A walnut cross-section based negative poisson's ratio lattice structure and a regulation method thereof

Abstract

The application discloses a kind of based on walnut cross section biomimetic negative poisson's ratio lattice structure and its regulation method, structure includes multiple periodic arrangement lattice unit, lattice unit includes acute angle structure, two similar triangle kernels, and by specific ellipse equation and geometric parameter (,,,,,,, ) constraint its form.Opposite to prior art, by adjusting geometric parameter to change the length and included angle of each section of acute angle structure, the optimization of equivalent negative poisson's ratio, platform stress and energy absorption efficiency of structure is realized;The structure has the characteristics of lightweight, high energy absorption and controllable deformation, and is suitable for collision protection in the fields of spacecraft, sports equipment, precision instrument packaging, etc.

Description

Technical Field

[0001] This invention relates to the field of mechanical metamaterials technology, specifically to a negative Poisson's ratio lattice structure based on the biomimetic cross-section of a walnut and its control method. Background Technology

[0002] In fields such as transportation, precision instrument packaging, and special protective equipment, structural materials often need to simultaneously achieve lightweight load-bearing capacity, high energy absorption, and controllable deformation. Currently, structures meeting these requirements are mainly divided into three categories: Porous lattice structures: such as face-centered cubic, body-centered cubic, and their derivative configurations, relying on high porosity to achieve lightweight and basic energy absorption, suitable for conventional static or low-load conditions, but lacking in fatigue resistance and damage tolerance, and prone to stress concentration and weak instability resistance. Negative Poisson's ratio structures: including honeycomb, star, and hinge types, possessing excellent impact resistance, deformation coordination, and high theoretical specific energy absorption due to the "tensile effect," but traditional structures often have poor load-bearing capacity and are difficult to use alone in heavy-load conditions. Biomimetic fusion structures: such as honeycomb-like and bamboo-like composite structures, although capable of handling complex conditions, still have room for improvement in the precision of structural topology and the synergy of mechanical response. With the maturity of 3D printing technology, the fabrication of complex configurations has become possible. However, effectively integrating the high porosity advantage of lattice structures with the expansion effect of negative Poisson's ratio structures to overcome the performance limitations of single structures remains a pressing technical challenge in this field. Therefore, a novel negative Poisson's ratio lattice structure and its control method are urgently needed to address these technical problems. Summary of the Invention

[0003] Purpose of the invention: The present invention aims to overcome the above-mentioned defects and provide a negative Poisson's ratio lattice structure based on the biomimetic cross section of a walnut and its control method, so as to solve the technical problems of weak anti-instability ability of existing lattice structures, insufficient load-bearing capacity of traditional negative Poisson's ratio structures, and poor synergy of existing biomimetic structures.

[0004] Technical Solution: To achieve the above objectives, the present invention provides a negative Poisson's ratio lattice structure based on a walnut cross-section, comprising multiple periodically arranged lattice unit cells. Each lattice unit cell cross-section includes multiple acute-angled structures radially and uniformly distributed around a central axis, and two triangular-like nuclei symmetrically arranged vertically along the central axis. Each triangular-like nuclei includes a first line segment, a second line segment that does not intersect the first line segment, and a base connecting the lower endpoints of the first and second line segments. An opening is provided between the upper endpoints of the first and second line segments, and the first and second line segments form acute angles with and from the base. The two triangular-like nuclei within the same lattice unit cell are planar symmetrical about the vertical central axis, and each triangular-like nuclei has its own axis of symmetry perpendicular to the central axis. The multiple acute-angled structures are rotationally symmetrical about the central axis. Each acute-angled structure includes a main body segment, a branch segment, and a connecting segment connected sequentially. Two triangular-like nuclei are connected by multiple acute-angled structures.

[0005] Furthermore, there are ten acute-angle structures, with five on the left and five on the right, perpendicular to the central axis; one end of the main body segment is connected to a triangular core or an adjacent acute-angle structure, the other end of the main body segment is connected to one end of the bifurcation segment, the other end of the bifurcation segment is connected to one end of the connecting segment, and the other end of the connecting segment is connected to a triangular core or an adjacent acute-angle structure; the connection point between the main body segment and the bifurcation segment is a bifurcation node.

[0006] Furthermore, adjacent lattice units are connected in the vertical direction through extreme points k3 or k8; adjacent lattice units are interlocked or overlapped in the horizontal direction through connecting segments.

