A bionic gradient spiral structure composite laminate and its design and preparation method

Abstract

The present invention discloses a bionic gradient spiral structure composite laminate and a design and preparation method, belonging to the technical field of composite materials. The composite laminate of the present invention comprises a plurality of fiber spiral units coaxially stacked along the thickness direction; the fiber spiral units are stacked layer by layer through carbon fiber prepreg, and each laid fiber layer is rotated by the same angle compared with the fiber direction of the previous layer, and finally a cumulative rotation of 180° is a unit cycle; different fiber spiral units have different rotation angles. The present invention adjusts the out-of-plane impact damage characteristics and damage distribution of the composite laminate through the synergistic effect of fiber spiral units with different rotation angles, thereby improving the out-of-plane impact resistance of the composite laminate.

Description

Technical Field

[0001] The invention belongs to the technical field of composite materials, and in particular relates to a bionic gradient spiral structure composite material laminate and a design and preparation method thereof. Background Art

[0002] With the widespread application of composite laminates in various fields, they will inevitably be subjected to external impact loads during actual service, and improving their impact resistance is an urgent problem to be solved. At present, the main technical methods to improve the impact resistance of laminates include suture, three-dimensional weaving and Z-pin implantation, but these technologies will cause the reduction of the in-plane performance of the laminates, and also increase the difficulty of the operability of the preparation process. For fiber-reinforced composite materials, the ply design directly affects the stress distribution and damage characteristics inside the composite material, and the different mechanical properties presented provide a broad space for the design of composite laminates.

[0003] With the rapid development of modern bionics, bionics and materials science have been combined, infiltrated and influenced to design a large number of new composite materials, which has become an important part of the research and development of modern scientific research. Among them, the peacock mantis shrimp has attracted much attention due to its excellent impact resistance. There is a typical structural feature of spiral stacking of chitin fiber sheets inside the appendage phalanx. A large number of fiber spiral units are continuously gathered to form a periodic area, and the pitch of these fiber spiral units is not equidistant, but shows a gradient decrease from the outer layer of the organism to the inner side. This is a biological structure optimization design strategy to cope with the situation where the biological structure is in different stress states due to external dynamic loads, and plays an important role in dissipating energy and delaying the complete failure of the structure. Inspired by it, the optimization design of bionic impact-resistant structures can start from the positioning and adjustment of local ply design, and by introducing fiber spiral units with different rotation angles in the local area of ​​the laminate, the impact damage behavior of the local structure is regulated to achieve the improvement of the global performance of the composite laminate. Therefore, this bionic gradient spiral structure composite material can reduce the difficulty of the preparation process without affecting the in-plane mechanical properties of the composite material, and improve the impact resistance of the composite laminate by regulating the impact response of the local area of ​​the composite laminate. This is of great significance to the development of carbon fiber composite materials in engineering fields such as aerospace. Summary of the invention

[0004] The purpose of the present invention is to solve the complexity of the existing technology for improving the impact resistance of composite laminates. From the perspective of bionics, a bionic gradient spiral structure composite laminate and a design and preparation method are provided to improve the impact resistance of composite laminates through a simple method of layer design.

[0005] The specific technical solutions adopted by the present invention are as follows:

[0006] In the first aspect, the present invention provides a bionic gradient spiral structure composite laminate, which comprises a plurality of fiber spiral units coaxially stacked along the vertical (i.e. thickness) direction; the fiber spiral units are stacked layer by layer through carbon fiber prepreg, and each laid fiber layer is rotated by the same angle compared with the fiber direction of the previous layer, and finally a cumulative rotation of 180° is a unit period; different fiber spiral units have different rotation angles.

