Method for analyzing strength of carbon fiber laminated plate and foam sandwich structure adhesive joint

Abstract

The invention provides a method for analyzing the strength of a carbon fiber laminated plate and foam sandwich structure adhesive joint. The method comprises the following steps: carrying out a shear strength test on a test piece according to a preset test condition, establishing a test finite element model corresponding to the test piece based on the test condition, operating the test finite element model to carry out simulation calculation and the like. According to the method, through test and simulation combined analysis, the bearing capacity difference and the failure mode of the rubber-riveted joint in the carbon fiber laminated plate and the foam sandwich structure which are connected in a rubber-riveted mode under shearing and drawing loads are revealed, a high-precision finite element model is established, possibility can be provided for accurately predicting the performance of the rubber-riveted joint and optimizing key design parameters, and the method has the advantages of being high in reliability and high in reliability. And the limitation of the existing theoretical model or simplified model is broken through.

Description

Technical Field

[0001] This invention relates to the field of structural strength simulation and analysis technology, and more specifically, to a method for strength analysis of adhesive riveting joints in carbon fiber laminate and foam sandwich structures. Background Technology

[0002] The content in this section only provides background information related to this invention and may not constitute prior art.

[0003] With the development of rail transit equipment towards higher speeds and lighter weights, carbon fiber laminates, made of carbon fiber composite materials, have been widely used in main load-bearing structures such as car bodies and bogies due to their excellent properties such as high specific strength, high specific stiffness, and fatigue resistance. To further improve the bending stiffness of these main load-bearing structures and control weight, composite structures composed of carbon fiber laminates and foam sandwich structures have become the mainstream design. In these composite structures, the connection between the carbon fiber laminate and the foam sandwich structure is a key weak point affecting the overall reliability of the structure.

[0004] Due to the properties of carbon fiber composites, the connection between carbon fiber laminates and foam sandwich structures can typically only be achieved through adhesive bonding, mechanical connection, or a combination of both. Among these, adhesive riveting combines the advantages of uniform stress distribution in adhesive bonding and high reliability in mechanical connections, making it an effective connection solution. However, in adhesive riveting, the strength performance of the joint is affected by multiple parameters, including adhesive layer thickness, rivet diameter, overlap area, and sandwich thickness, resulting in extremely complex mechanical behavior and failure modes.

[0005] Currently, there are many challenges in the strength analysis of such adhesive-fitted joints: First, there is a lack of systematic experimental research and accurate evaluation methods for the load-bearing capacity of adhesive-fitted joints under complex load conditions (such as shear, pull-out and their coupling); second, existing theoretical models or simplified finite element models are difficult to accurately simulate the progressive damage process of adhesive-fitted joints, especially in predicting the failure of anisotropic carbon fiber laminates, the compressive shear behavior of foam sandwich structures, and the interfacial fracture of adhesive layers, resulting in conservative designs or potential risks; third, due to the lack of fully validated high-precision simulation models, it is difficult to carry out effective parametric design and optimization, which restricts the further improvement of the performance of adhesive-fitted joints and their standardized and reliable application in major equipment. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide a method for strength analysis of adhesive riveting joints of carbon fiber laminates and foam sandwich structures, so as to overcome the technical problem that existing methods are difficult to accurately analyze the strength of adhesive riveting joints formed after adhesive riveting of carbon fiber laminates and foam sandwich structures.

[0007] The objective of this invention is achieved through the following technical solution: In a first aspect, the present invention provides a method for strength analysis of a structural adhesive joint between a carbon fiber laminate and a foam sandwich structure, comprising the following steps: Shear strength tests are conducted on the test specimens under predetermined test conditions to obtain the failure modes and test load-displacement data corresponding to the test specimens; the test specimens include carbon fiber laminates and foam sandwich structures, and the carbon fiber laminates and foam sandwich structures are connected by adhesive layers and rivets. Based on the aforementioned test conditions, an experimental finite element model corresponding to the test specimen was established. In the experimental finite element model, a custom subroutine was used to simulate the anisotropic progressive damage behavior of the carbon fiber laminate. The three-dimensional Hashin criterion was used as the failure criterion for the carbon fiber laminate, and the damage evolution process of the carbon fiber laminate was described by combining the linear degradation method controlled by energy dissipation. The foam core material in the foam sandwich structure was simulated using a compressible foam model. The adhesive layer was modeled using three-dimensional cohesive elements based on cohesion theory. Its initial damage criterion adopted a quadratic criterion based on nominal stress, and the damage evolution process was described by the Benzeggaggh-Kenane criterion. The experimental finite element model was run to perform simulation calculations to obtain simulated load-displacement data corresponding to the test specimen; the simulated load-displacement data was compared with the experimental load-displacement data to verify the accuracy of the simulation calculation results.

[0008] Optionally, the custom subroutine is VUMAT; and in the experimental finite element model, the adhesive layer is bonded to the adjacent carbon fiber laminate and foam sandwich structure through tie constraints.

