Compression test method for impacted arc edge of composite laminated board

Abstract

The invention belongs to the technical field of compression strength testing, and discloses a compression test method for a composite laminated board after arc edge impact, which comprises the following steps: determining the design configuration of a test piece; determining boundary constraint conditions of the test piece based on the design configuration of the test piece; carrying out simulation analysis of a compression test on the test piece according to the design configuration and the boundary constraint condition of the test piece; if the simulation result meets the test requirement, executing the step S4; if the simulation result does not meet the test requirement, the step S1 to the step S3 are executed again until the simulation result meets the test requirement; according to the design configuration of the test piece, manufacturing the test piece and introducing impact damage to the arc edge of the test piece; clamping and fixing the test piece according to the boundary constraint condition of the test piece, and carrying out a compression test; and obtaining test data obtained by the compression test, and processing and analyzing the test data. According to the method, instability can be effectively prevented, and the actual compression breaking strength can be accurately obtained.

Description

Technical Field

[0001] This invention relates to the field of compressive strength testing technology, and in particular to a method for compressive testing of composite laminates after impact with the arc edge. Background Technology

[0002] Carbon fiber composites, due to their excellent specific stiffness and specific strength, have become key materials in the field of aerospace structures. Composite laminates, as fundamental components of aircraft structures, have their performance parameters directly impacting the rationality of the load-bearing capacity in aircraft structural design. The compressive performance of composite laminates after impact damage is one of the core indicators for evaluating their mechanical properties. The compression test of composite laminate edges after impact is one of the important testing methods to obtain their compressive performance. This test can accurately determine the compressive load-bearing capacity retained by the laminate edges after impact damage and analyze the influence of impact damage on the residual strength of the laminate edges.

[0003] Currently, when performing compression tests on composite laminates after edge impact, for laminates with rounded edges, the buckling load during compression is often lower than the compression failure load due to the large size and thin thickness of the laminate itself, coupled with the impact damage from the rounded edges. This makes it very easy for the laminate to buckle and become unstable, making it difficult to obtain accurate compression failure strength in the test.

[0004] Therefore, there is an urgent need to propose a compression test method for composite laminates after impact with the arc edge to solve the above-mentioned technical problems. Summary of the Invention

[0005] The purpose of this invention is to provide a compression test method for composite laminates after impact with a circular arc edge. This method can effectively avoid buckling instability during compression and accurately obtain the actual compressive failure strength of the composite laminate after impact damage with a circular arc edge. This ensures the accuracy and reliability of the test data and provides effective experimental support for accurately analyzing the influence of impact with a circular arc edge on the remaining compressive bearing capacity of the composite laminate.

[0006] Based on the above concept, the technical solution adopted by this invention is as follows: This invention provides a compression test method for composite laminates after impact with a circular arc edge, the compression test method comprising the following steps: S1. Determine the design configuration of the test specimen; S2. Based on the design configuration of the test specimen, determine the boundary constraint conditions of the test specimen; S3. Based on the design configuration and boundary constraints of the test specimen, conduct a simulation analysis of the compression test on the test specimen; if the simulation results meet the test requirements, proceed to step S4; if the simulation results do not meet the test requirements, repeat steps S1 to S3 until the simulation results meet the test requirements. S4. According to the design configuration of the test piece, manufacture the test piece and introduce impact damage to the arc edge of the test piece; S5. According to the boundary constraints of the test piece, clamp and fix the test piece, and perform a compression test; S6. Obtain the test data obtained from the compression test, and process and analyze the test data.

[0007] In some embodiments, step S1 includes: Determine the dimensions of the test specimen; The test piece has symmetrical arc-shaped openings at both ends along its width direction, and the arc-shaped openings form the arc edges of the test piece, and the arc radius of the arc edges is determined. Obtain impact damage data for the arc edge.

[0008] In some embodiments, step S2 specifically includes: A fixed support constraint is provided at the bottom end of the test piece; A simply supported top constraint is provided at the top of the test piece; Along the length of the test piece, both transverse and longitudinal simply supported constraints are provided in the regions on both sides of the arc edge.

[0009] In some embodiments, acquiring impact damage data of the arc edge specifically includes: To obtain the relationship between impact energy and crack length, the relationship between impact energy and pit depth, and the relationship between impact energy and damage depth.

[0010] In some embodiments, the width of the test specimen is greater than or equal to twice the sum of the damage depth and the radius of the arc.

[0011] In some embodiments, the length of the test specimen is greater than or equal to three times the depth of damage.