[0007] In a second aspect, the present invention provides a design method for a bionic gradient spiral structure composite laminate, which is as follows:

[0008] S1: Determine the total number of plies N of the laminate;

[0009] S2: According to the determined total number of layers N, set the rotation angle θ to be selected i Parameters, a single fiber layer is stacked layer by layer starting from 0°, and each fiber is laid with an angle θ compared to the fiber direction of the previous layer i , and finally according to the ply order [0 / θ i / 2θ i / 3θ i ...180] ns The composite laminate is stacked into a symmetrical spiral structure, wherein the subscript n represents the number of fiber spiral units and the subscript s represents the symmetrical ply;

[0010] S3: For each linearly increasing rotation angle θ to be selected i , for the rotation angle θ i The impact load F when the initial shear crack forms in the impact contact area is theoretically derived for the symmetrical spiral structure composite laminate stacked together. s ;

[0011] S4: For each linearly increasing rotation angle θ to be selected i , for the rotation angle θ i The normalized energy release rate G of the matrix crack tip on the back of the laminate is derived based on the linear elastic fracture mechanics model theory for the spiral structure composite laminate stacked up.

[0012] S5: For each linearly increasing rotation angle θ i The spiral structure composite material laminated plate is stacked and formed, and the impact load F when the shear crack is formed in the impact area is determined according to step S3. s , select F sA relatively large rotation angle is used as the preferred impact side of the bionic gradient helical structure composite laminate, and at the same time, the energy release rate G of the crack tip on the back of the helical structure composite laminate is determined according to step S4, and a rotation angle that makes G relatively small is selected as the preferred back side of the gradient helical structure composite laminate;

[0013] S6: According to step S5, a plurality of fiber spiral units with different rotation angles selected from the local area are stacked and combined to form a gradient spiral structure composite laminate.

[0014] Preferably, the linearly increasing rotation angle θ i Satisfy 0°<θ i <90° and can be divided by 180°, ensuring that the symmetrical spiral structure composite laminate has 2n complete fiber spiral units.

[0015] Preferably, the material of the bionic gradient helical structure composite laminate is a carbon fiber composite material or a glass fiber composite material.

[0016] Preferably, in step S3, the impact load F s Expressed as

[0017]

[0018] Where R is the radius of the impactor, E'1 is the modulus of the impactor; E'2 is the effective modulus in the out-of-plane direction of the spiral structure composite laminate, which is related to the selected rotation angle θ i is related; h is the thickness of the helical composite laminate and τ is the shear strength of the helical composite laminate, which depends on the properties of the composite matrix.

[0019] Preferably, in step S4, the normalized energy release rate G is expressed as

[0020]

[0021] In the above formula, φ is the relative torsion angle between the crack tip and the initial crack tip, α * is the effective inclination angle of the crack surface, where X represents the change value of the initial crack tip along the crack propagation direction, Y represents the change value of the initial crack tip along the fiber direction, d represents the single layer thickness of the spiral structure composite laminate, and υ represents the Poisson's ratio of the spiral structure composite laminate.

[0022] In a third aspect, the present invention provides a method for preparing a bionic gradient spiral structure composite laminate, which is as follows:

[0023] S1: According to the design requirements, the carbon fiber prepreg is cut by a CNC cutting machine to obtain a large number of fiber sheets with the fiber directions arranged at specific angles;

[0024] S2: Laying the fiber sheets layer by layer on a flat mold according to the optimized laying sequence, wherein vacuuming and pre-compacting are performed every time 4 fiber sheets are laid;

[0025] S3: performing high temperature and high pressure molding of the prepregs stacked according to step S2 according to a hot-press molding process, and finally taking the finished product out of the mold to obtain a bionic gradient spiral structure composite laminate.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. The embodiment of the present invention is based on the structural feature of spirally stacked chitin fiber sheets inside organisms, draws on the design strategy of biological gradient structure, integrates it with the ply design of carbon fiber composite laminates, and optimizes the design according to the requirements of lightweight and high-strength structural materials in existing engineering technology, and provides a ply design method to improve the out-of-plane impact resistance of composite laminates;

[0028] 2. The embodiments of the present invention solve the complex operability of the current technology for improving the out-of-plane impact resistance of composite laminates, and the present invention does not reduce the in-plane mechanical properties on the basis of improving the out-of-plane mechanical properties of composite laminates. The bionic gradient spiral ply design method provides new design ideas and technical support for the research and application of new impact-resistant composite materials.

