A design method and core structure for a three-dimensional gradient minimal curved surface sandwich structure

Abstract

This invention discloses a design method and core structure for a three-dimensional gradient minimal surface sandwich structure, belonging to the field of minimal surface sandwich structure design. The method includes the following steps: S1, constructing a three-dimensional density distribution characteristic model; S2, constructing the modeling equations for the three-dimensional geometric model of the Gyroid minimal surface structure; S3, obtaining the modeling equations for the three-dimensional gradient minimal surface structure; S4, obtaining the three-dimensional model of the three-dimensional gradient minimal surface structure using modeling software; S5, preparing the three-dimensional gradient minimal surface structure using additive manufacturing technology; S6, obtaining the three-dimensional gradient minimal surface sandwich structure; S7, performance evaluation. By employing the above-mentioned design method and core structure for a three-dimensional gradient minimal surface sandwich structure, and by designing a surface with minimal gradient change in relative density in all three dimensions, the energy absorption performance of the structure is effectively improved, while simultaneously achieving more effective protection of the target.

Description

Technical Field

[0001] This invention relates to the field of minimal surface sandwich structure design technology, and in particular to a design method and sandwich structure for a three-dimensional gradient minimal surface sandwich structure. Background Technology

[0002] With the rapid development of military technology, the destructive effects of blast shockwaves on vehicles, armored vehicles, and personnel in modern warfare are constantly increasing. Therefore, there is an urgent need to further improve the blast resistance of protective structures to cope with increasingly complex and severe battlefield environments. Against this backdrop, minimally curved surface structures, as a novel type of porous structure, possess the following significant advantages: 1. Stable mechanical response: Minimally curved surface structures maintain a relatively stable mechanical response when subjected to external impacts, avoiding the brittle fracture or instability that easily occurs in traditional materials under impact loads; 2. Excellent energy absorption performance: Compared to traditional porous structures, minimally curved surface structures can continuously absorb energy over a wider deformation range, thereby effectively reducing the impact of impact energy on the protected object; 3. Stable deformation behavior: Minimally curved surface structures exhibit relatively uniform deformation characteristics under stress, which helps to disperse impact energy, reduce local stress concentration, and improve the overall protective effect. It is evident that minimally curved surface structures, due to their stable mechanical response, excellent energy absorption performance, and stable deformation behavior, have gradually attracted widespread attention from researchers.

[0003] Furthermore, existing research indicates that gradient design of porous structures can significantly improve their energy absorption performance. Using gradient porous structures as the core layer of sandwich structures can not only significantly enhance the overall blast resistance and protection of the sandwich structure, but also optimize the weight and space utilization of the structure.

[0004] On the other hand, the development of 3D printing technology has greatly facilitated the design and fabrication of complex core structures. This advanced manufacturing technology can not only achieve high-precision, highly complex structural molding, but also quickly adjust and optimize design schemes according to actual needs, greatly shortening the research and development cycle and reducing costs.

[0005] Although core materials such as aluminum foam are widely used in sandwich structures, traditional core materials have the following limitations:

[0006] 1. Low strength: Traditional materials such as aluminum foam have low strength and are prone to failure when faced with high-intensity impacts, making it difficult to meet current protection requirements;

[0007] 2. Uneven platform stress: Traditional materials do not exhibit stable platform stress under strong impact loads such as explosions, which is not conducive to providing reliable protection.

[0008] Compared to uniform structures, minimal surface structures based on two-dimensional surface density distribution exhibit significant improvements in platform stress and energy absorption performance. However, under strong impact loads such as explosions, the overly stable platform stress of the structure is not conducive to effectively protecting the target object. Summary of the Invention

[0009] The purpose of this invention is to provide a design method and a sandwich structure for a three-dimensional gradient minimal curved surface, thereby solving the above-mentioned technical problems.

