Finite element modeling method for post-impact dent of composite laminates

Abstract

The application provides a composite laminate impact pit finite element modeling method, and relates to the technical field of material geometric simulation design, and comprises the following steps: constructing a single-layer plate plane model of a composite laminate, performing discretization processing on the single-layer plate plane model to obtain isolated grids; copying the isolated grids for several times, adjusting the positions of the copied isolated grids to obtain a plurality of layers of isolated grids arranged in sequence, searching nodes in each layer of isolated grids according to pit geometric characteristic parameters and an impact center point position, wherein it is determined whether the searched nodes are located in a pit area to obtain target nodes, fitting offset values according to the spatial positions of the target nodes and the pit geometric characteristic parameters; and adjusting the spatial positions of the corresponding target nodes through the offset values to obtain a composite laminate three-dimensional finite element model with a pit geometric morphology, so that the application can realize fine modeling of a geometric pit of a composite laminate after impact.

Description

Technical Field

[0001] This invention relates to the field of material geometry simulation design technology, and more specifically, to a finite element modeling method for impact-induced dents in composite laminates. Background Technology

[0002] Composite laminates, due to their superior properties such as high specific strength and high specific stiffness, have been widely used in aerospace, rail transportation, and high-end equipment manufacturing. During actual service, composite structures inevitably suffer from low-velocity impact loads, resulting in damage such as delamination, matrix cracking, and localized surface indentations. Among these, the indentations formed after impact affect the local stiffness and stress distribution of the structure, thus influencing the residual load-bearing capacity and failure behavior of the composite laminate after impact. Therefore, appropriately considering the geometric characteristics of the indentations after impact is of significant engineering importance when analyzing the post-impact performance of composite laminates.

[0003] Currently, the research process for post-impact compression analysis of composite laminates is roughly as follows: 1. Based on the test methods and specimen dimensions specified in ASTM D7136 "Standard Test Method for Drop Weight Impact Damage Resistance of Fiber Reinforced Polymer Composites", a finite element model of the composite laminate was established and the impact process was simulated and analyzed. 2. Export the damage from the model in the impact simulation analysis results; 3. Establish a new compression test specimen model and import the above damage data into the model; 4. Perform post-impact compression test simulation analysis on the finite element model with introduced damage according to the test methods specified in ASTM D7137, "Standard Test Method for Post-Impact Compression Properties (CAI) of Fiber Reinforced Polymer Matrix Composites".

[0004] Current research still uses an initial, complete laminate geometry model for post-impact compression tests, without refining the model of the actual impact dents. This neglect of actual geometric features can lead to deviations in the mechanical response of stress concentration areas, thus affecting the accuracy of the residual strength assessment. Therefore, it is necessary to design a finite element modeling method that can realistically reflect the geometry of post-impact dents to improve the accuracy of simulation results. Summary of the Invention

[0005] In view of this, the present invention proposes a finite element modeling method for impact-induced dents in composite laminates to solve the problems existing in the prior art.

[0006] To achieve the above objectives, this invention proposes a finite element modeling method for impact-induced dents in composite laminates, comprising: A single-layer planar model of the composite laminate is constructed, and the single-layer planar model is discretized to obtain an isolated mesh; The isolated mesh is copied several times, and the positions of the copied isolated mesh are adjusted to obtain several layers of isolated mesh arranged in sequence, wherein adjacent isolated meshes form composite material lay-ups or cohesive layers. Obtain the geometric feature parameters of the crater and the position of the impact center point. Based on the geometric feature parameters of the crater and the position of the impact center point, search the nodes in each isolated grid layer, wherein the search node is located in the crater region to obtain the target node. Based on the spatial position of the target node and the geometric feature parameters of the crater, fit the bias value to obtain the bias value. By adjusting the spatial position of the corresponding target node using the offset value, a three-dimensional finite element model of the composite laminate with a pitted geometry is obtained.

[0007] Optionally, the process of obtaining the isolated mesh includes: The single-layer plate planar model is discretized using finite element meshing, and the processed mesh is removed from the single-layer plate planar model to obtain an isolated mesh; wherein, the single-layer plate planar model is the initial two-dimensional geometric model of the composite laminate.