[0029] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the following is a detailed description with specific embodiments and accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The basis provided by the embodiment of the present invention is θ i Schematic diagram of the structure of a stacked symmetrical laminate: (a) θ i =9°; (b)θ i =18°; (c)θ i =36°; (d)θ i =45°;

[0031] Figure 2 is the theoretical impact load when the initial shear crack appears on the impact side of the composite laminate that can be obtained by the present invention;

[0032] Figure 3 is the normalized energy release rate of the back bending crack tip of the composite laminate that can be obtained by the present invention;

[0033] Figure 4A schematic diagram of the structure of a bionic gradient spiral structure composite laminate designed in an embodiment of the present invention;

[0034] Figure 5 The experimental verification results under 10J impact energy are provided in the embodiments of the present invention: (a) impact load-displacement curve; (b) impact energy-time curve. DETAILED DESCRIPTION

[0035] The present invention is further described and illustrated below in conjunction with the accompanying drawings and specific embodiments. The technical features of each embodiment of the present invention can be combined accordingly without conflicting with each other.

[0036] The present invention provides a bionic gradient spiral structure composite laminate and design and preparation method. The method is inspired by the impact-resistant structural characteristics of the inner part of the phalanges of the mantis shrimp. By combining multiple fiber spiral units with different rotation angles, the different impact responses of the impact side and back side of the composite laminate are responded to, and the formation of initial impact damage in each local area is delayed. On the one hand, the gradient spiral ply design method can avoid the limitations of complex manufacturing process operations and additional in-plane performance damage during the manufacturing process; on the other hand, it can effectively regulate the initial impact damage of the composite laminate and improve the impact resistance of the laminate.

[0037] The bionic gradient spiral structure composite laminate of the present invention comprises a plurality of fiber spiral units coaxially stacked in the vertical (thickness) direction. Each fiber spiral unit is stacked layer by layer through carbon fiber prepreg, and each laid fiber layer is rotated by the same angle compared with the fiber direction of the previous layer, and finally a cumulative rotation of 180° is a unit cycle; and different fiber spiral units have different rotation angles.

[0038] In actual use, facing impact load conditions, the bionic gradient spiral structure composite laminate of the present invention is in different stress distribution states along the thickness direction. The impact side causes shear cracks to form due to the local existence of higher shear stress, which then evolves into lamination damage. The back side causes bending cracks to form due to the existence of higher bending tensile stress, and torsional expansion occurs under the induction of the spiral arrangement of fibers. The evolution of these initial damages significantly affects the impact response of the structure.

[0039] Based on the above loading conditions, the present invention provides a design method for a bionic gradient spiral structure composite laminate, which is as follows:

[0040] S1: Determine the total number of plies N of the composite laminate based on the mechanical properties and performance requirements of the laminate structure.

[0041] In practical application, according to the present invention, the above method of preliminarily determining the total number of plies according to the mechanical properties and performance requirements of the composite laminate structure is not particularly limited and is based on methods well known in the art.

[0042] S2: According to the determined total number of layers N, set the rotation angle θ to be selected i Parameters, a single fiber layer is stacked layer by layer starting from 0°, and each fiber is laid with an angle θ compared to the fiber direction of the previous layer i , and finally according to the ply order [0 / θ i / 2θ i / 3θ i ...180] ns A symmetrical spiral structure composite laminate is stacked together; the subscript n represents the number of fiber spiral units, and the subscript s represents symmetrical plies.

[0043] In actual use, according to the present invention, the rotation angle θ is set i Should satisfy 0°<θ i <90° and divisible by 180°, ensuring that the laminate has 2n complete fiber spiral units.

[0044] S3: For each linearly increasing rotation angle θ to be selected i For laminated plates, an analysis method based on classical laminate theory is required to predict the impact load F when the initial shear crack on the impact side of the laminate is formed. s The classical laminate theory used in the present invention is a method well known in the art and will not be described in detail. s The theoretical calculation formula is:

[0045]

[0046] Where R is the radius of the impactor, E'1 is the modulus of the impactor, and E'2 is the effective modulus in the out-of-plane direction of the laminate (with respect to the selected rotation angle θ i related), h is the thickness of the laminate, and τ is the shear strength of the composite laminate, which depends on the properties of the composite matrix.

