A method and apparatus for testing the mode iii interlaminar fracture toughness of a composite material

Abstract

This application provides a method and apparatus for testing the type III interlaminar fracture toughness of composite materials, belonging to the field of composite material testing technology. The method specifically includes determining the initial positions of four loading points on the test specimen and simulating the loading of the specimen; performing simulation calculations under multiple working conditions with the same load but adjusting only the spacing between loading points; calculating the proportion of type III interlaminar fracture strain energy release rate to the total interlaminar fracture strain energy release rate and the uniformity of the type III interlaminar fracture strain energy release rate distribution; and determining the final loading point positions by calculating a weighted average index. The processing scheme of this application improves the accuracy of the test results.

Description

Technical Field

[0001] This application relates to the field of composite material testing, and in particular to a method and apparatus for testing the type III interlaminar fracture toughness of composite materials. Background Technology

[0002] Composite materials have been widely used in aerospace, shipbuilding, rail transportation, automotive, energy and other industrial fields due to their excellent mechanical properties. The main forms of damage are matrix cracking, fiber breakage, interfacial debonding and interlayer delamination, among which delamination damage is the most common and the most dangerous.

[0003] The thickness-direction strength of carbon fiber laminates is much lower than their in-plane strength. When subjected to thickness-direction stress exceeding their strength, delamination damage occurs. Once delamination damage occurs, delamination propagation is dominated by interlaminar fracture toughness. Depending on the loading method at the delamination crack tip, three types of interlaminar fracture can be classified: Type I (opening), Type II (slipping), and Type III (tearing). In actual structures, delamination propagation is unlikely to be a single mode but rather a mixture of several modes. Accurately and reliably determining the interlaminar fracture toughness of Type I, II, and III, as well as the mixed interlaminar fracture toughness under different combinations, is a pressing problem for the characterization of composite material mechanical properties, material identification, and structural design, analysis, and evaluation. However, existing tests for Type III interlaminar fracture toughness of composite materials use a uniform loading point for specimens of different sizes, which cannot accurately guide the specimens to undergo Type III interlaminar fracture, thus affecting the accuracy of the test results. Summary of the Invention

[0004] In view of this, this application provides a method and apparatus for testing the type III interlaminar fracture toughness of composite materials, which solves the problems in the prior art and improves the accuracy of the test results of the type III interlaminar fracture toughness test of composite materials.

[0005] On the one hand, the method for testing the type III interlaminar fracture toughness of composite materials provided in this application adopts the following technical solution:

[0006] A method for testing the type III interlaminar fracture toughness of composite materials includes: The initial positions of the four loading points of the rectangular plate-shaped test specimen are determined. The four loading points are the first loading point, the second loading point, the third loading point, and the fourth loading point. The first and second loading points are located on the first side of the test specimen, and the third and fourth loading points are located on the second side of the test specimen. The first and second sides are two opposite sides of the test specimen. The first and second loading points are located on the first diagonal of the first side, and the third and fourth loading points are located on the second diagonal of the second side. The first and second diagonals intersect each other. The distance between the first and second loading points is equal to the distance between the third and fourth loading points. The centers of the first and second loading points coincide with the center of the first side, and the centers of the third and fourth loading points coincide with the center of the second side. A simulation finite element model for the Type III interlaminar fracture toughness test using the edge crack torsion method was established. The simulation finite element model includes a test specimen model and a loading structure model corresponding to each loading point. The pre-crack leading edge is marked on the test specimen model. The pre-crack leading edge is located at the center of the width direction of the test specimen model and is parallel to the length direction of the test specimen model. The simulation finite element model is then meshed. With a fixed test specimen model and a fixed loading structure model, simulation calculations are performed based on multiple load boundary conditions given at the initial positions of four loading points. Among the multiple load boundary conditions, the loads on each loading point are the same, the spacing between the first and second loading points is different, and the spacing between the third and fourth loading points is different. Obtain the proportion of the type III interlaminar fracture strain energy release rate at the pre-existing crack lead location to the total interlaminar fracture strain energy release rate under different load boundary conditions. ; Obtain the uniformity of strain energy release rate at the pre-crack front location of type III interlaminar fracture under different load boundary conditions. ; Calculate the weighted average index , ; According to the weighted average index The distance between the first and second loading points, and the distance between the third and fourth loading points in the minimum load boundary condition, determine the final positions of the four loading points; Confirm the relative positions of each loading structure on the test loading device based on the final positions of the four loading points; Place the test specimen on the test loading device and begin the test.

[0007] Optionally, the proportion of the type III interlaminar fracture strain energy release rate at the pre-existing crack front location to the total interlaminar fracture strain energy release rate under different load boundary conditions can be obtained. The steps include: Calculate the mesh nodes at the pre-existing crack front under various load boundary conditions. Type I interlaminar fracture strain energy release rate component , mesh nodes of pre-fabricated crack front Type II interlaminar fracture strain energy release rate component , mesh nodes of pre-fabricated crack front Type III interlaminar fracture strain energy release rate component ; Calculate the mean value of the strain energy release rate component of the pre-existing crack front at the type I interlaminar fracture under various load boundary conditions. Mean value of strain energy release rate component of type II interlaminar fracture at the pre-crack front Mean value of strain energy release rate component of type III interlaminar fracture at the pre-existing crack front : ; ; ; in, The dimension of the mesh on the test specimen model that borders the pre-existing crack front along the width of the test specimen model. The length of the test specimen model, This represents the total number of mesh nodes at the pre-fabricated crack front. Calculate the total interlaminar fracture strain energy release rate : ; calculate : .

