3D printing deformation recoverable shape memory alloy mechanical metamaterial

Abstract

The invention relates to the technical field of mechanical metamaterial additive manufacturing, and discloses a 3D printing deformation-recoverable shape memory alloy mechanical metamaterial which comprises the following steps: S1, defining the shape, the geometric dimension and the design boundary of a mechanical metamaterial unit according to the use environment requirement and the processing and manufacturing requirement of the mechanical metamaterial; s2, completing the design and drawing of a two-dimensional line diagram of the mechanical metamaterial unit; s3, constructing a three-dimensional unit grid model based on the mechanical metamaterial unit two-dimensional line graph; s4, a corresponding shape memory alloy component system is selected, and the structure and the phase change temperature of the mechanical metamaterial are further regulated and controlled through alloy component proportion optimization, 3D printing process parameter optimization and aftertreatment system formulation; and S5, preparing the deformation-recoverable shape memory alloy mechanical metamaterial through a 3D printing technology according to the optimized 3D printing process parameters. The mechanical properties such as the elastic modulus, the yield strength and the Poisson ratio can be manually regulated and controlled.

Description

Technical Field

[0001] The present invention relates to the technical field of additive manufacturing of mechanical metamaterials, and particularly to a 3D printable shape memory alloy mechanical metamaterial with deformable and recoverable properties. Background Art

[0002] Metamaterials refer to artificial structures or composite materials with extraordinary physical properties that natural materials do not possess. According to their realized properties and application fields, they can be divided into mechanical metamaterials, thermal metamaterials, acoustic metamaterials, electromagnetic metamaterials, etc. Shape Memory Alloys (SMAs), due to their microstructure and unique phase transformation, possess excellent shape memory effect and superelasticity, and are thus also known as "intelligent materials". However, conventional materials, traditional structures, and manufacturing processes are difficult to meet the requirements of mechanical metamaterials such as deformable and recoverable properties and negative Poisson's ratio effect. Summary of the Invention

[0003] Based on this, in view of the problem that conventional materials, traditional structures, and manufacturing processes are difficult to meet the requirements of mechanical metamaterials such as deformable and recoverable properties and negative Poisson's ratio effect, the present invention provides a 3D printable shape memory alloy mechanical metamaterial with deformable and recoverable properties.

[0004] The present invention uses an innovative mechanical metamaterial structure design strategy, fully combining the material property advantages of shape memory alloys and the technical advantages of additive manufacturing. The prepared shape memory alloy mechanical metamaterial simultaneously possesses advantages such as high flexibility, low stiffness, uniform deformation, ultra-high deformation recovery rate, vibration damping, and energy absorption.

[0005] A 3D printable shape memory alloy mechanical metamaterial comprises the following steps:

[0006] S1. Define the shape, geometric dimensions, and design boundaries of the mechanical metamaterial unit according to the usage environment requirements and processing and manufacturing requirements of the mechanical metamaterial;

[0007] S2. Based on the shape and design boundaries of the mechanical metamaterial unit, reconstruct the polygon unit of the mechanical metamaterial into a secondary rotating polygon by means of polygon unit vectorization and setting secondary vertices, embed a negative Poisson's ratio honeycomb structure inside the secondary rotating polygon, and use geometric transformation to reconstruct the geometric shape of the unit side lines to complete the design and drawing of the two-dimensional line diagram of the mechanical metamaterial unit;

[0008] S3. Construct a three-dimensional unit grid model based on the two-dimensional line diagram of the mechanical metamaterial unit, set the structure parameters, construct a mechanical metamaterial model according to the anti-chiral unit array mode, and optimize the manufacturability of the grid file of the three-dimensional unit grid model;

[0009] S4. According to the requirements of the service environment of the mechanical metamaterial for temperature conditions, mechanical properties, corrosion resistance, biocompatibility, cost, and manufacturability, select the corresponding shape memory alloy composition system. By optimizing the alloy composition ratio, optimizing the 3D printing process parameters, and formulating the post-treatment system, further regulate the microstructure and phase transformation temperature of the mechanical metamaterial, so that the mechanical metamaterial exhibits the required shape memory effect or superelasticity directionally under the temperature conditions, and obtain optimized strength, plasticity, and toughness;

[0010] S5. Slice the mechanical metamaterial model through software, and use the shape memory alloy powder with the optimized alloy composition ratio to prepare a deformable and recoverable shape memory alloy mechanical metamaterial through 3D printing technology with the optimized 3D printing process parameters.

[0011] The present application discloses a 3D printable deformable and recoverable shape memory alloy mechanical metamaterial. Through the mechanical metamaterial unit structure design strategies of reconstructing secondary rotating polygons, embedding negative Poisson's ratio honeycombs inside the secondary rotating polygons, and reconstructing the geometric structure of the side edges, as well as the anti-chiral array pattern and various three-dimensional model construction methods, the flexibility and deformation performance of the mechanical metamaterial are improved from multiple dimensions such as multiple design parameters and various design schemes, and the mechanical properties such as elastic modulus, yield strength, and Poisson's ratio can be artificially regulated. The reasonable selection of the shape memory alloy composition system and 3D printing process parameters realizes the high-precision and high-performance forming of the mechanical metamaterial, and achieves the integration of multiple functions such as energy absorption and vibration damping, large-range deformation recoverability, and zero Poisson's ratio deformation. This method uses additive manufacturing materials for additive manufacturing, which can quickly and efficiently form customized complex structures. This method uses a design method targeting mechanical metamaterial units, and can provide various mechanical metamaterials with different geometric shapes to meet the needs of different structural shapes. By constructing secondary rotating polygons inside the polygon units, this method can achieve precise regulation of zero / negative Poisson's ratio deformation and stiffness, and adapt to various complex working environments. By embedding negative Poisson's ratio honeycombs with different configurations, this method can customize the deformation behavior, adjust mechanical properties such as modulus and strength, and meet various personalized needs. Through the optimization of alloy composition ratio, the optimization of 3D printing process parameters, and the formulation of post-treatment systems, this method realizes the regulation of the microstructure and phase transformation temperature of the shape memory alloy, enables the alloy material to directionally exhibit shape memory effect or superelasticity, and obtains optimized strength, plasticity, and toughness, which are beneficial to the achievement of the required performance for mechanical metamaterial applications, the realization of intelligence, and the increase of service life. This method uses additive manufacturing technology for forming, has green manufacturing attributes such as reducing energy consumption, reducing material waste, and reducing environmental pollution, and has advantages such as environmental protection and sustainable production. This method can realize the deformable and recoverable function of the shape memory alloy mechanical metamaterial and customize various mechanical properties by adjusting the mechanical metamaterial model construction method, design parameters, alloy system, forming process parameters, and processing and manufacturing process, and has high engineering value and broad application prospects.