[0047] S4: For each linearly increasing rotation angle θ to be selected i The laminated plate is easy to have initial bending cracks on the back under the same impact load because the bottom layer is all 0° fiber layer, and then it is affected by the fiber rotation angle θ i Therefore, it is necessary to use the linear elastic fracture mechanics model to theoretically derive the normalized energy release rate at the back bending crack tip to characterize the different rotation angles θ. i The ability to resist bending crack torsion, the specific theoretical calculation formula is:

[0048]

[0049] In the above formula, φ is the relative torsion angle between the crack tip and the initial crack tip, α * is the effective inclination angle of the crack surface, where X represents the change value of the initial crack tip along the crack propagation direction, Y represents the change value of the initial crack tip along the fiber direction, d represents the single layer thickness of the spiral structure composite laminate, and υ represents the Poisson's ratio of the spiral structure composite laminate.

[0050] S5: For each linearly increasing rotation angle θ i The spiral structure composite material laminated plate is stacked and formed, and the impact load F when the shear crack is formed in the impact area is determined according to step S3. s , select F s A relatively large rotation angle is used as the preferred impact side of the bionic gradient helical structure composite laminate, and at the same time, the energy release rate G of the crack tip on the back of the helical structure composite laminate is determined according to step S4, and a rotation angle that makes G relatively small is selected as the preferred back side of the gradient helical structure composite laminate;

[0051] S6: According to step S5, a plurality of fiber spiral units with different rotation angles selected from the local area are stacked and combined to form a gradient spiral structure composite laminate.

[0052] According to the present invention, the spiral ply design method of bionic composite laminate is not limited to the unified design of total ply number and thickness, and the appropriate total ply number and thickness can be selected according to actual needs.

[0053] According to the present invention, the composite material laminate is not particularly limited, and is preferably a carbon fiber composite material or a glass fiber composite material.

[0054] The present invention will be further described in detail below in conjunction with specific implementation examples, taking the design of unidirectional carbon fiber prepreg and the preparation of a bionic gradient spiral structure composite laminate as an example to illustrate the present invention.

[0055] Example

[0056] This embodiment provides a bionic composite material spiral ply design method, the method steps are as follows:

[0057] (1) The total number of plies N is preliminarily determined to be 42, and the selected carbon fiber prepreg is USN 15000 / EPW from Guangwei Composites, and the thickness of the single layer after curing is 0.141 mm;

[0058] (2) Setting θ i There are 4 parameters to be selected, namely θ i=9°, 18°, 36°, 45°, and according to [0 / θ i / 2θ i / 3θ i ...180 n ] s The plies were stacked sequentially to prepare four kinds of composite laminates with symmetrical spiral plies. Figure 1 This is the basis provided by the embodiment of the present invention. i Schematic diagram of the structure of stacked symmetrical laminates;

[0059] (3) From a theoretical analysis perspective, the impact load when the initial shear crack appears on the impact side of the composite laminate is predicted to evaluate the rotation angle θ i Resistance to shear cracking; also predicts the energy release rate at the bending crack tip on the back side of the laminate, as a function of the rotation angle θ i Resistance to torsional propagation of bending cracks:

[0060] 1. For the four selected linearly increasing rotation angles θ i For laminated plates, the impact load F that causes the initial shear crack on the impact side of the laminate can be calculated using Formula I. s ,like Figure 2 shown.

[0061] 2. For the four selected linearly increasing rotation angles θ i For laminated plates, the normalized energy release rate G at the bending crack tip on the back side of the laminate can be calculated using formula Ⅱ, as follows: Figure 3 shown.

[0062] 3. From Figure 2 It can be seen that the impact load F at which the initial shear crack appears on the impact side of the laminate is s It decreases with the increase of the rotation angle, indicating that the fiber spiral unit with a relatively small rotation angle is suitable for being placed on the impact side of the laminate to delay the formation of shear crack damage; Figure 3 It can be seen that with the increase of the rotation angle, the energy release rate at the crack tip gradually decreases, and the ability of the back side of the laminate to resist the torsional expansion of the bending crack increases accordingly, indicating that the fiber spiral unit with a large rotation angle is suitable for being placed on the back side of the laminate to alleviate the violent propagation of the bending crack.