[0008] Optionally, calculate the mesh nodes of the pre-existing crack front under various load boundary conditions. Type I interlaminar fracture strain energy release rate component , mesh nodes of pre-fabricated crack front Type II interlaminar fracture strain energy release rate component , mesh nodes of pre-fabricated crack front Type III interlaminar fracture strain energy release rate component The method is as follows: Extract the mesh nodes of the pre-existing crack front under various load boundary conditions. along Axial load , mesh nodes of pre-fabricated crack front along Axial load , mesh nodes of pre-fabricated crack front along Axial load ,in, The axis is parallel to the length direction of the test specimen model. The axis is parallel to the width direction of the test specimen model. The axis is parallel to the thickness direction of the test specimen model; Obtain the mesh node closest to the pre-existing crack tip on the side of the crack surface along the width of the test specimen model. along Position in the axial direction Obtain the mesh node closest to the pre-existing crack front edge on the lower side of the crack surface along the width direction of the test specimen model. along Position in the axial direction Obtain the mesh node closest to the pre-fabricated crack front edge on the side of the crack surface along the width direction of the test specimen model. along Position in the axial direction Obtain the mesh node closest to the pre-existing crack front edge on the lower side of the crack surface along the width direction of the test specimen model. along Position in the axial direction Obtain the mesh node closest to the pre-fabricated crack front edge on the side of the crack surface along the width direction of the test specimen model. along Position in the axial direction Obtain the mesh node closest to the pre-existing crack front edge on the lower side of the crack surface along the width direction of the test specimen model. along Position in the axial direction ; , and The calculation formulas are as follows: ; ; ; in, The dimension of the mesh on the test specimen model that borders the pre-existing crack front along the width of the test specimen model. The spacing of the mesh nodes is used to prefabricate the crack front. The mesh size on the test specimen model is consistent along the length direction.

[0009] Optionally, obtain the uniformity of the distribution of strain energy release rate at the pre-crack front location during type III interlaminar fracture under different load boundary conditions. The method is as follows: To each , , pass Regularization was performed to obtain the mesh nodes of the pre-existing crack front. Type I interlaminar fracture strain energy release rate regularization component , mesh nodes of pre-fabricated crack front Type II interlaminar fracture strain energy release rate regularization component , mesh nodes of pre-fabricated crack front Type III interlaminar fracture strain energy release rate regularization component ; ; in, This represents the total number of mesh nodes at the pre-fabricated crack front.

[0010] Optionally, the mesh size on the test specimen model gradually increases along the width direction of the test specimen model from the pre-crack leading edge to the two long sides of the test specimen model.

[0011] On the other hand, the device for testing the type III interlaminar fracture toughness of composite materials provided in this application adopts the following technical solution: An apparatus for testing the type III interlaminar fracture toughness of composite materials, comprising: A base is used to fix it on the worktable of the testing machine. A first sliding seat and a second sliding seat are slidably provided on the base. The first sliding seat and the second sliding seat slide in a horizontal direction and the sliding directions of the first sliding seat and the second sliding seat are perpendicular to each other. A first loading rod is provided on the first sliding seat and a second loading rod is provided on the second sliding seat. The first loading rod and the second loading rod are used to abut against the bottom surface of the test piece. A crossbeam has a third sliding seat and a fourth sliding seat slidably mounted on it. The sliding direction of the third and fourth sliding seats is parallel to the horizontal direction and parallel to the length direction of the crossbeam. The third sliding seat has a third loading rod, and the fourth sliding seat has a fourth loading rod. The third and fourth loading rods are used to abut against the top surface of the test piece. The center of the crossbeam has a vertical connecting hole, and a connecting rod passes through the connecting hole. The connecting rod and the connecting hole are rotatably engaged to adjust the length direction of the crossbeam so that the crossbeam is parallel to the diagonal of different test pieces. One end of the connecting rod is fixedly mounted on the crossbeam by a nut, and the other end of the connecting rod is located above the crossbeam for being clamped by the upper chuck of the testing machine. A sliding locking assembly is used to fix the positions of the first and second sliding seats on the base, and to fix the positions of the third and fourth sliding seats on the crossbeam; The first limiting structure is slidably mounted on the base. The first limiting structure is used to abut against the side corresponding to the long side of the test piece. The first limiting structure slides along the width direction of the test piece. The second limiting structure is slidably mounted on the base. The second limiting structure is used to abut against the side corresponding to the short side of the test piece. The second limiting structure slides along the length direction of the test piece. A limit locking structure is used to lock the positions of the first limit structure and the second limit structure on the base; The device is configured to adjust the positions of the first loading rod, the second loading rod, the third loading rod, and the fourth loading rod according to the final positions of the four loading points determined by the above method. The first loading rod, the second loading rod, the third loading rod, and the fourth loading rod are respectively used to abut against the first loading point, the second loading point, the third loading point, and the fourth loading point.