[0010] To achieve the above objectives, the present invention provides a design method for a three-dimensional gradient-minimum curved surface sandwich structure, comprising the following steps:

[0011] S1. Construct a three-dimensional density distribution feature model based on a combination of two-dimensional saddle surface functions and linear functions;

[0012] S2. Based on the Gyroid minimum surface equation, construct the modeling equations for the three-dimensional geometric model of the Gyroid minimum surface structure;

[0013] S3. The three-dimensional density distribution feature model constructed in step S1 is combined with the modeling equation of the three-dimensional geometric model of the Gyroid minimal surface structure constructed in step S2 to obtain the modeling equation of the three-dimensional gradient minimal surface structure.

[0014] S4. Based on the modeling equation of the three-dimensional gradient minimum surface structure obtained in step S3, a three-dimensional model of the three-dimensional gradient minimum surface structure is obtained through modeling software.

[0015] S5. Based on the three-dimensional model described in step S4, a three-dimensional gradient minimal surface structure is prepared by additive manufacturing technology.

[0016] S6. Using the three-dimensional gradient minimum surface structure obtained in step S5 as the core layer, set up panels in the upper and lower planes of the core layer respectively, and combine the panels with the core layer to obtain a three-dimensional gradient minimum surface gradient sandwich structure.

[0017] S7. The performance of the three-dimensional gradient minimum surface gradient sandwich structure obtained in step S6 is evaluated, and the final three-dimensional gradient minimum surface gradient sandwich structure is determined based on the performance evaluation results.

[0018] Preferably, in step S1, mathematical software is used to construct a two-dimensional surface of the structural density distribution based on a two-dimensional saddle surface function. By changing the parameter values ​​of the two-dimensional saddle surface function, the values ​​of each point in the two-dimensional surface of the structural density distribution are adjusted, so that the relative density values ​​present a saddle surface distribution in the xy plane. At the same time, a linear function is combined to make the relative density produce a linear change in the z direction, thus obtaining a three-dimensional density gradient distribution model.

[0019] Preferably, the two-dimensional surface of the structural density distribution mentioned in step S1 includes a saddle surface, and the expression of the saddle surface is as follows:

[0020] z1=a(bx 2 -by 2 )+c (1);

[0021] In the formula, z1, x, and y represent the z-axis, x-axis, and y-axis coordinates in three-dimensional space, respectively; a represents a constant term used to adjust the height variation of the two-dimensional surface in the z-direction; b represents a constant term used to adjust the width variation of the two-dimensional surface in the x and y directions; and c represents a constant term used to adjust the translation of the entire two-dimensional surface in the z-direction.

[0022] The linear function expression is as follows:

[0023] z2=kz+m (2);

[0024] In the formula, z2 represents the output variable; k and m are both constants;

[0025] The expression for the three-dimensional density gradient distribution model is as follows:

[0026] γ(x,y,z)=z1z2 (3);

[0027] In the formula, γ(x,y,z) represents the density at coordinates (x,y,z) in three-dimensional space.

[0028] Preferably, the modeling equation expression for the three-dimensional geometric model of the Gyroid minimal surface structure described in step S2 is as follows:

[0029]

[0030] In the formula, The density of the Gyroid structure at the original coordinates (x, y, z) is described; (X, Y, Z) represents the normalized coordinates of the period length α, and X = 2απx, Y = 2βπy, Z = 2γπz, where α, β and γ are constants used to control the number of unit cells of the Gyroid minimal surface structure along the three directions of x, y and z.

[0031] Preferably, in step S3, a three-dimensional density distribution feature model is introduced into the Gyroid minimum surface equation, so that the relative density of the Gyroid minimum surface structure in the plane is distributed according to the characteristics of the three-dimensional density distribution feature model, thereby obtaining the modeling equation of the three-dimensional gradient minimum surface structure, and the expression of the modeling equation of the three-dimensional gradient minimum surface structure is as follows:

[0032]

[0033] Preferably, in step S5, SLM additive manufacturing technology is used to perform additive manufacturing with aluminum alloy powder or titanium alloy powder as the substrate.

[0034] Preferably, in step S6, the panel and the core layer are bonded together by adhesive.

