A structure imparting strain-strengthening characteristics to a metamaterial and a design method thereof

Abstract

The application discloses a structure for imparting strain hardening performance to metamaterials and a design method thereof. In the structure for imparting strain hardening performance to metamaterials, unit bodies are periodically arranged in a shared edge mode to obtain an interlaced structure between layers, the structure is deformed from the upper and lower end surface layers, the yield strength of the structure nodes is higher than the yield strength of the deformed layers, the structure is deformed layer by layer, meanwhile, the structure has multiple degrees of freedom of deformation, high tolerance to local strain, high energy absorption, and the generation and expansion of cracks caused by stress concentration are delayed. The mechanical metamaterial prepared by using the photocuring 3D printing technology exhibits the strain hardening characteristics in the compression test, has high specific peak strength (9.6 MPa·cm 3 ·g ‑1 ), specific yield strength (4.3 MPa·cm 3 ·g ‑1 ), specific stiffness (1.26 MPa) and large plasticity (28.2%), and is superior to the octahedral truss lattice structure commonly used in the truss lattice structure under the condition that the materials are the same, the rod diameters and the rod lengths are the same (the rod length-diameter ratio is the same).

Description

Technical Field

[0001] This invention belongs to the field of structural engineering technology and relates to a structure and its design method that endows metamaterials with strain-strengthening properties. Background Technology

[0002] Porous and multicellular materials found in nature, such as honeycomb-like wood and cork, foam-like beams, plant parenchyma, and sponges, combine the advantages of low weight and good mechanical properties. For example, lightweight balsa wood has a strength / stiffness-density ratio comparable to steel under axial loading. Inspired by these naturally occurring porous and multicellular structures, various man-made lightweight porous and multicellular materials have been widely used in structural components, energy absorption, heat exchange, catalyst supports, and biomaterials, collectively referred to as metamaterials.

[0003] In mechanical metamaterials, truss lattice structures consist of straight bars and are classified into axially dominant and bending-dominant types. Since the former's bars bear compressive or tensile loads, while the latter bear bending loads, axially dominant structures typically have a higher strength / stiffness-density ratio than bending-dominant structures. Octahedral truss lattice structures are the most common type of axially dominant structure; however, due to their susceptibility to localized joint fractures under compression, their strength and plasticity still need improvement. While simultaneously enhancing the strength and plasticity of structures from a material perspective is common, methods for endowing metamaterials with strain-strengthening properties from a structural design perspective have not yet been reported. Summary of the Invention

[0004] To address the issues of low compressive strength and poor plasticity in truss lattice structures, this invention provides a structure and its design method that imparts metamaterial strain-strengthening properties.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A structure that imparts strain-strengthening properties to metamaterials involves designing the metamaterial as a unit cell layered structure to impart strain-strengthening mechanical properties to the metamaterial; the unit cells are stacked and expanded in three-dimensional space with struts on the outer contour of the shared unit cell to form an abab-like interlayered spatial topology.

[0007] Furthermore, when the unit cell is based on a quadrangular prism, four branches of equal length extend outward from the vertices of the four lateral faces of the prism and converge at a node along the perpendicular bisector of each face. All branches and the outwardly extending branches in the quadrangular prism are of the same length. Eight branches of equal length extend inward from the vertices of the prism and converge at a node at the body center of the prism. All branches in the unit cell have the same diameter. The length-to-diameter ratio of the branches is between 4.5 and 5.5.

[0008] The design method is as follows:

[0009] (1) Formation of monomers

[0010] Using a quadrangular prism as the main body, firstly, four supports of the same length are extended outward from the vertices of the four sides of the quadrangular prism, and then converge at the perpendicular bisector of each face to form a node, ensuring that all supports in the quadrangular prism and the extended supports are of the same length; then, eight supports of the same length are extended inward from the vertices of the quadrangular prism, and then converge at the body center of the quadrangular prism to form a node; finally, all supports in the unit body have the same diameter, and the yield strength of the node is ensured to be higher than the yield strength of the single-layer structure, and the overall structure deforms layer by layer during compression;

[0011] (2) The monomers are closely packed.

[0012] The monomers formed in step (1) are closely packed together. At the same time, the interaction between the rods after the nodes are compressed delays the generation and propagation of cracks caused by stress concentration.

[0013] Furthermore, when the unit cell is based on a triangular prism, three branches of equal length extend outward from the vertices of the three lateral faces of the prism and converge at a node along the perpendicular bisector of each face. All branches and the outwardly extending branches in the triangular prism are of the same length. Six branches of equal length extend inward from the vertices of the prism and converge at the center of the prism. All branches in the unit cell have the same diameter. The length-to-diameter ratio of the branches is between 4.5 and 5.5.

