Device and method for testing high-temperature forming limit of continuous fiber reinforced composite material

Abstract

The invention belongs to the field of composite material forming, and relates to a continuous fiber reinforced composite material high-temperature forming limit testing device and method. The upper blank holder and the lower blank holder are vertically opposite in position, a test piece is clamped between the upper blank holder and the lower blank holder, and the upper blank holder and the lower blank holder are fixed on the supporting plate through bolts; heating devices are respectively arranged on the opposite sides of the upper blank holder and the lower blank holder; a heating device is also arranged in the hemispherical punch; holes are formed in the positions, opposite to the hemispherical punch, of the upper blank holder and the lower blank holder, and blank pressing ribs are arranged on the inner walls of the holes; two CCD digital cameras are placed under the round hole of the supporting plate and used for tracking surface displacement of the test piece in real time, and real-time strain is analyzed through a DIC-3D three-dimensional digital image related system. The device has the advantages of simplicity in installation, flexibility in operation, convenience in maintenance and the like, and can monitor and record the full-field strain and the evolution process of the test piece in real time.

Description

Technical Field

[0001] The invention belongs to the field of composite material forming, and relates to a device and method for testing the high-temperature forming limit of a continuous fiber reinforced composite material. Background Art

[0002] Lightweight design is one of the effective ways to improve the range of new energy vehicles and traditional fuel vehicles and reduce energy consumption. Lightweight materials are the cornerstone of the development of lightweight vehicles. Among many lightweight materials, composite materials have the advantages of stable chemical properties, excellent mechanical properties, and excellent weight reduction effect. With the continuous improvement of the mechanical properties of domestic composite materials and the continuous decline in the cost of raw materials, advanced, high-strength and low-cost composite materials have begun to be used in land transportation vehicles such as automobiles and rail trains, especially in the manufacture of electric vehicle body parts. At present, traditional metal materials can no longer meet the growing demand for lightweight vehicles, especially in the design and manufacture of electric vehicle body parts. By gradually replacing traditional metal body materials with lightweight composite materials or mixing the two, the lightweight effect and comprehensive performance of the whole vehicle and parts can be significantly improved. For example, the application of composite materials in parts such as body panels, doors, hoods and roofs of electric vehicles not only reduces weight, but also improves structural strength and impact resistance. According to the length of fiber reinforcement, resin-based composite materials can be divided into short fiber / long fiber / continuous fiber reinforced composite materials. In comparison, continuous fiber reinforced composite materials have higher mechanical properties and good formability, and can be used for the production of automotive interior and exterior covers, secondary load-bearing components and main load-bearing components. Continuous fiber reinforced composite materials can be quickly formed into automotive parts with complex contours through the molding process, with the advantages of high production efficiency and high degree of integration.

[0003] However, the current research on the failure mechanism of continuous fiber reinforced composite materials at home and abroad is not comprehensive enough, and the industry still lacks reliable forming limit evaluation criteria, which hinders the formulation and optimization of process solutions for continuous fiber reinforced composite automotive parts and seriously restricts its further promotion and application in the automotive field. Therefore, for electric vehicle body parts, the construction and application of forming limit diagrams of continuous fiber reinforced composite materials is of great significance to improving production efficiency and product quality.

[0004] In the actual forming process of electric vehicle body parts, unreasonable process schemes, layer angles or mold designs may cause continuous fiber reinforced composite materials to wrinkle, delaminate or crack during forming. Especially for electric vehicle body parts with complex curved surfaces, such as body panels, doors, hoods, etc., cracking defects are the most common and one of the most fatal failure modes. This defect will not only seriously reduce the forming quality of the product surface, but also seriously damage the service performance of the parts. It is crucial to establish a reliable evaluation criterion for cracking forming defects to improve the forming performance of continuous fiber reinforced composite products. The forming limit diagram characterizes the formability of thin plate materials according to the distribution of principal strain and secondary strain. The forming limit curve composed of the upper envelope in the forming limit diagram reflects the limit strain state of the sheet material at the moment before failure. The forming limit diagram can reliably characterize the stamping forming performance of metal sheet materials and is widely used in the automotive industry, including the manufacture of electric vehicle body parts. However, continuous fiber reinforced composites are composed of resin matrix and fibers, and have obvious anisotropic mechanical properties and multi-scale structural characteristics. The deformation process of fiber yarn and resin matrix during hot molding of continuous fiber reinforced composites is completely different from the flow process of metal sheet materials. The construction method of traditional metal sheet material forming limit diagram and forming limit curve is no longer applicable to continuous fiber reinforced composites. It is urgent to develop a new type of high-temperature forming limit test device and method for continuous fiber reinforced composites.