[0012] Optionally, the base is provided with T-shaped grooves for the first and second sliding seats to slide, and the crossbeam is provided with T-shaped grooves for the third and fourth sliding seats to slide. The first, second, third, and fourth sliding seats each include a T-shaped slider that slides along the corresponding T-shaped groove and a support block that slides along the opening side of the corresponding T-shaped groove. The first, second, third, and fourth loading rods are fixed on the corresponding support blocks. The support blocks and the T-shaped sliders are connected by first bolts. The first bolts pass through the opening side of the T-shaped groove. The first bolts on the first, second, third, and fourth sliding seats constitute the sliding locking assembly.

[0013] Optionally, both the first and second limiting structures include a base plate, multiple vertical cylindrical rods, and a second bolt. The vertical cylindrical rods are fixed to the base plate. The multiple vertical cylindrical rods of the first limiting structure are used to abut against the side corresponding to the long side of the test piece, and the multiple vertical cylindrical rods of the second limiting structure are used to abut against the side corresponding to the short side of the test piece. The base plate is provided with multiple strip grooves, and the second bolt corresponds one-to-one with the strip grooves. The second bolt passes through the strip grooves and is threaded to the base. The length direction of the strip grooves of the first limiting structure is set along the width direction of the test piece, and the length direction of the strip grooves of the second limiting structure is set along the length direction of the test piece.

[0014] In summary, this application includes the following beneficial technical effects: The method for testing the type III interlaminar fracture toughness of composite materials provided in this application establishes a simulated finite element model of the edge crack torsion method and performs mesh generation. Under multiple working conditions with the same load and only varying the spacing between loading points, the proportion and distribution uniformity of the strain energy release rate of type III interlaminar fracture are calculated. The optimal loading point position is determined by using the minimum value of the weighted average index. This method effectively reduces the interference components of type I and type II interlaminar fractures, improves the accuracy, stability, and repeatability of the test results of the type III interlaminar fracture toughness of composite materials, and solves the problems of traditional edge crack torsion method where the loading position is set based on experience and the data is highly dispersed. Attached Figure Description

[0015] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 A schematic diagram of the overall structure of the device for testing the type III interlaminar fracture toughness of composite materials; Figure 2 This is a structural schematic diagram of the crossbeam; Figure 3 This is a schematic diagram of the structure of the first sliding seat; Figure 4 This is a schematic diagram of the first limiting structure.

[0017] Explanation of reference numerals in the attached drawings: 1. Base; 2. Crossbeam; 3. First sliding seat; 4. Second sliding seat; 5. Third sliding seat; 6. Fourth sliding seat; 7. First loading rod; 8. Second loading rod; 9. Third loading rod; 10. Fourth loading rod; 11. First limiting structure; 12. Second limiting structure; 13. T-shaped groove; 14. T-shaped slider; 15. Support block; 16. First bolt; 17. Base plate; 18. Vertical cylindrical rod; 19. Strip groove; 20. Second bolt; 21. Connecting rod; 22. Connecting hole; 23. Test piece. Detailed Implementation

[0018] The embodiments of this application will now be described in detail with reference to the accompanying drawings.

[0019] The following specific examples illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. This application can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this application. It should be noted that, in the absence of conflict, the following embodiments and features in the embodiments can be combined with each other. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0020] It should be noted that various aspects of embodiments within the scope of the appended claims are described below. It will be apparent that the aspects described herein can be embodied in a wide variety of forms, and any particular structure and / or function described herein is merely illustrative. Based on this application, those skilled in the art will understand that one aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number of aspects set forth herein can be used to implement the device and / or practice the method. Additionally, this device and / or method can be implemented using structures and / or functionalities other than one or more of the aspects set forth herein.

[0021] It should also be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of this application. The illustrations only show the components related to this application and are not drawn according to the number, shape and size of the components in actual implementation. In actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0022] Furthermore, specific details are provided in the following description to facilitate a thorough understanding of the examples. However, those skilled in the art will understand that the described aspects can be practiced without these specific details.

[0023] This application provides a method for testing the type III interlaminar fracture toughness of composite materials. The test specimen used in this method is a rectangular plate.

[0024] A method for testing the type III interlaminar fracture toughness of composite materials includes: Step 1: Determine the initial positions of the four loading points of the rectangular plate-shaped test specimen. The four loading points are designated as the first loading point, the second loading point, the third loading point, and the fourth loading point. The first and second loading points are located on the first side of the test specimen, and the third and fourth loading points are located on the second side of the test specimen. The first and second sides are two opposite sides of the test specimen. The first and second loading points are located on the first diagonal of the first side, and the third and fourth loading points are located on the second diagonal of the second side. The first and second diagonals intersect each other. The distance between the first and second loading points is equal to the distance between the third and fourth loading points. Furthermore, the centers of the first and second loading points coincide with the center of the first side, and the centers of the third and fourth loading points coincide with the center of the second side.