[0014] The design process is as follows:

[0015] (1) Formation of monomers

[0016] When the unit body is based on a triangular prism, firstly, three supports of the same length are extended outward from the vertices of the three lateral faces of the triangular prism, and then converge at the perpendicular bisectors of each face to form a node, ensuring that all supports in the triangular prism and the extended supports are of the same length; then, six supports of the same length are extended inward from the vertices of the triangular prism, and then converge at the body center of the triangular prism to form a node; ensuring that all supports in the unit body have the same diameter; ensuring that the yield strength of the node is higher than the yield strength of the single-layer structure, and that the overall structure deforms layer by layer during compression;

[0017] (2) The monomers are closely packed.

[0018] The monomers formed in step (1) are closely packed together. At the same time, the interaction between the rods after the nodes are compressed delays the generation and propagation of cracks caused by stress concentration.

[0019] The specific preparation, testing, and simulation schemes adopted in this invention are as follows:

[0020] Step 1: Use 3D modeling software to draw and export the structural file, slice it in 2D and print the physical object layer by layer in 3D, clean it with alcohol to remove uncured resin, and then cure it with ultraviolet light to obtain the test sample or initial sample.

[0021] Step 2: Place the initial sample from Step 1 into a vacuum chamber for magnetron sputtering coating to obtain the test sample;

[0022] Step 3: Perform a compression test on the sample from Step 1 or Step 2, ensuring the compression deformation rate remains consistent at 10. -3 s -1 The linearly fitted stress-strain curve shows the elastic deformation stage, plateau stage, and densification stage. The intersection of the fitted lines for the plateau stage and the densification stage is the densification initiation point.

[0023] Step 4: In HyperMesh software, the surface of the solid model from Step 1 is first divided into two-dimensional triangular meshes. The mesh quality is checked by the mesh size. Meshes that are too large or too small, as well as nearby meshes, are optimized. Then, a three-dimensional tetrahedral mesh is generated from the two-dimensional triangular mesh.

[0024] Step 5: In Abaqus CAE software, perform static structural analysis on the solid model with meshed data from Step 4 in the elastic stage of the material to obtain stress simulation cloud diagrams.

[0025] Furthermore, in step 1, when drawing the structural model, the rod diameter and rod length of the unit body outer contour are drawn as 360 μm and 1810 μm respectively, to ensure low material consumption while the structure has good compressibility.

[0026] Furthermore, in step 5, the bottom boundary conditions of the simulation are set to be fixed in the xyz direction, and the top boundary conditions are set to be free in the load application direction, i.e., the z-axis direction, and fixed in the xy direction, to ensure the closest approximation to the actual compression condition.

[0027] The preparation, testing, and simulation processes of the topological structure designed in this invention and the octahedral truss lattice structure used for comparison are the same.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. The structural design method of the present invention is to design the metamaterial as a unit cell layered structure to endow the metamaterial with strain-strengthened mechanical properties. The structure is characterized as follows: due to the interlayered structure of the unit cell, the upper and lower end layers of the metamaterial are preferentially subjected to stress and deformation. When the yield strength of the node is higher than the yield strength of the first deformed layer, the structure deforms layer by layer, and the plasticity is improved.

[0030] 2. At the same time, due to the interaction of the optimized rod forces generated by the optimized rod connection, the structure has a large degree of freedom in deformation after node compression and a high tolerance for local strain. Therefore, the generation and propagation of cracks caused by stress concentration are effectively suppressed, the structure has high energy absorption, and the structural strength is improved. In summary, the structure undergoes strain strengthening.

[0031] Figure and Table Description

[0032] The present invention will be further described below with reference to the accompanying drawings.

[0033] Figure 1 (ac) is a side view and a top view of the first type of metamaterial unit cell and its two two-dimensional close-packed topologies; (df) is a side view and a top view of the second type of metamaterial unit cell and its two two-dimensional close-packed topologies.

[0034] Figure 2 These are the compressive stress-strain curves of six metamaterials (Examples 1 to 5 and Comparative Example 1).

[0035] Figure 3 yes Figure 1 (f) Compressive stress cloud diagrams of metamaterials with two-dimensional close-packed topology extended in the third-dimensional direction (Example 6) and octahedral truss lattice structures (Comparative Example 2).