[0035] Preferably, step S7 specifically includes the following steps:

[0036] S71. Perform a quasi-static compression test on the three-dimensional gradient minimum surface structure specimen with multiple specification parameters obtained in S5, obtain the stress-strain curve and force-displacement curve of the three-dimensional gradient minimum surface structure specimen, and then calculate the platform stress and energy absorption of the three-dimensional gradient minimum surface gradient sandwich structure, wherein the specification parameters include size parameters and weight parameters.

[0037] Wherein the platform stress σ m The calculation formula is as follows:

[0038]

[0039] In the formula, E V The integral of the stress-strain curve of a three-dimensional gradient-minimum surface structure specimen; ε D Represents the dense strain of a three-dimensional gradient minimum surface structure;

[0040] The expression for energy absorption E is as follows:

[0041]

[0042] In the formula, σ(ε) represents the stress-strain relationship function; dε represents the strain increment; V represents the volume of the three-dimensional gradient minimum surface structure;

[0043] S72. Based on the calculation results of formulas (6) and (7) mentioned in S71, the final three-dimensional gradient minimum surface gradient sandwich structure is obtained by screening.

[0044] A sandwich structure is designed using a method for designing a three-dimensional gradient minimal surface sandwich structure.

[0045] Preferably, the sandwich structure is a three-dimensional gradient minimum surface gradient sandwich structure, which includes a core layer formed by the three-dimensional gradient minimum surface structure and panels disposed on both sides of the core layer. The three-dimensional gradient minimum surface structure has the following characteristics: the relative density in the xy plane is distributed in a two-dimensional surface gradient, and the relative density in the z direction is distributed in a linear gradient.

[0046] Therefore, the present invention employs the above-mentioned design method and sandwich structure for a three-dimensional gradient minimal curved surface, which has the following beneficial effects:

[0047] 1. Uniform and controllable density distribution: By combining saddle surface functions and linear functions, the density is precisely controlled in different directions, so that the structure has different mechanical properties in different regions, meeting a variety of application requirements;

[0048] 2. Minimal surface characteristics: Gyroid's minimal surface structure has high specific strength, low density, and good mechanical properties, which can effectively improve the load-bearing capacity and energy absorption capacity of the structure;

[0049] 3. Gradual density design: A linear gradient change in relative density is achieved in the z-direction, which further enhances the stability and impact resistance of the structure and is suitable for application scenarios that require gradual mechanical properties;

[0050] 4. High-efficiency additive manufacturing: Using additive manufacturing technologies such as SLM, complex structures can be manufactured quickly and accurately, reducing the limitations and costs of traditional manufacturing processes;

[0051] 5. Excellent energy absorption performance: Verified through quasi-static compression tests, the structure has high plateau stress and energy absorption capacity, and can effectively absorb and disperse energy during the stress process, reducing the damage of impact to the system;

[0052] 6. Lightweight design: The minimally curved surface structure itself has a low density. Combined with the gradient density design, the overall weight is lighter, which helps to improve the performance and efficiency of the equipment.

[0053] In summary, the sandwich structure design method based on a three-dimensional gradient minimum surface described in this invention uses a three-dimensional gradient structure as the core layer to further improve the overall explosion-proof and impact-resistant performance and target protection performance of the sandwich structure. Through precise mathematical modeling and advanced manufacturing technology, it achieves precise control of structural density and significant improvement in mechanical properties, thereby enhancing the energy absorption and explosion-proof and impact-resistant performance of the sandwich structure. Its unique advantages make it widely applicable in multiple fields, especially performing well in application scenarios that require high performance, lightweight design, and good energy absorption capacity.

[0054] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0055] Figure 1 This is a flowchart illustrating the design method of a three-dimensional gradient minimal surface sandwich structure according to the present invention;

[0056] Figure 2 This is a schematic diagram of the sandwich structure described in this invention;

[0057] Figure 3 This is a two-dimensional saddle surface diagram of the sandwich structure described in this invention;

[0058] Figure 4 This is a diagram showing the relative density distribution of the xy-plane minimal curved surface structure of the sandwich structure described in this invention.