[0007] Furthermore, the lattice unit cell (1) has 10 extreme points (k1~k... 10 ); including eight extreme points (k1, k2, k4, k5, k6, k7, k9, k 10 ) are the vertices of eight acute-angle structures (2), and the eight extreme points (k1, k2, k4, k5, k6, k7, k9, k) are the vertices of these structures. 10 Located on the same ellipse, the other two extreme points k3 and k8 are the midpoints of the intersection points of the ellipse formed by the ellipse and the outer periphery of the adjacent lattice unit cell (1) and the... The intersection of the axes, and simultaneously the endpoints of the bifurcation segment (5) and the connecting segment (6).

[0008] Furthermore, the three elliptical circumferences formed by the outer periphery of the three adjacent lattice unit cells (1) are designated as the first ellipse, the second ellipse, and the third ellipse. Two of the three lattice unit cells (1) are adjacent to each other in the horizontal direction, and the third is above the two lattice unit cells (1). The cross-section of the three lattice unit cells (1) as a whole is circumferentially symmetrical. The equations of the three elliptical circumferences are as follows: First ellipse: Second ellipse: The third ellipse: ;in, It is the semi-major axis of the ellipse. It is the minor semi-axis of the ellipse. , , Let be the offset parameter of the ellipse center, and satisfy the geometric compatibility constraints: Furthermore, the lattice unit cell has a first group of internal nodes (P1, P4, P5, P8), which are acute-angled bifurcated nodes, and all are located at extreme points (k1~k...). 10 P1 lies on the angle bisector of the triangle formed by extreme points k1, k2 and B2; P4 lies on the angle bisector of the triangle formed by extreme points k5, k4 and B3; P5 lies on the angle bisector of the triangle formed by extreme points k6, k7 and B6; P8 lies on the angle bisector of the triangle formed by extreme points k9, k2, k3, B6 and B7. 10 On the angle bisector of the triangle formed by B7 and B7.

[0009] Furthermore, the lattice unit cell has a second set of internal nodes (P2, P3, P6, P7), which are also acute-angled bifurcated nodes. P2 is located on the line connecting B2 and k3, and satisfies... P3 lies on the line connecting B3 and k3, and satisfies... P6 lies on the line connecting B6 and k8, and satisfies... P7 lies on the line connecting B7 and k8, and satisfies... .

[0010] Furthermore, the contour of the triangular kernel is defined by eight specific internal nodes (B1, B2, B3, B4, B5, B6, B7, B8); wherein the absolute values ​​of the x-coordinates of the specific internal nodes B1, B4, B5, and B8 are less than the extreme points k1, k5, k6, and k7, respectively. 10 The absolute value of the x-coordinate; the absolute value of the x-coordinate of specific internal nodes B2, B3, B6, and B7. The absolute value of the ordinate is Furthermore, the triangles formed by B2, B3, and the origin, as well as the triangles formed by B6, B7, and the origin, are all isosceles triangles with base angles of . ,and .

[0011] Furthermore, the thickness of the rod in the acute-angled structure is And satisfy the following geometric constraints: ,and .

[0012] A method for controlling a negative Poisson's ratio lattice structure based on walnut cross-section biomimicry includes the following steps:

[0013] S1 sets the ellipse parameter set ( , , , ) and triangular kernel parameter set ( , , , );

[0014] S2 is based on the parameter set in S1 ( , , , , , , , Calculate the extreme points (k1~k 10 The coordinates of the lattice unit cell are obtained, and the geometric profile of the lattice unit cell is generated.

[0015] S3 determines the positions of internal nodes (P1~P8) and specific internal nodes (B1~B8) based on the angle bisector and line segment ratio constraints, and defines the geometry of the acute angle structure and the triangular-like core.

[0016] S4 adjusts the parameter set ( , , , , , , , The value of ) is changed to alter the length and angle of each segment of the acute-angled structure, thereby continuously adjusting at least one of the following: the equivalent negative Poisson's ratio, plateau stress, and energy absorption efficiency of the lattice structure during compression.

[0017] Beneficial Effects: Compared with existing technologies, this invention has the following significant advantages: By mimicking the central symmetry and interlocking concave-convex features of a walnut cross-section, it deeply integrates the high porosity of the lattice structure with the tensile effect of the negative Poisson's ratio structure, achieving multi-directional synergistic inward contraction and interlocking deformation, significantly improving energy dissipation efficiency and structural stability. The structural morphology is defined by a complete set of geometric parameters and constraint equations, allowing mechanical properties (such as Poisson's ratio, stiffness, and energy absorption) to be systematically optimized by adjusting a few key parameters, resulting in high design flexibility. Finite element simulation and experimental verification show that under axial compression, the structure exhibits a significant negative Poisson's ratio effect, and the force-displacement curve shows a smooth upward plateau, indicating that it has excellent progressive crushing energy absorption capacity and high specific energy absorption. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the mechanical model of the lattice unit cell structure described in this invention.