[0012] In some embodiments, the arc length of the arc edge is at least 20 mm greater than the crack length.

[0013] In some embodiments, step S3 includes: Obtain the material mechanical property parameters of the test specimen; Obtain the allowable compressive strain value of the material of the test specimen; Substituting the buckling load into the applied load of the test specimen, the maximum strain value of the arc edge of the test specimen is obtained; Compare the maximum strain value of the arc edge with the allowable compressive strain value of the test piece. If 0.9 times the maximum strain value of the arc edge is greater than the allowable compressive strain value of the test piece, the simulation result meets the test requirements; if 0.9 times the maximum strain value of the arc edge is less than or equal to the allowable compressive strain value of the test piece, the simulation result does not meet the test requirements.

[0014] In some embodiments, step S5 includes: Strain gauges are attached to the surface of the test specimen; The test piece is clamped and fixed in place; Connect the strain gauges of the test piece to the dynamic strain gauge and check whether the data acquisition system and the display of each strain channel of the dynamic strain gauge are normal. Apply a preload to the test piece for centering and adjustment; The test specimen was subjected to formal loading until it failed.

[0015] In some embodiments, step S6 specifically includes: calculating the average value, standard deviation, and coefficient of variation of each measurement performance index based on the test data.

[0016] The beneficial effects of this invention are: The present invention provides a method for compression testing of composite laminates after impact with a circular arc edge. This method first determines the design configuration and boundary constraints of the test specimen, then iteratively optimizes these conditions through simulation analysis to meet the compression test requirements. It scientifically adapts the structure and constraint methods of the test specimen from the outset. Subsequently, based on the optimized parameters, the manufacturing of the test specimen, the introduction of impact damage, the adaptation design of the test fixture, the clamping of the test specimen, and the implementation of the compression test are completed. This method effectively avoids buckling instability during compression and accurately obtains the actual compressive failure strength of the composite laminate after impact damage with a circular arc edge, ensuring the accuracy and reliability of the test data. It provides effective experimental support for accurately analyzing the influence of circular arc edge impact on the remaining compressive bearing capacity of composite laminates. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the content of the embodiments of the present invention and these drawings without creative effort.

[0018] Figure 1 This is a flowchart of the compression test method provided in the embodiments of the present invention; Figure 2 This is a schematic diagram of the structure of the test specimen provided in the embodiment of the present invention; Figure 3 This is a schematic diagram of the constraint arrangement of the test specimen provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of the structure of the test fixture provided in the embodiment of the present invention; Figure 5 This is a cross-sectional structural diagram of the test fixture and test piece provided in the embodiments of the present invention.

[0019] In the picture: 100, Test specimen; 110, Arc edge; 200, Fixed support constraint; 300, Top simply supported constraint; 400, Lateral simply supported constraint; 500, Longitudinal simply supported constraint; 600, Bottom loading platform; 700, End loading clamp; 800, Side positioning support. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0021] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0022] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0023] In the description of this invention, it should be noted that the terms "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0024] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set" and "connection" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0025] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0026] Embodiments of the present invention are described in detail below. Examples of these 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. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0027] like Figures 1-3 As shown, this embodiment provides a compression test method for a composite laminate after impact with its arc-shaped edge, including the following steps: S1. Determine the design configuration of test specimen 100; Specifically, in this embodiment, the test piece 100 is a composite material laminate, which is plate-shaped and has a rounded edge 110. The damage from the drop hammer impact is located at the lowest point of the arc-shaped depression of the rounded edge 110. S2. Based on the design configuration of test specimen 100, determine the boundary constraint conditions of test specimen 100; Specifically, based on the structural characteristics of the test specimen 100, the preset location of impact damage, and the mechanical loading requirements of the compression test, the boundary constraints such as the constraint area and degree of freedom restriction of the test specimen 100 are determined from a theoretical perspective, providing a theoretical boundary basis for subsequent simulation analysis; S3. Based on the design configuration and boundary constraints of the test piece 100, conduct a simulation analysis of the compression test on the test piece 100; if the simulation results meet the test requirements, proceed to step S4; if the simulation results do not meet the test requirements, repeat steps S1 to S3 until the simulation results meet the test requirements. In other words, if the simulation results do not meet the experimental requirements, the design configuration and boundary constraints of the test piece 100 will be readjusted based on the simulation results. S4. Based on the design configuration of the test piece 100, manufacture the test piece 100 and introduce impact damage to the arc edge 110 of the test piece 100; S5. According to the boundary constraint conditions of the test piece 100, clamp and fix the test piece 100 and carry out the compression test; Specifically, based on the boundary constraints of the test piece 100, a suitable test fixture is designed to clamp and fix the test piece 100. S6. Obtain the test data from the compression test, and process and analyze the test data.