[0059] Figure 5 The following are density distribution diagrams of three samples in the embodiment: (a) is the density distribution diagram of the uniform Gyroid model, (b) is the density distribution diagram of the three-dimensional density gradient distribution model, and (c) is the density distribution diagram of the Gyroid model with a linear gradient change in relative density in the z direction.

[0060] Figure 6 The mechanical response and plateau stress curves of the six specimens in the embodiment are shown in (a) and (b) are the plateau stress distribution diagrams of the six specimens; and (c) is the energy absorption histogram of the six specimens.

[0061] Figure 7 This is a diagram illustrating the deformation process of the three-dimensional gradient minimal surface sandwich structure described in the embodiment.

[0062] Figure Labels

[0063] 1. Core layer; 2. Panel. Detailed Implementation

[0064] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely illustrative of the embodiments of the present invention and are not intended to limit the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of this application. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout.

[0065] It should be noted that the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion, such as a process, method, system, product, or server that includes a series of steps or units, not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such process, method, product, or device.

[0066] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0067] like Figure 1 As shown, a design method for a three-dimensional gradient-minimum surface sandwich structure includes the following steps:

[0068] S1. Construct a three-dimensional density distribution feature model based on a combination of two-dimensional saddle surface functions and linear functions;

[0069] In step S1, mathematical software is used to construct a two-dimensional surface for the structural density distribution based on a two-dimensional saddle surface function. By changing the parameter values ​​of the two-dimensional saddle surface function, the values ​​of each point in the two-dimensional surface for the structural density distribution are adjusted, so that the relative density values ​​present a saddle surface distribution in the xy plane. At the same time, a linear function is combined to make the relative density produce a linear change in the z direction, thus obtaining a three-dimensional density gradient distribution model.

[0070] The two-dimensional surface of the structural density distribution mentioned in step S1 includes a saddle surface, and the expression of the saddle surface is as follows:

[0071] z1=a(bx 2 -by 2 )+c (1);

[0072] In the formula, z1, x, and y represent the z-axis, x-axis, and y-axis coordinates in three-dimensional space, respectively; a represents a constant term used to adjust the height variation of the two-dimensional surface in the z-direction; b represents a constant term used to adjust the width variation of the two-dimensional surface in the x and y directions; and c represents a constant term used to adjust the translation of the entire two-dimensional surface in the z-direction.

[0073] The linear function expression is as follows:

[0074] z2=kz+m (2);

[0075] In the formula, z2 represents the output variable; k and m are both constants;

[0076] The expression for the three-dimensional density gradient distribution model is as follows:

[0077] γ(x,y,z)=z1z2 (3);

[0078] In the formula, γ(x,y,z) represents the density at coordinates (x,y,z) in three-dimensional space;

[0079] S2. Based on the Gyroid minimum surface equation, construct the modeling equations for the three-dimensional geometric model of the Gyroid minimum surface structure;

[0080] The modeling equation for the three-dimensional geometric model of the Gyroid minimal surface structure described in step S2 is as follows:

[0081]

[0082] In the formula, The density of the Gyroid structure at the original coordinates (x, y, z) is described; X, Y, Z) represent the normalized coordinates of the period length α, and X = 2απx, Y = 2βπy, Z = 2γπz, where α, β and γ are constants used to control the number of unit cells of the Gyroid minimal surface structure along the three directions of x, y and z.

[0083] Figure 2 The three-dimensional gradient Gyroid structure described in (b) has a relative density that varies with gradients in all three dimensions. Figure 2 (c) The Gyroid minimal surface structure is described with a linear gradient of relative density only in the Z direction. The relative density and surface value of the Gyroid minimal surface structure at each point in the XY plane correspond one-to-one.

[0084] S3. The three-dimensional density distribution feature model constructed in step S1 is combined with the modeling equation of the three-dimensional geometric model of the Gyroid minimal surface structure constructed in step S2 to obtain the modeling equation of the three-dimensional gradient minimal surface structure.