[0019] Figure 2 This is a three-dimensional structural diagram of the original lattice unit cell structure described in this invention.

[0020] Figure 3 This is a schematic diagram of the original lattice unit cell truncation described in this invention.

[0021] Figure 4 This is a schematic diagram of the structure of the lattice unit cell described in this invention.

[0022] Figure 5 This is a schematic diagram of the lattice structure described in this invention.

[0023] Figure 6-1 The lattice structure described in this invention, before being subjected to axial compression... Schematic diagram of experimental results and finite element simulation results.

[0024] Figure 6-2 The lattice structure described in this invention, after being subjected to axial compression, i.e. Schematic diagram of experimental results and finite element simulation results.

[0025] Figure 7 This is a comparison diagram of the force-displacement curves of the sample compression test of the present invention. Detailed Implementation

[0026] This invention discloses a negative Poisson's ratio lattice structure based on a walnut cross-section and its control method. Please refer to [reference needed]. Figures 1 to 5 The following is a detailed description of the negative Poisson's ratio lattice structure based on the biomimetic cross-section of a walnut and its control method provided by the present invention: The structure includes multiple periodically arranged lattice unit cells 1, which are assembled through mutual linkage to form a structure as shown below. Figure 5The overall lattice structure is shown. In this specific embodiment, the cross-section of each lattice unit cell 1 includes ten acute-angled structures 2 radially and uniformly distributed around the central axis, and two triangular cores 3 symmetrically arranged vertically along the central axis. Each triangular core 3 includes a first line segment, a second line segment that does not intersect the first line segment, and a base connecting the lower endpoints of the first and second line segments. An opening is provided between the upper endpoints of the first and second line segments, and the first and second line segments form acute angles with each other. The two triangular cores 3 within the same lattice unit cell 1 are planar symmetrical about the vertical central axis, and each triangular core 3 has its own axis of symmetry perpendicular to the central axis. Multiple acute-angled structures 2 are rotationally symmetrical about the central axis, with five on each of the left and right sides perpendicular to the central axis. Each acute-angled structure 2 includes a main body segment 4, a branch segment 5, and a connecting segment 6, forming an overall acute-angled branched rod unit. One end of the main body segment 4 connects to the triangular core 3 or another acute-angled structure 2, and the other end of the main body segment connects to one end of the bifurcation segment 5. The other end of the bifurcation segment 5 connects to one end of the connecting segment 6, and the other end of the connecting segment 6 connects to the triangular core 3 or another acute-angled structure 2. The connection point between the main body segment 4 and the bifurcation segment 5 is a bifurcation node. The bifurcation design is a key geometric feature that induces the negative Poisson's ratio effect in the structure. The connection between adjacent lattice unit cells 1 is achieved through geometric nodes. In the vertical direction, adjacent lattice unit cells are connected through extreme points k3 and k8; in the horizontal direction, adjacent lattice unit cells are interlocked or overlapped through the connecting segment 6, thereby achieving in-plane and out-of-plane linkage and forming a stable periodic structure. Figures 2 to 4 As shown, the solid thickness is formed by stretching the centrally symmetrical reference contour line to both sides at equal offsets, with a thickness range of 0.8 to 2 mm. In the area where the sharp corners of the contour intersect, the overlapping interference boundary of the adjacent structural layers is precisely cut off to eliminate the overlapping area and retain the assembly and mating contour.

[0027] The control method includes the following steps: Step 1: Set the ellipse parameter set ( , , , ) and triangular kernel parameter set ( , , , Step 2: Based on the parameter set in S1 ( , , , , , , , Calculate the extreme points (k1~k 10The first step is to determine the coordinates of the point cell and generate the geometric outline of the lattice unit cell 1; the second step is to determine the positions of the internal nodes (P1~P8) and specific internal nodes (B1~B8) based on the angle bisector and line segment ratio constraints, and define the geometry of the acute-angle structure and the triangular-like kernel; the third step is to adjust the parameter set ( , , , , , , , The value of ) is used to change the length and angle of each segment (main segment, bifurcation segment, and connecting segment) of the acute-angle structure, thereby adjusting the equivalent negative Poisson's ratio, plateau stress, and energy absorption efficiency of the lattice structure. Step four uses a multi-objective genetic algorithm or gradient descent algorithm for automatic optimization; the objective function is defined as maximizing specific energy absorption (SEA) and / or keeping the negative Poisson's ratio constant within a specific strain range; the constraints are defined as geometric compatibility constraints and interference-free constraints; the optimal parameter combination is output, and the corresponding lattice structure CAD model data is generated.