[0005] Since the bending stiffness of fiber materials is extremely small, in order to avoid compression bending deformation of continuous fiber reinforced composite materials during the molding process, a certain horizontal pre-tensioning force is usually applied to them by using spring components and blank holder components to induce shear deformation of fiber yarns to avoid wrinkling defects. It should be noted that fiber yarns also bear tensile loads during shear deformation, and the tensile fracture strain of fiber yarns is much smaller than that of the resin matrix. The fracture failure of fiber yarns will directly lead to rupture defects in the product. Based on this, the fiber limit strain can be used as a forming limit evaluation index for continuous fiber reinforced composite materials. In addition, the traditional method of constructing the forming limit diagram has a strong dependence on the strain path. For this reason, the strain path effect can be effectively eliminated by introducing the primary and secondary strain ratio (i.e., secondary strain / primary strain) into the forming limit diagram. In addition, due to the continuity of fibers, the traditional hourglass-shaped metal sheet bulging specimen processing method will cause continuous fiber breakage, and thus cannot accurately obtain the true limit strain of the continuous fiber yarn in the bulging test. The slotted specimen design method can ensure the continuity of the fiber, and by changing the size of the slot, the fiber limit strain under various deformation modes can be obtained through the bulging test, thereby completely constructing the forming limit diagram of the continuous fiber composite material. Summary of the invention

[0006] In view of the above technical problems, the present invention proposes a device and method for testing the high-temperature forming limit of continuous fiber reinforced composite materials. A series of slotted continuous fiber reinforced composite material specimens with different sizes are designed, and high-temperature hemispherical bulging tests are carried out on them respectively. A non-contact optical measurement system is used to record the evolution of the principal strain and secondary strain on the surface of the specimen, and the fiber limit strain is obtained by using a coordinate transformation method. The high-temperature forming limit diagram and forming limit curve of the continuous fiber reinforced composite material are drawn according to the principal and secondary strain ratio and the fiber limit strain. The present invention is applicable to both continuous fiber reinforced thermosetting composite materials and continuous fiber reinforced thermoplastic composite materials. The bulging device has the advantages of simple processing, easy assembly, convenient operation, and low cost.

[0007] The specific technical solution is:

[0008] A continuous fiber reinforced composite material high temperature forming limit test device, comprising a base, a column, a support plate, a clamping mechanism and a hemispherical punch;

[0009] The base is connected to the support plate through a column; the clamping mechanism is installed on the support plate, and the hemispherical punch is located above the clamping mechanism;

[0010] The clamping mechanism comprises an upper pressure ring and a lower pressure ring, the upper pressure ring and the lower pressure ring are located opposite to each other, the test piece is clamped between the upper pressure ring and the lower pressure ring, and the upper pressure ring and the lower pressure ring are fixed to the support plate by bolts; a heating device is respectively provided on the opposite sides of the upper pressure ring and the lower pressure ring;

[0011] The hemispherical punch is also provided with a heating device;

[0012] Holes are provided at positions of the upper and lower pressure rings opposite to the hemispherical punch, and pressure ribs are provided on the inner walls of the holes;

[0013] A circular hole is provided at the position of the support plate corresponding to the hemispherical punch. Two CCD digital cameras are placed directly below the circular hole to track the surface displacement of the specimen in real time and analyze the real-time strain through the DIC-3D three-dimensional digital image correlation system.

[0014] Furthermore, the inner wall of the lower pressure ring hole is provided with double pressure ribs, and the transition area of ​​the pressure ribs is set as a chamfer.

[0015] Specifically, the heating device includes a heating tube and a thermocouple.

[0016] A method for testing the forming limit of continuous fiber reinforced composite materials at high temperature comprises the following steps:

[0017] First, fix the lower pressure ring on the support plate with bolts, place the upper pressure ring directly above it, turn on the computer host equipped with the testing machine; turn on the power button of the testing machine; put the test piece between the upper pressure ring and the lower pressure ring at room temperature, conduct heat through the heating device, and press after the temperature reaches the predetermined value;

[0018] Install the hemispherical punch; adjust the shooting angle of the CCD digital camera, set the shooting parameters and light intensity; tighten the bolts after installing the specimen and center the ball head; perform DIC pre-photographing and calculation to ensure that the speckle can be effectively calculated; slowly move the hemispherical punch to the surface of the specimen, reset the load and displacement after slight contact, and prepare to start the test; take an image when the test starts; the hemispherical punch moves downward at a constant speed close to the continuous fiber composite material specimen, and the fiber yarn stretching and shear deformation occur in the deformable area of ​​the specimen until the specimen breaks and the test is terminated.