[0009] Optionally, the method for strength analysis of the adhesive joint between the carbon fiber laminate and the foam sandwich structure further includes the following steps: A global finite element model corresponding to the actual engineering structure is established, and a local area containing the glued riveting joint in the global finite element model is extracted as the master finite element model; the glued riveting joint is simplified in the global finite element model. The method for establishing the experimental finite element model is used to refine the main finite element model to obtain the sub-finite element model; Simulation calculations were performed using the overall finite element model and the sub-finite element model to obtain displacement contour maps and stress contour maps in each direction corresponding to the overall finite element model, as well as displacement contour maps and stress contour maps in each direction corresponding to the sub-finite element model. The displacement contour maps and stress contour maps in each direction of the overall finite element model and the sub-finite element model are compared and analyzed to verify the accuracy of the sub-finite element model.

[0010] Optionally, in the sub-finite element model, the carbon fiber laminate, foam sandwich structure, rivets and adhesive layer included are all modeled using solid elements; the boundary constraints of the sub-finite element model are inherited from the displacement information extracted from the overall finite element model.

[0011] Optionally, the simplified modeling is as follows: the carbon fiber laminate is simulated using shell elements, the foam sandwich structure is simulated using solid elements, the rivets are simulated using beam elements and rigid elements, and the adhesive layer is not modeled separately.

[0012] Optionally, the test specimen includes a first specimen, a second specimen, and a third specimen; the thickness of the foam sandwich structure in the first specimen is less than the thickness of the foam sandwich structure in the second specimen; the thickness of the foam sandwich structure in the second specimen is equal to the thickness of the foam sandwich structure in the third specimen.

[0013] Optionally, the shear strength test of the test specimen is performed using an MTS tensile-torsion testing machine; In the shear strength test of the first specimen, the testing machine applies a planar shear load to the first specimen; In the shear strength test of the second specimen, the testing machine applies a planar shear load to the second specimen; In the shear strength test of the third specimen, the testing machine applied a vertical pull-out load to the third specimen.

[0014] Optionally, in the experimental finite element model, the carbon fiber laminate, foam sandwich structure, and rivets in the test specimen are all modeled using three-dimensional solid elements; the boundary conditions of the experimental finite element model are set with reference to the shear strength test.

[0015] In a second aspect, the present invention provides an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the strength analysis method for the adhesive riveting joint of the carbon fiber laminate and foam sandwich structure as described above.

[0016] Thirdly, the present invention provides a readable storage medium storing a computer program, which, when executed by a processor, implements the strength analysis method for the adhesive riveting joint of carbon fiber laminate and foam sandwich structure as described above.

[0017] The technical solutions of the embodiments of the present invention have at least the following advantages and beneficial effects: This invention employs shear strength tests on three types of test specimens to reveal the differences in load-bearing capacity and failure modes of adhesive-fitted joints in carbon fiber laminates and foam sandwich structures under shear and pull-out loads. It quantifies the influence of foam sandwich structures of different thicknesses on residual load-bearing capacity, thus solving the problem of structural performance evaluation deviations caused by differences in load conditions in traditional designs. This method can accurately predict the failure risk of adhesive-fitted joints under complex service conditions, significantly improving the reliability and safety of such lightweight composite structures.

[0018] This invention successfully constructs a high-precision experimental finite element model corresponding to the test specimen based on experimental conditions. This facilitates the clarification of the influence mechanism of key structural parameters such as adhesive layer thickness, rivet diameter, overlap area, and core thickness on the performance of adhesive-fitted riveted joints through parametric analysis, providing a scientific basis for the optimized design of adhesive-fitted riveted joints. This method can quickly identify the optimal combination of structural parameters, shorten the R&D cycle, reduce experimental costs, and significantly improve design efficiency and engineering applicability.

[0019] This invention verifies the accuracy of the finite element model in predicting mechanical response and failure behavior through a combined experimental and simulation verification, overcoming the limitations of existing theoretical or simplified models. Furthermore, by incorporating sub-model technology for localized detailed analysis of key areas including adhesive-fitted joints, it accurately captures stress concentration regions, providing a reliable tool for strength verification of complex structures and ensuring that design results meet safety requirements under demanding conditions such as rail transit. Attached Figure Description

[0020] Figure 1 A flowchart of a method for strength analysis of adhesive-fitted joints in carbon fiber laminate and foam sandwich structures provided in an embodiment of the present invention; Figure 2 A three-dimensional geometric model of the first specimen provided for an embodiment of the present invention; Figure 3 This is a dimensional drawing of the first specimen; where, Figure 3 (a) is the front view of the first specimen; Figure 3 (b) is a top view of the first specimen; Figure 4 A three-dimensional geometric model of the second specimen provided for an embodiment of the present invention; Figure 5 This is a dimensional drawing of the second specimen; where, Figure 5 (a) is the front view of the second specimen; Figure 5 (b) is a side view of the second specimen. Figure 5 (c) is a top view of the second specimen; Figure 6 A three-dimensional geometric model of the third specimen provided for an embodiment of the present invention; Figure 7This is the dimensional drawing of the third specimen; where, Figure 7 (a) is the front view of the third specimen; Figure 7 (b) is a side view of the third specimen. Figure 7 (c) is a top view of the third specimen; Figure 8 The experimental finite element model diagram corresponding to the first specimen; Figure 9 A schematic diagram of the boundary conditions for the experimental finite element model corresponding to the first specimen; Figure 10 The experimental finite element model diagram corresponding to the second specimen; Figure 11 A schematic diagram of the boundary conditions for the experimental finite element model corresponding to the second specimen; Figure 12 The experimental finite element model diagram corresponding to the third specimen; Figure 13 A schematic diagram of the boundary conditions for the experimental finite element model corresponding to the third specimen; Figure 14 This is a comparison chart of the load-displacement curves of the first specimen under experimental and simulation analysis conditions; Figure 15 This is a comparison chart of the load-displacement curves of the second specimen under experimental and simulation analysis conditions; Figure 16 This is a comparison chart of the load-displacement curves of the third specimen under experimental and simulation analysis conditions; Figure 17 A finite element model diagram of an actual engineering structure provided for an embodiment of the present invention; Figure 18 for Figure 17 The diagram shows the master finite element model in the overall finite element model of a certain actual engineering structure. Figure 19 The diagram shows the sub-finite element model corresponding to the main finite element model; Figure 20 This is the displacement contour plot corresponding to the main finite element model; Figure 21 This is the displacement contour plot corresponding to the sub-finite element model.

