Preparation method of composite biaxial mechanical sample

Abstract

The invention discloses a preparation method of a biaxial mechanical sample of a composite material, and belongs to the field of complex load testing of the composite material, and the preparation method comprises the following steps: S1, grouping prepreg square sheets; s2, setting a laying layer sequence, arranging the laying layer sequence layer by layer, and rotating the laying layer sequence to a preset angle; s3, pre-cutting is carried out respectively, so that a reinforced area prepreg group A, a reinforced area prepreg group B and a sample prepreg group C are obtained; s4, cutting a thinning area D corresponding to the to-be-cut test area from the prepreg group A in the reinforcing area, and cutting a thinning area E corresponding to the to-be-cut test area from the prepreg group B in the reinforcing area; s5, a plurality of positioning holes are coaxially formed; s6, carrying out laminated arrangement, and placing a positioning pin; s7, placing in a forming mold to obtain a cured base material; and S8, the cured base material is taken out and cut, and the composite biaxial mechanical sample is obtained. With the adoption of the method, the thinning area is prefabricated, so that the failure of adaptation between the machined cut-off fiber and the adhesive is avoided, and the mechanical property test of the sample is ensured to be accurate and real.

Description

Technical Field

[0001] This invention relates to the field of complex load testing technology for composite materials, and in particular to a method for preparing a biaxial mechanical specimen of composite materials. Background Technology

[0002] Fiber-reinforced composite materials are widely used as load-bearing components in special vehicles in aviation, aerospace, and marine fields. The study of their mechanical properties under complex stress states is particularly important. At present, the uniaxial mechanical property testing technology and standards for this material have been developed and matured. Although there are existing national standards for biaxial mechanical property testing, the corresponding sample preparation methods have poor universality.

[0003] Specifically, the traditional preparation method of fiber-reinforced composite biaxial specimens requires machining after the parent material has been cured and molded. This process causes irreversible damage to the fibers inside the specimen, resulting in a significant difference between the mechanical properties of the prepared specimen and the mechanical properties of the actual material structure. This makes it impossible to accurately reflect the mechanical properties of the material in practical applications. Furthermore, the specimen preparation method used in the current biaxial testing standard requires the use of adhesives to connect and fit the relevant structures. These adhesives need to be compatible with the specimen body and the reinforcing sheet, which is difficult to meet the preparation and compatibility requirements of various fiber-reinforced composite materials. This limits the applicability of the method and fails to provide effective support for the biaxial mechanical property testing of different types of fiber-reinforced composite materials. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing biaxial mechanical specimens of composite materials, thereby solving the above-mentioned technical problems.

[0005] To achieve the above objectives, the present invention provides a method for preparing a biaxial mechanical specimen of a composite material, comprising the following steps: S1. Determine the total number of prepreg layers required to prepare biaxial mechanical specimens of composite materials, and divide the prepreg sheets into prepreg sheet group A, prepreg sheet group B and prepreg sheet group C; S2. Set a uniform layup sequence for prepreg sheets A, B and C. Arrange the prepreg sheets in each group layer by layer according to the layup sequence, and rotate each layer of prepreg sheets to the preset angle corresponding to the layup sequence so that the three groups can complete the fiber orientation positioning by using the same layup rule. S3. The prepreg sheets A, B, and C that were rotated and arranged in S2 are pre-cut to obtain three sets of reinforced area prepreg A, reinforced area prepreg B, and sample prepreg C with the same side length and matching mold size. S4. The sample prepreg C group has multiple test areas to be cut and tested corresponding to the finished sample. On the prepreg square sheet of the reinforcing area prepreg A group, a thinning area D including multiple cutting area alignment holes is cut out corresponding to the multiple test areas. On the prepreg square sheet of the reinforcing area prepreg B group, a thinning area E including multiple cutting area alignment holes is cut out corresponding to the multiple test areas. S5. Multiple positioning holes are coaxially opened at the four corners of the prepreg sheets of reinforced area prepreg A group, reinforced area prepreg B group, and sample prepreg C group. S6. After the positioning holes are opened in S5, the prepreg A group of reinforced area, the prepreg B group of reinforced area, and the prepreg C group of sample are stacked from top to bottom in the order of A group-C group-B group, and positioning pins are inserted into the corresponding positioning holes to achieve stacking fixation, thus obtaining the square piece group. S7. Place the stacked square pieces arranged in S6 into a molding mold for curing and molding to obtain the cured base material. S8. Remove the cured base material, and cut the thinned area of ​​the cured base material based on the positions of the first and second cutting area alignment holes and multiple positioning holes on the cured base material to obtain a biaxial mechanical specimen of the composite material.

