Variable-stiffness curve spiral impact-resistant composite material layering configuration and automatic laying forming method thereof

Abstract

The invention belongs to the field of continuous fiber reinforced resin-based composite material layer design methods, and particularly relates to a variable-stiffness curve spiral impact-resistant composite material layer structure and an automatic laying forming method of the variable-stiffness curve spiral impact-resistant composite material layer structure. The method is inspired by a fiber microstructure of a natural spiral biological material, the design freedom degree of the material in the in-plane direction is further activated by adopting a continuous curve fiber ply configuration, the ply angle is linearly increased, and a symmetrical curve spiral ply configuration laminated plate is stacked according to the ply sequence; a three-dimensional bionic microstructure is constructed by cooperatively designing an in-plane curve fiber path and a spiral stacking sequence in the thickness direction, the impact resistance, the deformation resistance and the damage tolerance of the composite material are remarkably improved, and meanwhile, the interlayer performance can be further improved by inhibiting layering damage. The variable-stiffness curve spiral laminated plate is prepared by adopting an automatic fiber placement technology (AFP) and a hot pressing process. The invention provides a new thought for design and manufacturing of the high-performance impact-resistant composite material.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of composite material design and manufacturing method, and particularly relates to a variable stiffness curve spiral impact-resistant composite material layer configuration and an automatic laying forming method thereof. BACKGROUND

[0002] In the field of aerospace, composite materials are often used for structures that bear high strength and high load, and are particularly sensitive to impact damage. Improving the impact resistance of composite materials is of great significance to the safety and reliability of components. Fiber-reinforced composites are prone to interlaminar delamination under multiple impacts, which causes delamination instability and delamination propagation at lower loads, leading to structural failure.

[0003] Biomimetic spiral structure (Boul igand structure) has good strength and toughness. Inspired by biological micro-spiral structure, a small interlaminar angle is introduced spirally in the unidirectional layer, which can greatly reduce the interlaminar stress of carbon fiber and glass fiber reinforced composites under load and thus strengthen the overall interlaminar performance, out-of-plane bearing and impact resistance. However, compared with quasi-isotropic CFRP, spiral layer samples exhibit larger in-plane damage area in low-speed impact and post-impact compression tests, and the design freedom of in-plane fiber direction has not been developed.

[0004] Curved fiber laying variable stiffness plate is a new type of laminated plate with in-plane curved fiber trajectory manufactured by automatic fiber placement (AFP) technology. Its core advantage is that by manipulating and optimizing the spatial trajectory distribution of the fibers within the layer, the overall stiffness field of the laminated plate can be controlled while keeping the total number of layers, single layer thickness and overall geometric size unchanged. Reasonable fiber path design can significantly improve the comprehensive mechanical properties of the laminated plate and effectively suppress or eliminate stress concentration phenomenon. Therefore, to further improve the impact resistance of the material, the present application first creates a variable stiffness curve spiral layer unit configuration, which combines the microstructure characteristics of curved fiber path and spiral layer stacking sequence, and has more excellent impact resistance. Its manufacturing method is simple and universal, and has great potential for engineering application. SUMMARY

[0005] To solve the above problems, the application discloses a variable stiffness curve spiral impact-resistant composite material layer configuration and an automatic laying forming method thereof.

[0006] To solve the above problems, the application discloses a variable stiffness curve spiral impact-resistant composite material layer configuration and an automatic laying forming method thereof.

[0007] A novel curve spiral impact-resistant composite material layer configuration and an automatic laying forming method thereof, comprising the following steps:

[0008] S1 defines the design characteristics of the curve spiral biomimetic microstructure as follows: (1) in the in-plane direction, each single layer adopts a non-linear, continuously changing curve fiber track, realizing the continuous and controllable gradient distribution of in-plane stiffness; (2) in the thickness direction, the adjacent layers are stacked in a specific spiral angle, forming a spiral configuration throughout the thickness.