[0036] Table 1 shows... Figure 2 Characteristic values ​​of the compressive stress-strain curves of the six samples, including specific elastic modulus, specific yield strength, specific peak strength, and plastic deformation at the stress peak. Detailed Implementation

[0037] The invention will be further described below with reference to experimental data, and specific embodiments include, but are not limited to, these. The compressive strain strengthening performance brought about by this design method is specifically illustrated through a structure with interlayer staggered features of unit cells. Those skilled in the art will make changes to the specific embodiments and application scope based on the ideas of the invention; therefore, the content of this specification should not be construed as limiting the invention.

[0038] Example 1

[0039] Step 1: Use 3D modeling software to draw and export the structural file. The diameter of the rods in the drawn unit body outline is 360 μm and the length is 1810 μm. The thickness of the 2D slice is 0.050 mm. Use methyl methacrylate photopolymer gray light-curing resin raw material to 3D print the physical object. Clean with alcohol for 10 minutes to remove uncured resin. After drying, cure with ultraviolet light for 40 minutes to obtain the test sample.

[0040] Test sample: Figure 1(a) is a single unit, which is expanded into 3×3 units in a two-dimensional plane by sharing edges, resulting in a two-layer structure (ab). Figure 1 (b) ), extending in the third-dimensional direction as a 3×3×8 abab… (8 pairs in total) interlayered columnar structure with shared sides, the rod diameter is approximately 367 µm, the rod length is approximately 1932 µm, and the length-to-diameter ratio is 5.3. Based on weighing and measuring the outer contour dimensions of the structure, the density is calculated to be 0.283 g·cm³. -3 .

[0041] Step 2: Perform a compression test on the sample from Step 1, with a strain rate of 10. -3 s -1 The linear fitting of the compressive stress-strain curve identifies the elastic deformation stage, plateau stage, and densification stage. The intersection of the fitted lines for the plateau stage and the densification stage is the densification initiation point.

[0042] Stress-strain curves: such as Figure 2 The elastic stage deformation was 2.0%, and the specific strength was 1.9 MPa·cm. 3 ·g -1 Subsequently, significant strain hardening occurred, with a specific strength reaching approximately 15.7 MPa·cm. 3 ·g -1 At this point, the deformation is approximately 54.7%. Subsequently, the rod experiences severe buckling and node fracture, and the compressive strength gradually decreases. When the deformation reaches 71.1%, the damaged or fractured parts of the rod begin to contact. As the compressive strain increases, the crystal lattice gradually densifies, at which point the specific strength is approximately 13.4 MPa·cm. 3 ·g -1 .

[0043] Example 2

[0044] Step 1: Use 3D modeling software to draw and export the structural file. The diameter of the rods in the drawn unit body outline is 360 μm and the length is 1810 μm. The thickness of the 2D slice is 0.050 mm. Use methyl methacrylate photopolymer gray light-curing resin raw material to 3D print the physical object. Clean with alcohol for 10 minutes to remove uncured resin. After drying, cure with ultraviolet light for 40 minutes to obtain the test sample.

[0045] Test sample: Figure 1 (a) is a single unit, which is expanded into 2×2 units in a two-dimensional plane by sharing edges, resulting in a two-layer structure of ab. At the central hole, four support rods extend from the four vertices of the mid-plane closest to the two-dimensional plane, with the center of the hole as the node. Figure 1(c) In the third dimension, it extends into a 2×2×6 abab… (6 pairs in total) interlayered columnar structure with shared sides. The rod diameter is approximately 374 µm, the rod length is approximately 1912 µm, and the length-to-diameter ratio is 5.1. After weighing the mass and measuring the outer contour dimensions of the structure, the density is calculated to be 0.306 g·cm³. -3 .

[0046] Step 2: Perform a compression test on the sample from Step 1, with a strain rate of 10. -3 s -1 The linear fitting of the compressive stress-strain curve identifies the elastic deformation stage, plateau stage, and densification stage. The intersection of the fitted lines for the plateau stage and the densification stage is the densification initiation point.

[0047] Stress-strain curves: such as Figure 2 The elastic stage deformation was 1.9%, and the specific strength was 1.6 MPa·cm. 3 ·g -1 Subsequently, significant strain hardening occurred, with a specific strength reaching approximately 13.5 MPa·cm. 3 ·g -1 At this point, the deformation is approximately 42.1%. Subsequently, the rod experiences severe buckling and node fracture, and the compressive strength gradually decreases. When the deformation reaches 69.4%, the damaged or fractured parts of the rod begin to contact. As the compressive strain increases, the crystal lattice gradually densifies, at which point the specific strength reaches approximately 8.8 MPa·cm. 3 ·g -1 .