[0012] In any of the above technical solutions, the shapes of the mechanical metamaterial units include regular triangular prisms and cuboids. The corresponding cross-sectional shapes of the regular triangular prisms and cuboids are equilateral triangles and rectangles respectively. The geometric dimensions are defined by the stretching height and the dimensions of the cross-sectional shapes. The geometric dimensions are respectively the side length of the equilateral triangle and the length and width of the rectangle. The design boundary is the internal area of the cross-section, which is orthogonal to the stretching height direction. Setting the cross-sectional shape of the mechanical metamaterial unit as an equilateral triangle or a rectangle can provide a good representative cell pattern for the construction of the mechanical metamaterial, facilitate the macroscopic regulation of various mechanical properties of the mechanical metamaterial using the relevant design parameters of the unit, and the design boundary being orthogonal to the stretching height direction helps to achieve the customization of the deformation behavior and improve the manufacturability of 3D printing.

[0013] In any of the above technical solutions, the geometric transformation includes buckling and bending.

[0014] In any of the above technical solutions, the structural parameters include one or more of thickness, wall thickness, and rod diameter.

[0015] In any of the above technical solutions, in step S2, the reconstruction of the polygonal unit of the mechanical metamaterial into a secondary rotating polygon specifically includes the following steps:

[0016] a. Vectorization of the polygonal unit: Within the design boundary, the mechanical metamaterial unit is represented by its cross-section. The cross-section of the mechanical metamaterial unit corresponds to the polygonal unit of the mechanical metamaterial unit. Select any vertex of the polygonal unit as the starting vertex, and starting from the starting vertex in any direction along one of the two connected sides, after passing through the remaining vertices and side lines and returning to this starting vertex, there are n segments of running paths including direction and length along the side lines during the process from the starting vertex to returning to the starting vertex. The n segments of running paths are respectively denoted as where i = 1, 2, …, n, and n is the number of sides of the polygon (3 or 4), then it is necessary to satisfy:

[0017]

[0018] In this way, the polygonal unit is transformed into a ring structure formed by connecting n vectors end to end, completing the vectorization of the polygonal unit. At the same time, the chirality characteristics of the polygonal unit can be defined: Based on the same direction perpendicular to the design interface, if the ring structure formed by connecting the vectors end to end is clockwise, it is defined as a left-handed unit; if it is counterclockwise, it is defined as a right-handed unit.

[0019] b. Setting the secondary vertices of the rotating polygon: For each vertex A i and the vector side starting from it , define a scale factor p to set the position of the secondary vertex B i :

[0020]

[0021] where i = 1, 2, …, n, n is the number of sides of the polygon, and the scale factor p ∈ (0, 1), which is uniquely determined after the first setting of the secondary vertex position.

[0022] c. Connect all the secondary vertices in sequence to construct a secondary rotating polygon; Delete or only retain the side line A i B i or only retain the side line A i B i .

[0023] Reconstructing the polygon unit into a secondary rotating polygon according to the method can convert the original axial deformation into the rotational deformation of the secondary polygon, thereby significantly improving flexibility, reducing stiffness, and initially introducing a way to achieve zero / negative Poisson's ratio deformation function; the deformation behavior and mechanical properties such as strength and stiffness of the mechanical metamaterial can be conveniently and quickly regulated by the scaling factor p.

[0024] In any of the above technical solutions, in step S2, the embedding of the negative Poisson's ratio honeycomb structure specifically includes the following steps:

[0025] a. Select a negative Poisson's ratio honeycomb structure: Based on the cross-section of the mechanical metamaterial unit, select a negative Poisson's ratio honeycomb structure. If the cross-section of the mechanical metamaterial unit is an equilateral triangle, select a double-V negative Poisson's ratio honeycomb structure or a triangular star negative Poisson's ratio honeycomb structure; if the cross-section of the mechanical metamaterial unit is a rectangle, select a re-entrant negative Poisson's ratio honeycomb structure or a star negative Poisson's ratio honeycomb structure.

[0026] b. By changing the geometric characteristics of the side edges, that is, by buckling or bending the side edges corresponding to the embedding direction of the negative Poisson's ratio honeycomb, the negative Poisson's ratio honeycomb structure is compound-embedded in the cross-section of the mechanical metamaterial unit.

[0027] By selecting to embed a double-V negative Poisson's ratio honeycomb, a triangular star negative Poisson's ratio honeycomb structure, a re-entrant negative Poisson's ratio honeycomb structure, or a star negative Poisson's ratio honeycomb structure, a variety of mechanical metamaterial configuration schemes can be developed to achieve customized combinations of different deformation behaviors and mechanical properties. Different negative Poisson's ratio honeycomb structures have different mechanical characteristics. For example, the double-V negative Poisson's ratio honeycomb and the re-entrant negative Poisson's ratio honeycomb have strong mechanical anisotropy, while the star negative Poisson's ratio honeycomb has a lower tangential stiffness. Different embedding directions also affect the anisotropy of the mechanical metamaterial and the stress transfer and deformation between mechanical metamaterial units.

[0028] In any of the above technical solutions, there are 3 embedding directions for the double-V negative Poisson's ratio honeycomb structure, 1 embedding direction for the triangular star negative Poisson's ratio honeycomb structure, 2 embedding directions for the re-entrant negative Poisson's ratio honeycomb structure, and 1 embedding direction for the star negative Poisson's ratio honeycomb structure. Different embedding directions of the honeycomb structure in the secondary rotating polygon unit of the metamaterial will form combined structures with different structures. Different embedding directions also affect the anisotropy of the metamaterial and the stress transfer and deformation between units.

[0029] In any of the above technical solutions, the specific steps for the geometric reconstruction of the side lines of the reconstruction unit are as follows: For the retained side lines, reconstruction methods including buckling, bending, deletion, or retention are used; buckling means modifying the original straight side line into two concave broken lines, and ensuring that each end point is connected to the end points of the original side line to form a closed triangle; bending includes modifying and replacing with curves such as arcs, parabolas, and Bezier curves, and other reconstruction methods include replacing with other side line geometric configurations such as multi-segment broken lines.

[0030] By reconstructing the geometric shape of the side lines of the polygon unit through the above specific method, the space for unit rotation deformation and negative Poisson's ratio deformation can be further liberated, achieving the design goals of increasing the deformation range, improving the deformation uniformity, reducing the stiffness, and enhancing the flexibility. The reconstruction methods and design parameters involved in the reconstruction steps can also be used to regulate the mechanical properties of the developed mechanical metamaterials.

[0031] In any of the above technical solutions, in step S3, the three-dimensional unit mesh model is a rod-based or thin-walled three-dimensional unit mesh model. The specific steps for constructing the three-dimensional unit mesh model include the following:

[0032] a. Model three-dimensionalization: Based on different modeling software or programming languages; if a rod-based structure model is constructed, a sphere with a diameter of d moves along all the side lines of the two-dimensional unit line diagram once in space, and the outer contour of the space covered by it is the outer surface of the three-dimensionalized rod-based model, and the rod diameter is d; if a thin-walled structure model is constructed, a circle with a diameter of d' moves along all the side lines of the two-dimensional unit line diagram once in the two-dimensional plane, and the outer contour of the covered area is the cross-sectional shape of the three-dimensionalized model. Stretch a certain height h along the normal direction of the two-dimensional plane to construct a three-dimensionalized thin-walled model, and its wall thickness is d'.

[0033] b. Model manufacturability optimization: According to the requirements of additive manufacturing, the model is transferred and stored as a mesh type file, and the mesh type file includes.STL,.OBJ,.AMF formats.