[0028] The compression test method for composite laminates after impact with a circular arc edge provided in this embodiment first determines the design configuration and boundary constraints of the test specimen 100, and then iteratively optimizes the design configuration and boundary constraints of the test specimen 100 through simulation analysis until they meet the compression test requirements. This method scientifically adapts the structure and constraint method of the test specimen 100 from the source. Subsequently, based on the optimized parameters, the manufacturing of the test specimen 100, the introduction of impact damage, the adaptation design of the test fixture, the clamping of the test specimen 100, and the implementation of the compression test are completed. This method effectively avoids buckling instability during compression and accurately obtains the actual compressive failure strength of the composite laminate after impact damage with a circular arc edge, ensuring the accuracy and reliability of the test data. It provides effective experimental support for accurately analyzing the influence of circular arc edge impact on the remaining compressive bearing capacity of the composite laminate.

[0029] It is understood that the compression test method for the composite laminate after impact on the arc edge in this embodiment is applicable not only to the evaluation of the remaining compressive strength after impact damage to the arc edge, but also to the testing of the compressive strength of the arc edge in the non-impact state.

[0030] like Figure 2 As shown, in some embodiments, step S1 includes: Determine the dimensions of the test specimen 100; specifically, this includes determining the length L, width W, and thickness of the test specimen 100. The test piece 100 has symmetrical arc-shaped openings at both ends along its width direction, forming arc-shaped edges 110 of the test piece 100. The arc radius of the arc edge 110 is determined; the arc radius of the arc edge 110 is R, and the opening distance between the two arc edges 110 is e. Obtain the impact damage data of the arc edge 110. The depth of the crater formed after impact damage to the arc edge 110 is ha, the crack length is LL, and the damage depth is d.

[0031] Thus, the test piece 100 adopts a symmetrical arrangement of the arc edge 110 in the width direction, which helps to eliminate the coupling effect caused by uneven load.

[0032] For example, the arc edge 110 can be a 180° arc, which can verify arc structures ranging from 180° to 360°. Simultaneously, for large arc structures, arcs smaller than 180° can be used for testing, satisfying the verification requirements for large openings. For arc structures smaller than 180°, the length of the opening distance e can be adjusted adaptively according to the arc shape of the arc structure itself for testing. In other words, the compression test method for the arc edge of the composite laminate provided in this embodiment has a wide range of applications and can be adapted to arc structures of both large and small sizes.

[0033] In some embodiments, acquiring impact damage data of the arc edge 110 specifically includes: The relationships between impact energy and crack length LL, impact energy and pit depth ha, and impact energy and damage depth d were obtained.

[0034] By obtaining the correspondence between impact energy and various damage parameters, the damage degree of the arc edge 110 under different impact energies can be accurately quantified, providing a quantitative damage reference for subsequent boundary constraint setting, simulation analysis and interpretation of experimental data.

[0035] Optionally, the width W of the test specimen 100 is greater than or equal to twice the sum of the damage depth d and the radius R of the arc, i.e., W≥2d+2R. With such a dimensional constraint, sufficient width margin can reduce the additional bending or torsion caused by insufficient width of the test specimen 100 during compression, reduce the risk of premature buckling instability, and ensure that the test can proceed smoothly to the failure stage.

[0036] Optionally, the length L of the test piece 100 is greater than or equal to three times the damage depth d, i.e., L≥3d. This ensures that the damaged area has sufficient deformation space in the length direction.

[0037] Optionally, the arc length of the arc edge 110 is at least 20 mm greater than the crack length LL. The arc length refers to the circumference of the arc edge 110. This setting ensures that the impact-induced crack is entirely within the arc shape of the arc edge 110.

[0038] like Figure 3 As shown, in some embodiments, step S2 specifically includes: A fixed support 200 is provided at the bottom end of the test specimen 100; A top-end simply supported constraint 300 is set at the top of the test specimen 100; Along the length of the test piece 100, transverse simply supported constraints 400 and longitudinal simply supported constraints 500 are set in the areas on both sides of the arc edge 110.