[0009] S2: determine the total number of laminates N of the laminate, design the in-plane curve fiber path and the thickness direction spiral stacking sequence, form the symmetrical variable stiffness curve spiral layer configuration, and control the angle deviation between the adjacent layers within 5°±2°; start from 0° layer and increase the spiral angle θ layer by layer, according to The variable stiffness laminate is stacked in a spiral shape, wherein the superscript wavy line represents the variable stiffness layer, and the subscript s represents the symmetrical layer.

[0010] S3: according to the determined starting angle T0, the ending angle T1, the laminate length d and the number of layers N, the variable stiffness biomimetic spiral laminate modeling script is written through Python to complete the rapid modeling of the variable stiffness laminate, wherein the fiber path follows a linear variable angle equation, and the expression is:

[0011]

[0012] In the formula, T0 is the starting angle of the fiber curve, T1 is the ending angle of the curve, and d is the length of the laminate.

[0013] S4: the variable stiffness biomimetic spiral laminate is prepared through automatic fiber placement (AFP) technology and hot press forming, and the curing procedure is: heating at 1-2℃ / min to 120℃, keeping for 90 minutes, and then naturally cooling to below 60℃ for demolding.

[0014] S5: After demolding, the spiral layer composite laminate is processed by water cutting, 150mm x 100mm size samples are cut according to ASTM D7136 standard, and low-velocity impact (LVI) performance test is carried out to evaluate the impact resistance.

[0015] S6: Using finite element analysis method, the generated model file is imported into Abaqus to obtain the macroscopic mechanical response and damage characteristics of the laminate under a specific low-velocity impact energy;

[0016] As preferred, the AFP technology and autoclave molding process comprise the following steps:

[0017] Material preparation: select carbon fiber reinforced epoxy resin ultra-thin prepreg with appropriate filament width and thickness (prepreg thickness t = 0.05mm), and install it on the AFP laying head, clean the mold, paste PTFE / Glass release cloth above the mold, and prepare the variable stiffness biomimetic spiral laminate according to the layer design on the release cloth.

[0018] Path planning: according to the design requirements, the fiber laying path and angle are calculated by Python program, and the control program of the laying path is generated.

[0019] Laying fiber: the equipment automatically lays the fiber according to the predetermined angle and sequence to the substrate surface by precise control of the laying head, forming the layer structure of the composite material.

[0020] Lamination and compaction: during the laying process, the fibers are stacked layer by layer, and the pressure is ensured to tightly combine each layer of fibers, avoiding bubbles and uneven laying.

[0021] Curing: after completing the laying, the laid material is wrapped with a vacuum bag, vacuumized and maintained in a vacuum state, transferred to an autoclave, and then cured according to the curing program to harden the resin and bond the fibers, finally completing the preparation of the variable stiffness biomimetic spiral composite laminate.

[0022] Preferably, the path planning includes programming simulation and program checking, wherein the program executed by the automatic fiber laying machine is programmed according to the laminate layer, each layer is controlled by program parameters, and the program includes rotation angle, curvature control, gap between each group of yarns, edge coverage rate and other parameters.

[0023] Preferably, the curing requirement is to heat the laminate from room temperature to 120℃ at a heating rate of 1-2℃ / min, keep it at 120℃ for 90 minutes, and naturally cool to below 60℃ for demolding.

[0024] As preferred, the thickness direction spiral stacking sequence of the laminated plate stacked at any linearly increasing rotation angle theta is a symmetric ply, the interlaminar angle transition is uniform, the interlaminar shear stress along the thickness direction shows a nonlinear distribution, the shear stress peak value has a significant downward trend compared with the linear spiral ply and the orthogonal ply form, and the stress distribution is more uniform.