[0025] Step 2: Establish a simulation finite element model for the Type III interlaminar fracture toughness test using the edge crack torsion method. The simulation finite element model includes a test specimen model and loading structure models corresponding to each loading point. Mark the pre-crack leading edge on the test specimen model. The pre-crack leading edge is located at the center of the width direction of the test specimen model and is parallel to the length direction of the test specimen model. Mesh the simulation finite element model. The size of the mesh on the test specimen model gradually increases from the pre-crack leading edge to the two long sides of the test specimen model along the width direction. In this embodiment, the width dimension of the mesh adjacent to the pre-crack leading edge is 0.2 mm, and the length dimension of the mesh is uniformly 1 mm.

[0026] Step 3: With the test specimen model and the loading structure model fixed, multiple load boundary conditions are given based on the initial positions of the four loading points for simulation calculation. Among the multiple load boundary conditions, the loads on each loading point are the same, the distances between the first and second loading points are different, and the distances between the third and fourth loading points are different. The multiple load boundary conditions are pre-selected based on experience. Specifically, the distances between the first and second loading points, and between the third and fourth loading points, are determined by the pre-given distance ranges between the loading points and the long and short sides of the test specimen model.

[0027] Step 4: Obtain the proportion of the type III interlaminar fracture strain energy release rate at the pre-existing crack front location to the total interlaminar fracture strain energy release rate under different load boundary conditions. ; Step 5: Obtain the uniformity of strain energy release rate distribution at the pre-crack front location of type III interlaminar fracture under different load boundary conditions. ; Step 6, Calculate the weighted average index , ; Step 7, based on the weighted average index The distance between the first and second loading points, and the distance between the third and fourth loading points in the minimum load boundary condition, determine the final positions of the four loading points; Step 8: Confirm the three-dimensional relative positions of each loading structure on the test loading device based on the final positions of the four loading points; Step 9: Place the test specimen on the test loading device and begin the test.

[0028] The method for testing the type III interlaminar fracture toughness of composite materials provided in this application establishes a simulated finite element model of the edge crack torsion method and performs mesh generation. Under multiple working conditions with the same load and only varying the spacing between loading points, the proportion and distribution uniformity of the strain energy release rate of type III interlaminar fracture are calculated. The optimal loading point position is determined by using the minimum value of the weighted average index. This method effectively reduces the interference components of type I and type II interlaminar fractures, improves the accuracy, stability, and repeatability of the test results of the type III interlaminar fracture toughness of composite materials, and solves the problems of traditional edge crack torsion method where the loading position is set based on experience and the data is highly dispersed.

[0029] In step 4, the proportion of the type III interlaminar fracture strain energy release rate at the pre-existing crack front location to the total interlaminar fracture strain energy release rate is obtained under different load boundary conditions. The steps include: Calculate the mesh nodes at the pre-existing crack front under various load boundary conditions. Type I interlaminar fracture strain energy release rate component , mesh nodes of pre-fabricated crack front Type II interlaminar fracture strain energy release rate component , mesh nodes of pre-fabricated crack front Type III interlaminar fracture strain energy release rate component ; Calculate the mean value of the strain energy release rate component of the pre-existing crack front at the type I interlaminar fracture under various load boundary conditions. Mean value of strain energy release rate component of type II interlaminar fracture at the pre-crack front Mean value of strain energy release rate component of type III interlaminar fracture at the pre-existing crack front : ; ; ; in, The dimension of the mesh on the test specimen model that borders the pre-existing crack front along the width of the test specimen model. The length of the test specimen model, This represents the total number of mesh nodes at the pre-fabricated crack front. Calculate the total interlaminar fracture strain energy release rate : ; calculate : .

[0030] Calculate the mesh nodes at the pre-existing crack front under various load boundary conditions. Type I interlaminar fracture strain energy release rate component , mesh nodes of pre-fabricated crack front Type II interlaminar fracture strain energy release rate component , mesh nodes of pre-fabricated crack front Type III interlaminar fracture strain energy release rate component The method is as follows: Extract the mesh nodes of the pre-existing crack front under various load boundary conditions. along Axial load , mesh nodes of pre-fabricated crack front along Axial load , mesh nodes of pre-fabricated crack front along Axial load ,in, The axis is parallel to the length direction of the test specimen model. The axis is parallel to the width direction of the test specimen model. The axis is parallel to the thickness direction of the test specimen model; Obtain the mesh node closest to the pre-existing crack tip on the side of the crack surface along the width of the test specimen model. along Position in the axial direction Obtain the mesh node closest to the pre-existing crack front edge on the lower side of the crack surface along the width direction of the test specimen model. along Position in the axial direction Obtain the mesh node closest to the pre-fabricated crack front edge on the side of the crack surface along the width direction of the test specimen model. along Position in the axial direction Obtain the mesh node closest to the pre-existing crack front edge on the lower side of the crack surface along the width direction of the test specimen model. along Position in the axial direction Obtain the mesh node closest to the pre-fabricated crack front edge on the side of the crack surface along the width direction of the test specimen model. along Position in the axial direction Obtain the mesh node closest to the pre-existing crack front edge on the lower side of the crack surface along the width direction of the test specimen model. along Position in the axial direction ; , and The calculation formulas are as follows: ; ; ; in, The dimension of the mesh on the test specimen model that borders the pre-existing crack front along the width of the test specimen model. The spacing of the mesh nodes for the pre-fabricated crack front edge.