[0028] The core of this invention lies in precisely defining the structural morphology through a set of parameterized geometric constraints. In this specific embodiment, such as... Figure 1 As shown, the geometric profile of lattice unit cell 1 passes through 10 extreme points (k1~k... 10 The definition includes 8 extreme points (k1, k2, k4, k5, k6, k7, k9, k...). 10 ) are the vertices of an eight-acute-angle structure, and these eight extreme points (k1, k2, k4, k5, k6, k7, k9, k) are... 10 The other two extreme points k3 and k8 are located on the same ellipse, and are the midpoints of the intersection points of the ellipse formed by this ellipse and the outer perimeter of the adjacent lattice unit cell 1. The intersection of the axes, and simultaneously the endpoints of the bifurcation segment and the connecting segment. The three elliptical perimeters formed by the outer perimeters of three adjacent lattice unit cells 1 are designated as the first ellipse, the second ellipse, and the third ellipse. Two of these three lattice unit cells 1 are horizontally adjacent, and the third is above the other two lattice unit cells 1. The cross-sections of the three lattice unit cells 1 are circumferentially symmetrical. The equations of the three elliptical perimeters are as follows: First Ellipse : The second ellipse : The third ellipse : Where a is the major semi-axis of the ellipse, and b is the minor semi-axis of the ellipse. ), g and f are the offset parameters of the ellipse center. To ensure structural geometric compatibility, i.e., the upper and lower ellipses have two intersection points, the parameters must satisfy the geometric compatibility constraints: Extreme points (k1~k10 The specific coordinates are as follows:

[0029]

[0030] The lattice unit cell 1 has a first group of internal nodes (P1, P4, P5, P8). The first group of internal nodes are bifurcated nodes of an acute-angle structure, and all of them are located at extreme points (k1~k). 10 P1 lies on the angle bisector of the triangle formed by extreme points k1, k2 and B2; P4 lies on the angle bisector of the triangle formed by extreme points k5, k4 and B3; P5 lies on the angle bisector of the triangle formed by extreme points k6, k7 and B6; P8 lies on the angle bisector of the triangle formed by extreme points k9, k2, k3, B6 and B7. 10 On the angle bisector of the triangle formed by B and B7. The lattice unit cell 1 has a second set of internal nodes (P2, P3, P6, P7). These second set of internal nodes are also bifurcated nodes of an acute-angle structure, and each is located on the line connecting a specific internal node and an extreme point; P2 is located on the line connecting B2 and k3, and satisfies... P3 lies on the line connecting B3 and k3, and satisfies... P6 lies on the line connecting B6 and k8, and satisfies... P7 lies on the line connecting B7 and k8, and satisfies... All internal nodes lie on the angle bisectors of the corresponding triangles, specifically within the following ranges:

[0031]

[0032] The lattice unit cell 1 also has specific internal nodes (B1, B2, B3, B4, B5, B6, B7, B8) that define the contour of the triangular kernel. The specific constraints are as follows: (1) The absolute values ​​of the abscissas of the specific internal nodes B1, B4, B5, B8 are less than the extreme points k1, k5, k6, k7, k8. 10 (1) The absolute value of the x-coordinate; (2) The absolute value of the x-coordinate of specific internal nodes B2, B3, B6, and B7. The absolute value of the ordinate is Furthermore, the triangles formed by B2, B3, and the origin, as well as the triangles formed by B6, B7, and the origin, are all isosceles triangles with base angles of . ,and The triangle formed by it and the origin is the base angle. The coordinates of the isosceles triangle are as follows:

[0033]

[0034] In this specific embodiment, the key geometric parameters of the lattice unit cell are as follows: semi-major axis of the ellipse. ; minor semi-axis of the ellipse Vertical offset parameters ; Element spacing parameter ; Trigonometric nucleus half-height Characteristic length of diagonal bar ; rod thickness The base angle of an isosceles triangle Key interior angle parameters , The overall structural thickness is 1.2 mm. Substituting these parameters into the geometric compatibility constraint formula for verification, the calculated result is as follows: =115136 > 0, satisfying the design requirement that the upper and lower ellipses have two intersection points, and the structure is geometrically compatible. Simultaneously, the node spacing is verified based on Heron's formula, and the verification is also performed. >0 and (20 > 3) Confirm that all geometric assembly relationships are physically feasible and that there is no self-interference between the members.