[0025] As preferred, the laminated plate model generation program comprises the following steps:

[0026] (1) determine the structure size, grid size, divide the grid, and determine the node;

[0027] (2) calculate the coordinates of each node and element;

[0028] (3) determine the spiral angle theta;

[0029] (4) calculate the center coordinates of the element after spiral;

[0030] (5) substitute the center coordinates into the function of the fiber angle on the reference fiber path to calculate the angle of the element ply;

[0031] (6) write the above information into the inp file.

[0032] The beneficial effects of the present application are:

[0033] (1) improve the impact resistance: by combining the variable stiffness design and the bionic spiral structure, the impact resistance of the composite material is significantly improved. The variable stiffness design optimizes the interlaminar stiffness distribution, so that the laminated plate can transmit stress more uniformly when stressed, reducing interlaminar slip and fatigue-induced performance degradation. The bionic spiral structure simulates the spiral arrangement of biological exoskeleton in nature, effectively disperses the impact stress, and reduces the risk of interlaminar peeling and crack propagation.

[0034] (2) optimize stress distribution: the variable angle laminated plate realizes the continuous change of stiffness through the curved laying of fibers, further optimizes the stress distribution. Compared with the traditional linear spiral ply and orthogonal ply form, the interlaminar shear stress peak value in the present application is significantly reduced, and the stress distribution is more uniform, thereby enhancing the overall mechanical properties of the structure.

[0035] (3) improve interlaminar toughness by inhibiting crack propagation: the bionic spiral structure introduces a small interlaminar angle, which can inhibit the propagation of dynamic matrix cracks and delamination cracks through crack deflection and redirection, significantly improve the interlaminar toughness of the composite material, and enhance the stability and durability of the composite material under complex dynamic load conditions.

[0036] (4) Simplified manufacturing process: The present application simplifies the preparation process of composite materials by combining automatic fiber placement (AFP) technology with autoclave molding process. AFP technology can accurately control the laying path and angle of fibers, ensuring close combination between each layer of fibers, avoiding the problems of bubbles and uneven laying. The autoclave molding process ensures the curing quality of the composite materials through precise temperature control.

[0037] (5) Efficient and reliable solution: The present application provides an efficient and reliable solution for the innovative design and application of composite materials by combining bionic spiral structure with fiber laying angle variable stiffness design, which can effectively solve the problems of composite materials in impact resistance, interlaminar toughness and stress distribution optimization, and provide more inspiration for variable stiffness impact-resistant layer design. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 Figure 1 is a schematic diagram of a bionic variable stiffness laminate spiral layer (spiral angle = 5°);

[0039] Figure 2 Figure 2 is a schematic diagram of an angle linear change fiber path;

[0040] Figure 3 Figure 3 is a laminate curing temperature curve;

[0041] Figure 4 Figure 4 is a force-time curve of four example laminates;

[0042] Figure 5 Figure 5 is a force-displacement curve of four example laminates;

[0043] Figure 6 Figure 6 is a schematic diagram of the expansion along the delamination interface and the transition to delamination cracks. DETAILED DESCRIPTION

[0044] The present application will be further illustrated in conjunction with the drawings and specific embodiments, it should be understood that the following specific embodiments are only used to illustrate the present application and not to limit the scope of the present application. It should be noted that the words "front", "back", "left", "right", "up" and "down" used in the following description refer to the directions in the drawings, and the words "in" and "out" refer to the directions towards or away from the geometric center of a particular component.

[0045] The variable stiffness curve spiral impact-resistant composite layer configuration and its automatic placement molding method of the present embodiment are as follows:

[0046] (1) Determine the total number of laminates N, according to the determined number of laminates, start from 0° layer and increase the spiral angle θ of each layer, according to The layers are stacked into a symmetrical spiral variable stiffness laminate, where the layers with superscript wavy line are variable stiffness layers.Figure 1 It can be seen that the variable stiffness curve spiral structure realizes the three-dimensional layup configuration characteristics by the synergistic design of guiding the curve fiber to the Bouligand spiral stacking: the curve fiber arrangement is presented in the plane, and the small-angle spiral stacking sequence is formed in the thickness direction.