[0048] Example 3

[0049] Step 1: Use 3D modeling software to draw and export the structural file. The diameter of the rods in the drawn unit body outline is 360 μm and the length is 1810 μm. The thickness of the 2D slice is 0.050 mm. Use methyl methacrylate photopolymer gray light-curing resin raw material to 3D print the physical object. Clean with alcohol for 10 minutes to remove uncured resin. After drying, cure with ultraviolet light for 40 minutes to obtain the test sample.

[0050] Test sample: Figure 1 (d) is a single unit cell, which is expanded into 6×7 unit cells in a two-dimensional plane by sharing edges, resulting in a two-layer structure (ab). Figure 1 (e)), 6 represents 6. Figure 1(d) A large unit cell is formed by the unit cells sharing a common edge. Seven large unit cells continue to expand into an interconnected structure by sharing a common edge. In the third dimension, the unit cells expand into a staggered columnar structure of 6×7×11 abab… (11 pairs in total) by sharing a common edge. The diameter of the rod is approximately 355 µm, the length of the rod is approximately 1691 µm, and the length-to-diameter ratio is 4.7. After weighing the mass and measuring the outer contour dimensions of the structure, the density is calculated to be 0.244 g·cm³. -3 .

[0051] Step 2: Perform a compression test on the sample from Step 1, with a strain rate of 10. -3 s -1 The linear fitting of the compressive stress-strain curve identifies the elastic deformation stage, plateau stage, and densification stage. The intersection of the fitted lines for the plateau stage and the densification stage is the densification initiation point.

[0052] Stress-strain curves: such as Figure 2 The elastic stage deformation is 2.0%, and the specific strength is 2.0 MPa·cm. 3 ·g -1 Subsequently, significant strain hardening occurred, with a specific strength reaching approximately 8.2 MPa·cm. 3 ·g -1 At this point, the deformation is approximately 29.6%. Subsequently, the rod experiences severe buckling and node fracture, and the compressive strength gradually decreases. When the deformation reaches 66.3%, the damaged or fractured parts of the rod begin to contact. As the compressive strain increases, the crystal lattice gradually densifies, at which point the specific strength is approximately 5.3 MPa·cm. 3 ·g -1 .

[0053] Example 4

[0054] Step 1: Use 3D modeling software to draw and export the structural file. The diameter of the rods in the drawn unit body outline is 360 μm and the length is 1810 μm. The thickness of the 2D slice is 0.050 mm. Use methyl methacrylate photopolymer gray light-curing resin raw material to 3D print the physical object. Clean with alcohol for 10 minutes to remove uncured resin. After drying, cure with ultraviolet light for 40 minutes to obtain the test sample.

[0055] Test sample: Figure 1 (d) is a single unit cell, which is expanded into 6×7 unit cells in a two-dimensional plane by sharing edges, resulting in a two-layer structure ab. 6 represents 6 units. Figure 1 (d) The unit cells form a large unit cell with shared edges. The seven large unit cells continue to expand into an interconnected structure with shared edges. At the seven central holes, six support rods extend from the six vertices of the midplane close to the two-dimensional plane, with the center of the hole as the node. Figure 1(f)); In the third-dimensional direction, it extends into a 6×7×11 abab… (11 pairs in total) interlayered columnar structure with shared sides. The rod diameter is approximately 349µm, the rod length is approximately 1696µm, and the length-to-diameter ratio is 4.9. After weighing the mass and measuring the outer contour dimensions of the structure, the density is calculated to be 0.264 g·cm³. -3 .

[0056] Step 2: Perform a compression test on the sample from Step 1, with a strain rate of 10. -3 s -1 The linear fitting of the compressive stress-strain curve identifies the elastic deformation stage, plateau stage, and densification stage. The intersection of the fitted lines for the plateau stage and the densification stage is the densification initiation point.

[0057] Stress-strain curves: such as Figure 2 The elastic stage deformation is 2.0%, and the specific strength is 2.5 MPa·cm. 3 ·g -1 Subsequently, significant strain hardening occurred, with a specific strength reaching approximately 9.6 MPa·cm. 3 ·g -1 At this point, the deformation is approximately 30.2%. Subsequently, the rod experiences severe buckling and node fracture, and the compressive strength gradually decreases. When the deformation reaches 69.3%, the damaged or fractured parts of the rod begin to contact. As the compressive strain increases, the crystal lattice gradually densifies, at which point the specific strength reaches approximately 8.3 MPa·cm. 3 ·g -1 .