[0006] Preferably, in S1, the thickness of the single-layer prepreg square sheet is measured in advance. And thickness This is the average value after measuring multiple single-layer prepreg squares, and the thickness of the composite biaxial mechanical specimen is preset to be... The number of prepreg squares The formula for calculating is: .

[0007] Preferably, in S1, the thickness of the prepreg sheet group C is... The thickness of the prepreg sheet in group A is The thickness of the prepreg sheet in group B is ,and ; and the number of prepreg sheets in group C is The number of prepreg sheets in group A is The number of prepreg sheets in group B is .

[0008] Preferably, the number of prepreg sheets in group A and group B is the same.

[0009] Preferably, in S4, the alignment holes one in the cutting area of ​​the prepreg group A and the alignment holes two in the cutting area of ​​the prepreg group B are both distributed in the thinning area array and arranged coaxially.

[0010] Preferably, in S5, there are 4 positioning holes, and the diameter of each positioning hole is smaller than the diameter of the first alignment hole and the second alignment hole in the cutting area.

[0011] Preferably, in S6, the diameter of the positioning pin is clearance-fitted with the aperture of the positioning hole, and the length of the positioning pin is the same as the total thickness of the biaxial mechanical specimen of the composite material. After being fixed by the positioning pin, the thinning area of ​​the prepreg group C of the specimen is located between the thinning area D and the thinning area E.

[0012] Therefore, the present invention employs the above-mentioned method for preparing a biaxial mechanical specimen of a composite material, which has the following beneficial effects: 1. The reference thickness of a single-layer prepreg sheet is obtained by averaging multiple measurements. Based on the preset total thickness of the sample, the total number of prepreg sheets is quantitatively calculated using a formula. The prepreg sheets are then divided into three groups, A, B, and C, according to the functional areas of the sample. The number of sheets in groups A and B is the same, ensuring that the number of prepreg layers is precisely matched with the thickness requirements of each functional area of ​​the sample. The symmetrical quantitative design of groups A and B ensures that the upper and lower reinforcing areas of the sample have consistent structures. This avoids thickness deviation problems from the perspective of raw material quantitative analysis, laying a precise structural foundation for the overall molding of the sample and avoiding stress eccentricity and test result distortion during biaxial testing.

[0013] 2. By setting a uniform layup sequence for prepreg sheets A, B, and C and arranging and rotating them layer by layer according to this sequence, the fiber orientation of the reinforced area and the test area of ​​the sample can be kept consistent. This ensures that the reinforced area has sufficient load-bearing capacity to avoid premature failure during clamping and stressing, while allowing the test area to accurately respond to complex biaxial stress states. At the same time, it achieves stable stress transfer within the sample, eliminating stress concentration and uneven loading caused by layup differences. This ensures that the prepared biaxial sample can truly reflect the mechanical properties of the material, significantly improving the accuracy and reliability of biaxial mechanical property test results.