[0034] Modeling the unit as a rod-based or thin-walled three-dimensional unit mesh model with the above idea is beneficial to reducing errors such as cracks and distortions in the three-dimensional model, improving the model accuracy, and providing a basis for high-precision additive manufacturing.

[0035] In any of the above technical solutions, in step S3, the anti-chiral unit array mode specifically includes the following steps: If a 2.5D mechanical metamaterial is finally constructed, it is modeled by continuously mirroring and repeating the array of mechanical metamaterial units along each side direction. The units sharing a boundary surface with the left-handed unit are all right-handed units, and any units sharing a boundary surface with the right-handed unit are all left-handed units. If a 3D mechanical metamaterial is constructed, after constructing a 2.5D model through the above operations, a 3D model is constructed by orthogonally arranging multiple identical models. The construction principle needs to ensure good connectivity at each node.

[0036] Two types of mechanical metamaterials can be constructed through the anti-chiral unit array mode, which are suitable for different working environments and requirements. At the same time, such an array modeling method can ensure good structural connectivity and stable deformation mechanism between adjacent mechanical metamaterial units, providing a basis for realizing overall uniform deformation and stress transfer. The finally constructed 2.5D mechanical metamaterial is suitable for the cases where the mechanical metamaterial units are triangular prisms and cuboids, and the finally constructed 3D mechanical metamaterial is suitable for the cases where the mechanical metamaterial units are cuboids.

[0037] In any of the above technical solutions, in step S3, the manufacturability optimization specifically includes the following steps: including rounding and chamfering some areas of the model according to geometric dimensions and manufacturing process requirements; post-processing the model mesh for subsequent slicing and additive manufacturing processes. The post-processing includes mesh redrawing, repairing interfering shells, holes, bad edges, overlapping and intersecting triangular meshes.

[0038] The manufacturability optimization helps to reduce the accumulation of thermal stress during the additive manufacturing process. Among them, the mesh post-processing program is also beneficial to reducing the probability of errors such as cracks and distortions in the three-dimensional model, facilitating slicing processing, and providing a basis for high-precision additive manufacturing.

[0039] In any of the above technical solutions, in step S4, the shape memory alloy system includes one of the nickel-titanium-based shape memory alloy systems (such as NiTi alloy, NiTiNb alloy, etc.), copper-based shape memory alloy systems (such as CuAlMn alloy, CuAlNi alloy, etc.) and high-entropy shape memory alloy systems.

[0040] Selecting a shape memory alloy system according to the specific use environment of mechanical metamaterials helps to meet its requirements for temperature conditions, mechanical properties, corrosion resistance, biocompatibility, cost, and manufacturability. For example, the nickel-titanium-based shape memory alloy system has better and more stable shape memory effect and superelasticity, as well as good strength, corrosion resistance, and biocompatibility. Moreover, the phase transition temperature has a wide adjustable range, enabling it to adapt to more use environments, but it is expensive and difficult to process. The copper-based shape memory alloy system has good shape memory effect and superelasticity, but poor corrosion resistance, and is not suitable for marine environments or industrial acidic wastewater. The iron-based shape memory alloy system has high strength, good plasticity, low cost, and easy processing, but its superelasticity is weak, and the phase transition temperature has a narrow adjustable range.

[0041] In any of the above technical solutions, the optimization of the alloy composition ratio includes adjusting the atomic ratio of each component in the alloy system and adding additional components; the optimization of the 3D printing process parameters includes the optimization of scanning strategy, layer thickness, scanning spacing, output power, scanning speed, printing direction, and support strategy; the formulation of the post-treatment system includes no additional post-treatment, heat treatment, hot isostatic pressing treatment, cold treatment, and alternating cold and heat treatment.

[0042] By optimizing the alloy composition ratio by adjusting the atomic ratio of each component in the alloy system and adding additional components, optimizing the 3D printing process parameters, and formulating the post-treatment system, it is possible to effectively control its microstructure, phase composition, and phase content, so as to optimize mechanical properties such as strength, plasticity, and toughness, and widely control its martensitic transformation temperature and reverse martensitic transformation temperature, thereby directionally exhibiting the shape memory effect or superelasticity. For example, when the mechanical metamaterial is deformed under load below the martensitic transformation termination temperature and then heated to the martensitic transformation termination temperature by an external thermal field excitation, it can restore its original shape, realizing the recoverable deformation of the shape memory effect. When it is deformed under load in a use environment above the austenitic transformation termination temperature and the load is removed, the mechanical metamaterial undergoes austenite phase transformation and restores its original shape, realizing the recoverable deformation of the superelasticity. This step also helps to solve the problems of warping, deformation, and cracking of 3D printed shape memory alloy metamaterials.

[0043] In any of the above technical solutions, in step S5, the 3D printing technology includes one of laser powder bed fusion, electron beam powder bed fusion, and laser directed energy deposition. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 is a schematic flow chart of a 3D printed deformable and recoverable shape memory alloy mechanical metamaterial according to the present invention;

[0045] Figure 2 is a schematic diagram of a two-dimensional line drawing of a mechanical metamaterial unit according to the present invention;

[0046] Figure 3 Schematic diagram of the three-dimensional unit grid model of the mechanical metamaterial constructed according to the present invention;

[0047] Figure 4 Schematic diagram of the thin-walled mechanical metamaterial model constructed by the anti-chiral array method of the present invention;

[0048] Figure 5 Schematic diagram of the DSC curve of the formed NiTi shape memory alloy after optimizing the alloy system composition ratio and process parameters of the present invention;

[0049] Figure 6 Schematic diagram of the Hex-type and Star-type NiTi alloy mechanical metamaterials formed by SLM of the present invention and the control group Square-type;

[0050] Figure 7 Schematic diagram of the stress-strain curves of the Hex-type and Star-type NiTi alloy mechanical metamaterials of the present invention and the control group Square-type;

[0051] Figure 8 Schematic diagram of the elastic moduli of the Hex-type and Star-type NiTi alloy mechanical metamaterials of the present invention and the control group Square-type;

[0052] Figure 9 Schematic diagram of the stress distribution at 5% strain of the Hex-type and Star-type NiTi alloy mechanical metamaterials of the present invention and the control group Square-type;

[0053] Figure 10 Schematic diagram of the 10-cycle cyclic response of the Hex-type and Star-type NiTi alloy mechanical metamaterials of the present invention and the control group Square-type;

[0054] Figure 11 Schematic diagram of the energy absorption and elastic hysteresis performance of the Hex-type and Star-type NiTi alloy mechanical metamaterials of the present invention and the control group Square-type within 10 cycles;

[0055] Figure 12 Schematic diagram of the deformation recovery rate of the Hex-type and Star-type NiTi alloy mechanical metamaterials of the present invention and the control group Square-type under cyclic loading and after 10 cycles;

[0056] Figure 13 Schematic diagram of the embedded negative Poisson's ratio honeycomb structure related to the present invention. Detailed implementation manners

[0057] To better understand the above-mentioned objects, features, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, without conflict, the embodiments of the present application and the features in the embodiments can be combined with each other.

[0058] In the following description, many specific details are set forth in order to fully understand the present invention. However, the present invention may be implemented in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited by the specific embodiments disclosed below.

[0059] The following describes some embodiments of the 3D printed deformable and recoverable shape memory alloy mechanical metamaterial of the present invention with reference to the accompanying drawings.