[0058] Example 5

[0059] Step 1: Use 3D modeling software to draw and export the structural file. The diameter of the rods in the drawn unit body is 360 μm and the length is 1810 μm. The thickness of the 2D slice is 0.050 mm. Use methyl methacrylate photopolymer gray light-curing resin raw material to 3D print the physical object. Clean with alcohol for 10 minutes to remove uncured resin. After drying, cure with ultraviolet light for 40 minutes to obtain the initial sample.

[0060] Initial sample: Figure 1 (d) is a single unit cell, which is expanded into 6×7 unit cells in a two-dimensional plane by sharing edges, resulting in a two-layer structure ab. 6 represents 6 units. Figure 1 (d) The unit cells form a large unit cell with shared edges. The seven large unit cells continue to expand into an interconnected structure with shared edges. At the seven central holes, six support rods extend from the six vertices of the midplane close to the two-dimensional plane, with the center of the hole as the node. Figure 1(f)); In the third-dimensional direction, it extends into a 6×7×11 abab… (11 pairs in total) interlayered columnar structure with shared sides. The rod diameter is approximately 349µm, the rod length is approximately 1696µm, and the length-to-diameter ratio is 4.9. After weighing the mass and measuring the outer contour dimensions of the structure, the density is calculated to be 0.264 g·cm³. -3 .

[0061] Step 2: A Cu layer is deposited on the initial sample from Step 1 using magnetron sputtering. 50 Zr 50 The membrane was evacuated in the sputtering chamber to a vacuum level of 9.0 × 10⁻� -5 The argon atmosphere was maintained at 0.5 Pa, and the sample was sputtered at 60 W DC power for 7.5 h. After sputtering for 60 s, the sputtering was paused for 10 s to allow for cooling and stress release, and the sample to be tested was obtained.

[0062] Test sample: The initial sample from step 1 and the conformal Cu 50 Zr 50 The composite material structure composed of a membrane has a rod diameter of approximately 380 µm, a rod length of approximately 1708 µm, and an aspect ratio of 4.5. Based on weighing and measuring the outer dimensions of the structure, the density was calculated to be 0.322 g·cm³. -3 .

[0063] Step 3: Perform a compression test on the sample from Step 2, with a strain rate of 10. -3 s -1 The linear fitting of the compressive stress-strain curve identifies the elastic deformation stage, plateau stage, and densification stage. The intersection of the fitted lines for the plateau stage and the densification stage is the densification initiation point.

[0064] Stress-strain curves: such as Figure 2 The elastic stage deformation was 2.0%, and the specific strength was 3.1 MPa·cm. 3 ·g -1 Subsequently, significant strain hardening occurred, with a specific strength reaching approximately 12.0 MPa·cm. 3 ·g -1 At this point, the deformation is approximately 37.6%. Subsequently, the rod experiences severe buckling and node fracture, and the compressive strength gradually decreases. When the deformation reaches 64.2%, the damaged or fractured parts of the rod begin to contact. As the compressive strain increases, the crystal lattice gradually densifies, at which point the specific strength is approximately 8.4 MPa·cm. 3 ·g -1 .

[0065] Example 6

[0066] Step 1: Use 3D modeling software to draw the structural file. The diameter of the rods in the drawn unit body outline is 360 μm and the length is 1810 μm.

[0067] Structural model: such as Figure 3 (a), with Figure 1 (d) is a single unit cell, which is expanded into 6×1 unit cells in a two-dimensional plane by sharing edges, resulting in a two-layer structure ab, where 6 represents 6 units. Figure 1 (d) A large unit body is formed by sharing edges. At the central hole of the large unit body, six support rods extend from the six vertices of the midplane close to the two-dimensional plane, with the center of the hole as the node. In the third-dimensional direction, it expands into a 6×1×3 ababab interlayered columnar structure of unit bodies.

[0068] Step 2: In HyperMesh software, the surface of the solid structure model from Step 1 is first divided into two-dimensional triangular meshes. The mesh quality is checked by the mesh size. Meshes that are too large or too small, as well as nearby meshes, are optimized. Then, a three-dimensional tetrahedral mesh is generated from the two-dimensional triangular mesh.

[0069] Step 3: In Abaqus CAE software, set the bottom boundary conditions of the solid model with meshed data from Step 2 to be fixed in the xyz direction, and the top boundary conditions to be free in the load application direction (z-axis) and fixed in the xy direction. Perform static structural analysis in the elastic stage of the material to obtain stress simulation cloud diagram.