[0047] For the laminated plate with any linearly increasing rotation angle stacking, the interlaminar shear stress along the thickness direction shows a nonlinear distribution, and the peak value of the shear stress has a significant downward trend compared with the linear spiral layup and orthogonal layup forms, and the stress distribution is more uniform. The linearly increasing rotation angle should satisfy

[0048] (2) According to the determined starting angle, ending angle, length of the laminate and the number of plies N, a variable stiffness biomimetic spiral symmetric laminate model generation program is written through python, wherein the reference path expression is Figure 2 :

[0049]

[0050] In the formula, T0 is the starting angle of the fiber curve, T1 is the ending angle of the curve, and d is the length of the laminate.

[0051] According to the present application, the laminate model generation program comprises the following steps:

[0052] 1) Determine the structure size, grid size, divide the grid, and determine the node;

[0053] 2) Calculate the coordinates of each node and element;

[0054] 3) Determine the spiral angle θ;

[0055] 4) Calculate the center coordinates of the element after the spiral;

[0056] 5) Substitute the center coordinates into the function of the fiber angle on the reference fiber path to calculate the angle of the element layup;

[0057] 6) Write the above information into the inp file.

[0058] The reference path, in the global coordinate system, the fiber angle of any point in the laminate is:

[0059] θ(x,y)=φ+θ(x′)

[0060] In the formula, φ is the angle between the reference coordinate system and the global coordinate system, and the angle linearly changes the fiber path as shown in Figure 2 .

[0061] (3) A variable stiffness spiral biomimetic laminate was prepared by AFP technology and autoclave molding process, and impact testing and simulation were completed. The impact test data and numerical simulation results were analyzed to explain the impact toughening mechanism.

[0062] According to the present invention, the AFP technology and autoclave molding process are characterized by comprising the following steps:

[0063] Material preparation: Select the appropriate prepreg and install it on the laying head of the AFP equipment.

[0064] Path planning: Based on Matlab and linear variable angle functions, a linear variable angle filament placement trajectory is written and converted to an overall coordinate form. A text file of the path point coordinates that the filament placement machine can recognize is generated. A small filament width (3.175mm) and ultra-thin prepreg (0.05mm) are selected, and its barrel is installed on the AFP placement head. The mold is cleaned and PTFE / Glass release cloth is pasted on. A variable stiffness biomimetic spiral laminate is prepared according to the layup design.

[0065] Fiber Laying: By precisely controlling the laying head, fibers are automatically laid onto the substrate surface at a predetermined angle and sequence to form a composite material layup structure.

[0066] Layering and compaction: During the laying process, fibers are stacked layer by layer, and a certain pressure is applied to ensure that each layer of fibers is tightly bonded together, avoiding air bubbles and uneven laying.

[0067] Hot-press curing: After the laying is completed, the laid material is wrapped in a vacuum bag and vacuumed to maintain a vacuum state. It is then transferred to a hot-press can and cured according to the curing procedure to harden the resin and combine it with the fiber, thus completing the preparation of the variable stiffness biomimetic spiral composite laminate.

[0068] The automatic yarn laying machine executes a program based on the layering of the laminate. Each layer is controlled by program parameters, including parameters such as rotation angle, curvature control, gap between each group of yarns, and edge coverage.

[0069] The curing requirements are as follows: Figure 3 As shown, the shelf is heated from room temperature to 120°C at a heating rate of 1-2°C / min, kept at 120°C for 90 minutes, and then naturally cooled to below 60°C before demolding.

[0070] The present invention will be further described in detail below with reference to specific embodiments, taking the preparation of biomimetic symmetrical spiral layered composite materials from unidirectional carbon fiber prepreg as an example.