[0085] In step S3, a three-dimensional density distribution feature model is introduced into the Gyroid minimum surface equation, so that the relative density of the Gyroid minimum surface structure in the plane is distributed according to the characteristics of the three-dimensional density distribution feature model, thus obtaining the modeling equation of the three-dimensional gradient minimum surface structure. The expression of the modeling equation of the three-dimensional gradient minimum surface structure is as follows:

[0086]

[0087] The range of relative density of the minimal surface structure in the (x,y,z) plane is achieved by adjusting the values ​​of parameters α, β, γ, c, k, and m. A three-dimensional geometric model is generated by writing a program using mathematical modeling software.

[0088] S4. Based on the modeling equation of the three-dimensional gradient minimum surface structure obtained in step S3, a three-dimensional model of the three-dimensional gradient minimum surface structure is obtained through modeling software.

[0089] S5. Based on the three-dimensional model described in step S4, a three-dimensional gradient minimal surface structure is prepared by additive manufacturing technology.

[0090] In step S5, SLM additive manufacturing technology is used to perform additive manufacturing with aluminum alloy powder or titanium alloy powder as the substrate.

[0091] S6. Using the three-dimensional gradient minimum surface structure obtained in step S5 as the core layer, set up panels in the upper and lower planes of the core layer respectively, and combine the panels with the core layer to obtain a three-dimensional gradient minimum surface gradient sandwich structure.

[0092] In step S6, the panel and the core layer are bonded together using an adhesive method.

[0093] S7. The performance of the three-dimensional gradient minimum surface gradient sandwich structure obtained in step S6 is evaluated, and the final three-dimensional gradient minimum surface gradient sandwich structure is determined based on the performance evaluation results.

[0094] Step S7 specifically includes the following steps:

[0095] S71. Perform a quasi-static compression test on the three-dimensional gradient minimum surface structure specimen with multiple specification parameters obtained in S5, obtain the stress-strain curve and force-displacement curve of the three-dimensional gradient minimum surface structure specimen, and then calculate the platform stress and energy absorption of the three-dimensional gradient minimum surface gradient sandwich structure, wherein the specification parameters include size parameters and weight parameters.

[0096] Wherein the platform stress σ m The calculation formula is as follows:

[0097]

[0098] In the formula, E V The integral of the stress-strain curve of a three-dimensional gradient-minimum surface structure specimen; ε D Represents the dense strain of a three-dimensional gradient minimum surface structure;

[0099] The expression for energy absorption E is as follows:

[0100]

[0101] In the formula, σ(ε) represents the stress-strain relationship function; dε represents the strain increment; V represents the volume of the three-dimensional gradient minimum surface structure;

[0102] S72. Based on the calculation results of formulas (6) and (7) mentioned in S71, the final three-dimensional gradient minimum surface gradient sandwich structure is obtained by screening.

[0103] Example

[0104] In this embodiment, gradient Gyroid minimal surface structures were prepared using SLM additive manufacturing technology. The matrix material for the Gyroid minimal surface structures was 316L metal powder provided by Guangzhou Leijia Additive Manufacturing Technology Co., Ltd. The parameters of the additively manufactured samples are shown in Table 1.

[0105] Table 1 Parameters of the Sample

[0106] Sample number Actual size / mm mass / g Loading speed JY-0-1# 25.06×25.02×25.46 40.01 1.5mm / min JY-0-2# 25.01×24.99×25.04 39.99 1.5mm / min SWTD-1-1# 25.10×25.01×25.0 40.09 1.5mm / min SWTD-1-2# 25.04×25.06×25.08 39.86 1.5mm / min XXTD-2-1# 25.10×25.16×25.02 39.72 1.5mm / min XXTD-2-2# 25.06×25.12×25.04 40.02 1.5mm / min

[0107] Note: The sample numbers shown in the table represent the following: uniform Gyroid lattice structure (JY-0-1#; JY-0-2#), three-dimensional gradient lattice structure (SWTD-1-1#; SWTD-1-2#), and linear gradient lattice structure (XXTD-2-1#; XXTD-2-2#).