[0019] The blank holder of the present invention adopts the design of upper and lower double blank holders, wherein the blank holder component contains blank holder ribs. Since the bending stiffness of the fiber yarn is extremely small, for complex test pieces of continuous fiber reinforced composite materials, in order to avoid wrinkling defects caused by compression of the fiber yarn during the molding process, it is necessary to apply a certain blank holder force around the test piece to induce shear deformation of the fiber yarn, so that it can smoothly fit the surface of the hemispherical punch during the punching process, avoid wrinkling and deformation of the fiber yarn and improve the forming quality of the product. The heating device includes a blank holder, a heating tube and a thermocouple arranged in the hemispherical punch, and a temperature controller connected thereto, which can heat it to a preset test temperature. The strain measurement system includes two CCD digital cameras, a plane light source and DIC-3D three-dimensional digital image correlation post-processing software, which can monitor the strain changes on the test piece surface in real time, calculate the instantaneous rotation increment, instantaneous overall normal strain and shear strain increment using the coordinate transformation method, and obtain the instantaneous increment of fiber strain. By accumulating the instantaneous fiber strain increment during the entire bulging process, the final total fiber strain can be obtained. The fiber strain near the rupture area just before the failure of the specimen is the fiber limit strain. The forming limit diagram of continuous fiber reinforced composite materials can be drawn with the major and minor strain ratio as the horizontal coordinate and the fiber strain as the vertical coordinate.

[0020] Preferably, the test adopts a double-holding rib design, which can better limit the free sliding of the specimen during the bulging process and provide a better holding force, ensuring that the fiber yarn undergoes tensile and shear deformation, avoiding wrinkling and deformation of the fiber yarn and improving the forming quality of the product.

[0021] Preferably, during the test, the slotted bulging specimen design method can ensure the continuity characteristics of the fiber yarn, avoid the traditional hourglass specimen cutting method that damages the fiber yarn and cannot obtain the accurate fiber limit strain.

[0022] Preferably, the hemispherical punch in the testing device is connected to the tensile testing machine to ensure the stability of the punching process and the accuracy of the data.

[0023] Preferably, the special fixture for hemispherical bulging is an open device. This design can facilitate equipment layout, thereby providing operability for obtaining full-field strain of the material during the bulging process.

[0024] Preferably, during the bulging test, two CCD digital cameras are added, the load-displacement curve is automatically recorded by the sensor of the universal tensile testing machine, two CCD digital cameras are set up at the bottom of the specimen to shoot the bulging deformation process of the specimen, and the DIC-3D digital image correlation technology is used to obtain the full-field strain information of the specimen surface.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows: the special fixture for the bulging test in the test is a set of detachable clamping devices designed separately, which is mainly used to clamp the prefabrication of the test piece and the blank holder, and is connected to the tensile testing machine, and has the advantages of simple installation, flexible operation, and easy maintenance. The slotted specimen design method used for the specimen better maintains the integrity of the specimen and the continuity of the fiber, and reduces the occurrence of fiber pull-out failure. In addition, the boundary conditions of the slotted specimen at the blank holder ring are improved, which can significantly enhance the bending resistance of the specimen in the curvature transition zone and reduce the probability of bending-shear coupling failure. The slotted specimen design is more suitable for the establishment of the forming limit diagram of continuous fiber reinforced composite materials than the traditional hourglass specimen. In addition, two CCD digital cameras are connected to the 3D digital image correlation system (DIC-3D), which can further monitor and record the full-field strain of the specimen and its evolution process in real time, and more deeply reveal the material flow mechanism and crack defect generation mechanism of continuous fiber reinforced composite materials during the forming process. It can optimize the process plan, layup angle and mold design, thereby improving the lightweight effect and overall performance of electric vehicle body components. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of the structure of the testing device in the present invention;

[0027] Figure 2 It is a schematic diagram of the axonometric structure of the testing device in the present invention;