[0063] (4) According to the theoretical analysis results, the rotation angle θ to be selected i The composite laminate GH (45-36-18-9) with a total of 42 layers was designed and prepared. Figure 4As shown, specifically, the impact side of the upper part is a 9° fiber spiral unit, and the lower part is arranged in sequence with an 18° fiber spiral unit, a 36° fiber spiral unit and a 45° fiber spiral unit.

[0064] (5) The composite laminate is subjected to a drop weight low-speed impact test to verify that: Figure 5 a shows that under a low-energy impact of 10J, the designed bionic gradient spiral structure composite material has the highest impact load, significantly delays the formation of initial damage, and the energy dissipation is between the symmetrical spiral laminates, combining the impact response characteristics of spiral units with different fiber rotation angles.

[0065] In this embodiment, the ply period can be reasonably adjusted according to the ply rotation angle and the single-layer thickness of the fiber sheet.

[0066] The present invention adjusts the out-of-plane impact damage characteristics and damage distribution of the composite laminate through the synergistic effect of fiber spiral units with different rotation angles, thereby improving the out-of-plane impact resistance of the composite laminate.

[0067] The above-described embodiment is only a preferred solution of the present invention, but it is not intended to limit the present invention. A person skilled in the relevant technical field may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, any technical solution obtained by equivalent replacement or equivalent transformation falls within the protection scope of the present invention.

Claims

1. A design method for a bionic gradient spiral structure composite laminate, characterized in that: The details are as follows: S1: Determine the total number of plies N of the laminate; S2: According to the determined total number of layers N, set the rotation angle θ to be selected i Parameters, a single fiber layer is stacked layer by layer starting from 0°, and each fiber is laid with an angle θ compared to the fiber direction of the previous layer i , and finally according to the ply order [0 / θ i / 2θ i / 3θ i ...180] ns The composite laminate is stacked into a symmetrical spiral structure, wherein the subscript n represents the number of fiber spiral units and the subscript s represents the symmetrical ply; S3: For each linearly increasing rotation angle θ to be selected i , for the rotation angle θ i The impact load F when the initial shear crack forms in the impact contact area is theoretically derived for the symmetrical spiral structure composite laminate stacked together. s ; S4: For each linearly increasing rotation angle θ to be selected i , for the rotation angle θ i The normalized energy release rate G of the matrix crack tip on the back of the laminate is derived based on the linear elastic fracture mechanics model theory for the spiral structure composite laminate stacked up. S5: For each linearly increasing rotation angle θ i The spiral structure composite material laminated plate is stacked and formed, and the impact load F when the shear crack is formed in the impact area is determined according to step S3. s , select F s A relatively large rotation angle is used as the preferred impact side of the bionic gradient helical structure composite laminate, and at the same time, the normalized energy release rate G of the crack tip on the back of the helical structure composite laminate is determined according to step S4, and a rotation angle that makes G relatively small is selected as the preferred back side of the gradient helical structure composite laminate; S6: According to step S5, a plurality of fiber spiral units with different rotation angles selected from the local area are stacked and combined to form a gradient spiral structure composite laminate.

2. The design method according to claim 1, characterized in that: The linearly increasing rotation angle θ i Satisfy 0°<θ i <90° and can be divided by 180°, ensuring that the symmetrical spiral structure composite laminate has 2n complete fiber spiral units.

3. The design method according to claim 1, characterized in that: The material of the bionic gradient spiral structure composite material laminate is a carbon fiber composite material or a glass fiber composite material.

4. The design method according to claim 1, characterized in that: In step S3, the impact load F s Expressed as Where R is the radius of the impactor, E1' is the modulus of the impactor; E'2 is the effective modulus in the out-of-plane direction of the spiral structure composite laminate, which is related to the selected rotation angle θ i is related; h is the thickness of the helical composite laminate and τ is the shear strength of the helical composite laminate, which depends on the properties of the composite matrix.

5. The design method according to claim 1, characterized in that: In step S4, the normalized energy release rate G is expressed as In the above formula, φ is the relative torsion angle between the crack tip and the initial crack tip, α * is the effective inclination angle of the crack surface, where X represents the change value of the initial crack tip along the crack propagation direction, Y represents the change value of the initial crack tip along the fiber direction, d represents the single layer thickness of the spiral structure composite laminate, and υ represents the Poisson's ratio of the spiral structure composite laminate.

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