[0060] Embodiment 1

[0061] A 3D printed deformable and recoverable shape memory alloy mechanical metamaterial, comprising the following steps:

[0062] S1. Define the shape, geometric dimensions, and design boundaries of the mechanical metamaterial unit according to the usage environment requirements and manufacturing requirements of the mechanical metamaterial.

[0063] S2. Based on the shape and design boundaries of the mechanical metamaterial unit, reconstruct the polygon unit of the mechanical metamaterial into a secondary rotating polygon by means of polygon unit vectorization and setting secondary vertices, embed a negative Poisson's ratio honeycomb structure inside the secondary rotating polygon, and use geometric transformation to reconstruct the geometry of the unit side lines to complete the design and drawing of the two-dimensional line diagram of the mechanical metamaterial unit.

[0064] S3. Construct a three-dimensional unit mesh model based on the two-dimensional line diagram of the mechanical metamaterial unit, set the structural parameters, construct the mechanical metamaterial model according to the anti-chiral unit array mode, and optimize the manufacturability of the mesh file of the three-dimensional unit mesh model.

[0065] S4. According to the requirements of the service environment of the mechanical metamaterial for temperature conditions, mechanical properties, corrosion resistance, biocompatibility, cost, and manufacturability, select the corresponding shape memory alloy composition system, and further regulate the microstructure and phase transformation temperature of the mechanical metamaterial through alloy composition ratio optimization, 3D printing process parameter optimization, and post-treatment system formulation, so that the mechanical metamaterial exhibits the desired shape memory effect or superelasticity in the temperature conditions, and obtains optimized strength, plasticity, and toughness.

[0066] S5. Slice the mechanical metamaterial model through software, and use the shape memory alloy powder after alloy composition ratio optimization to prepare a deformable and recoverable shape memory alloy mechanical metamaterial by 3D printing technology with the optimized 3D printing process parameters.

[0067] The present application discloses a 3D-printed deformable and recoverable shape memory alloy mechanical metamaterial. Through the mechanical metamaterial unit structure design strategies of reconstructing secondary rotating polygons, embedding negative Poisson's ratio honeycombs inside the secondary rotating polygons, and reconstructing the geometric structure of the side lines, as well as the anti-chiral array pattern and various three-dimensional model construction methods, the flexibility and deformation performance of the mechanical metamaterial are improved from multiple dimensions such as multiple design parameters and various design schemes, and the mechanical properties such as elastic modulus, yield strength, and Poisson's ratio can be artificially regulated. The reasonable selection of the shape memory alloy composition system and 3D printing process parameters realizes the high-precision and high-performance forming of the mechanical metamaterial, and achieves the integration of multiple functions such as energy absorption and vibration reduction, large-range deformability recovery, and zero Poisson's ratio deformation. This method uses additive manufacturing materials for additive manufacturing and can quickly and efficiently form customized complex structures. This method uses a design method targeting mechanical metamaterial units and can provide various mechanical metamaterials with different geometric shapes to meet the requirements of different structural shapes. By constructing secondary rotating polygons within the polygonal units, this method can achieve precise regulation of zero / negative Poisson's ratio deformation and stiffness, adapting to various complex working environments. By embedding negative Poisson's ratio honeycombs with different configurations, this method can customize the deformation behavior, adjust mechanical properties such as modulus and strength, and meet various personalized requirements. Through the optimization of alloy composition ratios, 3D printing process parameter optimization, and the formulation of post-treatment systems, this method realizes the regulation of the microstructure and phase transformation temperature of the shape memory alloy, enabling the alloy material to exhibit the shape memory effect or superelasticity directionally, and obtaining optimized strength, plasticity, and toughness, which are beneficial for achieving the required performance for mechanical metamaterial applications, realizing intelligence, and increasing the service life. This method uses additive manufacturing technology for forming, has green manufacturing attributes such as reducing energy consumption, reducing material waste, and reducing environmental pollution, and has advantages such as environmental protection and sustainable production. By adjusting the mechanical metamaterial model construction method, design parameters, alloy system, forming process parameters, and processing and manufacturing process, this method can realize the deformable and recoverable function of the shape memory alloy mechanical metamaterial and customize various mechanical properties, with high engineering value and broad application prospects.

[0068] In any of the above technical solutions, the shapes of the mechanical metamaterial units include regular triangular prisms and cuboids. The corresponding cross-sectional shapes of the regular triangular prisms and cuboids are equilateral triangles and rectangles respectively. The geometric dimensions are defined by the stretching height and the dimensions of the cross-sectional shapes. The geometric dimensions are respectively the side length of the equilateral triangle and the length and width of the rectangle. The design boundary is the internal area of the cross-section, which is orthogonal to the stretching height direction. Setting the cross-sectional shape of the mechanical metamaterial unit as an equilateral triangle or a rectangle can provide a good representative cell pattern for the construction of the mechanical metamaterial, facilitating the macroscopic control of various mechanical properties of the mechanical metamaterial using the relevant design parameters of the unit. The fact that the design boundary is orthogonal to the stretching height direction helps to achieve the customization of the deformation behavior and improve the manufacturability of 3D printing.

[0069] In any of the above technical solutions, the geometric transformation includes buckling and bending.

[0070] In any of the above technical solutions, the structural parameters include one or more of thickness, wall thickness, and rod diameter.

[0071] In any of the above technical solutions, in step S2, the reconstruction of the polygonal unit of the mechanical metamaterial into a secondary rotating polygon specifically includes the following steps:

[0072] a. Vectorization of the polygonal unit: Inside the design boundary, the mechanical metamaterial unit is represented by its cross-section. The cross-section of the mechanical metamaterial unit corresponds to the polygonal unit of the mechanical metamaterial unit. Select any vertex of the polygonal unit as the starting vertex. Starting from the starting vertex, go in any direction along one of the two connected sides. After passing through the remaining vertices and side lines, return to this starting vertex. During the process from the starting vertex to returning to the starting vertex, there are n segments of running paths including direction and length along the side lines. The n segments of running paths are respectively denoted as where \(i = 1, 2, \ldots, n\), and \(n\) is the number of sides of the polygon (3 or 4), then it is necessary to satisfy:

[0073]

[0074] In this way, the polygonal unit is transformed into a circular structure formed by connecting the n vectors end to end, completing the vectorization of the polygonal unit. At the same time, the chirality characteristics of the polygonal unit can be defined: taking the same direction perpendicular to the design interface as the reference, if the vector forms a circular structure connected end to end in a clockwise direction, it is defined as a left-handed unit, and if it is counterclockwise, it is defined as a right-handed unit;

[0075] b. Setting the secondary vertices of the rotating polygon: For each vertex A i and the vector side starting from it define a scale factor p to set the position of the secondary vertex B i where it is located:

[0076]

[0077] where \(i = 1, 2, \ldots, n\), \(n\) is the number of sides of the polygon, and the scaling factor \(p\in(0, 1)\) is uniquely determined after the first setting of the secondary vertex positions.

[0078] c. Connect all the secondary vertices in sequence to construct a secondary rotating polygon; remove or only retain the side line A i B i Delete or only retain the side line A i B i .