[0039] This setup employs out-of-plane support to prevent instability in the test specimen 100. Specifically, a fixed restraint 200 clamps the bottom of the specimen 100; a top simply supported restraint 300 is used at the top of the specimen 100 to facilitate loading from the top; and transverse simply supported restraints 400 and longitudinal simply supported restraints 500 are arranged in the upper and lower regions of the specimen 100 to prevent instability during compressive loading. Notably, no other constraints are present in the middle region of the specimen 100 to avoid coupling effects between damage propagation and the constraint structure of the specimen 100 during compressive loading.

[0040] In some embodiments, the test specimen 100 is clamped by knife edges on both sides in the width direction. The knife edge clamping provides simple support constraint for the test specimen 100 to further prevent instability. The distance between the center line of the knife edge and the corresponding side is about 5 mm.

[0041] In some embodiments, step S3 includes: Obtain the material mechanical properties parameters of test specimen 100; The allowable compressive strain ε of the material in specimen 100 was obtained. 许用 ; Substituting the buckling load into the loading load of specimen 100, the maximum strain value ε of the arc edge 110 of specimen 100 is obtained. max ; Compare the maximum strain value ε of the 110 arc edge. max The allowable compressive strain ε of the material of test specimen 100 许用 To ensure the maximum strain value ε of the circular arc edge 110 under buckling load. max Significantly greater than the allowable compressive strain ε of the material 许用 The recommended value is significantly higher than 10%; that is: If the maximum strain value ε at the arc edge 110 max The allowable compressive strain ε of the material is 0.9 times greater than that of the test specimen 100. 许用 (ε)max ×0.9>ε 许用 If the simulation results meet the experimental requirements, then the simulation results will be satisfactory. If the maximum strain value ε at the arc edge 110 max The allowable compressive strain ε of the material is 0.9 times less than or equal to 100 mm. 许用 (ε) max ×0.9≤ε 许用 If the simulation results do not meet the experimental requirements, then the simulation results will not meet the experimental requirements.

[0042] By setting it up in this way, the relationship between the maximum strain value of the arc edge 110 under buckling load and the allowable compressive strain value of the material is quantitatively verified. This ensures that the test piece 100 reaches the allowable strain of the material and undergoes compressive failure before buckling. This completely avoids the problem of buckling instability occurring before compressive failure from the simulation level, and ensures that subsequent physical tests can accurately obtain the real compressive failure strength.

[0043] The determination of buckling load specifically includes: Buckling eigenvalue analysis was performed on the test specimen 100 to solve and obtain at least the first three buckling load values. The verified first buckling load value was then substituted into the loading load of the test specimen 100 as the buckling load.

[0044] In some embodiments, step S5 includes: Strain gauges are attached to the surface of test specimen 100; The test piece 100 is clamped and fixed. For example, the test piece 100 is placed in a suitable anti-instability test fixture. The test fixture should include the fixed support constraint 200, the top simple support constraint 300, the transverse simple support constraint 400, and the longitudinal simple support constraint 500 mentioned above. When clamping the test piece 100 to the test fixture, bolt connection is often used. Tightening torque is applied to the bolts at the connection part of the test fixture. Generally, a torque of 7 N·m is used. It is recommended that when the size of the test piece 100 or the load it is subjected to is large, the tightening torque can be appropriately increased to ensure the stable clamping of the test piece 100. Connect the strain gauge of test piece 100 to the dynamic strain gauge and check whether the data acquisition system and the display of each strain channel of the dynamic strain gauge are normal. Preload was applied to test specimen 100 for centering and adjustment; that is, before the formal test, test specimen 100 was preloaded, and the bending percentage was calculated using the strain value at 10% of the estimated failure load, and it was determined that the bending percentage of the strain gauge at the maximum force should be ≤10%. Apply formal loading to test specimen 100 until it fails, and record the failure load, failure location, and failure mode. The test loading should employ a beam displacement control method, with a recommended loading rate of 1 mm / min.

[0045] like Figure 4 and Figure 5 As shown, in some embodiments, the test fixture includes a bottom loading platform 600, an end loading chuck 700, and two side positioning supports 800. A bottom clamping plate is provided on the bottom loading platform 600, which can clamp the bottom of the test piece 100 with bolts. The end loading chuck 700 can clamp the top of the test piece 100 with bolts. A compression test is performed by applying a compressive load at the end loading chuck 700 using a compression testing machine. The two side positioning supports 800 are bolted to the bottom loading platform 600 and are located on opposite sides of the test piece 100 in the width direction. The spacing between the two side positioning supports 800 is adjustable to accommodate test pieces 100 of different widths. The aforementioned anti-instability knife-edge clamps on both sides of the test piece 100 in the width direction can be bolted to the corresponding side positioning supports 800.