[0008] Optionally, the process of obtaining the several layers of isolated meshes includes: The isolated mesh is copied, and the copied isolated mesh is positively biased to obtain a second isolated mesh; the original isolated mesh and the second isolated mesh form a composite material layup; The second isolated mesh is copied, and the copied second isolated mesh is positively biased to obtain the third isolated mesh. The second isolated mesh and the third isolated mesh form a cohesive layer. Repeat the above replication and forward biasing process until the total number of layers of the composite laminate is met, resulting in a number of isolated meshes containing several composite layups and cohesive layers; wherein the forward bias is along the same direction, and the value of the forward bias is set according to the thickness of the corresponding layup of the composite laminate.

[0009] Optionally, the process of obtaining the target node includes: Obtain the normal coordinates of each isolated grid layer; based on the crater geometric feature parameters and the normal coordinates of each layer, obtain the search radius of each layer; based on the impact center point position and the search radius, search for nodes in each isolated grid layer to determine whether the node is located in the crater region, and obtain the target node; wherein the crater geometric feature parameters include crater depth and crater radius.

[0010] Optionally, the process of obtaining the search radius includes: Based on the geometric feature parameters of the pits and the normal coordinates of each layer, the search radius of the nodes in the isolated mesh of each layer is calculated using a functional relationship.

[0011] Optionally, the process of obtaining the bias value includes: Based on the relationship between the spatial location of the target node and the depth of the pit in the geometric feature parameters of the pit, and combined with the surface function of the actual pit, the offset value of the normal of each target node is calculated.

[0012] Optionally, the process of adjusting the spatial position of the corresponding target node using the offset value includes: In the spatial position of the target node, the normal position in the spatial position is adjusted according to the corresponding offset value to adjust the normal coordinate of the target node. After modifying all target nodes, a three-dimensional finite element model of composite laminate is obtained.

[0013] On the other hand, the present invention provides a finite element modeling system for impact-induced dents in composite laminates, for performing the above-described method.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. It achieves refined modeling of geometric indentations after impact, making up for the shortcomings of traditional analysis methods and improving the accuracy of simulation results; 2. Through layer-by-layer node search and coordinate offset mechanism, the contours of pits at different depths can be accurately reconstructed in multilayer composite material structures, which is suitable for complex ply configurations; 3. Improved the realism of structural mechanical response in post-impact compression simulation analysis, which helps to more reliably assess the remaining load-bearing capacity of the structure. Attached Figure Description

[0015] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. In the drawings: Figure 1 This is a schematic diagram of the composite material single-layer plate model established in the embodiments of the present invention; Figure 2 This is a schematic diagram of the mesh division of a single-layer plate model in an embodiment of the present invention; Figure 3 This is a schematic diagram of all nodes N1 of the isolated mesh layer M1 in this embodiment of the invention; Figure 4 This is a schematic diagram of all nodes N2 of the isolated mesh layer M2 in this embodiment of the invention; Figure 5This is a schematic diagram of the first composite material layup formed by isolated grid layer M1 and isolated grid layer M2 in an embodiment of the present invention; Figure 6 This is a schematic diagram of all nodes N3 of the isolated mesh layer M3 in this embodiment of the invention; Figure 7 This is a schematic diagram of the first cohesive layer formed by isolated grid layer M2 and isolated grid layer M3 in an embodiment of the present invention; Figure 8 This is a schematic diagram of the search radius SR of each layer node in an embodiment of the present invention; Figure 9 This is a finite element model of the impact dent formed in the embodiment of the present invention. Detailed Implementation

[0016] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the disclosure to those skilled in the art. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0017] This invention belongs to the field of aircraft structural design and strength analysis, and specifically relates to a finite element modeling method for simulating the formation of surface geometric pits in composite laminates under low-speed impact loads.

[0018] This invention aims to address the common problem in existing finite element analysis of composite material impact compression that fails to consider the impact-induced surface geometric indentations on the structural mechanical response. Current mainstream simulation methods still rely on initial geometric configurations for subsequent compressive performance studies, neglecting the local geometric deformation caused by impact damage. This leads to biases in the analysis of the mechanical response in the impact region and decreased accuracy in residual strength assessment.

[0019] To overcome the shortcomings of the prior art, this invention provides a finite element method that can reconstruct the three-dimensional morphology of surface pits formed on composite laminates under low-speed impact, thereby improving the accuracy of structural performance simulation.