[0021] Icons: 100 - First specimen, 200 - Second specimen, 300 - Third specimen, 10 - Carbon fiber laminate, 20 - Foam sandwich structure, 30 - Rivet, 40 - Adhesive layer. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments. The same reference numerals in the accompanying drawings represent the same components. It should be noted that the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the described embodiments of this invention without creative effort are within the scope of protection of this invention.

[0023] Compared to the embodiments shown in the accompanying drawings, feasible embodiments within the scope of protection of this invention may have fewer components, other components not shown in the drawings, different components, components with different arrangements, or components with different connections, etc. Furthermore, two or more components in the drawings may be implemented in a single component, or a single component shown in the drawings may be implemented as multiple separate components.

[0024] Example 1 Embodiment 1 of the present invention provides a method for strength analysis of the joint between a carbon fiber laminate 10 and a foam sandwich structure 20. The foam sandwich structure 20 described in this invention can also be understood as a foam sandwich panel. Figure 1 The flowchart illustrating the strength analysis method provided in Embodiment 1 of the present invention is shown in the illustration.

[0025] like Figure 1 As shown, in an embodiment of the present invention, the intensity analysis method may include the following steps: Step S100. Prepare test specimens.

[0026] Specifically, the test specimen described in this embodiment of the invention includes a carbon fiber laminate 10 and a foam sandwich structure 20. The carbon fiber laminate 10 and the foam sandwich structure 20 are connected by adhesive layer 40 and rivets 30. The adhesive layer 40 and the rivets 30 together constitute an adhesive-riveted joint.

[0027] To simplify the structure of the test specimens as much as possible and cover the typical working conditions of such composite structures, this invention initially designed three typical test specimens containing adhesive riveting joints, namely, the first specimen 100, the second specimen 200, and the third specimen 300. The thickness of the foam sandwich structure 20 in the first specimen 100 is much smaller than the thickness of the foam sandwich structure 20 in the second and third specimens 200, while the thickness of the foam sandwich structure 20 in the second and third specimens 300 is equal.

[0028] The first specimen 100 is mainly used to simulate the composite structure formed after the thin foam sandwich structure 20 and the carbon fiber laminate 10 are glued and riveted together. For example... Figure 2As shown, the foam sandwich structure 20 in the first specimen 100 overlaps one side of the carbon fiber composite plate of the specimen along its own length. The two are mechanically fixed with rivets 30, and the connection strength is further enhanced by an adhesive layer 40 to ensure the high strength and lightweight characteristics of the composite structure, and the foam sandwich structure 20 provides additional support. This design not only enhances the overall load-bearing capacity of the composite structure, but also effectively reduces the self-weight of the specimen, making it suitable for use in lightweight, high-strength structures.

[0029] The dimensional parameters of the foam sandwich structure 20 and the carbon fiber laminate 10 in the first specimen 100 can be referred to Figure 3 As shown. Specifically, the length and width of the foam sandwich structure 20 of the first specimen 100 can be 120mm and 33mm respectively, and the thickness is 4mm; further, the thickness of the foam core material of the foam sandwich structure 20 is 2.8mm, and the thickness of the carbon fiber panels on both sides of the foam core material is 0.6mm; the length and width of the carbon fiber laminate 10 of the first specimen 100 can be 120mm and 33mm respectively, and the thickness is 2mm. In the subsequent shear strength test of the first specimen 100, the load applied to the first specimen 100 is a planar shear load.