[0014] 3. The prepreg sheets of group C correspond to the thinning area of ​​the sample. Regions D and E, which precisely match the thinning area, are cut out from the prepreg sheets of groups A and B, respectively. Alignment holes 1 and 2, arranged in an array, are set in regions D and E, with their positions corresponding one-to-one. This allows for the spatial prefabrication of the thinning area during the prepreg processing stage, avoiding the fiber cutting problem caused by machining the thinning area after traditional curing. This ensures the continuity of the composite fiber. The arrayed alignment holes allow for precise spatial alignment between regions D and E of groups A and B and the thinning area of ​​group C, ensuring the structural matching degree between the reinforcing area and the testing area. This effectively solves the problem of the mechanical properties of the sample not matching the actual structure due to fiber structure damage.

[0015] 4. The coaxial positioning holes ensure the concentricity of the three sets of square pieces, and the clearance-fitting positioning pins achieve rigid fixation of the stacked structure, effectively preventing the relative displacement of each set of square pieces during the curing process. At the same time, the stacking method of ACB allows the sample reinforcement area and the test area to form a precise spatial structure, solving the problems of sample structure displacement and uneven force during biaxial testing caused by inaccurate positioning in traditional stacking, and improving the spatial position accuracy of sample molding.

[0016] 5. By adopting a composite curing method, the reinforced area and the test area of ​​the sample form an integrated structure, avoiding the adhesive compatibility problem caused by traditional adhesive bonding between the reinforcing sheet and the sample, and preventing the failure of the bonded area first during biaxial testing; the plastic film laid in the mold can prevent the base material from sticking to the mold, the injection of adhesive improves the interlayer bonding force of each group of squares, and the high temperature heat treatment further enhances the structural strength and integrity of the cured base material, solving the problem of poor interlayer bonding force and easy delamination during testing of adhesive-bonded samples.

[0017] 6. The positioning reference for the entire sample preparation process is unified with the dimensional reference for the finished product cutting. The precision of the positioning holes ensures the dimensional accuracy and geometric center position accuracy of the thinning zone cutting, keeping the thinning zone at the geometric center of the sample. This ensures that the stress can be uniformly applied in the thinning zone during biaxial mechanical testing, solving the problems of dimensional deviation and stress eccentricity caused by traditional direct cutting of the thinning zone, and improving the accuracy and reliability of the biaxial mechanical property test results of composite materials.

[0018] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0019] Figure 1 A structural diagram of the specimen in a method for preparing a biaxial mechanical specimen of a composite material provided by the present invention; Figure 2 This invention provides a method for preparing a biaxial mechanical composite material specimen, including a specimen cutting dimension diagram. Figure 3 The location diagram of the thinning region D and the thinning region E in the preparation method of a composite biaxial mechanical specimen provided by the present invention; Figure 4 A diagram showing the location of the positioning holes in a method for preparing a biaxial mechanical specimen of a composite material provided by the present invention; Figure 5 A schematic diagram of the upper mold structure when placing the square piece group into the molding die in a method for preparing a biaxial mechanical specimen of composite material provided by the present invention; Figure 6 This is a schematic diagram of the lower mold structure when the square piece group is placed in the molding die in a method for preparing a biaxial mechanical specimen of composite material provided by the present invention.

[0020] Figure Labels 1. Reinforced prepreg group A; 11. Thinned area D; 2. Reinforced prepreg group B; 21. Thinned area E; 3. Sample prepreg group C; 4. Positioning holes. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely illustrative of the embodiments of the present invention and are not intended to limit the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of this application. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout.

[0022] It should be noted that the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion, such as a process, method, system, product, or server that includes a series of steps or units, not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such process, method, product, or device.

[0023] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0024] The widespread application of fiber-reinforced composite materials in load-bearing components of special vehicles in aviation, aerospace, and marine fields has created a real need to study their mechanical properties under complex stress states. While the uniaxial mechanical property testing technology for this material is mature, the biaxial mechanical property testing has existing national standards, but the sample preparation methods have significant shortcomings. Traditional machining methods for preparing biaxial samples can disrupt fiber continuity, resulting in the mechanical properties of the samples not matching the actual structure. Furthermore, the preparation methods in the current standards are limited by the compatibility issues of adhesives.

