, and 70Kpa environment for 2 hours; finally based on Standard, the specimen should meet the plane strain condition and be made by plane milling machine to process the laminate The plane strain conditions of the test specimen are as follows: , , Where H is the specimen height, B is the specimen width, and a is the length of the prefabricated crack.

[0026] Understandably, placing the polytetrafluoroethylene to the edge is to better hold the molding in place and prevent serious misalignment.

[0027] Before the dynamic fracture test, the surface of the specimens was painted with matte paint ( The plane is sprayed with white paint, and black speckle is sprayed after air drying. A high-speed camera is used to capture the image of the current random speckle as the reference image for the subsequent calculation of the opening displacement function. A resistance strain gauge is pasted near the prefabricated crack tip on the other side of the specimen to test the effective strain information. The strain gauge is selected Model polyimide film base strain gauge. Wipe the pasting position with alcohol and drip it after it dries. Use the type of patch adhesive to press the strain gauge onto the surface of the sample until it is firm. Then weld the strain gauge lead wire and add pins. After completion, re-measure the strain gauge resistance value to ensure it is within the error range.

[0028] Preferably, a multimeter is used to measure the resistance of the strain gauge. The resistance value of the strain gauge is , considering the instrument error of the multimeter, the measurement can be within this range.

[0029] S2: A three-stage bending fracture loading test is performed on the sample using a split Hopkinson bar SHPB, 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.

[0030] The Hopkinson bar (SHPB) impact test requires the installation of bullets, incident bars, transmission bars and strain bridge boxes SDY2301, debugging of ultra-dynamic strain gauges, data acquisition systems, high-speed photography devices, etc. After installing each component, it is necessary to check whether the position of each component is correct and whether the function is normal. After verification, the integrated DIC and SHPB are used to perform an impact fracture test on the sample. By releasing compressed air in a closed air chamber, the bullet hits 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 shown in the attached figure. Figure 3 shown.

[0031] S3: The fracture process image is processed using DIC analysis software to obtain an opening displacement function of the crack tip, a mode I dynamic stress intensity factor of the crack tip of the sample at the moment 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.

[0032] The fracture process image is processed using DIC analysis software to obtain the crack tip opening displacement function, which specifically includes: The reference image is divided into multiple sub-regions. The speckle pattern in each sub-region is searched and matched in the deformed image. The search range of each sub-region in the deformed image is set according to the expected maximum displacement. Within the search range of each sub-region, the correlation function (e.g., normalized cross-correlation coefficient) of the sub-region between the reference image and the deformed image (each fracture process image taken) is calculated. , NCC)), 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 the displacement of the sub-region can be calculated. According to the displacement of the sub-region at each best matching position, the displacement field of the whole field is constructed to describe the deformation of the object surface. Finally, the opening displacement function can be obtained by analyzing and calculating the displacement of the whole field. In addition, the extreme point in the sample strain signal is selected as the crack initiation time.

[0033] 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 includes: A1: 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.

[0034] It is understandable that the shooting time of a high-speed camera is generally difficult to completely coincide with the crack initiation time. Therefore, the present invention selects two fracture process images before and after the crack initiation time as the basis for the subsequent calculation of the type I dynamic stress intensity factor.

[0035] A2: 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 calculation equation of the type I dynamic stress intensity factor is: , in, is the distance from the crack tip, To capture the moment, is the shear modulus, is the Poisson's ratio of the sample, is the opening displacement function.

[0036] A3: Set the time as the crack initiation time, and substitute it into the time-intensity factor fitting equation to obtain the type I dynamic stress intensity factor at the crack initiation time.

[0037] 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 moment of crack initiation, and E is the elastic modulus.

[0038] S4: 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 capture high-resolution images of the fracture process of the sample.

[0039] An integrated synchrotron radiation device is introduced based on the existing integrated DIC and SHPB devices. The synchrotron radiation central line station delivers the strong X-ray beam to the sample position. The slow shutter and fast shutter are synchronized with the camera, SHPB and oscilloscope to minimize the sample heat load caused by the incident X-rays. of Single crystal scintillators are used to convert X-rays into visible light. Impact fracture tests are then carried out on the specimens, which are recorded by high-speed cameras to obtain high-resolution images of the fracture process.

[0040] Understandably, under dynamic loading, during the fracture of composite materials, there is a difference in the time scale between the high-speed crack expansion and the propagation of stress waves. Therefore, it is necessary to conduct a multi-scale analysis of the fracture process of the sample in time and space to deeply understand the fracture mechanism of the sample. However, conventional testing methods (SHPB) cannot determine the order of damage between the matrix and the fiber, 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 final failure displacement and initial damage displacement correction.

[0041] S5: 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.

[0042] The correcting the final failure displacement based on the high-resolution image and the crack initiation time includes: B1: 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.

[0043] As mentioned above, it is generally difficult for the shooting time of a high-speed camera to completely coincide with the crack initiation time. Therefore, the present invention selects two high-resolution images before and after the crack initiation time as the basis for subsequent correction of the final failure displacement.

[0044] B2: Calculate 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 take the larger opening displacement value as the final failure displacement.