[0020] The objective of this invention is achieved through the following technical solution: 1. Establish a single-layer planar model: Based on the dimensional parameters of the standard specimen, construct an initial two-dimensional geometric model of the composite laminate, such as... Figure 1 As shown; 2. Mesh Generation: The planar model is discretized using the finite element method, such as... Figure 2 As shown; 3. Generate isolated mesh: Convert the mesh of the single-layer plate planar model into an isolated mesh M1 detached from the original geometry, and label all nodes on the isolated mesh M1 as N1, such as... Figure 3 As shown; 4. Set ply parameters: Set information such as the number of ply layers, single ply thickness, and single ply thickness of the inserted cohesive layer for the composite laminate; 5. Construct the first composite material layup: Duplicate the isolated mesh M1 transformed in step three and offset it along the positive Z-axis by the thickness of a single composite material layup. Label the offset isolated mesh as M2, and label all nodes on isolated mesh M2 as N2, as follows. Figure 4 As shown, M1 and M2 together form the first composite material layup, as... Figure 5 As shown; 6. Construct the first cohesive layer: Duplicate the isolated mesh M2 and offset it upwards by the thickness of a single cohesive layer. Mark the offset isolated mesh as M3, and mark all nodes on the isolated mesh M3 as N3, as follows. Figure 6 As shown, M2 and M3 together form the first cohesive layer, as... Figure 7 As shown; 7. Stacking multi-layer structures: Repeat steps 5 and 6 until the number of composite material lay-ups and the number of cohesive layers meet the parameters set in step 4; 8. Input dent parameters: Set the key geometric feature parameters of the dent after impact, including the minimum circumscribed circle radius (dent radius) R and dent depth D obtained from experimental measurements; 9. Obtain Z-coordinates for each layer: Read the current spatial Z-coordinate value of each isolated grid layer; 10. Calculate the search radius SR: Based on the pit parameters D and R and the Z coordinates of each layer, the following functional relationship is used: , Where z is the z-coordinate of each single layer, and the search radius SR of each layer node is calculated to reflect the characteristic of the pit gradually decreasing from the surface to the depth, such as... Figure 8 As shown; 11. Identify target nodes: Using the impact center (x0, y0, z0) as the center and SR as the radius, search for all nodes located within the circular area in each layer of the grid and obtain their X, Y, and Z coordinates; 12. Calculate node offset: Based on the spatial coordinates (x, y) of each node... i ,y i ,z iThe relationship between the pit depth D and the indentation depth D is based on the functional relationship: , Calculate the Z-axis bias value δ to be applied to each node. z ; 13. Update node coordinates: Apply the calculated Z-axis offset value to the corresponding node, modify its Z-coordinate, and complete the spatial position adjustment; repeat this process until all nodes meeting the conditions have been processed, ultimately forming a three-dimensional finite element model with realistic pit geometry, such as... Figure 9 As shown.

[0021] Compared with the prior art, the beneficial effects of the finite element modeling method for impact dents in composite materials provided by this invention are as follows: 1. It achieves refined modeling of geometric indentations after impact, making up for the shortcomings of traditional analysis methods and improving the accuracy of simulation results; 2. Through layer-by-layer node search and coordinate offset mechanism, the contours of pits at different depths can be accurately reconstructed in multilayer composite material structures, which is suitable for complex ply configurations; 3. Improved the realism of structural mechanical response in post-impact compression simulation analysis, which helps to more reliably assess the remaining load-bearing capacity of the structure.

[0022] To enable those skilled in the art to implement the present invention, its specific embodiments will be described in detail below with reference to the accompanying drawings.