[0071] Example item: In addition, [0 / 5 / 10 / … / 85 / 90 / 85]s, [0 / 45 / 90 / -45]5s are used for comparison. The superposed wave of the upper layer is a variable stiffness layer, and s represents a symmetrical layer.

[0072] (1) The total number of composite laminate layers is preliminarily determined to be 40 layers, the single layer thickness is 0.05 mm, the starting angle is -10°, the ending angle is 10°, and the laminate is 150*100 mm; wherein Figure 1 is a structural schematic diagram of a variable stiffness curve spiral layer provided by the application.

[0073] (2) The above example is tested by low-speed impact test in the manner of experiment and numerical simulation verification. As shown in Figure 4 , when the rotation angle is 5°, the impact peak load of the variable stiffness spiral layer laminate is increased by 9.33% compared with the straight line, and the displacement corresponding to the peak load is increased by 0.51 mm; when the rotation angle is increased to 45°, the impact peak load of the variable stiffness spiral layer laminate is increased by 26.55% compared with the straight line, and the displacement corresponding to the peak load is increased by 1.5 mm; as shown in Figure 5 , with the increase of the rotation angle, the stiffness (the slope of the straight line segment of the force-displacement curve) of the spiral layer composite laminate shows an upward trend.

[0074] (3) Impact toughening mechanism: the matrix crack induced by the impact load in a single layer is usually perpendicular to the fiber direction or along the fiber / matrix interface, at this time, a high stress concentration area will be generated at the crack tip, these stress concentrations may directly drive the debonding of the interlayer interface near the crack tip, and induce delamination. And change the local stiffness of the material around the crack, causing the interlaminar shear stress to increase significantly at the interlayer interface, thus becoming the main driving force for inducing delamination. At this time, the matrix crack is "captured" by the delamination interface, and the crack path is deflected, as shown in Figure 6 , along the delamination interface and turns into a delamination crack. For the curved fiber path, the matrix crack is difficult to penetrate the interface in a straight line to induce delamination, and the delamination crack is also difficult to expand along the straight line interface quickly. After being deflected, it may enter the layer or encounter a more tough area, the matrix crack will interact through the interlayer stress, and finally cause the area between these cracks to delaminate, thereby connecting the isolated matrix cracks and delamination, forming a larger and more complex damage area. In addition, the curved fiber path causes the local fiber direction and the principal stress direction to change constantly. When the crack expands to the area where the fiber angle changes, its tip will encounter varying material anisotropy, and the crack tends to deviate from its original straight expansion path and be forced to turn to a direction with lower energy release rate (usually parallel to the local fiber direction or along a new weak interface).

[0075] The embodiment can effectively solve the problems of the composite material in impact resistance, interlaminar toughness and stress distribution optimization. Specifically, the variable stiffness laminated plate changes the in-plane stiffness of the laminated plate, so that the uneven impact force load on the laminated plate plane can be well distributed along the pre-impregnated material curve laying track, thereby improving the carrying capacity and impact resistance of the structure. At the same time, the bionic spiral structure significantly improves the impact resistance and interlaminar toughness of the composite material by imitating the spiral arrangement of the biological exoskeleton in nature, effectively disperses the impact stress, and reduces the risk of interlaminar peeling and crack propagation. In addition, the variable angle laminated plate realizes the continuous change of stiffness through the curve laying of fibers, further optimizes the stress distribution, and enhances the overall mechanical properties of the structure. The present application combines the bionic spiral structure with the fiber angle variable stiffness design to provide an efficient and reliable solution for the innovative design and application of composite materials.

[0076] The technical means disclosed in the present application scheme is not limited to the technical means disclosed in the above-mentioned embodiments, but also includes the technical solutions composed of any combination of the above technical features.

Claims

1. A variable stiffness curve helical impact resistant composite layup configuration, characterized by: The angle of the spiral is increased by θ for each layer starting from 0° for the first layer, according to The plies are stacked into a symmetric spiral variable stiffness laminate, where the plies with the superscript wavy line are the variable stiffness plies.