[0031] In step 5, the uniformity of the distribution of strain energy release rate at the pre-crack front location of type III interlaminar fracture under different load boundary conditions is obtained. The method is as follows: To each , , pass Regularization was performed to obtain the mesh nodes of the pre-existing crack front. Type I interlaminar fracture strain energy release rate regularization component , mesh nodes of pre-fabricated crack front Type II interlaminar fracture strain energy release rate regularization component , mesh nodes of pre-fabricated crack front Type III interlaminar fracture strain energy release rate regularization component ; ; in, This represents the total number of mesh nodes at the pre-fabricated crack front.

[0032] This application regularizes the strain energy release rate components of each mesh node at the pre-existing crack front, and obtains the uniformity of the strain energy release rate distribution at the Type III interlaminar fracture location under different load boundary conditions based on the regularized data. It can eliminate the influence of factors such as load size and specimen size on uniformity evaluation, so that the distribution uniformity of strain energy release rate of type III interlaminar fracture under different loading point spacing has a unified and comparable evaluation benchmark, ensuring that the weighted evaluation index calculation is more objective and the final loading point position is more accurate.

[0033] This application also discloses an apparatus for testing the type III interlaminar fracture toughness of composite materials.

[0034] like Figures 1 to 4 As shown, an apparatus for testing the type III interlaminar fracture toughness of composite materials includes: The base 1 is used to fix it on the worktable of the testing machine. The base 1 is slidably provided with a first sliding seat 3 and a second sliding seat 4. The first sliding seat 3 and the second sliding seat 4 slide in the horizontal direction and the sliding directions of the first sliding seat 3 and the second sliding seat 4 are perpendicular to each other. The first sliding seat 3 is provided with a first loading rod 7 and the second sliding seat 4 is provided with a second loading rod 8. The first loading rod 7 and the second loading rod 8 are used to abut against the bottom surface of the test piece 23. A crossbeam 2 has a third sliding seat 5 and a fourth sliding seat 6 slidably mounted on it. The sliding direction of the third sliding seat 5 and the fourth sliding seat 6 is parallel to the horizontal direction and parallel to the length direction of the crossbeam 2. The third sliding seat 5 is provided with a third loading rod 9, and the fourth sliding seat 6 is provided with a fourth loading rod 10. The third loading rod 9 and the fourth loading rod 10 are used to abut against the top surface of the test piece 23. The center of the crossbeam 2 has a vertical connecting hole 22. A connecting rod 21 passes through the connecting hole 22. The connecting rod 21 and the connecting hole 22 are rotatably engaged to adjust the length direction of the crossbeam 2 so that the crossbeam 2 is parallel to the diagonals of different test pieces 23. One end of the connecting rod 21 is fixedly mounted on the crossbeam 2 by a nut, and the other end of the connecting rod 21 is located above the crossbeam 2 for being clamped by the upper chuck of the testing machine. The sliding locking assembly is used to fix the positions of the first sliding seat 3 and the second sliding seat 4 on the base 1, and to fix the positions of the third sliding seat 5 and the fourth sliding seat 6 on the crossbeam 2. The first limiting structure 11 is slidably mounted on the base 1. The first limiting structure 11 is used to abut against the side corresponding to the long side of the test piece 23. The first limiting structure 11 slides along the width direction of the test piece 23. The second limiting structure 12 is slidably mounted on the base 1. The second limiting structure 12 is used to abut against the side corresponding to the short side of the test piece 23. The second limiting structure 12 slides along the length direction of the test piece 23. A limit locking structure is used to lock the positions of the first limit structure 11 and the second limit structure 12 on the base 1; The device is configured to adjust the positions of the first loading rod 7, the second loading rod 8, the third loading rod 9, and the fourth loading rod 10 to the final positions of the four loading points determined by the above method. The first loading rod 7, the second loading rod 8, the third loading rod 9, and the fourth loading rod 10 are respectively used to abut against the first loading point, the second loading point, the third loading point, and the fourth loading point.