[0025] Based on the core logic of meeting the accuracy requirements of biaxial mechanical property testing of composite materials, addressing the inherent defects of existing biaxial specimen preparation methods, and adapting to the testing application needs of various fiber-reinforced composite materials, this invention was designed. (See appendix) Figure 1-6 A method for preparing a biaxial mechanical specimen of a composite material includes the following steps: S1. Determine the total number of prepreg layers required to prepare biaxial mechanical specimens of composite materials, and divide the prepreg sheets into prepreg sheet group A, prepreg sheet group B and prepreg sheet group C; In S1, the thickness of the single-layer prepreg sheet is measured in advance. And thickness This is the average value after measuring multiple single-layer prepreg squares, and the thickness of the composite biaxial mechanical specimen is preset to be... The number of prepreg squares The formula for calculating is: .

[0026] The thickness of prepreg sheet group C is The thickness of the prepreg sheet in group A is The thickness of the prepreg sheet in group B is ,and ; and the number of prepreg sheets in group C is The number of prepreg sheets in group A is The number of prepreg sheets in group B is .

[0027] The number of prepreg sheets in group A and group B is the same.

[0028] Specifically, the thickness of a single-layer prepreg sheet The thickness of prepreg sheets in group C is 0.2 mm, and the thickness of prepreg sheets in groups A and B is 0.8 mm. Therefore, the calculated number of prepreg sheets in group A and group B is 8, and the number of prepreg sheets in group C is 4.

[0029] S2. Set a uniform layup sequence for prepreg sheets A, B and C. Arrange the prepreg sheets in each group layer by layer according to the layup sequence, and rotate each layer of prepreg sheets to the preset angle corresponding to the layup sequence so that the three groups can complete the fiber orientation positioning by using the same layup rule. In S2, the layup sequence is a sequence formed by repeating the basic layup units of 0°, +45°, −45°, and 0°. The prepreg sheets A, B, and C all use the same basic layup units, arrangement order, and number of repetitions to complete the layer-by-layer arrangement and angular rotation.

[0030] Specifically, the arrangement of the prepreg sheets in prepreg sheet group A, prepreg sheet group B, and prepreg sheet group C during the prepreg layering process is as follows: This layup method uses 0°, +45°, -45°, and 0° as a basic layup unit, repeated five times to form a laminated structure. Based on the complex composite stress loading characteristics of biaxial mechanical testing of composite materials, fibers with different orientations bear corresponding stresses. The 0° oriented fibers mainly bear the axial tensile and compressive stresses in the biaxial test, while the ±45° oriented fibers efficiently bear the shear stress and biaxial composite stress. This unified layup method is simultaneously applied to groups A and B, which serve as the upper and lower reinforcement zones, and group C, which serves as the test thinning zone. This ensures that the fiber arrangement system of the three groups of prepreg sheets is consistent, forming a stable stress transmission path. Groups A and B achieve balanced tensile, compressive, and shear mechanical properties thanks to this layup structure. The first group can withstand the clamping force and stress transfer force during testing. The second group, through its multi-oriented fiber arrangement, accurately responds to the complex stress state of biaxial testing. This fully leverages the anisotropy of fiber-reinforced composite materials, allowing the test area to accurately reflect the true mechanical properties of the composite material under complex biaxial stress. It also ensures that the reinforced area has sufficient structural strength and mechanical bearing capacity, preventing premature failure in non-test areas during testing. At the same time, the unified layup method of the three groups improves the overall structural mechanical consistency and stress uniformity of the sample, effectively avoiding problems such as stress concentration and off-center loading caused by layup differences. This ensures that the stress of biaxial mechanical testing can be accurately applied to the test area, guaranteeing the accuracy and reliability of the test data.

[0031] S3. The prepreg sheets A, B and C that were rotated and arranged in S2 are pre-cut to obtain three sets of reinforced area prepreg A1, reinforced area prepreg B2 and sample prepreg C3 with the same side length and matching mold size. Specifically, all three sets of prepreg sheets were cut into 300mm x 300mm squares.