[0030] The second specimen 200 is mainly used to simulate the composite structure formed after the thick foam sandwich structure 20 and the carbon fiber laminate 10 are glued and riveted together. For example... Figure 4 As shown, the foam sandwich structure 20 in the second specimen 200 is located at the bottom of the carbon fiber composite plate and is essentially cubic. Connection holes are provided at the four corners of the foam sandwich structure 20 to facilitate connection with the fixtures of the testing machine during shear strength testing. The carbon fiber laminate 10 of the second specimen 200 is supported on the foam sandwich structure 20, with one side of the carbon fiber laminate 10 flush with one side of the foam sandwich structure 20 along its length, and the other side protruding beyond the foam sandwich structure 20. The top center of the foam sandwich structure 20 of the second specimen 200 is riveted to the carbon fiber laminate 10. By using a thicker foam sandwich structure 20, the tensile strength and stiffness of the composite structure can be effectively improved, and the entire composite structure exhibits high stiffness and lightweight characteristics. The second specimen 200 was designed to test the performance of the adhesive-fitted joints in the thick foam sandwich structure 20 under planar shear loads. By using a high-strength carbon fiber laminate 10, the foam sandwich structure 20 can effectively withstand external planar shear loads, while the foam core material within the structure provides support and absorbs some energy. In subsequent shear strength tests, this second specimen 200 will be subjected to planar shear loads to analyze its failure modes under ultimate planar shear loads.

[0031] The dimensional parameters of the foam sandwich structure 20 and the carbon fiber laminate 10 in the second specimen 200 can be referred to Figure 5 As shown. Specifically, the length and width of the foam sandwich structure 20 of the second specimen 200 can be 80mm and 80mm respectively, and the thickness is 44mm; further, the thickness of the foam core material of the foam sandwich structure 20 is 40mm, and the thickness of the carbon fiber panels on both sides of the foam core material is 2mm; the length and width of the carbon fiber laminate 10 of the second specimen 200 can be 140mm and 20mm respectively, and the thickness is 2mm.

[0032] The third specimen 300 has a similar structure to the second specimen 200, and is also used to simulate the composite structure formed by the glued connection of the thick foam sandwich structure 20 and the carbon fiber laminate 10. Unlike the second specimen 200, the load in the subsequent shear strength test of the third specimen 300 is applied in a vertical pull-out direction to facilitate the study of the pull-out resistance of the thick foam sandwich structure 20 under vertical pull-out loads. Therefore, to facilitate the application of vertical pull-out loads, as... Figure 6 As shown, the carbon fiber laminate 10 protrudes from the foam sandwich structure 20 on both sides along its length.

[0033] The dimensional parameters of the foam sandwich structure 20 and the carbon fiber laminate 10 in the third specimen 300 can be referred to Figure 7 As shown. Specifically, the length and width of the foam sandwich structure 20 of the third specimen 300 can be 80mm and 80mm respectively, and the thickness is 44mm; further, the thickness of the foam core material of the foam sandwich structure 20 is 2.8mm, and the thickness of the carbon fiber panels on both sides of the foam core material is 0.6mm; the length and width of the carbon fiber laminate 10 of the third specimen 300 can be 140mm and 20mm respectively, and the thickness is 2mm.

[0034] Step S200. Conduct a shear strength test.

[0035] After the test specimen is prepared based on step S100, a shear strength test is performed on the test specimen under predetermined test conditions to obtain the failure mode and test load-displacement data corresponding to the test specimen.

[0036] Among them, the shear strength test for the three types of test specimens mentioned above can be carried out using the MTS tensile-torsion testing machine, and the test conditions corresponding to each test specimen are different.

[0037] Specifically, in the shear strength test of the first specimen 100, the test conditions corresponding to the first specimen 100 are as follows: the foam sandwich structure 20 in the first specimen 100 is held by the upper clamp of the testing machine, and the carbon fiber laminate 10 in the first specimen 100 is held by the lower clamp of the testing machine; the lower clamp of the testing machine stretches the first specimen 100 at a constant rate, and the loading rate of the testing machine can be set to 2 mm / min to apply a planar shear load to the first specimen 100 until the first specimen 100 fails. The failure mode of the first specimen 100 is recorded during the test to analyze and derive the failure mode of the first specimen 100. After the test, the load-displacement curve corresponding to the first specimen 100 is exported from the testing machine to obtain the test load-displacement data corresponding to the first specimen 100.

[0038] Reference Figure 14 In the initial loading stage, the first specimen 100 exhibited elastic deformation, with the load increasing approximately linearly, indicating that the load was primarily borne by the adhesive layer 40. As the load increased, the adhesive layer 40 reached its ultimate bearing capacity and fractured instantaneously, causing a sharp drop in load. After the adhesive layer 40 fractured, the rivets 30 began to bear the load, and the foam sandwich structure 20 was subjected to the compressive force of the rivets 30. As loading continued, the foam sandwich structure 20 gradually underwent plastic deformation, the load gradually decreased, and ultimately, the first specimen 100 completely failed.

[0039] In the shear strength test of the second specimen 200, the test conditions corresponding to the second specimen 200 are as follows: the end of the carbon fiber laminate 10 protruding from the foam sandwich structure 20 in the second specimen 200 is held by the upper clamp of the testing machine, and the foam sandwich structure 20 in the second specimen 200 is bolted to the lower clamp of the testing machine; the lower clamp of the testing machine stretches the second specimen at a constant rate, and the loading rate of the testing machine can also be set to 2 mm / min to apply a planar shear load to the second specimen 200 until the second specimen 200 fails. The failure mode of the second specimen 200 is recorded during the test to analyze and derive the failure mode of the second specimen 200, and the load-displacement curve corresponding to the second specimen 200 is exported from the testing machine after the test to obtain the test load-displacement data corresponding to the second specimen 200.