[0035] During the experiment, the positions of each loading point were determined according to the above method and marked on the test piece 23. Based on the distance between the first loading point and the second loading point, the positions of the first sliding seat 3, the second sliding seat 4, the first limiting structure 11, and the second limiting structure 12 were adjusted so that the first loading rod 7 was aligned with the first loading point, the second loading rod 8 was aligned with the second loading point, the long side of the test piece 23 abutted against the first limiting structure 11, and the short side of the test piece 23 abutted against the second limiting structure 12, all of which were satisfied simultaneously. Then, the position of the base 1 on the worktable of the testing machine was adjusted so that the center of the line connecting the first loading rod 7 and the second loading rod 8 was aligned with the center of the upper clamp of the testing machine. The base 1 was fixed on the worktable of the testing machine, and the test piece 23 was placed on the base 1. The test piece 23 was supported by the first loading rod 7 and the second loading rod 8 and positioned by the first limiting structure 11 and the second limiting structure 12. Then, adjust the positions of the third sliding seat 5 and the fourth sliding seat 6 according to the distance between the third and fourth loading points, so that the center distance between the third loading rod 9 and the fourth loading rod 10 is equal to the distance between the third and fourth loading points, and the distance from the center of the third loading rod 9 and the fourth loading rod 10 to the center of the crossbeam 2 is equal; align the third loading rod 9 with the third loading point and the fourth loading rod 10 with the fourth loading point to determine the length direction of the crossbeam 2, and fix the connecting rod 21 to the crossbeam 2 with a nut. The upper chuck of the testing machine clamps the connecting rod 21; the installation of the device is completed, the upper chuck of the testing machine moves downward and applies a preset load to the test piece 23, and the test begins.

[0036] The device for testing the interlaminar fracture toughness of composite materials provided in this application, by setting a bidirectional sliding and lockable sliding seat and a loading rod on the base 1 and the crossbeam 2, and in conjunction with the adjustable first limiting structure 11 and the second limiting structure 12, can quickly and accurately position the loading point according to the above method, and achieve universal adaptation for test pieces 23 of different sizes and different loading point spacings.

[0037] Specifically, such as Figure 1 and 3As shown, the base 1 is provided with T-shaped grooves 13 for the sliding of the first sliding seat 3 and the second sliding seat 4, respectively. The crossbeam 2 is provided with T-shaped grooves 13 for the sliding of the third sliding seat 5 and the fourth sliding seat 6. The first sliding seat 3, the second sliding seat 4, the third sliding seat 5, and the fourth sliding seat 6 each include a T-shaped slider 14 that slides along the corresponding T-shaped groove 13 and a support block 15 that slides along the opening side of the corresponding T-shaped groove 13. The first loading rod 7, the second loading rod 8, the third loading rod 9, and the fourth loading rod 10 are fixed on the corresponding support block 15. The support block 15 and the T-shaped slider 14 are connected by a first bolt 16, which passes through the opening side of the T-shaped groove 13. The first bolts 16 on the first sliding seat 3, the second sliding seat 4, the third sliding seat 5, and the fourth sliding seat 6 constitute the sliding locking assembly. Moreover, the first loading rod 7, the second loading rod 8, the third loading rod 9, and the fourth loading rod 10 of different sizes can be replaced by replacing the support block 15. In this embodiment, the first loading rod 7, the second loading rod 8, the third loading rod 9, and the fourth loading rod 10 each include an integrally formed cylindrical connecting rod and a hemispherical head. The cylindrical connecting rod is connected to the support block 15, and the hemispherical head is used to contact the test piece 23. In this embodiment, the support block 15 is provided with marking lines, which are aligned with the axes of the corresponding first loading rod 7, second loading rod 8, third loading rod 9, and fourth loading rod 10 on each support block 15. This facilitates adjustment and measurement of the distance between the first loading rod 7 and the second loading rod 8, as well as the distance between the third loading rod 9 and the fourth loading rod 10.

[0038] like Figure 4 As shown, both the first limiting structure 11 and the second limiting structure 12 include a base plate 17, multiple vertical cylindrical rods 18, and a second bolt 20. The vertical cylindrical rods 18 are fixed to the base plate 17. The multiple vertical cylindrical rods 18 of the first limiting structure 11 are used to abut against the side corresponding to the long side of the test piece 23, and the multiple vertical cylindrical rods 18 of the second limiting structure 12 are used to abut against the side corresponding to the short side of the test piece 23. The base plate 17 is provided with multiple strip grooves 19. The second bolt 20 corresponds one-to-one with the strip grooves 19. The second bolt 20 passes through the strip grooves 19 and is threaded to the base 1. The length direction of the strip grooves 19 of the first limiting structure 11 is set along the width direction of the test piece 23, and the length direction of the strip grooves 19 of the second limiting structure 12 is set along the length direction of the test piece 23. In this application, both the first limiting structure 11 and the second limiting structure 12 have two vertical cylindrical rods 18 and two strip grooves 19. The test piece 23 is limited by parallel vertical cylindrical rods 18, while forming line contact with the test piece 23, thereby improving the positioning accuracy.

[0039] In other embodiments, the multiple vertical cylindrical rods 18 arranged side by side can be replaced with a single plate.