[0079] Reconstructing the polygon unit into a secondary rotating polygon according to the above method can convert the original axial deformation into the rotational deformation of the secondary polygon, thereby significantly improving flexibility, reducing stiffness, and initially introducing a way to achieve zero / negative Poisson's ratio deformation function; the mechanical properties such as the deformation behavior, strength, and stiffness of the mechanical metamaterial can also be conveniently and quickly regulated by the scaling factor \(p\).

[0080] In any of the above technical solutions, in step S2, the embedding of the negative Poisson's ratio honeycomb structure specifically includes the following steps:

[0081] a. Select a negative Poisson's ratio honeycomb structure: Based on the cross-section of the mechanical metamaterial unit, select a negative Poisson's ratio honeycomb structure. If the cross-section of the mechanical metamaterial unit is an equilateral triangle, select a double-V-shaped negative Poisson's ratio honeycomb structure or a triangular star-shaped negative Poisson's ratio honeycomb structure; if the cross-section of the mechanical metamaterial unit is a rectangle, select a re-entrant negative Poisson's ratio honeycomb structure or a star-shaped negative Poisson's ratio honeycomb structure.

[0082] b. By changing the geometric characteristics of the side lines, that is, by buckling or bending the side lines corresponding to the embedding direction of the negative Poisson's ratio honeycomb, realize the composite embedding of the negative Poisson's ratio honeycomb structure within the cross-section of the mechanical metamaterial unit.

[0083] By selecting to embed a double-V-shaped negative Poisson's ratio honeycomb, a triangular star-shaped negative Poisson's ratio honeycomb structure, a re-entrant negative Poisson's ratio honeycomb structure, or a star-shaped negative Poisson's ratio honeycomb structure, a variety of mechanical metamaterial configuration schemes can be developed to achieve customized combinations of different deformation behaviors and mechanical properties. Different negative Poisson's ratio honeycomb structures have different mechanical characteristics. For example, the double-V-shaped negative Poisson's ratio honeycomb and the re-entrant negative Poisson's ratio honeycomb have strong mechanical anisotropy, while the star-shaped negative Poisson's ratio honeycomb has a lower tangential stiffness. Different embedding directions also affect the anisotropy of the mechanical metamaterial and the stress transfer and deformation between mechanical metamaterial units.

[0084] In any of the above technical solutions, there are 3 embedding directions for the double-V negative Poisson's ratio honeycomb structure, 1 embedding direction for the triangular star negative Poisson's ratio honeycomb structure, 2 embedding directions for the re-entrant negative Poisson's ratio honeycomb structure, and 1 embedding direction for the star negative Poisson's ratio honeycomb structure. Different embedding directions of the honeycomb structure into the secondary rotating polygon unit of the metamaterial unit will form composite structures with different structures. Different embedding directions also affect the anisotropy of the metamaterial and the stress transfer and deformation between units.

[0085] In any of the above technical solutions, the specific steps for the geometric shape of the reconstructed unit edges are as follows: For the remaining edges, reconstruction methods including buckling, bending, deletion, or retention are used; Buckling means modifying the original straight edge into two concave broken lines, and each end point is connected to the end point of the original edge to form a closed triangle; Bending includes modifying and replacing with curves such as arcs, parabolas, and Bezier curves, and other reconstruction methods include replacing with other edge geometric configurations such as multi-segment broken lines.

[0086] By reconstructing the geometric shape of the polygon unit edges through the above specific method, the space for unit rotational deformation and negative Poisson's ratio deformation can be further liberated, achieving the design goals of increasing the deformation range, improving the deformation uniformity, reducing the stiffness, and enhancing the flexibility. The reconstruction methods and design parameters involved in the reconstruction steps can also be used to regulate the mechanical properties of the developed mechanical metamaterials.

[0087] In any of the above technical solutions, in step S3, the three-dimensional unit mesh model is a rod system or thin-walled three-dimensional unit mesh model. The specific steps for constructing the three-dimensional unit mesh model include the following:

[0088] a. Model three-dimensionalization: Based on different modeling software or programming languages; If a rod system structure model is constructed, a sphere with a diameter of d moves along all the edges of the two-dimensional unit line diagram once in space, and the outer contour of the space covered by it is the outer surface of the three-dimensionalized rod system model, and the rod diameter is d; If a thin-walled structure model is constructed, a circle with a diameter of d' moves along all the edges of the two-dimensional unit line diagram once in the two-dimensional plane, and the outer contour of the covered area is the cross-sectional shape of the three-dimensionalized model. Stretch a certain height h along the normal direction of the two-dimensional plane to construct a three-dimensionalized thin-walled model, and its wall thickness is d'.

[0089] b. Model manufacturability optimization: According to the requirements of additive manufacturing, the model is saved as a mesh type file, and the mesh type file includes.STL,.OBJ,.AMF formats.

[0090] Modeling the unit as a rod system or thin-walled three-dimensional unit mesh model with the above idea is beneficial to reducing errors such as cracks and distortions in the three-dimensional model, improving the model accuracy, and providing a basis for high-precision additive manufacturing.

[0091] In any of the above technical solutions, in step S3, the specific steps of the anti-chiral unit array pattern are as follows: If it is finally constructed into a 2.5D mechanical metamaterial, the mechanical metamaterial units are modeled by continuously mirroring and repeating the array along each side direction. The units sharing a common boundary surface with the left-handed units are all right-handed units, and any units sharing a common boundary surface with the right-handed units are all left-handed units; If it is constructed into a 3D mechanical metamaterial, after constructing a 2.5D model through the above operations, a 3D model is constructed by orthogonally arranging multiple identical models, and the construction principle needs to ensure good connectivity at each node.

[0092] Two types of mechanical metamaterials can be constructed through the anti-chiral unit array pattern, which are suitable for different working environments and requirements. At the same time, such an array modeling method can ensure good structural connectivity and stable deformation mechanism between adjacent mechanical metamaterial units, providing a basis for realizing overall uniform deformation and stress transfer. The finally constructed 2.5D mechanical metamaterial is suitable for the cases where the mechanical metamaterial units are triangular prisms and cuboids, and the finally constructed 3D mechanical metamaterial is suitable for the cases where the mechanical metamaterial units are cuboids.

[0093] In any of the above technical solutions, in step S3, the specific steps of the manufacturability optimization include: rounding and chamfering some areas of the model according to geometric dimensions and manufacturing process requirements; post-processing the model mesh for subsequent slicing and additive manufacturing processes, and the post-processing includes mesh redrawing, repairing interfering shells, holes, bad edges, overlapping and intersecting triangular facets.

[0094] The manufacturability optimization helps to reduce the accumulation of thermal stress during the additive manufacturing process. Among them, the mesh post-processing program is also beneficial to reducing the probability of errors such as cracks and distortions in the three-dimensional model, facilitating slicing processing, and providing a basis for high-precision additive manufacturing.

[0095] In any of the above technical solutions, in step S4, the shape memory alloy system includes one of the nickel-titanium-based shape memory alloy systems (such as NiTi alloy, NiTiNb alloy, etc.), copper-based shape memory alloy systems (such as CuAlMn alloy, CuAlNi alloy, etc.) and high-entropy shape memory alloy systems.