[0040] Reference Figure 15 Before the failure of the adhesive layer 40, the second specimen 200 exhibited similar mechanical characteristics to the first specimen 100. The initial load increased linearly, indicating that the adhesive strength of the adhesive layer 40 was dominant. After reaching the ultimate load, the adhesive layer 40 fractured and entered the second stage, where the rivet 30 began to bear the load. Because the carbon fiber laminate 10 of the second specimen 200 was thinner than its own foam sandwich structure 20, the compressive force of the rivet 30 caused fiber breakage in the carbon fiber laminate 10, ultimately leading to the failure of the second specimen 200.

[0041] In the shear strength test of the third specimen 300, the test conditions corresponding to the third specimen 300 are as follows: the carbon fiber laminate 10 in the third specimen 300 protrudes from both ends of the foam sandwich structure 20 and is held by the upper clamp of the testing machine; the foam sandwich structure 20 in the third specimen 300 is bolted to the lower clamp of the testing machine; the lower clamp of the testing machine stretches the third specimen at a constant rate, and the loading rate of the testing machine can also be set to 2 mm / min to apply a vertical tensile load to the third specimen 300 until the third specimen 300 fails. The failure mode of the third specimen 300 is recorded during the test to analyze the failure mode of the third specimen 300, and the load-displacement curve corresponding to the third specimen 300 is exported from the testing machine after the test to obtain the test load-displacement data corresponding to the third specimen 300.

[0042] Reference Figure 16 The load-displacement curve of the third specimen 300 is basically the same as that of the first specimen 100 and the second specimen 200, and also shows a two-stage load-bearing trend. The difference is that the third specimen 300 is subjected to a vertical tensile load, which causes its adhesive layer 40 to fail brittlely under a lower load, and the overall ultimate load-bearing capacity is also significantly lower.

[0043] It is worth noting that by conducting shear strength tests on three types of test specimens, the differences in load-bearing capacity and failure modes of the adhesive-fitted joints in the carbon fiber laminate 10 and foam sandwich structure 20 under shear and pull-out loads were revealed. The influence of foam sandwich structures 20 with different thicknesses on the residual load-bearing capacity was quantified, solving the problem of structural performance evaluation deviations caused by differences in load conditions in traditional designs. This method can accurately predict the failure risk of adhesive-fitted joints under complex service conditions, significantly improving the reliability and safety of such lightweight composite structures.

[0044] Step S300. Establish the experimental finite element model corresponding to the test specimen; Based on the test conditions corresponding to the test specimens in step S200, corresponding test finite element models are established in ABAQUS based on the three-dimensional geometric models of various test specimens, and the carbon fiber laminate 10, foam sandwich structure 20, rivet 30 and adhesive layer 40 in the test specimens are modeled respectively.

[0045] In the experimental finite element model, the carbon fiber laminate 10, foam sandwich structure 20, and rivets 30 in the test specimen are all modeled using three-dimensional solid elements (C3D8R), and the boundary conditions of the experimental finite element model are set according to the shear strength test in step S200. The elastic constants and strength parameters of the carbon fiber laminate 10 can be obtained through corresponding experiments, and the anisotropic progressive damage behavior of the carbon fiber laminate 10 is simulated using a custom subroutine VUMAT. The three-dimensional Hashin criterion is used as the failure criterion of the carbon fiber laminate 10, and the damage evolution process of the carbon fiber laminate 10 is described by combining the linear degradation method controlled by energy dissipation.

[0046] The foam core material in the foam sandwich structure 20 can be simulated using the compressible foam model built into ABAQUS to fully consider its nonlinear compressive response and shear damage mechanism. The adhesive layer 40 is modeled using a three-dimensional cohesive element (COH3D8R) based on cohesion theory. Its initial damage criterion adopts a quadratic criterion based on nominal stress, and the damage evolution process is described by the Benzeggaggh-Kenane (BK) criterion, which can reflect crack propagation behavior under shear and peeling modes. The adhesive layer 40 is bonded to the adjacent carbon fiber laminate 10 and foam sandwich structure 20 through tie constraints.

[0047] It is worth noting that since no failure of rivet 30 was observed in the shear strength test carried out in step S200, only its elastic response was considered in the simulation analysis, and its damage behavior was not considered.

[0048] Furthermore, referring to Figure 8 and Figure 9 As shown, when establishing the experimental finite element model corresponding to the first specimen 100, the mesh size of the adhesive layer 40 and its bonding area of ​​the first specimen 100 is 1 mm; the mesh size of the rivet 30 area is 1.5 mm, and the mesh size of the remaining areas is 5 mm. The model contains 37,167 C3D8R elements and 3,166 COH3D8R elements. The boundary conditions are set according to the shear strength test settings described above. Full constraints are applied to the upper and lower surfaces of the clamping section of the foam sandwich structure 20 to simulate the clamping method in the test; the upper and lower surfaces of the clamping section of the carbon fiber laminate 10 are coupled through a reference point, and a displacement load is applied to the reference point.