[0070] Stress simulation cloud map: such as Figure 3 (a) The bright white area represents the stress concentration region. Due to the staggered characteristics of the unit layer, the upper and lower end layers of the metamaterial are preferentially subjected to stress and deformation. Subsequently, the force extends from the end layer to the middle layer. When the yield strength of the node is higher than the yield strength of the first deformed layer, the structure deforms layer by layer, which increases the plasticity. At the same time, the interaction of forces between the rods after the node is compressed delays the stress concentration and increases the structural strength. In summary, the structure undergoes strain hardening.

[0071] Comparative Example 1

[0072] Step 1: Use 3D modeling software to draw and export the structural file. The diameter of the rods in the drawn unit body is 360 μm and the length is 1810 μm. The thickness of the 2D slice is 0.050 mm. Use methyl methacrylate photopolymer gray light-curing resin raw material to 3D print the physical object. Clean with alcohol for 10 minutes to remove uncured resin. After drying, cure with ultraviolet light for 40 minutes to obtain the initial sample.

[0073] Test sample: An octahedral truss lattice structure using octahedrons as unit cells, expanding into 4×4 unit cells in a two-dimensional plane by sharing vertices, and further expanding into a 4×4×6 columnar structure (aaaa… in total) by sharing vertices in the three-dimensional direction. The column diameter is approximately 342 µm, the column length is approximately 1689 µm, and the length-to-diameter ratio is 4.9. Based on weighing and measuring the outer contour dimensions of the structure, the density was calculated to be 0.307 g·cm³. -3 .

[0074] Step 2: Perform a compression test on the sample from Step 1, with a strain rate of 10. -3 s -1 The linear fitting of the compressive stress-strain curve identifies the elastic deformation stage, plateau stage, and densification stage. The intersection of the fitted lines for the plateau stage and the densification stage is the densification initiation point.

[0075] Stress-strain curves: such as Figure 2 The elastic stage deformation was 2.0%, and the specific strength was 2.2 MPa·cm. 3 ·g -1 The subsequent strain hardening phase is very brief, with the specific strength reaching a peak of 5.4 MPa·cm at a deformation of 10.2%. 3 ·g -1 Subsequently, the compressive strength gradually decreases, and as buckling and localized nodal fractures propagate within the lattice, a broad stress-strain plateau appears on the curve. At 62.9% deformation, the damaged or fractured rod begins to contact; as the compressive strain increases, the lattice gradually densifies, at which point the specific strength is approximately 5.2 MPa·cm. 3 ·g -1 .

[0076] Comparative Example 2

[0077] Step 1: Use 3D modeling software to draw the structural file. The diameter of the rods in the drawn unit body outline is 360 μm and the length is 1810 μm.

[0078] Structural model: Octahedral truss lattice structure, such as Figure 3 (b) Using an octahedron as the unit, it expands into 2×2 unit bodies in a two-dimensional plane by sharing vertices, and expands into a 2×2×3 columnar structure in the third-dimensional direction by sharing vertices.

[0079] Step 2: In HyperMesh software, the surface of the solid structure model from Step 1 is first divided into two-dimensional triangular meshes. The mesh quality is checked by the mesh size. Meshes that are too large or too small, as well as nearby meshes, are optimized. Then, a three-dimensional tetrahedral mesh is generated from the two-dimensional triangular mesh.

[0080] Step 3: In Abaqus CAE software, set the bottom boundary conditions of the solid model with meshed data from Step 2 to be fixed in the xyz direction, and the top boundary conditions to be free in the load application direction (z-axis) and fixed in the xy direction. Perform static structural analysis in the elastic stage of the material to obtain stress simulation cloud diagram.

[0081] Stress simulation cloud map: such as Figure 3 (b) The bright white area is the stress concentration region. During the compression process, all nodes of the octahedral lattice topology experience stress concentration simultaneously and preferentially. Subsequently, the stress extends to the middle of the rod.

[0082] Table 1

[0083] <![CDATA[Specific stiffness (MPa·cm 3 ·g -1 )]]> <![CDATA[Specific yield strength (MPa·cm 3 ·g -1 )]]> <![CDATA[Specific peak intensity (MPa·cm 3 ·g -1 )]]> Plastic deformation at peak stress (%) Example 1 0.94 2.9 15.7 52.7 Example 2 0.85 2.4 13.5 40.2 Example 3 0.99 3.3 8.2 27.6 Example 4 1.26 4.3 9.6 28.2 Example 5 1.46 5.0 12.0 35.6 Comparative Example 1 1.06 4.1 5.4 8.2

[0084] Note: Example 5 is a composite structure sample after a metal film is deposited on the gray resin of Example 4; the rest are gray resin structures.