[0096] Selecting a shape memory alloy system according to the specific use environment of mechanical metamaterials helps to meet its requirements for temperature conditions, mechanical properties, corrosion resistance, biocompatibility, cost, and manufacturability. For example, the nickel-titanium-based shape memory alloy system has better and more stable shape memory effect and superelasticity, as well as good strength, corrosion resistance, and biocompatibility. Moreover, the phase transformation temperature has a wide adjustable range, enabling it to adapt to more use environments. However, it is expensive and difficult to process. The copper-based shape memory alloy system has good shape memory effect and superelasticity, but poor corrosion resistance, and is not suitable for marine environments or industrial acidic wastewater. The iron-based shape memory alloy system has high strength, good plasticity, low cost, and is easy to process, but its superelasticity is weak and the adjustable range of phase transformation temperature is narrow.

[0097] In any of the above technical solutions, the optimization of the alloy composition ratio includes adjusting the atomic ratio of each component in the alloy system and adding additional components; the optimization of the 3D printing process parameters includes the optimization of scanning strategy, layer thickness, scanning spacing, output power, scanning speed, printing direction, and support strategy; the formulation of the post-treatment system includes not performing additional post-treatment, heat treatment, hot isostatic pressing treatment, cold treatment, and alternating hot and cold treatment.

[0098] By optimizing the alloy composition ratio by adjusting the atomic ratio of each component in the alloy system and adding additional components, optimizing the 3D printing process parameters, and formulating the post-treatment system, it is possible to effectively control its microstructure, phase composition, and phase content, so as to optimize mechanical properties such as strength, plasticity, and toughness, and widely control its martensitic transformation temperature and reverse martensitic transformation temperature, thereby directionally exhibiting the shape memory effect or superelasticity. For example, when the mechanical metamaterial is deformed under load below the martensitic transformation termination temperature and then heated to the martensitic transformation termination temperature by an external heat field excitation, it can restore its original shape, realizing the recoverable deformation of the shape memory effect. When it is deformed under load in a use environment above the austenitic transformation termination temperature and the load is removed, the mechanical metamaterial undergoes austenite phase transformation and restores its original shape, realizing the recoverable deformation of the superelasticity. This step also helps to solve the problems of warping, deformation, and cracking of 3D printed shape memory alloy metamaterials.

[0099] In any of the above technical solutions, in step S5, the 3D printing technology includes one of laser powder bed fusion, electron beam powder bed fusion, and laser directed energy deposition.

[0100] Example 2

[0101] In step S1, aiming at the usage requirements of the uniform deformation, recoverable deformation, and zero Poisson's ratio mechanical metamaterials required for the deformed wing skin, the shape of the mechanical metamaterial unit is defined as a cuboid, with its geometric dimensions being 10mm×10mm×4mm, and the design boundary is its 10mm×10mm square, that is, its cross-sectional area, which is orthogonal to the stretching direction.

[0102] In step S2, as Figure 2 shown, the reconstruction of the polygon unit of the mechanical metamaterial into a secondary rotating polygon specifically includes the following steps:

[0103] a. Vectorization of the polygon unit: Within the design boundary, the mechanical metamaterial unit appears as its cross-section, and the cross-section of the mechanical metamaterial unit corresponds to the polygon unit of the mechanical metamaterial unit. Taking the quadrilateral unit as an example. Select the vertex of quadrilateral unit A1 and move in the direction of its A2. After passing through the remaining vertices and side lines and returning to this starting vertex, the four paths with directions and lengths along the side lines are respectively denoted as where i = 1, 2, 3, 4, then it is necessary to satisfy:

[0104]

[0105] In this way, the polygon unit is transformed into a ring structure formed by four vectors connected end to end, completing the vectorization of the polygon unit, and at the same time, this unit can be defined as a right-handed unit.

[0106] b. Setting the secondary vertices of the rotating polygon: For each vertex A i and the vector side starting from it , define the scale factor p to set the position of the secondary vertex B i :

[0107]

[0108] where i = 1, 2, 3, 4, and the scale factor p = 0.37, which is uniquely determined after the first setting of the secondary vertex position.

[0109] c. Connect all the secondary vertices in sequence to construct a secondary rotating polygon. Delete the side line A i B i .

[0110] Embedding the negative Poisson's ratio honeycomb structure specifically includes the following steps:

[0111] a. Selecting the negative Poisson's ratio honeycomb structure: The cross-section of the mechanical metamaterial unit is a square, so the re-entrant negative Poisson's ratio honeycomb structure and the star-shaped negative Poisson's ratio honeycomb structure are respectively selected, and the embedding direction is the compression force direction. For the above two kinds of honeycombs, the generated metamaterial models are respectively named with Hex and Star related information;

[0112] b. By changing the geometric characteristics of the side line, that is, by buckling the side line corresponding to the honeycomb embedding direction, the negative Poisson's ratio honeycomb structure is compoundly embedded within the unit cross-section.

[0113] The specific method for reconstructing the geometric shape of the unit boundary lines is to use the buckling reconstruction method for the boundary lines that were not deleted in step S2. Buckling means modifying the original straight boundary line into two concave broken lines. All the triangles formed during the buckling operation contain two 30° base angles, and its longest side is the boundary line that was not deleted.

[0114] In step S3, as Figure 3 shown, a three-dimensional unit grid model is constructed based on the two-dimensional line diagram of the mechanical metamaterial unit, and adjustable structural parameters such as thickness, wall thickness, or rod diameter are set. The specific steps are as follows;

[0115] a. Three-dimensionalization of the model: Construct a thin-walled structure model. In the two-dimensional plane, a circle with a diameter of d’ = 0.4 mm moves along all the boundary lines of the two-dimensional unit line diagram once, and the outer contour of the covered area is the cross-sectional shape of this three-dimensionalized model; stretch a certain height h = 4 mm along the normal direction of this plane to construct a three-dimensional thin-walled model, and its wall thickness is d’ = 0.4 mm;

[0116] b. Optimization of model manufacturability: According to the requirements of additive manufacturing, the model is saved as an.STL format file of the mesh type.

[0117] In step S3, as Figure 4 shown, a thin-walled mechanical metamaterial model is constructed according to the anti-chiral unit array pattern. The number of arrays is 4×4, and the total size after array is 40.4 mm×40.4 mm. To facilitate mechanical property testing, fixture clamping areas are additionally modeled on both sides. According to the geometric dimensions and manufacturing process requirements, the acute angle areas of the model are rounded. Post-processing is performed on the model mesh for subsequent slicing and additive manufacturing processes. The post-processing includes mesh redrawing, repair of interfering shells, holes, bad edges, overlapping, and intersecting triangular patches.

[0118] In step S4, based on the excellent and stable superelasticity, good strength, and corrosion resistance required for the deformable wing skin, a near-equiatomic ratio NiTi shape memory alloy is selected. By changing the atomic ratio and 3D printing process parameters, its plasticity and phase transformation temperature are comprehensively regulated, and the composition is optimized to Ni 50.8 Ti 49.2 (at.%), using the SLM technology, its process window is narrowed to a laser power P = 125 - 145 W and a scanning speed v = 550 - 750 mm / s, without additional post-processing; finally, a NiTi shape memory alloy with an elongation of 8.2% and a martensitic reverse transformation termination temperature of 20.2 °C is obtained. As Figure 5 shown by the DSC curve of the formed NiTi shape memory alloy, it shows stable superelasticity at room temperature, providing a material-level basis for realizing the deformable recoverable function.