[0049] Reference Figure 10 and Figure 11As shown, when establishing the experimental finite element model corresponding to the second specimen 200, the mesh size of the adhesive layer 40 and the bonding area of ​​the second specimen 200 is 0.6 mm; the mesh size of the rivet 30 area is 1.5 mm, and the mesh size of the remaining areas is 4 mm. The model contains a total of 72033 C3D8R elements and 5276 COH3D8R elements. The boundary conditions are set according to the shear strength test described above. Full constraints are applied to the lower surface of the foam sandwich structure 20 and the bolt hole positions. The upper and lower surfaces of the carbon fiber laminate clamping section are coupled through a reference point, and then a displacement load is applied to the reference point.

[0050] Reference Figure 12 and Figure 13 As shown, when establishing the experimental finite element model corresponding to the third specimen 300, the mesh size of the adhesive layer 40 and the bonding area of ​​the third specimen 300 is 0.6 mm; the mesh size of the rivet 30 area is 1.5 mm, and the mesh size of the remaining areas is 4 mm. The model contains a total of 71,642 C3D8R elements and 3,072 COH3D8R elements. The boundary conditions are set according to the shear strength test described above. In addition to applying full constraints to the lower surface of the foam sandwich structure 20 and the bolt hole positions, a fixture model used to apply vertical pull-out loads in the testing machine is also introduced and coupled to the fixture surface through a reference point before applying displacement loads.

[0051] It is worth noting that this invention successfully constructed a high-precision experimental finite element model corresponding to the test specimen based on the experimental conditions. This facilitates the clarification of the influence mechanism of key structural parameters such as the 40mm adhesive layer thickness, 30mm rivet diameter, overlap area, and core thickness on the performance of the adhesive-fitted riveted joint through parametric analysis, providing a scientific basis for the optimized design of the joint. This method can quickly identify the optimal combination of structural parameters, shorten the R&D cycle, reduce experimental costs, and significantly improve design efficiency and engineering applicability.

[0052] Step S400. Conduct finite element simulation analysis and verification.

[0053] Run the experimental finite element model corresponding to the test specimen to perform simulation calculations to obtain the simulated load-displacement data corresponding to the test specimen; compare the simulated load-displacement data with the test load-displacement data obtained in the aforementioned step S200 to verify the accuracy of the simulation calculation results.

[0054] The accuracy of the simulation results for the three test specimens will be analyzed below, based on specific experimental results and simulation calculation results.

[0055] Figure 14A comparison of the load-displacement curves of the first specimen 100 under experimental and simulation analysis conditions is shown. According to the test results of the shear strength test on the first specimen 100, its ultimate tensile load ranges from 11.25 kN to 14.9 kN, with an average value of 12.63 kN. Based on the calculation results of the finite element simulation analysis, the ultimate tensile load of the first specimen 100 under the same loading conditions is 13.3 kN, and the error between the simulation calculation result and the experimental result is 5.3%.

[0056] Depend on Figure 14 It can be seen that in the initial loading stage, the load-displacement curves of both the experimental and simulation results exhibit approximately linear characteristics, indicating that the external load is mainly borne by the adhesive layer 40 at this stage. As the load increases, the adhesive layer 40 fractures after reaching its ultimate bearing capacity, and the rivet 30 begins to bear the main load-bearing function. The foam sandwich structure 20 is continuously damaged under the compression of the rivet 30, ultimately leading to the failure of the first specimen 100. A comparison shows that the overall trend of the load-displacement curves of the experimental and simulation results is consistent, thus proving the accuracy of the simulation results for the first specimen 100.

[0057] Figure 15 The load-displacement curves of the second specimen 200 under experimental and simulation analysis conditions are shown in the figure. According to the test results of the shear strength test on the second specimen 200, its ultimate tensile load ranges from 11.08 kN to 14.9 kN, with an average value of 11.87 kN. Based on the calculation results of the finite element simulation analysis, the ultimate tensile load of the second specimen 200 under the same loading conditions is 12.24 kN, and the error between the simulation calculation result and the experimental result is 3.12%.

[0058] Depend on Figure 15 It can be seen that the second specimen 200 exhibits a similar failure mode to the first specimen 100. Specifically, the adhesive layer 40 bears the load initially, then fractures instantaneously upon reaching its limit. After the adhesive layer 40 fails, the rivet 30 begins to bear the load, compressing the carbon fiber laminate 10 and causing its failure. When the rivet 30 is completely pulled out of the second specimen 200, the load-bearing capacity of the second specimen 200 drops to zero. Overall, the test results of the second specimen 200 show a consistent trend with the load-displacement curves in the simulation calculations.

[0059] Figure 16A comparison of the load-displacement curves of the third specimen 300 under experimental and simulation analysis conditions is shown. The test results of the shear strength test on the third specimen 300 show that its ultimate tensile load ranges from 0.69 kN to 0.92 kN, with an average value of 0.852 kN. According to the calculation results of the finite element simulation analysis, the ultimate tensile load of the second specimen 200 under the same loading conditions is 0.92 kN, and the error between the simulation calculation result and the experimental result is 7.98%. Although the simulation calculation result deviates slightly from the experimental result, it is still within a reasonable range, demonstrating that the finite element model corresponding to the third specimen 300 has good predictive ability for this type of connection.