[0032] S4. The prepreg C group 3 of the sample prepreg has multiple test areas to be cut and tested. The prepreg square of the reinforcing area prepreg A group 1 is cut with a thinning area D11 including multiple cutting area alignment holes 1 corresponding to the multiple test areas to be cut and tested. The prepreg square of the reinforcing area prepreg B group 2 is cut with a thinning area E21 including multiple cutting area alignment holes 2 corresponding to the multiple test areas to be cut and tested. In S4, the alignment holes one in the cutting area of ​​the reinforced prepreg group A and the alignment holes two in the cutting area of ​​the reinforced prepreg group B both correspond to the thinning area array distribution.

[0033] For details, see Figure 3 As shown, both the first and second alignment holes in the cutting area are square holes with rounded corners. The straight side length of each side is 8mm, the diameter of each corner is 6mm, and the distance between the center of the hole and the edge of the square piece is 77.5mm.

[0034] S5. Multiple positioning holes 4 are coaxially opened at the four corners of the prepreg square sheet of the reinforced area prepreg group A1, the prepreg square sheet of the reinforced area prepreg group B2, and the prepreg square sheet of the sample prepreg group C3. In S5, there are 4 positioning holes 4, and the diameter of each positioning hole 4 is smaller than the diameter of the first and second alignment holes in the cutting area, and the diameter of each positioning hole 4 is 5mm.

[0035] See Figure 4 As shown, the position of each positioning hole 4 is precisely determined according to the preset dimensions, that is, the distance between the axis of the positioning hole 4 and the edge of the square is 30mm.

[0036] S6. After opening the positioning hole 4 in S5, the reinforcing area prepreg group A1, the reinforcing area prepreg group B2, and the sample prepreg group C3 are stacked from top to bottom in the order of group A-group C-group B. At the same time, adhesive is brushed between each layer, and positioning pins are inserted into the corresponding positioning hole 4 to achieve stacking and fixation, thus obtaining the square piece group. In S6, the diameter of the positioning pin is clearance-fitted with the diameter of the positioning hole 4. The diameter of the positioning pin is 4.95 mm, and the length of the positioning pin is the same as the total thickness of the biaxial mechanical specimen of the composite material, that is, the height of the positioning pin is 4 mm. After being fixed by the positioning pin, the thinning area of ​​the prepreg group C3 of the specimen is located between the thinning area D11 and the thinning area E21.

[0037] S7. Place the stacked square pieces arranged in S6 into a molding mold for curing and molding to obtain the cured base material. The specific process of curing and molding is as follows: a polyester plastic film is laid in the mold cavity of the molding mold, and then the assembly formed by the stacked and fixed square pieces and the positioning pin is sent into the molding mold. After the mold is closed, the adhesive is injected into the mold. Then the mold is placed in a high temperature environment chamber for heat treatment at 60°C for 12 hours. After the heat treatment is completed, the mold is taken out and cooled to room temperature. Finally, the cured master material is demolded.

[0038] S8. Take out the cured parent material, and cut the thinned area of ​​the cured parent material based on the positions of the first cutting area alignment hole, the second cutting area alignment hole, and the multiple positioning holes 4 on the cured parent material to obtain a biaxial mechanical specimen of composite material.

[0039] In a specific embodiment of this invention, the cured parent material is cut based on the dimensional requirements for preparing biaxial mechanical specimens of composite materials. Dimensions are specified in the provided text. Figure 2 As shown, the cured parent material was cut and processed into corresponding specimen shapes according to these dimensions, and the edges were ground to obtain four biaxial carbon fiber reinforced composite biaxial specimens suitable for biaxial mechanical testing. See [link to documentation]. Figure 1 As shown.