[0035] In this specific embodiment, the lattice structure is made of aluminum alloy (AlSi10Mg) powder and integrally formed by selective laser melting (SLM) additive manufacturing technology. After forming, the sample is subjected to hot isostatic pressing to eliminate residual stress and sandblasting to obtain a flat surface.

[0036] To verify its mechanical properties, a quasi-static axial compression test was conducted on the printed specimen, and finite element simulation was performed using Abaqus software. Figure 6-1 , 6-2 As shown, under axial compressive load, the lattice structure of this invention exhibits a significant tensile expansion effect. Quasi-static compression test results show that with increasing axial strain, the structural cell arms undergo directional bending and configuration contraction, the sample continuously shrinks in the horizontal direction, and a concave contour is formed around the perimeter, visually demonstrating the negative Poisson's ratio characteristic, providing a mechanical basis for its application in buffering and energy absorption. (Figure...) This represents compressive strain in engineering, defined as the ratio of the change in height of a structure under compressive load to its original height. and A detailed comparison was made between the experimental morphology and the finite element simulation results. The comparison results show that the two methods have similar initial configurations, The simulation results show a high degree of agreement in terms of the overall negative Poisson's ratio contraction deformation mode, ligament buckling location, cell collapse sequence, and deformation symmetry. The simulation can accurately reproduce the actual deformation behavior of the structure, verifying the rationality and accuracy of the finite element modeling method of this invention. Figure 7The figure shows a comparison of force-displacement curves during the compression process of the sample of this invention. The solid line represents the experimental test results, and the dashed line represents the finite element simulation results. This indicates that the overall trends of both are highly consistent, showing a gradual increase with increasing displacement, and the curves exhibit a long, stable compaction stage. This not only verifies the reliability of the finite element model but also proves that the structure possesses excellent energy absorption capacity and a stable deformation mode. Calculations show that the negative Poisson's ratio of this embodiment within a specific strain range is approximately... Its specific energy absorption (SEA) value is superior to that of a traditional concave hexagonal honeycomb structure of the same density.

Claims

1. A negative Poisson's ratio lattice structure based on the biomimetic effect of a walnut cross-section, characterized in that, It includes multiple periodically arranged lattice units (1); the cross-section of each lattice unit (1) includes multiple acute-angled structures (2) radially and uniformly distributed around the central axis, and two triangular nuclei (3) symmetrically arranged vertically along the central axis; each triangular nuclei (3) includes a first line segment, a second line segment that does not intersect with the first line segment, and a base connecting the lower end of the first line segment and the lower end of the second line segment, with an opening between the upper end of the first line segment and the upper end of the second line segment, and the first line segment and the base forming an acute angle, and the second line segment and the base also forming an acute angle; the two triangular nuclei (3) in the same lattice unit (1) are planarly symmetrical about the vertical central axis, and each triangular nuclei (3) has its own axis of symmetry perpendicular to the central axis; the multiple acute-angled structures (2) are rotationally symmetrical about the central axis; each acute-angled structure (2) includes a main body segment (4), a bifurcation segment (5) and a connecting segment (6) connected in sequence; the two triangular nuclei (3) are connected by multiple acute-angled structures (2).

2. The negative Poisson's ratio lattice structure based on walnut cross-section biomimicry according to claim 1, characterized in that, The acute angle structure (2) has ten parts, with five on the left and five on the right side perpendicular to the central axis; one end of the main body segment (4) is connected to the triangular core (3) or the adjacent acute angle structure (2), the other end of the main body segment (4) is connected to one end of the bifurcation segment (5), the other end of the bifurcation segment (5) is connected to one end of the connecting segment (6), and the other end of the connecting segment (6) is connected to the triangular core (3) or the adjacent acute angle structure (2); the connection between the main body segment (4) and the bifurcation segment (5) is a bifurcation node.

3. The negative Poisson's ratio lattice structure based on walnut cross-section biomimicry according to claim 2, characterized in that, Adjacent lattice units (1) are connected in the vertical direction through extreme points k3 or k8; adjacent lattice units (1) are interlocked or overlapped in the horizontal direction through connecting segments (6).