[0060] Depend on Figure 16 It can be seen that in the initial loading stage, the load-displacement curves of both the experimental and simulation results exhibit approximately linear characteristics, indicating that the load is borne by the adhesive layer 40. After the adhesive layer 40 fails, the load is borne by the rivets 30. Under the action of the rivets 30, the carbon fiber laminate 10 gradually undergoes partial fracture, but still has load-bearing capacity. As the displacement load increases, the carbon fiber laminate 10 continuously fractures and fails, eventually reaching the ultimate complete failure. Overall, the load-displacement curves of the third specimen 300 show a consistent trend with the simulation results.

[0061] Based on the above analysis of the test results and simulation calculation results of the three test specimens, it can be seen that the finite element model established by this invention has high accuracy in predicting the mechanical behavior of the glued joint. The good consistency between the test results and the simulation calculation results indicates that the finite element model established based on the test conditions can truly reflect the stress state and failure mode of the test specimen under external load.

[0062] It is worth noting that this invention verifies the accuracy of the finite element model in predicting mechanical response and failure behavior through a combination of experiment and simulation, overcoming the limitations of existing theoretical or simplified models.

[0063] Step S500. Practical application analysis.

[0064] Based on the verification of the effectiveness of the finite element simulation analysis method by conducting experiments and finite element simulation analysis on the test specimens through the aforementioned steps S100 to S400, the strength of the glued joints in actual engineering structures can be further analyzed by combining the sub-model method.

[0065] Step S500 specifically includes: Step S501. Establish the overall finite element model corresponding to the actual engineering structure (see...) Figure 17The model extracts a local area containing the adhesive riveting joint from the overall finite element model and uses it as the master finite element model. The adhesive riveting joint is modeled in a simplified manner within the overall finite element model. Specifically, the carbon fiber laminate 10 is simulated using shell elements, the foam sandwich structure 20 is simulated using solid elements, the rivet 30 is simulated using beam and rigid elements, and the adhesive layer 40 is not modeled separately. Figure 18 It shows from Figure 17 The main finite element model containing the adhesive riveting joint is shown as a cut-out from the overall finite element model of a certain actual engineering structure; wherein, the adhesive riveting joint is contained in the crossbeam made of foam sandwich structure 20 and the skirt made of carbon fiber laminate 10, and the two are connected by rivets 30 and adhesive layer 40.

[0066] Step S502. Using the method described in step S200 for establishing the experimental finite element model, the main finite element model is refined to obtain a sub-finite element model. In the sub-finite element model, the carbon fiber laminate 10, foam sandwich structure 20, rivets 30, and adhesive layer 40 are all modeled using solid elements; simultaneously, the boundary constraints of the sub-finite element model inherit the displacement information extracted from the overall finite element model to reproduce the stress state of the adhesive-riveted joint area as realistically as possible. See... Figure 19 .

[0067] Based on this, simulation calculations were performed on the overall finite element model and sub-finite element model of the actual engineering structure to obtain displacement cloud diagrams and stress cloud diagrams in each direction corresponding to the overall finite element model, as well as displacement cloud diagrams and stress cloud diagrams in each direction corresponding to the sub-finite element model.

[0068] The displacement contour maps and stress contour maps in each direction of the overall finite element model and the sub-finite element model are compared and analyzed to verify the accuracy of the sub-finite element model.

[0069] Figure 20 The displacement contour plots corresponding to the master finite element model in the overall finite element model are shown. Figure 21 The displacement contour plot corresponding to the sub-finite element model is shown. Figure 20 and Figure 21 It can be seen that the deformation distribution trends of the main finite element model and the sub-finite element model are basically consistent, with the maximum deformation occurring in the carbon fiber laminate 10 region, which serves as the skirt. In the main finite element model corresponding to the overall finite element model of the actual engineering structure, the maximum deformation is 0.534 mm, while the maximum deformation at the corresponding location in the sub-finite element model is 0.532 mm, a difference of only 0.002 mm. This indicates that the boundary displacement data transferred from the overall finite element model to the sub-finite element model is accurate and effective, ensuring the reliability of subsequent stress analysis in the sub-finite element model.

[0070] According to embodiments of the present invention, by combining sub-modeling technology to perform localized detailed analysis on key areas including glued joints, stress concentration areas can be accurately captured, providing a reliable tool for strength verification of complex structures and ensuring that the design results meet the safety requirements under harsh working conditions such as rail transit.

[0071] This invention, through collaborative innovation of experimentation and simulation, achieves refined, parameterized, and engineered strength analysis of adhesive riveting joints, significantly improving the scientific and economical nature of composite material structural connection design, and providing key technical support for the safe and reliable operation of lightweight equipment.

[0072] Example 2 Based on Embodiment 1, Embodiment 2 of the present invention further provides an electronic device. This electronic device includes a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the strength analysis method for the adhesive-fitted joint of the carbon fiber laminate and foam sandwich structure as described in Embodiment 1 above.

[0073] Memory can be implemented from any type of volatile or non-volatile storage device or a combination thereof, such as Static Random Access Memory (SRAM), Electrically Erasable Programmable Read-Only Memory (EEPROM), Erasable Programmable Read-Only Memory (EPROM), Programmable Read-Only Memory (PROM), Read-Only Memory (ROM), magnetic storage, flash memory, magnetic disk, or optical disk.