[0040] In summary, this invention solves the problems of traditional machining thinning processes that sever continuous fibers and cause mechanical property distortion, and adhesive bonding reinforcement sheets that are prone to premature failure due to poor adhesive compatibility. By pre-performing the pore opening operation to form the thinned area before curing the composite prepreg, and using an integrated curing process to form biaxial specimens, this invention not only fully preserves the continuous fiber structure of the thinned area, but also achieves a stable bond between the reinforcement area and the test area without the need for adhesives. It can truly and accurately reflect the mechanical properties of fiber-reinforced composite materials under complex biaxial stress, effectively improving the accuracy and reliability of the biaxial mechanical property test results of composite materials.

[0041] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a biaxial mechanical specimen of a composite material, characterized in that: Includes the following steps: S1. Determine the total number of prepreg layers for preparing biaxial mechanical specimens of composite materials, and divide the prepreg sheets into prepreg sheet group A, prepreg sheet group B and prepreg sheet group C. S2. Set a uniform layup sequence, arrange the prepreg sheets in each group layer by layer according to the layup sequence, and rotate each layer of prepreg sheets to the preset angle corresponding to the layup sequence so that the three groups of prepreg sheets can complete the fiber orientation positioning by using the same layup rule. S3. Cut the three groups of prepreg sheets in S2 to obtain reinforced area prepreg A group, reinforced area prepreg B group and sample prepreg C group that match the mold size. S4. The sample prepreg group C has multiple test areas to be cut. The prepreg group A of the reinforced region is cut into a thinned area D, which includes multiple cutting area alignment holes one, corresponding to the multiple test areas to be cut. The prepreg square of the prepreg group B of the reinforced region is cut into a thinned area E, which includes multiple cutting area alignment holes two, corresponding to the multiple test areas to be cut. S5. Multiple positioning holes are coaxially opened at the four corners of the reinforced area prepreg group A, reinforced area prepreg group B, and sample prepreg group C. S6. Arrange the pieces in the order of A-C-B from top to bottom, and insert positioning pins into the corresponding positioning holes to fix the stacking, thus obtaining a square piece group. S7. Place the square pieces from S6 into the molding mold for curing and molding to obtain the cured base material. S8. Remove the cured base material, and cut the thinned area of ​​the cured base material based on the positions of the first and second cutting area alignment holes and multiple positioning holes on the cured base material to obtain a biaxial mechanical specimen of the composite material.

2. The method for preparing a biaxial mechanical specimen of a composite material according to claim 1, characterized in that: In S1, the thickness of the single-layer prepreg sheet is measured in advance. And thickness This is the average value after measuring multiple single-layer prepreg squares, and the thickness of the composite biaxial mechanical specimen is preset to be... The number of prepreg squares The formula for calculating is: 。 3. The method for preparing a biaxial mechanical specimen of a composite material according to claim 2, characterized in that: In S1, the thickness of the prepreg sheet C group is The thickness of the prepreg sheet in group A is The thickness of the prepreg sheet in group B is ,and ; and the number of prepreg sheets in group C is The number of prepreg sheets in group A is The number of prepreg sheets in group B is .

4. The method for preparing a biaxial mechanical specimen of a composite material according to claim 3, characterized in that: The number of prepreg sheets in group A and group B is the same.

5. The method for preparing a biaxial mechanical specimen of a composite material according to claim 4, characterized in that: In S4, the alignment holes one in the cutting area of ​​the reinforced prepreg group A and the alignment holes two in the cutting area of ​​the reinforced prepreg group B are both distributed in the thinning area array and arranged coaxially.

6. The method for preparing a biaxial mechanical specimen of a composite material according to claim 5, characterized in that: In S5, there are 4 positioning holes, and the diameter of each positioning hole is smaller than the diameter of the first and second alignment holes in the cutting area.

7. The method for preparing a biaxial mechanical specimen of a composite material according to claim 6, characterized in that: In S6, the diameter of the positioning pin is clearance-fitted with the diameter of the positioning hole, and the length of the positioning pin is the same as the total thickness of the biaxial mechanical specimen of the composite material. After being fixed by the positioning pin, the thinning area of ​​the prepreg group C of the specimen is located between the thinning area D and the thinning area E.

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