[0028] Figure 3 It is a schematic diagram of the assembly of the test device in the present invention;

[0029] Figure 4 It is a schematic diagram of the structure of the punch in the present invention;

[0030] Figure 5 It is a schematic structural diagram of the upper blank holding ring in the present invention;

[0031] Figure 6It is a structural schematic diagram of the lower edge pressing ring in the present invention;

[0032] Figure 7 is a cross-sectional view of the upper blank holder in the present invention;

[0033] Figure 8 is a cross-sectional view of the lower edge pressing ring in the present invention;

[0034] Fig. 9 It is a structural schematic diagram of the support plate in the present invention;

[0035] Fig.10 Schematic diagram of slotted test pieces of different sizes in the present invention;

[0036] Fig.11 is a forming limit curve diagram of rupture failure of an embodiment. DETAILED DESCRIPTION

[0037] The specific technical solution of the present invention is described in conjunction with the accompanying drawings.

[0038] The device can perform forming limit tests on continuous fiber reinforced composite materials under high temperature conditions, which is crucial for optimizing the design and manufacturing process of electric vehicle body parts and improving their performance and safety under high temperature environments. Figure 1-Figure 8 As shown, the bulging fixture is an open structure, and the test device is mainly composed of a base 6, a column 5, a support plate 7, a clamping mechanism and a hemispherical punch 1. The base 6 is connected to the support plate 7 through the column 5; the clamping mechanism is installed on the support plate 7, and the hemispherical punch 1 is located above the clamping mechanism; the core purpose of this design is to facilitate the layout of the equipment, thereby providing operational convenience for obtaining full-field strain data for the material during the bulging test.

[0039] like Figure 1 The clamping mechanism includes an upper pressure ring 2 and a lower pressure ring 4, the upper pressure ring 2 and the lower pressure ring 4 are located opposite to each other, the test piece 3 is clamped between the upper pressure ring 2 and the lower pressure ring 4, and the upper pressure ring 2 and the lower pressure ring 4 are fixed to the support plate 7 by bolts 10; a heating device is provided on the opposite side of the upper pressure ring 2 and the lower pressure ring 4;

[0040] The hemispherical punch 1 is also provided with a heating device;

[0041] The upper and lower pressure rings 2 and 4 are provided with holes at positions opposite to the hemispherical punch 1, and the inner walls of the holes are provided with pressure ribs, such as Figures 5 to 8 The inner wall of the 4 holes of the lower pressure ring is provided with double pressure ribs, and the transition area of ​​the pressure ribs is set as chamfer.

[0042] A circular hole is provided at the position of the support plate 7 corresponding to the hemispherical punch 1, and two CCD digital cameras 11 are placed directly below the circular hole for real-time tracking of the surface displacement of the specimen 3 and analyzing the real-time strain through a DIC-3D three-dimensional digital image correlation system.

[0043] like Figure 4 The heating device includes a heating tube 8 and a thermocouple 9.

[0044] like Fig. 9 As shown, four through holes are opened around the support plate 7, and four columns 5 are fixed through the through holes of the support plate 7 and the base 6. Six threaded holes evenly arranged on the circumference are reserved on the upper pressure ring 2, and six threaded holes are provided on the corresponding parts of the lower pressure ring 4 and the support plate 7. Six bolts 10 are fixed through the threaded holes in the lower pressure ring 4 and the support plate 7. Heating tubes 8 are arranged on both sides of the upper pressure ring 2 and the lower pressure ring 4, and thermocouples 9 are arranged in the front and back. The hemispherical punch 1 is also provided with a heating tube and a thermocouple. The heating tube 8 is connected to an external temperature control system to heat to a preset temperature, and the temperature is measured and controlled by the thermocouple 9.

[0045] Specimen 3 uses a slotted specimen, such as Fig.10 The slotted specimen is characterized by two long notches with different aspect ratios on both sides. The distance between the two notches determines the width of the specimen, in order to maintain the continuity of the fibers in the narrowest part of the middle of the specimen as much as possible. In order to better provide the blanking force and to better limit the free sliding of the specimen 3 during the stamping process, the lower pressure ring 4 adopts a double pressure rib design, and the transition area of ​​the pressure rib is chamfered. The hemispherical punch 1 is connected to the tensile testing machine, which can control the stamping rate of the hemispherical punch 1 to make the test more accurate. The specimen 3 is fixed at the center of the upper pressure ring 2 and the lower pressure ring 4, and the hemispherical punch 1 can move up and down through the tensile testing machine. Two CCD digital cameras 11 are placed directly below the support plate 7. The two CCD digital cameras 11 are used in the test to track the surface displacement of the specimen 3 in real time, and the real-time strain is analyzed by the DIC-3D three-dimensional digital image correlation system.