[0085] Compared with the octahedral truss lattice structure commonly used in truss lattice structures (Comparative Example 1), when the rod diameter and length of the unit body outer contour of all the above embodiments (except the composite material after coating in Example 5) and the comparative example are the same within the error range (same rod length-to-diameter ratio), the experiment shows that ( Figure 2 Table 1) Specific stiffness: Example 4 > Comparative Example 1 > Example 3 > Example 1 > Example 2; Specific yield strength: Example 4 > Comparative Example 1 > Example 3 > Example 1 > Example 2; Specific peak strength: Example 1 > Example 2 > Example 4 > Example 3 > Comparative Example 1; Plastic deformation at stress peak: Example 1 > Example 2 > Example 4 > Example 3 > Comparative Example 1; Plastic deformation at the start of densification: Example 1 > Example 2 > Example 4 > Example 3 > Comparative Example 1. In summary, all performance indicators of Example 4 are superior to the octahedral truss lattice structure, making it the optimized structure of this invention, possessing a high specific peak strength (9.6 MPa·cm). 3 ·g -1 ), specific yield strength (4.3 MPa·cm) 3 ·g -1 It has high specific stiffness (1.26 MPa) and high plasticity (28.2%), while the peak specific strength of the octahedral truss lattice structure is only 5.4 MPa·cm. 3 ·g -1 Its specific yield strength is only 4.1 MPa·cm 3 ·g -1Its specific stiffness is only 1.06 MPa and its plasticity is only 8.2%. The total energy absorbed by the metamaterial from the initial deformation stage to the densification stage represents the toughness of the metamaterial. The toughness of the octahedral truss lattice structure mainly comes from the buckling of the rods and the wide stress-strain plateau formed by the expansion of local nodal fractures in the lattice, while the toughness of the unit cell interlayer staggered structure mainly comes from strain strengthening.

[0086] The truss lattice structure is obtained by periodically arranging unit cells according to a structural design method.

[0087] The first type of unit: such as Figure 1 (a) Using a quadrangular prism as the main body, four branches of the same length extend outward from the vertices of the four sides of the quadrangular prism and converge into a node on the perpendicular bisector of each face. All branches and the extended branches in the quadrangular prism are of the same length. Eight branches of the same length extend inward from the vertices of the quadrangular prism and converge into a node at the body center of the quadrangular prism. All branches in the unit body have the same diameter.

[0088] The second type of unit: such as Figure 1 (d) Using a triangular prism as the main body, three branches of the same length extend outward from the vertices of the three lateral faces of the triangular prism and converge into a node on the perpendicular bisector of each face. All branches and the extended branches in the triangular prism are of the same length. Six branches of the same length extend inward from the vertices of the triangular prism and converge into a node at the body center of the triangular prism. All branches in the unit body have the same diameter.

[0089] Two unit cells are stacked and extended in three dimensions by supporting rods on the outer contour of the common unit cell, forming an abab-like spatial topology. Both exhibit compressive strain strengthening performance, with high strength / stiffness-density ratio and large ductility, as in Examples 1 and 3.

[0090] After adding support rods to the large holes in the two topologies of the two unit cells mentioned above, experiments showed that the strain-strengthening characteristics of the structure were not changed, and the specific strength / stiffness and ductility were not necessarily increased, as in Examples 2 and 4.

[0091] After depositing a metal film on the topology of the above unit body using magnetron sputtering to form a composite material, experiments show that the strain strengthening characteristics of the structure remain unchanged, and the specific strength / stiffness and ductility of the structure are increased compared with those before coating, as in Example 5.

[0092] The simulated stress cloud diagrams of the topology structure with the second type of unit stacking expansion (Example 6) and the octahedral truss lattice structure (Comparative Example 2) further demonstrate that the structural design method provided by the present invention is more conducive to the generation of metamaterial compressive strain strengthening performance than the simultaneous stress on all nodes in the octahedral truss lattice structure.

Claims

1. A structure imparting strain hardening properties to a metamaterial, characterized in that: The metamaterial is designed as a unit cell layer staggered structure for imparting the strain hardening mechanical properties of the metamaterial; the unit cell is expanded in a three-dimensional space by stacking the struts on the common unit cell outer contour to form a spatial topology structure staggered in layers in an a-b-a-b manner; when the unit cell takes a quadrangular prism as the main body, the four vertices of the four sides of the quadrangular prism respectively extend four struts of the same length outward and converge into a node on the median line of each side, all the struts in the above quadrangular prism and the extended struts have the same length; the four vertices of the quadrangular prism respectively extend eight struts of the same length inward and converge into a node at the body center of the quadrangular prism; all the struts in the unit cell have the same diameter.