[0119] In step S5, use the Ni with optimized composition ratio50.8 Ti 49.2 (at.%) shape memory alloy powder is formed by the SLM technology using a DiMetal-150 metal 3D printer with a maximum power of 200W. The forming process is carried out in an argon protective atmosphere, and further optimized process parameters are used, including laser power P = 135W, scanning speed v = 650mm / s, scanning spacing h = 0.07mm, layer thickness t = 0.03mm, and the scanning angle rotates layer by layer at 67°, completing the additive manufacturing of NiTi alloy mechanical metamaterials.

[0120] The NiTi alloy mechanical metamaterials formed by SLM are as Figure 6 shown. The mechanical metamaterials obtained by using the method proposed in the present invention are named Hex and Star respectively, and a conventional rotating polygon mechanical metamaterial Square is additionally prepared as a control group to illustrate the effectiveness and dominant position of the present invention in obtaining deformable and recoverable mechanical metamaterials. The control group is only different from Hex and Star in configuration, and its unit shape, size, anti-chiral array mode, modeling process, forming material, and manufacturing process are exactly the same.

[0121] The mechanical properties and deformation recovery ability of the 3D printed deformable and recoverable shape memory alloy mechanical metamaterials selected in Example 1 of the present invention and the control group are tested according to the following standard process.

[0122] (1) Mechanical properties

[0123] Using a CMT5105 universal testing machine, a quasi-static compression experiment is carried out on the SLM formed NiTi alloy mechanical metamaterials at room temperature. The loading rate of the quasi-static compression experiment is set to 0.2mm / min; the compression response data is acquired and recorded through a sensor, and the cyclic deformation process is recorded by a fixed-position camera. Using Abaqus 2022 finite element simulation software, a static simulation is carried out on the NiTi alloy mechanical metamaterials.

[0124] As Figure 7 shown, the stress-strain curves of the Hex-type and Star-type NiTi alloy mechanical metamaterials and the control group Square-type under quasi-static compression show that the control group Square-type has broken at 10% strain and cannot continue to deform; while the Hex-type and Star-type have not broken at 30% strain, and their deformation form mainly bending makes their deformation range significantly higher than that of the control group, with stronger flexibility.

[0125] As Figure 8As shown, the comparison of the elastic moduli of Hex-type and Star-type NiTi alloy mechanical metamaterials and the control group Square-type. The elastic modulus of Square-type is 270.56 MPa, which is much higher than that of Hex-type (46.69 MPa) and Star-type (50.31 MPa). After normalization by volume fraction, the normalized elastic modulus of Star-type mechanical metamaterial is 0.90 times that of Hex-type and 0.13 times that of the control group Square-type, with the smallest stiffness and the strongest flexibility.

[0126] As Figure 9 shown, from the deformation of Hex-type and Star-type NiTi alloy mechanical metamaterials and the control group Square-type at 5% strain, it can be found that there is no fracture in Hex-type and Star-type, the overall structure of the mechanical metamaterial is intact, and the deformation is uniform. However, there are multiple fractures in the control group Square-type and the deformation cannot be recovered. The stress distribution results of Abaqus simulation show that the overall stress levels of Hex-type and Star-type are lower, reducing the possibility of the first stress fracture caused by stress concentration in the rigid region.

[0127] (2) Deformation recovery ability

[0128] Using a CMT5105 universal testing machine, a cyclic compression experiment was carried out on the SLM-formed NiTi alloy mechanical metamaterial at room temperature. One loading-unloading cycle was used, and a total of 10 cycles were carried out for each sample. The loading and unloading rates were set at 1 mm / min. The recoverable strain, strain recovery rate, etc. were calculated based on the cyclic curve. The ABAQUS2022 finite element simulation software was used to perform a single-cycle loading-unloading simulation on the NiTi alloy mechanical metamaterial.

[0129] As Figure 10 shown, the cyclic force-displacement curves of Hex-type and Star-type NiTi alloy mechanical metamaterials and the control group Square-type within 10 cycles show that the control group Square-type has strong rigidity, specifically manifested as the fracture of the structure in the first cycle. After the compression displacement further increases, the bearing capacity reaches the peak, and then the curve drops steeply, resulting in a destructive fracture and irreversible failure of the structure. However, the curves of the developed Hex-type and Star-type NiTi alloy mechanical metamaterials in 10 cycles are smooth and continuous, indicating that they have not been damaged and have good deformation behavior and deformation recovery performance.

[0130] As Figure 11As shown, the comparison of the energy absorption and elastic hysteresis performance of the Hex-type and Star-type NiTi alloy mechanical metamaterials and the control group Square-type within 10 cycles shows that the energy absorption and damping performance of the Hex-type and Star-type are better and more stable, while that of the control group Square-type decreases rapidly with the increase of the number of cycles, indicating that the fatigue damage accumulates extremely rapidly and failure occurs faster.

[0131] As Figure 12 shown, from the deformation recovery rates of the Hex-type and Star-type NiTi alloy mechanical metamaterials and the control group Square-type under cyclic loading and after 10 cycles, it can be seen that the deformation recovery rate of the Hex-type is always higher than 98%, while that of the Star-type always exceeds 99%, far higher than that of the control group Square-type; the deformation recovery rate of the control group Square-type after 10 cycles of hysteresis is only 61.05%, while those of the Hex-type and Star-type are 92.73% and 95.44% respectively; the above data show that the NiTi alloy mechanical metamaterials developed by the present invention have extremely strong advantages in large flexibility and deformation recovery ability and can be effectively applied to scenarios such as deformable wing skins.

[0132] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope recorded in this specification.

[0133] The above-described embodiments only represent several implementation manners of the present invention. Their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the invention patent should be subject to the appended claims.

Claims

1. A 3D-printed deformable and recoverable shape memory alloy mechanical metamaterial, characterized in that, It includes the following steps: S1. Define the shape, geometric dimensions, and design boundaries of the mechanical metamaterial unit according to the usage environment requirements and manufacturing requirements of the mechanical metamaterial; S2. Based on the shape and design boundaries of the mechanical metamaterial unit, reconstruct the polygon unit of the mechanical metamaterial into a secondary rotating polygon by means of polygon unit vectorization and setting secondary vertices, embed a negative Poisson's ratio honeycomb structure inside the secondary rotating polygon, and use geometric transformation to reconstruct the geometry of the unit side lines to complete the design and drawing of the 2D line diagram of the mechanical metamaterial unit; S3. Build a 3D unit mesh model based on the 2D line diagram of the mechanical metamaterial unit, set the structural parameters, construct a mechanical metamaterial model according to the anti-chiral unit array pattern, and optimize the manufacturability of the mesh file of the 3D unit mesh model; S4. According to the requirements of the mechanical metamaterial service environment for temperature conditions, mechanical properties, corrosion resistance, biocompatibility, cost, and manufacturability, select the corresponding shape memory alloy composition system, and further regulate the microstructure and phase transformation temperature of the mechanical metamaterial by optimizing the alloy composition ratio, optimizing the 3D printing process parameters, and formulating the post-treatment system, so that the mechanical metamaterial exhibits the required shape memory effect or superelasticity directionally under the temperature conditions, and obtain optimized strength, plasticity, and toughness; S5. Slice the mechanical metamaterial model through software, and use the shape memory alloy powder with optimized alloy composition ratio to prepare a deformable and recoverable shape memory alloy mechanical metamaterial by 3D printing technology with optimized 3D printing process parameters.