[0040] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for testing the type III interlaminar fracture toughness of composite materials, characterized in that, include: The initial positions of the four loading points of the rectangular plate-shaped test specimen are determined. The four loading points are the first loading point, the second loading point, the third loading point, and the fourth loading point. The first and second loading points are located on the first side of the test specimen, and the third and fourth loading points are located on the second side of the test specimen. The first and second sides are two opposite sides of the test specimen. The first and second loading points are located on the first diagonal of the first side, and the third and fourth loading points are located on the second diagonal of the second side. The first and second diagonals intersect each other. The distance between the first and second loading points is equal to the distance between the third and fourth loading points. The centers of the first and second loading points coincide with the center of the first side, and the centers of the third and fourth loading points coincide with the center of the second side. A simulation finite element model for the Type III interlaminar fracture toughness test using the edge crack torsion method was established. The simulation finite element model includes a test specimen model and a loading structure model corresponding to each loading point. The pre-crack leading edge is marked on the test specimen model. The pre-crack leading edge is located at the center of the width direction of the test specimen model and is parallel to the length direction of the test specimen model. The simulation finite element model is then meshed. With a fixed test specimen model and a fixed loading structure model, simulation calculations are performed based on multiple load boundary conditions given at the initial positions of four loading points. Among the multiple load boundary conditions, the loads on each loading point are the same, the spacing between the first and second loading points is different, and the spacing between the third and fourth loading points is different. Obtain the proportion of the type III interlaminar fracture strain energy release rate at the pre-existing crack lead location to the total interlaminar fracture strain energy release rate under different load boundary conditions. ; Obtain the uniformity of strain energy release rate at the pre-crack front location of type III interlaminar fracture under different load boundary conditions. ; Calculate the weighted average index , ; According to the weighted average index The distances between the first and second loading points, and the distances between the third and fourth loading points in the minimum load boundary conditions, determine the final positions of the four loading points; Confirm the relative positions of each loading structure on the test loading device based on the final positions of the four loading points; Place the test specimen on the test loading device and begin the test.

2. The method for testing the type III interlaminar fracture toughness of composite materials according to claim 1, characterized in that, Obtain the proportion of the type III interlaminar fracture strain energy release rate at the pre-existing crack lead location to the total interlaminar fracture strain energy release rate under different load boundary conditions. The steps include: Calculate the mesh nodes at the pre-existing crack front under various load boundary conditions. Type I interlaminar fracture strain energy release rate component , mesh nodes of pre-fabricated crack front Type II interlaminar fracture strain energy release rate component , mesh nodes of pre-fabricated crack front Type III interlaminar fracture strain energy release rate component ; Calculate the mean value of the strain energy release rate component of the pre-existing crack front at the type I interlaminar fracture under various load boundary conditions. Mean value of strain energy release rate component of type II interlaminar fracture at the pre-crack front Mean value of strain energy release rate component of type III interlaminar fracture at the pre-existing crack front : ； ； ； in, The dimension of the mesh on the test specimen model that borders the pre-existing crack front along the width of the test specimen model. The length of the test specimen model, This represents the total number of mesh nodes at the pre-fabricated crack front. Calculate the total interlaminar fracture strain energy release rate : ； calculate : 。 3. The method for testing the type III interlaminar fracture toughness of composite materials according to claim 2, characterized in that, Calculate the mesh nodes at the pre-existing crack front under various load boundary conditions. Type I interlaminar fracture strain energy release rate component , mesh nodes of pre-fabricated crack front Type II interlaminar fracture strain energy release rate component , mesh nodes of pre-fabricated crack front Type III interlaminar fracture strain energy release rate component The method is as follows: Extract the mesh nodes of the pre-existing crack front under various load boundary conditions. along Axial load , mesh nodes of pre-fabricated crack front along Axial load , mesh nodes of pre-fabricated crack front along Axial load ,in, The axis is parallel to the length direction of the test specimen model. The axis is parallel to the width direction of the test specimen model. The axis is parallel to the thickness direction of the test specimen model; Obtain the mesh node closest to the pre-existing crack tip on the side of the crack surface along the width of the test specimen model. along Position in the axial direction Obtain the mesh node closest to the pre-existing crack front edge on the lower side of the crack surface along the width direction of the test specimen model. along Position in the axial direction Obtain the mesh node closest to the pre-fabricated crack front edge on the side of the crack surface along the width direction of the test specimen model. along Position in the axial direction Obtain the mesh node closest to the pre-existing crack front edge on the lower side of the crack surface along the width direction of the test specimen model. along Position in the axial direction Obtain the mesh node closest to the pre-fabricated crack front edge on the side of the crack surface along the width direction of the test specimen model. along Position in the axial direction Obtain the mesh node closest to the pre-existing crack front edge on the lower side of the crack surface along the width direction of the test specimen model. along Position in the axial direction ; 、 and The calculation formulas are as follows: ； ； ； in, The dimension of the mesh on the test specimen model that borders the pre-existing crack front along the width of the test specimen model. The spacing of the mesh nodes is used to prefabricate the crack front. The mesh size on the test specimen model is consistent along the length direction.

4. The method for testing the type III interlaminar fracture toughness of composite materials according to claim 2, characterized in that, Obtain the uniformity of strain energy release rate at the pre-crack front location of type III interlaminar fracture under different load boundary conditions. The method is as follows: To each , , pass Regularization was performed to obtain the mesh nodes of the pre-existing crack front. Type I interlaminar fracture strain energy release rate regularization component , mesh nodes of pre-fabricated crack front Type II interlaminar fracture strain energy release rate regularization component , mesh nodes of pre-fabricated crack front Type III interlaminar fracture strain energy release rate regularization component ; ； in, This represents the total number of mesh nodes at the pre-fabricated crack front.