2. The structure for imparting strain stiffening characteristics of metamaterials according to claim 1, characterized in that: The length-diameter ratio of the rod is between 4.5 and 5.

5.

3. The structure for imparting strain stiffening characteristics of metamaterials according to claim 1, characterized in that: When the unit cell takes a triangular prism as the main body, the three vertices of the three sides of the triangular prism respectively extend three struts of the same length outward and converge into a node on the median line of each side, all the struts in the above triangular prism and the extended struts have the same length; the three vertices of the triangular prism respectively extend six struts of the same length inward and converge into a node at the body center of the triangular prism; all the struts in the unit cell have the same diameter.

4. The structure for imparting strain stiffening characteristics of a metamaterial according to claim 3, characterized by: The length-diameter ratio of the rod is between 4.5 and 5.

5.

5. A structure design method for imparting the strain hardening properties of the metamaterial according to any one of claims 1-2, characterized in that: (1) forming a single body Taking a quadrangular prism as the main body, first, the four vertices of the four sides of the quadrangular prism respectively extend four struts of the same length outward and converge into a node on the median line of each side, ensuring that all the struts in the quadrangular prism and the extended struts have the same length; then, the four vertices of the quadrangular prism respectively extend eight struts of the same length inward and converge into a node at the body center of the quadrangular prism; finally, all the struts in the unit cell have the same diameter, and the yield strength of the node is higher than the yield strength of the single-layer structure, and the overall structure deforms layer by layer during compression; (2) densely arranging the single body The single body formed in step (1) is densely arranged, and the interaction between the struts after the node is compressed delays the generation and expansion of cracks caused by stress concentration.

6. A method of designing a structure to impart strain stiffening properties to a metamaterial according to any one of claims 3-4, characterized by: The method is (1) forming a single body When the unit cell takes a triangular prism as the main body, first, the three vertices of the three sides of the triangular prism respectively extend three struts of the same length outward and converge into a node on the median line of each side, ensuring that all the struts in the triangular prism and the extended struts have the same length; then, the three vertices of the triangular prism respectively extend six struts of the same length inward and converge into a node at the body center of the triangular prism; ensure that all the struts in the unit cell have the same diameter; ensure that the yield strength of the node is higher than the yield strength of the single-layer structure, and the overall structure deforms layer by layer during compression; (2) densely arranging the single body The single body formed in step (1) is densely arranged, and the interaction between the struts after the node is compressed delays the generation and expansion of cracks caused by stress concentration.

7. A test method based on the structure of any one of claims 1 to 4, which imparts a strain-hardening characteristic to a metamaterial, characterized in that, The method is: Step 1, use a three-dimensional modeling software to draw and export a structure file, after two-dimensional slicing, 3D layer-by-layer printing of the real object, alcohol cleaning to remove uncured resin, drying, and then secondary curing under ultraviolet light to obtain a sample to be tested or an initial sample; Step 2, the initial sample of step 1 is put into a vacuum chamber for magnetron sputtering coating to obtain a sample to be tested; Step 3, compression test is performed on the sample to be tested in step 1 or step 2, the compression deformation rate is kept consistent, and is 10 -3 s -1 The linear fitting stress-strain curve is compressed, the platform stage and the densification stage, and the intersection point of the fitting line of the platform stage and the densification stage is the starting point of densification. Step 4, the surface of the entity model of step 1 is first divided into two-dimensional triangular meshes in HyperMesh software, grid quality is checked through grid size, and grids that are too large or too small and nearby grids are optimized to generate three-dimensional tetrahedral meshes from two-dimensional triangular meshes; Step 5, the entity model with divided grids of step 4 is subjected to static structure analysis in the elastic stage of the material in Abaqus CAE software to obtain a stress simulation cloud chart.

8. The method of testing a structure for imparting metamaterial strain hardening characteristics of claim 7, wherein: In step 1, the rod diameter and rod length of the outer contour of the unit body are respectively drawn as 360 μm and 1810 μ when the structure model is drawn.

9. The method of testing a structure for imparting metamaterial strain hardening characteristics of claim 7, wherein: In step 5, the bottom boundary condition of the simulation is set as fixed in the xyz direction, and the top boundary condition is set as free in the load application direction, i.e. the z-axis direction, and fixed in the xy direction.

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