[0108] like Figure 5 As shown, static pressure tests were conducted on three structures (each structure corresponding to two types of specimens, for a total of six specimens). The six specimens included two three-dimensional gradient lattice structures (SWTD-1-1# and SWTD-1-2#). Figure 5 b) Two uniform Gyroid minimal surface structures (JY-0-1#, JY-0-2#) Figure 5 a) and two linear gradient lattice structures (XXTD-2-1#, XXTD-2-2#) Figure 5 c) Conduct experiments using a quasi-static testing machine, and calculate the platform stress σ based on the experimental results and formulas (6) and (7). m And energy absorption E. The results are as follows: Figure 6 As shown, by Figure 6 As shown in (a) and (b), the yield stress of both gradient lattice structures is lower than that of the uniform Gyroid minimum surface structure. The average yield stress of the three-dimensional gradient lattice structure is 64.32 MPa, which is 19.11% lower than that of the uniform Gyroid minimum surface structure. Furthermore, it can be seen that the yield stresses of the linear gradient minimum surface and the three-dimensional gradient minimum surface are basically the same.

[0109] Depend on Figure 6 (c) It can be seen that the gradient minimum surface structure based on surface density distribution described in this invention has higher energy absorption performance under the same relative density, thus improving the structural mechanical properties. The three-dimensional gradient lattice structure has a lower yield stress than the uniform Gyroid minimum surface structure, but its overall energy absorption performance is higher, increasing by 17.04% compared to the traditional uniform Gyroid lattice. Furthermore, the three-dimensional gradient lattice structure increases energy absorption by 11.74% compared to the traditional linear gradient lattice structure. This indicates that the three-dimensional gradient lattice structure based on the saddle surface possesses superior energy absorption performance. Simultaneously, the lower yield stress of the three-dimensional gradient lattice structure means that under the same impact load, this invention can undergo plastic deformation earlier, thus achieving the purpose of protecting the protected object in advance.

[0110] Depend on Figure 7As can be seen, based on the deformation process of the three-dimensional gradient minimal curved surface structure, which is the structure with the best mechanical properties, under compressive load, it can be seen that the deformation of the structure exhibits a significant gradient yielding effect. This proves that the three-dimensional gradient minimal curved surface sandwich structure designed by this invention can achieve early yielding and deformation when facing impact loads to protect the protected target, thus proving the effectiveness of this invention.

[0111] like Figures 2-4 As shown, a sandwich structure is designed using a three-dimensional gradient minimal surface sandwich structure design method. The sandwich structure is a three-dimensional gradient minimal surface sandwich structure, comprising a core layer 1 formed by the three-dimensional gradient minimal surface structure and panels 2 disposed on both sides of the core layer 1. The positions of the upper and lower panels 2 are perpendicular to the z-direction of the core layer 1. The three-dimensional gradient minimal surface structure has the following characteristics: its relative density exhibits a two-dimensional surface gradient distribution in the xy-plane, and its relative density exhibits a linear gradient distribution in the z-direction.