4. The negative Poisson's ratio lattice structure based on walnut cross-section biomimicry according to claim 3, characterized in that, The lattice unit cell (1) has 10 extreme points (k1~k2). 10 ); including eight extreme points (k1, k2, k4, k5, k6, k7, k9, k 10 ) are the vertices of eight acute-angle structures (2), and the eight extreme points (k1, k2, k4, k5, k6, k7, k9, k) are the vertices of these structures. 10 Located on the same ellipse, the other two extreme points k3 and k8 are the midpoints of the intersection points of the ellipse formed by the ellipse and the outer periphery of the adjacent lattice unit cell (1) and the... The intersection of the axes, and simultaneously the endpoints of the bifurcation segment (5) and the connecting segment (6).

5. The negative Poisson's ratio lattice structure based on walnut cross-section biomimicry according to claim 4, characterized in that, The three elliptical circumferences formed by the outer periphery of the three adjacent lattice unit cells (1) are designated as the first ellipse, the second ellipse, and the third ellipse. Two of the three lattice unit cells (1) are adjacent to each other in the horizontal direction, and the third is above the two lattice unit cells (1). The cross-section of the three lattice unit cells (1) is circumferentially symmetrical. The equations of the three elliptical circumferences are as follows: First ellipse: Second ellipse: The third ellipse: ;in, It is the semi-major axis of the ellipse. It is the minor semi-axis of the ellipse. , , Let be the offset parameter of the ellipse center, and satisfy the geometric compatibility constraints: .

6. The negative Poisson's ratio lattice structure based on walnut cross-section biomimicry according to claim 4, characterized in that, The lattice unit cell (1) has a first group of internal nodes (P1, P4, P5, P8), which are the bifurcation nodes of the acute-angle structure (2) and are all located at the extreme points (k1~k). 10 P1 lies on the angle bisector of the triangle formed by extreme points k1, k2 and B2; P4 lies on the angle bisector of the triangle formed by extreme points k5, k4 and B3; P5 lies on the angle bisector of the triangle formed by extreme points k6, k7 and B6; P8 lies on the angle bisector of the triangle formed by extreme points k9, k2, k3, B6 and B7. 10 On the angle bisector of the triangle formed by B7 and B7.

7. The negative Poisson's ratio lattice structure based on walnut cross-section biomimicry according to claim 4, characterized in that, The lattice unit cell (1) has a second set of internal nodes (P2, P3, P6, P7). The second set of internal nodes is also a branch node of the acute angle structure (2). Among them, P2 is located on the line connecting B2 and k3, and satisfies P3 lies on the line connecting B3 and k3, and satisfies... P6 lies on the line connecting B6 and k8, and satisfies... P7 lies on the line connecting B7 and k8, and satisfies... .

8. The negative Poisson's ratio lattice structure based on walnut cross-section biomimicry according to claim 1, characterized in that, The contour of the triangular kernel (3) is defined by eight specific internal nodes (B1, B2, B3, B4, B5, B6, B7, B8); wherein the absolute values ​​of the x-coordinates of the specific internal nodes B1, B4, B5, B8 are less than the extreme points k1, k5, k6, k7, k8 respectively. 10 The absolute value of the x-coordinate; the absolute value of the x-coordinate of specific internal nodes B2, B3, B6, and B7. The absolute value of the ordinate is Furthermore, the triangles formed by B2, B3, and the origin, as well as the triangles formed by B6, B7, and the origin, are all isosceles triangles with base angles of . ,and .

9. The negative Poisson's ratio lattice structure based on walnut cross-section biomimicry according to claim 1, characterized in that, The thickness of the rods in the acute-angle structure (2) is And it satisfies the following geometric constraints: ,and .

10. A method for controlling a negative Poisson's ratio lattice structure based on walnut cross-section biomimicry as described in any one of claims 1 to 9, characterized in that, Includes the following steps: S1 sets the ellipse parameter set ( , , , ) and triangular kernel parameter set ( , , , ); S2 is based on the parameter set in S1 ( , , , , , , , Calculate the extreme points (k1~k 10 The coordinates of the lattice unit cell are obtained, and the geometric profile of the lattice unit cell is generated. S3 determines the positions of internal nodes (P1~P8) and specific internal nodes (B1~B8) based on the angle bisector and line segment ratio constraints, and defines the geometry of the acute angle structure and the triangular-like core. S4 adjusts the parameter set ( , , , , , , , The value of ) is changed to alter the length and angle of each segment of the acute-angled structure, thereby continuously adjusting at least one of the following: the equivalent negative Poisson's ratio, plateau stress, and energy absorption efficiency of the lattice structure during compression.

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