[0074] Example 3 Based on Embodiment 1, Embodiment 3 of the present invention further provides a readable storage medium. This readable storage medium stores a computer program, which, when executed by a processor, implements the strength analysis method for the adhesive-fitted joint of the carbon fiber laminate and foam sandwich structure described in Embodiment 1.

[0075] Specifically, the readable storage medium can be a USB flash drive, a portable hard drive, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk, or any other readable storage medium capable of storing program code.

[0076] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for strength analysis of adhesive-fitted joints in carbon fiber laminate and foam sandwich structures, characterized in that, Includes the following steps: Shear strength tests are conducted on the test specimens under predetermined test conditions to obtain the failure modes and test load-displacement data corresponding to the test specimens; the test specimens include carbon fiber laminates and foam sandwich structures, and the carbon fiber laminates and foam sandwich structures are connected by adhesive layers and rivets. Based on the aforementioned test conditions, an experimental finite element model corresponding to the test specimen was established. In the experimental finite element model, a custom subroutine was used to simulate the anisotropic progressive damage behavior of the carbon fiber laminate. The three-dimensional Hashin criterion was used as the failure criterion for the carbon fiber laminate, and the damage evolution process of the carbon fiber laminate was described by combining the linear degradation method controlled by energy dissipation. The foam core material in the foam sandwich structure was simulated using a compressible foam model. The adhesive layer was modeled using three-dimensional cohesive elements based on cohesion theory. Its initial damage criterion adopted a quadratic criterion based on nominal stress, and the damage evolution process was described by the Benzeggaggh-Kenane criterion. The experimental finite element model was run to perform simulation calculations to obtain simulated load-displacement data corresponding to the test specimen; the simulated load-displacement data was compared with the experimental load-displacement data to verify the accuracy of the simulation calculation results.

2. The method for strength analysis of the adhesive joint of carbon fiber laminate and foam sandwich structure according to claim 1, characterized in that, The custom subroutine is VUMAT; and in the experimental finite element model, the adhesive layer is bonded to the adjacent carbon fiber laminate and foam sandwich structure through tie constraints.

3. The method for strength analysis of the adhesive joint of carbon fiber laminate and foam sandwich structure according to claim 1, characterized in that, It also includes the following steps: A global finite element model corresponding to the actual engineering structure is established, and a local area containing the glued riveting joint in the global finite element model is extracted as the master finite element model; the glued riveting joint is simplified in the global finite element model. The method for establishing the experimental finite element model is used to refine the main finite element model to obtain the sub-finite element model; Simulation calculations were performed using the overall finite element model and the sub-finite element model to obtain displacement contour maps and stress contour maps in each direction corresponding to the overall finite element model, as well as displacement contour maps and stress contour maps in each direction corresponding to the sub-finite element model. The displacement contour maps and stress contour maps in each direction of the overall finite element model and the sub-finite element model are compared and analyzed to verify the accuracy of the sub-finite element model.

4. The method for strength analysis of the adhesive joint of carbon fiber laminate and foam sandwich structure according to claim 3, characterized in that, In the sub-finite element model, the carbon fiber laminate, foam sandwich structure, rivets and adhesive layer are all modeled using solid elements; the boundary constraints of the sub-finite element model are inherited from the displacement information extracted from the overall finite element model.

5. The method for strength analysis of the adhesive joint of carbon fiber laminate and foam sandwich structure according to claim 3, characterized in that, The simplified modeling is as follows: the carbon fiber laminate is simulated using shell elements, the foam sandwich structure is simulated using solid elements, the rivets are simulated using beam elements and rigid elements, and the adhesive layer is not modeled separately.

6. The method for strength analysis of the adhesive joint of carbon fiber laminate and foam sandwich structure according to claim 1, characterized in that, The test specimens include a first specimen, a second specimen, and a third specimen; the thickness of the foam sandwich structure in the first specimen is less than the thickness of the foam sandwich structure in the second specimen; the thickness of the foam sandwich structure in the second specimen is equal to the thickness of the foam sandwich structure in the third specimen.

7. The method for strength analysis of the adhesive joint of carbon fiber laminate and foam sandwich structure according to claim 6, characterized in that, The shear strength test of the test specimen was conducted using an MTS tensile-torsion testing machine. In the shear strength test of the first specimen, the testing machine applies a planar shear load to the first specimen; In the shear strength test of the second specimen, the testing machine applies a planar shear load to the second specimen; In the shear strength test of the third specimen, the testing machine applied a vertical pull-out load to the third specimen.

8. The method for strength analysis of the adhesive joint of carbon fiber laminate and foam sandwich structure according to claim 1, characterized in that, In the experimental finite element model, the carbon fiber laminate, foam sandwich structure, and rivets in the test specimen are all modeled using three-dimensional solid elements; the boundary conditions of the experimental finite element model are set with reference to the shear strength test.

9. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the strength analysis method for the adhesive riveting joint of the carbon fiber laminate and foam sandwich structure as described in any one of claims 1 to 8.

10. A readable storage medium storing a computer program, characterized in that, When the computer program is executed by the processor, it implements the strength analysis method for the adhesive riveting joint of the carbon fiber laminate and foam sandwich structure as described in any one of claims 1 to 8.

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