2. The 3D printed deformable and recoverable shape memory alloy mechanical metamaterial according to claim 1, wherein the shape of the mechanical metamaterial unit includes a regular triangular prism and a cuboid, the corresponding cross-sectional shapes of the regular triangular prism and the cuboid are an equilateral triangle and a rectangle respectively, the geometric dimensions are defined by the stretching height and the dimensions of the cross-sectional shape, the geometric dimensions are respectively the side length of the equilateral triangle and the length and width of the rectangle, and the design boundary is the internal area of the cross-section, orthogonal to the stretching height direction; and / or the geometric transformation includes buckling and bending; and / or the structural parameters include one or more of thickness, wall thickness, and rod diameter.

3. The 3D printed deformable and recoverable shape memory alloy mechanical metamaterial according to claim 1, characterized in that, In step S2, the reconstruction of the polygon unit of the mechanical metamaterial into a secondary rotating polygon specifically includes the following steps: a. Vectorization of polygon units: Within the design boundary, the mechanical metamaterial unit exhibits its cross-section, and the cross-section of the mechanical metamaterial unit corresponds to the polygon unit of the mechanical metamaterial unit. Select any vertex of the polygon unit as the starting vertex. Starting from the starting vertex, move in any direction along one of the two connected sides. After passing through the remaining vertices and side lines, return to this starting vertex. During the process from the starting vertex to the return of the starting vertex, there are n segments of running paths along the side lines, including direction and length. The n segments of running paths are respectively denoted as where i = 1, 2, …, n, and n is the number of sides of the polygon (3 or 4), then it is necessary to satisfy: In this way, the polygon unit is transformed into a ring structure formed by connecting n vectors end to end to complete the vectorization of the polygon unit. At the same time, the chirality characteristics of the polygon unit can be defined: taking the same direction perpendicular to the design interface as the reference, if the vector connection forms a clockwise ring structure, it is defined as a left-handed unit, and if it is counterclockwise, it is defined as a right-handed unit; b. Set the secondary vertices of the rotating polygon: For each vertex A i and the vector edge starting from it Define the scale factor p to set the position of the secondary vertex B i as follows: where i = 1, 2,..., n, n is the number of sides of the polygon, and the scaling factor p ∈ (0, 1), which is uniquely determined after the first secondary vertex position is set; c. Connect all secondary vertices in sequence to construct a secondary rotating polygon; delete or only retain side A i B i Delete or only retain side A i B i .

4. The 3D printed deformable and recoverable shape memory alloy mechanical metamaterial according to claim 1, characterized in that, In step S2, the embedding of the negative Poisson's ratio honeycomb structure specifically includes the following steps: a. Select a negative Poisson's ratio honeycomb structure: Based on the cross-section of the mechanical metamaterial unit, select a negative Poisson's ratio honeycomb structure. If the cross-section of the mechanical metamaterial unit is an equilateral triangle, select a double-V negative Poisson's ratio honeycomb structure or a triangular star negative Poisson's ratio honeycomb structure; if the cross-section of the mechanical metamaterial unit is a rectangle, a re-entrant negative Poisson's ratio honeycomb structure or a star negative Poisson's ratio honeycomb structure can be selected. b. By changing the geometric characteristics of the side edges, that is, by buckling or bending the side edges corresponding to the embedding direction of the negative Poisson's ratio honeycomb, a negative Poisson's ratio honeycomb structure is compoundly embedded within the cross-section of the mechanical metamaterial unit.

5. The 3D printed deformable and recoverable shape memory alloy mechanical metamaterial according to claim 1, characterized in that, In step S3, the three-dimensional unit grid model is a rod system or thin-walled three-dimensional unit grid model. The specific steps for constructing the three-dimensional unit grid model include the following: a. Model three-dimensionalization: Based on different modeling software or programming languages; if a rod system structure model is constructed, a sphere with a diameter of d moves along all the side edges of the two-dimensional unit line diagram once in space, and the spatial outer contour of the covered area is the outer surface of the three-dimensionalized rod system model, and the rod diameter is d; if a thin-walled structure model is constructed, a circle with a diameter of d' moves along all the side edges of the two-dimensional unit line diagram once in the two-dimensional plane, and the outer contour of the covered area is the cross-sectional shape of the three-dimensionalized model. Stretch a certain height h along the normal direction of the two-dimensional plane to construct a three-dimensionalized thin-walled model, and its wall thickness is d'. b. Model manufacturability optimization: According to the requirements of additive manufacturing, convert the model into a mesh type file, and the mesh type file includes.STL,.OBJ,.AMF formats.

6. The 3D printed deformable and recoverable shape memory alloy mechanical metamaterial according to claim 3, characterized in that, In step S3, the specific steps of the anti-chiral unit array pattern include the following: If a 2.5D mechanical metamaterial is finally constructed, it is modeled by continuously mirroring and repeating the array of mechanical metamaterial units along each side direction. The units sharing a common boundary surface with the left-handed unit are all right-handed units, and any unit sharing a common boundary surface with the right-handed unit is a left-handed unit. If a 3D mechanical metamaterial is constructed, after constructing a 2.5D model through the above operations, a 3D model is constructed by orthogonally arranging multiple identical models. The construction principle needs to ensure good connectivity at each node.

7. The 3D printed deformable and recoverable shape memory alloy mechanical metamaterial according to claim 1, characterized in that, In step S3, the specific steps of the manufacturability optimization include the following: According to the geometric dimensions and manufacturing process requirements, perform rounding and chamfering on some areas of the model; Perform post-processing on the model mesh for subsequent slicing and additive manufacturing processes. The post-processing includes mesh redrawing, repair of interfering shells, holes, bad edges, overlapping, and intersecting triangular patches.

8. The 3D printed deformable and recoverable shape memory alloy mechanical metamaterial according to claim 1, characterized in that, In step S4, the shape memory alloy system includes one of a nickel-titanium-based shape memory alloy system, a copper-based shape memory alloy system, and a high-entropy shape memory alloy system.

9. The 3D printable deformable and recoverable shape memory alloy mechanical metamaterial according to claim 1, wherein the optimization of the alloy composition ratio includes adjusting the atomic ratio of each component in the alloy system and adding additional components; and / or the optimization of the 3D printing process parameters includes the optimization of scanning strategy, layer thickness, scanning spacing, output power, scanning speed, printing direction, and support strategy; And / or the formulation of the post-processing regime includes not performing additional post-processing, heat treatment, hot isostatic pressing, cold treatment, and alternating hot and cold treatment.

10. The 3D printed deformable and recoverable shape memory alloy mechanical metamaterial according to claim 1, characterized in that, In the step S5, the 3D printing technology includes one of selective laser melting technology, electron beam selective melting technology, and laser direct energy deposition.

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