2. A variable stiffness curved spiral impact-resistant composite automatic placement forming method, characterized by: Specifically comprising the following steps: S1: defining a curved spiral biomimetic microstructure design, including in-plane and thickness direction design; S2: Determine the number of plies N of the laminate, design the in-plane curved fiber path and the thickness direction helical stacking sequence to form a symmetric variable stiffness curved spiral ply configuration with the angle deviation between adjacent plies controlled within 5°±2°; start from 0° ply and increment the helix angle θ layer by layer, according to The plies are stacked into a helical variable stiffness laminate, where the superscript wavy line indicates the variable stiffness ply and the subscript s indicates the symmetric ply; S3: according to the determined starting angle T0, the termination angle T1, the length of the laminate d and the number of plies N, the variable stiffness biomimetic spiral laminate modeling script is written through Python to complete the rapid modeling of the variable stiffness laminate, wherein the fiber path follows a linear variable angle equation, the expression of which is: In the formula: T0 is the starting angle of the fiber curve, T1 is the termination angle of the curve, d is the length of the laminate; S4: preparing the variable stiffness biomimetic spiral laminate through automatic fiber placement (AFP) technology and autoclave forming, the autoclave curing process is: heating to 120℃ at 1-2℃ / min, holding for 90 minutes, and then naturally cooling to below 60℃ for demolding; S5: after demolding, the spiral laminated composite laminate is processed by water cutting, the 150mm×100mm standard sample is cut according to ASTM D7136 standard, and the low-speed impact performance test is carried out to evaluate the impact resistance; S6: importing the generated model file into Abaqus to obtain the macroscopic mechanical response and damage characteristics of the laminate under a specific low-speed impact energy.

3. A variable stiffness curve helical impact resistant composite material automated placement forming method according to claim 2, characterized in that: In S1, (1) in the in-plane direction, each single layer adopts a non-linear, continuously changing curved fiber trajectory, realizing continuous and controllable gradient distribution of in-plane stiffness; (2) in the thickness direction, adjacent plies are stacked in sequence according to a specific spiral angle, forming a spiral configuration throughout the thickness.

4. A variable stiffness curve helical impact resistant composite material automated placement forming method according to claim 3, characterized in that: The in-plane curved fiber path is realized through AFP technology, the filament width of the fiber prepreg is 3.175mm, the single layer thickness of the prepreg is 0.05mm, and the fiber path curvature satisfies the manufacturing constraint condition.

5. A variable stiffness curve helical impact resistant composite material automated placement forming method according to claim 3, characterized in that: The spiral stacking sequence in the thickness direction is symmetrical plies, and the interlayer angle transition is uniform.

6. A variable stiffness curve helical impact resistant composite material automated placement forming method according to claim 3, characterized in that: The in-plane curved fiber path is realized through AFP technology, which includes: (a) calculating the fiber laying path and angle through Python program; (b) controlling the laying head to lay the fiber according to the designed path, ensuring that the interlayer bonding is tight and there is no bubble; (c) each layer of plies includes rotation angle, curvature limit and edge coverage.

7. A variable stiffness curve helical impact resistant composite material automated placement forming method according to claim 3, characterized in that: In the autoclave curing process in S4, the laminate needs to be vacuum bagged and vacuumed before being transferred to the autoclave for curing.

8. A variable stiffness curve helical impact resistant composite material automated placement forming method according to claim 3, characterized in that: The variable stiffness biomimetic spiral laminate modeling script generation program includes the following steps: (1) determine the structure size, mesh size, divide the mesh elements, and determine the nodes; (2) calculate the coordinates of each node and element; (3) determine the spiral angle θ; (4) calculate the center coordinates of the elements after spiraling; (5) substitute the center coordinates into the function of the fiber angle on the reference fiber path to calculate the angle of the element plies; (6) write the above information into the inp file.

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