5. The method for testing the type III interlaminar fracture toughness of composite materials according to claim 1, characterized in that, The mesh size on the test specimen model gradually increases from the pre-crack leading edge towards the two long sides of the test specimen model along the width direction.

6. An apparatus for testing the type III interlaminar fracture toughness of composite materials, characterized in that, include: A base (1) is used to fix it on the worktable of the testing machine. A first sliding seat (3) and a second sliding seat (4) are slidably provided on the base (1). The first sliding seat (3) and the second sliding seat (4) slide in the horizontal direction. The sliding directions of the first sliding seat (3) and the second sliding seat (4) are perpendicular to each other. A first loading rod (7) is provided on the first sliding seat (3), and a second loading rod (8) is provided on the second sliding seat (4). The first loading rod (7) and the second loading rod (8) are used to abut against the bottom surface of the test piece (23). A crossbeam (2) is provided with a third sliding seat (5) and a fourth sliding seat (6) slidably mounted on it. The sliding direction of the third sliding seat (5) and the fourth sliding seat (6) is parallel to the horizontal direction and parallel to the length direction of the crossbeam (2). A third loading rod (9) is provided on the third sliding seat (5), and a fourth loading rod (10) is provided on the fourth sliding seat (6). The third loading rod (9) and the fourth loading rod (10) are used to abut against the top surface of the test piece (23). (2) has a vertical connecting hole (22) in the center. A connecting rod (21) is inserted through the connecting hole (22). The connecting rod (21) and the connecting hole (22) are rotatably engaged to adjust the length direction of the crossbeam (2) so that the crossbeam (2) is parallel to the diagonal of different test pieces (23). One end of the connecting rod (21) is fixedly installed on the crossbeam (2) by a nut. The other end of the connecting rod (21) is located above the crossbeam (2) and is used to be clamped by the upper chuck of the testing machine. A sliding locking assembly is used to fix the positions of the first sliding seat (3) and the second sliding seat (4) on the base (1), and to fix the positions of the third sliding seat (5) and the fourth sliding seat (6) on the crossbeam (2); The first limiting structure (11) is slidably mounted on the base (1). The first limiting structure (11) is used to abut against the side corresponding to the long side of the test piece (23). The first limiting structure (11) slides along the width direction of the test piece (23). The second limiting structure (12) is slidably mounted on the base (1). The second limiting structure (12) is used to abut against the side corresponding to the short side of the test piece (23). The second limiting structure (12) slides along the length direction of the test piece (23). A limiting locking structure is used to lock the positions of the first limiting structure (11) and the second limiting structure (12) on the base (1); The device is configured to adjust the positions of the first loading rod (7), the second loading rod (8), the third loading rod (9), and the fourth loading rod (10) according to the final positions of the four loading points determined by the method of any one of claims 1-5, wherein the first loading rod (7), the second loading rod (8), the third loading rod (9), and the fourth loading rod (10) are respectively used to abut against the first loading point, the second loading point, the third loading point, and the fourth loading point.

7. The apparatus for testing the type III interlaminar fracture toughness of composite materials according to claim 6, characterized in that, The base (1) is provided with T-shaped grooves (13) for sliding of the first sliding seat (3) and the second sliding seat (4), and the crossbeam (2) is provided with T-shaped grooves (13) for sliding of the third sliding seat (5) and the fourth sliding seat (6). The first sliding seat (3), the second sliding seat (4), the third sliding seat (5) and the fourth sliding seat (6) each include a T-shaped slider (14) that slides along the corresponding T-shaped groove (13) and a support block that slides along the opening side of the corresponding T-shaped groove (13). 15), the first loading rod (7), the second loading rod (8), the third loading rod (9) and the fourth loading rod (10) are fixed on the corresponding support block (15), the support block (15) and the T-shaped slider (14) are connected by the first bolt (16), the first bolt (16) passes through the opening side of the T-shaped slide groove (13), and the first bolts (16) on the first sliding seat (3), the second sliding seat (4), the third sliding seat (5) and the fourth sliding seat (6) constitute the sliding locking assembly.

8. The apparatus for testing the type III interlaminar fracture toughness of composite materials according to claim 6, characterized in that, Both the first limiting structure (11) and the second limiting structure (12) include a base plate (17), multiple vertical cylindrical rods (18), and a second bolt (20). The vertical cylindrical rods (18) are fixed on the base plate (17). The multiple vertical cylindrical rods (18) of the first limiting structure (11) are used to abut against the side of the long side of the test piece (23), and the multiple vertical cylindrical rods (18) of the second limiting structure (12) are used to abut against the side of the short side of the test piece (23). On the corresponding side, the base plate (17) is provided with a plurality of strip grooves (19), the second bolt (20) and the strip grooves (19) correspond one to one, the second bolt (20) passes through the strip grooves (19) and is threadedly connected to the base (1), the length direction of the strip grooves (19) of the first limiting structure (11) is set along the width direction of the test piece (23), and the length direction of the strip grooves (19) of the second limiting structure (12) is set along the length direction of the test piece (23).

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