[0046] In some embodiments, step S6 specifically includes: calculating the average value, standard deviation, and coefficient of variation of each measured performance index based on the experimental data. The measured performance indexes include data such as compressive failure load and failure strain.

[0047] By calculating the mean, standard deviation, and coefficient of variation, quantitative statistical analysis of experimental data can be achieved, accurately characterizing the central tendency and dispersion of experimental results, and providing a reliable statistical basis for the objective evaluation of the compressive performance of the circular arc edge of composite laminate after impact.

[0048] Note that the above description is merely a preferred embodiment of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and various obvious changes, readjustments, and substitutions can be made without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the concept of the present invention, the scope of which is determined by the scope of the appended claims.

Claims

1. A method for compression testing of the circular arc edge of a composite laminate after impact, characterized in that, The compression test method includes the following steps: S1. Determine the design configuration of the test specimen; S2. Based on the design configuration of the test specimen, determine the boundary constraint conditions of the test specimen; S3. Based on the design configuration and boundary constraints of the test specimen, conduct a simulation analysis of the compression test on the test specimen; if the simulation results meet the test requirements, proceed to step S4; if the simulation results do not meet the test requirements, repeat steps S1 to S3 until the simulation results meet the test requirements. S4. According to the design configuration of the test piece, manufacture the test piece and introduce impact damage to the arc edge of the test piece; S5. According to the boundary constraints of the test piece, clamp and fix the test piece, and perform a compression test; S6. Obtain the test data obtained from the compression test, and process and analyze the test data.

2. The method for compression testing of composite laminate after impact with the arc edge according to claim 1, characterized in that, Step S1 includes: Determine the dimensions of the test specimen; The test piece has symmetrical arc-shaped openings at both ends along its width direction, and the arc-shaped openings form the arc edges of the test piece, and the arc radius of the arc edges is determined. Obtain impact damage data for the arc edge.

3. The method for compression testing of composite laminate after impact with the arc edge according to claim 2, characterized in that, Step S2 specifically includes: A fixed support constraint is provided at the bottom end of the test piece; A simply supported top constraint is provided at the top of the test piece; Along the length of the test piece, both transverse and longitudinal simply supported constraints are provided in the regions on both sides of the arc edge.

4. The method for compression testing of composite laminate after impact with the arc edge according to claim 2, characterized in that, Obtaining the impact damage data of the arc edge specifically includes: To obtain the relationship between impact energy and crack length, the relationship between impact energy and pit depth, and the relationship between impact energy and damage depth.

5. The method for compression testing of the circular arc edge of the composite laminate after impact according to claim 4, characterized in that, The width of the test piece is greater than or equal to twice the sum of the damage depth and the radius of the arc.

6. The method for compression testing of composite laminate after impact with the arc edge according to claim 4, characterized in that, The length of the test specimen is greater than or equal to three times the depth of the damage.

7. The method for compression testing of the circular arc edge of a composite laminate after impact according to claim 4, characterized in that, The arc length of the arc edge is at least 20 mm longer than the crack length.

8. The method for compression testing of composite laminates after impact with the arc edge according to any one of claims 1 to 7, characterized in that, Step S3 includes: Obtain the material mechanical property parameters of the test specimen; Obtain the allowable compressive strain value of the material of the test specimen; Substituting the buckling load into the applied load of the test specimen, the maximum strain value of the arc edge of the test specimen is obtained; Compare the maximum strain value of the arc edge with the allowable compressive strain value of the test piece. If 0.9 times the maximum strain value of the arc edge is greater than the allowable compressive strain value of the test piece, the simulation result meets the test requirements; if 0.9 times the maximum strain value of the arc edge is less than or equal to the allowable compressive strain value of the test piece, the simulation result does not meet the test requirements.

9. The method for compression testing of composite laminates after impact with the arc edge according to any one of claims 1 to 7, characterized in that, Step S5 includes: Strain gauges are attached to the surface of the test specimen; The test piece is clamped and fixed in place; Connect the strain gauges of the test piece to the dynamic strain gauge and check whether the data acquisition system and the display of each strain channel of the dynamic strain gauge are normal. Apply a preload to the test piece for centering and adjustment; The test specimen was subjected to formal loading until it failed.

10. The method for compression testing of composite laminates after impact with the arc edge according to any one of claims 1 to 7, characterized in that, Step S6 specifically includes: calculating the average value, standard deviation, and coefficient of variation of each measurement performance index based on the test data.

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