[0046] Preferably, the test adopts a double-holding rib design, which can better limit the free sliding of the test piece 3 during the punching process and provide a better holding force, ensuring that the continuous fiber yarn undergoes tensile and shear deformation.

[0047] Preferably, the hemispherical punch 1 in the testing device is connected to a tensile testing machine to ensure stability during the punching process and accuracy of the data.

[0048] Preferably, the special fixture for stamping is an open device. This design can facilitate the equipment layout, thereby providing operability for obtaining full-field strain of the material during the stamping process.

[0049] Preferably, by adding two CCD digital cameras 11, the load-displacement sensor of the tensile testing machine obtains the force-displacement curve of the material, and the full-field strain and deformation information during the stamping process is obtained through the DIC-3D system.

[0050] When the device is in use, the specific operating steps are as follows:

[0051] First, fix the lower pressure ring 4 on the support plate 7 by bolts, place the upper pressure ring 2 just above it, turn on the computer host equipped with the test machine; turn on the power button of the test machine; put the slotted test piece 3 between the upper pressure ring 2 and the lower pressure ring 4 at room temperature, conduct heat through the heating tube 8, and press it after the temperature reaches the predetermined value, and fix the pressure ring in the center of the mold to press it, so that the ideal test piece 3 with smaller defects can be obtained. Click the "up" or "down" button on the upper part of the control box, adjust the space under the beam, reset the load and then install the hemispherical punch 1; adjust the shooting angle of the CCD digital camera 11, set the shooting parameters and light intensity, ensure that the sample can be clearly photographed during the test, and avoid overexposure of the sample surface; after installing the test piece 3, tighten the bolts, center the ball head, and ensure that the sample speckle is facing the camera; perform DIC pre-photographing and calculation to ensure that the speckle can be effectively calculated; slowly move the ball head to the surface of the test piece 3, reset the load and displacement after slight contact, and prepare to start the test. Click "Start Test" and start the camera timer shooting at the same time, with the acquisition frequency set by yourself; the hemispherical punch 1 moves downward at a constant speed close to the continuous fiber composite material specimen 3, and the fiber yarn stretching and shear deformation occur in the deformable area of ​​the specimen 3 until the specimen 3 breaks and then the test is terminated.

[0052] The deformation process of the material is captured using a DIC-3D non-contact strain measurement system. The test equipment is based on optical principles and performs image calculation by identifying the speckle grayscale field on the surface of the material, thereby providing full-view 2D and 3D space morphology, displacement, strain and other data. The present invention uses the last image collected before failure to calculate the ultimate strain of the fiber. The principal strain and secondary strain in the traditional metal FLD are still applicable in the new strain forming limit diagram, but in the form of strain ratio (SR). Different strain ratio values ​​reflect the different deformation modes of specimen 3:

[0053]

[0054] SR is the major-minor strain ratio, ε Mionr represents the surface secondary strain, ε MajorRepresents the principal strain of the surface, which can be calculated by DIC software. With the principal and minor strain ratio as the horizontal coordinate and the fiber limit strain as the vertical coordinate, the forming limit diagram of the continuous fiber composite material can be drawn. The upper envelope of the forming limit diagram can be extracted to obtain the forming limit curve of the rupture failure, such as Fig.11 shown.

[0055] The device is mainly composed of upper and lower pressure rings 4, a hemispherical punch 1, a heating system, and a CCD digital camera 11. It has a simple structure and can be freely installed on a tensile testing machine. It is easy to disassemble and assemble. The design method of the slotted specimen 3 can ensure the continuity of the fiber yarn in the middle deformation area of ​​the specimen. The pressure ring assembly constrains the free sliding of the material around the specimen 3, thereby inducing significant shear deformation of the fiber yarn and dominating the entire forming process, overcoming the defects of the traditional hourglass specimen 3 that the fiber yarn is cut off, resulting in fiber pull-out failure in the bulging test and the inability to accurately record the failure strain.