[0045] As described above, the DIC analysis software obtains the method of opening displacement, based on which the opening displacement value of the material at the film tip position of the third fracture process image and the fourth fracture process image is obtained, and the larger of the third fracture process image and the fourth fracture process image is used as the final failure displacement value (i.e., the failure displacement boundary value).

[0046] B3: 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.

[0047] Among them, the shooting time of the third fracture process image and the fourth fracture process image is known. Based on the position change of the same point in the third fracture process image and the fourth fracture process, the displacement of the point can be calculated, and then the moving speed of the reference point can be obtained based on the change value of the displacement and the shooting time.

[0048] B4: 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.

[0049] Among them, the shooting time of the third fracture process image and the fourth fracture process image is known, and the opening displacement values ​​in the third fracture process image and the fourth fracture process image are calculated based on the DIC analysis software, and then the average crack opening speed can be obtained based on the change in the opening displacement value and the change in the shooting time.

[0050] B5: Calculate an average moving speed based on the first moving speed and the second moving speed.

[0051] B6: Correcting 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, including: , , 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.

[0052] The correcting the initial damage displacement based on the fracture toughness value and the high-resolution image comprises: C1: 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 .

[0053] Specifically, the collected images are processed using DIC analysis software to calculate the longitudinal strain value of each point on the sample surface. The strain distribution can be obtained by comparing the displacement of the speckle in the image before and after deformation, combined with the relevant algorithm, and the corresponding load value and the calculated longitudinal strain value are recorded. The load-strain curve is drawn, and the maximum load value corresponding to the strain value is found on the load-strain curve, which is the measured load peak value. The prefabricated crack in the present invention adopts the bilinear configuration of the cohesive force constitutive model. After determining the fracture toughness and the final failure displacement, the physical meaning of the constitutive curve and the area enclosed by the horizontal coordinate is used to calculate the theoretical load peak value using the following formula: , is the fracture toughness value, is the final failure displacement.

[0054] C2: Based on 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 value of the initial damage displacement, where the initial damage displacement refers to the damage displacement value of the pre-crack at the moment of crack initiation.

[0055] S6: constructing a finite element model of the CFRP laminate sample containing prefabricated cracks based on the fracture toughness value and the corrected final failure displacement and initial damage displacement.

[0056] Using commercial finite element software The geometric models of CFRP specimens and SHPB loading device were established, the ply angle was set for the specimen, the prefabricated cracks were set as cohesive units, and the corrected final failure displacement and initial damage displacement were assigned, thus establishing a finite element model of CFRP laminated material specimens that can accurately describe the mechanical properties.

[0057] Furthermore, in order to verify the effectiveness of the correction method proposed in the present invention, two groups of tests were set up in the present invention, in which the loading gas pressure was set to 0.05Mpa and 0.08MPa respectively. According to the actual test loading state, a loading pulse was given to the incident rod. After the numerical calculation was completed, the load-displacement curve of the sample was extracted. For the two bullet loading test conditions, the numerical calculation results were compared with the test results. Figure 4It was found that under dynamic impact conditions, the established simulation model was able to capture the nonlinear characteristics of the initial loading phase and reasonably predict the load peak and the overall shape of the curve, verifying the effectiveness and correctness of the cohesive force model parameter correction method.

[0058] Compared with the prior art, the present embodiment provides a method for constructing a CFRP laminate material simulation model based on DIC and synchrotron radiation, and calculates the interlaminar fracture toughness of the CFRP laminate material based on the digital image correlation technology DIC. Specifically, based on the SHPB test images before and after the crack initiation time taken by a high-speed camera, the longitudinal displacement of the pixel point at the crack initiation time is obtained by the least squares method, and the fracture toughness at the crack initiation time is obtained based on the calculation formula of the type I dynamic stress intensity factor and the calculation formula of the fracture toughness. Compared with the calculation method of the fracture toughness in the traditional theory, the method proposed by the present invention can obtain the accurate opening displacement value corresponding to the crack initiation time, so as to be able to A more accurate fracture toughness value at the crack initiation moment can be obtained; a synchrotron radiation device is introduced to obtain a high-resolution image of the fracture process, and the constitutive model parameters are directly observed through the ultrafast X-ray phase contrast imaging of the synchrotron as well as high time and high spatial resolution. Specifically, the final failure displacement is corrected based on the high-resolution image and the crack initiation time, and the initial damage displacement is corrected based on the fracture toughness value and the high-resolution image. The cohesive force model is combined with the material property parameters related to the strain rate effect, thereby establishing an accurate simulation model of CFRP laminated materials, which can more accurately describe the interlaminar fracture damage evolution of CFRP laminated materials under dynamic loading.

[0059] Those skilled in the art will appreciate that all or part of the processes of the above-mentioned embodiments can be implemented by instructing related hardware through a computer program, and the program can be stored in a computer-readable storage medium, wherein the computer-readable storage medium is a disk, an optical disk, a read-only storage memory, or a random access memory, etc.

[0060] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within 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; A finite element model of the CFRP laminate sample containing prefabricated cracks is constructed based on the fracture toughness value and the corrected final failure displacement and initial damage displacement.

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 4, characterized in that: 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 moment of crack initiation, and E is the elastic modulus.

6. 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.

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 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.

8. The method for constructing a CFRP laminate material simulation model based on DIC and synchrotron radiation according to claim 7, 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.

9. 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.

10. 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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