[0023] A finite element modeling method for impact dents in composite materials is implemented according to the following steps: (1) Based on the dimensional parameters of the composite material impact compression test specimen specified in ASTM D7136, a rectangular single-layer plate planar geometric model with a length of L and a width of W is established; (2) Perform finite element mesh generation on the planar model, using quadrilateral or triangular elements to control the size of the control unit to ensure the accuracy of subsequent offset operations; (3) Convert the mesh generated in step (2) into an isolated mesh M1, that is, an independent mesh entity detached from the original geometry, and mark all nodes on M1 as N1; (4) Set the total number of composite material layers LC, the thickness of a single layer LH, and the thickness of the inserted cohesive layer CH; (5) Copy the isolated mesh M1 to generate a new mesh layer, and offset it by a thickness LH along the positive Z-axis to form a new isolated mesh M2, on which all nodes are marked as N2; M1 and M2 are connected by solid elements to form the first layer of composite material layup. (6) Copy the isolated mesh M2 and offset it by a thickness CH along the positive Z-axis to generate an isolated mesh M3, with its nodes marked as N3; M2 and M3 are connected by cohesive elements to form the first cohesive layer; (7) Repeat steps (5) and (6) to stack the composite material layup and cohesive layer in sequence until the preset number of layup LC is reached; (8) Set the key geometric parameters of the impact crater: crater depth D and crater radius R; (9) Read the current Z-coordinate value of each isolated grid layer; (10) Based on the pit parameters D and R and the Z coordinates of each layer, the search radius SR of each node is calculated using a functional relationship. For example, SR can be set to decrease linearly with increasing Z, reflecting the characteristic that the pit gradually converges from the surface to the depth. (11) Using the impact point as the center and SR as the radius, search all nodes located within the circular area in each layer of the grid and obtain their X, Y, and Z coordinate values; (12) Based on the obtained node coordinates and the relationship between the pit depth D and the spatial position, calculate the Z-axis offset value δz that should be applied to each node; (13) Apply the calculated offset value δz to the corresponding node, modify its Z coordinate, and complete the node spatial position update; repeat this operation until all nodes that meet the conditions are processed, and finally form a three-dimensional finite element model with real pit geometry.

[0024] 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 it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A finite element modeling method for impact-induced dents in composite laminates, characterized in that, include: A single-layer planar model of the composite laminate is constructed, and the single-layer planar model is discretized to obtain an isolated mesh; The isolated mesh is copied several times, and the positions of the copied isolated mesh are adjusted to obtain several layers of isolated mesh arranged in sequence, wherein adjacent isolated meshes form composite material lay-ups or cohesive layers. Obtain the geometric feature parameters of the crater and the position of the impact center point. Based on the geometric feature parameters of the crater and the position of the impact center point, search the nodes in each isolated grid layer, wherein the search node is located in the crater region to obtain the target node. Based on the spatial position of the target node and the geometric feature parameters of the crater, fit the bias value to obtain the bias value. By adjusting the spatial position of the corresponding target node using the offset value, a three-dimensional finite element model of the composite laminate with a pitted geometry is obtained.

2. The method according to claim 1, characterized in that, The process of obtaining the isolated grid includes: The single-layer plate planar model is discretized using finite element meshing, and the processed mesh is removed from the single-layer plate planar model to obtain an isolated mesh; wherein, the single-layer plate planar model is the initial two-dimensional geometric model of the composite laminate.

3. The method according to claim 1, characterized in that, The process of obtaining the aforementioned isolated mesh layers includes: The isolated mesh is copied, and the copied isolated mesh is positively biased to obtain a second isolated mesh; the original isolated mesh and the second isolated mesh form a composite material layup; The second isolated mesh is copied, and the copied second isolated mesh is positively biased to obtain the third isolated mesh. The second isolated mesh and the third isolated mesh form a cohesive layer. Repeat the above replication and forward biasing process until the total number of layers of the composite laminate is met, resulting in a number of isolated meshes containing several composite layups and cohesive layers; wherein the forward bias is along the same direction, and the value of the forward bias is set according to the thickness of the corresponding layup of the composite laminate.

4. The method according to claim 1, characterized in that, The process of obtaining the target node includes: Obtain the normal coordinates of each isolated grid layer; based on the crater geometric feature parameters and the normal coordinates of each layer, obtain the search radius of each layer; based on the impact center point position and the search radius, search for nodes in each isolated grid layer to determine whether the node is located in the crater region, and obtain the target node; wherein the crater geometric feature parameters include crater depth and crater radius.

5. The method according to claim 4, characterized in that, The process of obtaining the search radius includes: Based on the geometric feature parameters of the pits and the normal coordinates of each layer, the search radius of the nodes in the isolated mesh of each layer is calculated using a functional relationship.

6. The method according to claim 1, characterized in that, The process of obtaining the bias value includes: Based on the relationship between the spatial location of the target node and the depth of the pit in the geometric feature parameters of the pit, and combined with the surface function of the actual pit, the offset value of the normal of each target node is calculated.

7. The method according to claim 1, characterized in that, The process of adjusting the spatial position of the corresponding target node using an offset value includes: In the spatial position of the target node, the normal position in the spatial position is adjusted according to the corresponding offset value to adjust the normal coordinate of the target node. After modifying all target nodes, a three-dimensional finite element model of composite laminate is obtained.

8. A finite element modeling system for impact dents in composite laminates, characterized in that, Used to perform the method described in any one of claims 1-7.

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