[0056] By constructing the major and minor strain ratio evaluation index, the dependence of the forming limit of continuous fiber composite materials on the strain path is effectively eliminated. The fiber limit strain evaluation index can accurately reflect the generation of rupture forming defects in continuous fiber composite materials. In the forming process of electric vehicle body parts, the mechanical properties of the material are extremely high. Therefore, the forming limit diagram constructed based on fiber strain and major and minor strain ratio can reliably evaluate the forming performance of continuous fiber composite materials, which is of great practical significance for the optimization design of process solutions for electric vehicle body parts.

[0057] In addition, based on this device and method, by conducting hemispherical bulging tests on continuous fiber composite materials under different temperature conditions, a three-dimensional forming limit diagram and forming limit curve including temperature, fiber strain, and major and minor strain ratios can be constructed.

Claims

1. A method for testing the high temperature forming limit of a continuous fiber reinforced composite material, using a device for testing the high temperature forming limit of a continuous fiber reinforced composite material; comprising a base (6), a column (5), a support plate (7), a clamping mechanism and a hemispherical punch (1); The base (6) and the support plate (7) are connected via a column (5); the clamping mechanism is mounted on the support plate (7), and the hemispherical punch (1) is located above the clamping mechanism; The clamping mechanism comprises an upper pressure ring (2) and a lower pressure ring (4), the upper pressure ring (2) and the lower pressure ring (4) are located opposite to each other in the upper and lower directions, the test piece (3) is clamped between the upper pressure ring (2) and the lower pressure ring (4), and the upper pressure ring (2) and the lower pressure ring (4) are fixed to the support plate (7) by bolts (10); heating devices are respectively provided on the opposite sides of the upper pressure ring (2) and the lower pressure ring (4); The hemispherical punch (1) is also provided with a heating device; The upper pressure ring (2) and the lower pressure ring (4) are provided with holes at positions opposite to the hemispherical punch (1), and the inner walls of the holes are provided with pressure ribs; A circular hole is provided at a position of the support plate (7) corresponding to the hemispherical punch (1), and two CCD digital cameras (11) are placed directly below the circular hole to track the surface displacement of the test piece (3) in real time and analyze the real-time strain through a DIC-3D three-dimensional digital image correlation system; The inner wall of the hole of the lower pressure ring (4) is provided with double pressure ribs, and the transition area of ​​the pressure ribs is set as a chamfer; The heating device comprises a heating tube (8) and a thermocouple (9); It is characterized in that The method comprises the following steps: First, a series of slotted continuous fiber reinforced composite material samples with different sizes are designed as test pieces (3), and high-temperature hemispherical bulging tests are carried out on them respectively. The lower pressure ring (4) is fixed to the support plate (7) by bolts, and the upper pressure ring (2) is placed directly above it. The computer host equipped with the test machine is turned on; the power button of the test machine is turned on; the test piece (3) is placed between the upper pressure ring (2) and the lower pressure ring (4) at room temperature, and heat is conducted through a heating device until the temperature reaches a predetermined value before pressing; Install the hemispherical punch (1); adjust the shooting angle of the CCD digital camera (11), set the shooting parameters and light intensity; after installing the test piece (3), tighten the bolts and center the ball head; perform DIC pre-photographing and calculation to ensure that the speckle can be effectively calculated; slowly move the hemispherical punch (1) to the surface of the test piece (3), reset the load and displacement after slight contact, and prepare to start the test; take an image when starting the test; the hemispherical punch (1) moves downward at a constant speed close to the continuous fiber reinforced composite material test piece (3), and the fiber yarn stretching and shear deformation occur in the deformable area of ​​the test piece (3), until the test piece (3) is ruptured and the test is terminated; The DIC-3D non-contact strain measurement system is used to capture images of the deformation process of the material. Based on optical principles, the image calculation is performed by identifying the speckle gray field on the material surface, thereby providing morphology, displacement and strain data in two-dimensional and three-dimensional space with full field of view; the last image collected before failure is used to calculate the ultimate strain of the fiber; different strain ratio values ​​reflect different deformation modes of the specimen (3): SR is the major-minor strain ratio, ε Mionr represents the surface secondary strain, ε Major Represents the surface principal strain, which is calculated by DIC software. With the major-minor strain ratio as the horizontal coordinate and the fiber limit strain as the vertical coordinate, the forming limit diagram of the continuous fiber composite material is drawn, and the rupture failure forming limit curve can be obtained by extracting the upper envelope of the forming limit diagram.

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