[0112] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A design method for a three-dimensional gradient-minimum surface sandwich structure, characterized in that: Includes the following steps: S1. Construct a three-dimensional density distribution feature model based on a combination of two-dimensional saddle surface functions and linear functions; In step S1, mathematical software is used to construct a two-dimensional surface for the structural density distribution based on a two-dimensional saddle surface function. By changing the parameter values ​​of the two-dimensional saddle surface function, the values ​​of each point in the two-dimensional surface for the structural density distribution are adjusted, so that the relative density values ​​present a saddle surface distribution in the xy plane. At the same time, a linear function is combined to make the relative density produce a linear change in the z direction, thus obtaining a three-dimensional density gradient distribution model. The two-dimensional surface of the structural density distribution mentioned in step S1 includes a saddle surface, and the expression of the saddle surface is as follows: z1=a(bx 2 -by 2 )+c (1); In the formula, z1, x, and y represent the z-axis coordinates, z-axis coordinates, and y-axis coordinates in three-dimensional space, respectively; a represents a constant term used to adjust the height variation of the two-dimensional surface in the z-direction; b represents a constant term used to adjust the width variation of the two-dimensional surface in the x and y directions; and c represents a constant term used to adjust the translation of the entire two-dimensional surface in the z-direction. The linear function expression is as follows: z2=kz+m (2); In the formula, z2 represents the output variable; k and m are both constants; The expression for the three-dimensional density gradient distribution model is as follows: γ(x,y,z)=z1z2 (3); In the formula, γ(x,y,z) represents the density at coordinates (x,y,z) in three-dimensional space; S2. Based on the Gyroid minimum surface equation, construct the modeling equations for the three-dimensional geometric model of the Gyroid minimum surface structure; S3. The three-dimensional density distribution feature model constructed in step S1 is combined with the modeling equation of the three-dimensional geometric model of the Gyroid minimal surface structure constructed in step S2 to obtain the modeling equation of the three-dimensional gradient minimal surface structure. In step S3, a three-dimensional density distribution feature model is introduced into the Gyroid minimum surface equation, so that the relative density of the Gyroid minimum surface structure in the plane is distributed according to the features of the three-dimensional density distribution feature model, and the modeling equation of the three-dimensional gradient minimum surface structure is obtained. S4. Based on the modeling equation of the three-dimensional gradient minimum surface structure obtained in step S3, a three-dimensional model of the three-dimensional gradient minimum surface structure is obtained through modeling software. S5. Based on the three-dimensional model described in step S4, a three-dimensional gradient minimal surface structure is prepared by additive manufacturing technology. S6. Using the three-dimensional gradient minimum surface structure obtained in step S5 as the core layer, set up panels in the upper and lower planes of the core layer respectively, and combine the panels with the core layer to obtain a three-dimensional gradient minimum surface gradient sandwich structure. S7. The performance of the three-dimensional gradient minimum surface gradient sandwich structure obtained in step S6 is evaluated, and the final three-dimensional gradient minimum surface gradient sandwich structure is determined based on the performance evaluation results.

2. The design method of a three-dimensional gradient minimal curved surface sandwich structure according to claim 1, characterized in that: The modeling equation for the three-dimensional geometric model of the Gyroid minimal surface structure described in step S2 is as follows: In the formula, The density of the Gyroid structure at the original coordinates (x, y, z) is described; (X, Y, Z) represents the normalized coordinates of the period length α, and X = 2απx, Y = 2βπy, Z = 2γπz, where α, β and γ are constants used to control the number of unit cells of the Gyroid minimal surface structure along the three directions of x, y and z.

3. The design method of a three-dimensional gradient minimal curved surface sandwich structure according to claim 2, characterized in that: In step S3, the modeling equation for the three-dimensional gradient minimum surface structure is expressed as follows:

4. The design method of a three-dimensional gradient minimal curved surface sandwich structure according to claim 3, characterized in that: In step S5, SLM additive manufacturing technology is used to perform additive manufacturing with aluminum alloy powder or titanium alloy powder as the substrate.

5. The design method of a three-dimensional gradient minimal curved surface sandwich structure according to claim 4, characterized in that: In step S6, the panel and the core layer are bonded together using an adhesive method.

6. The design method of a three-dimensional gradient minimal curved surface sandwich structure according to claim 5, characterized in that: Step S7 specifically includes the following steps: S71. Perform a quasi-static compression test on the three-dimensional gradient minimum surface structure specimen with multiple specification parameters obtained in S5, obtain the stress-strain curve and force-displacement curve of the three-dimensional gradient minimum surface structure specimen, and then calculate the platform stress and energy absorption of the three-dimensional gradient minimum surface gradient sandwich structure, wherein the specification parameters include size parameters and weight parameters. Wherein the platform stress σ m The calculation formula is as follows: In the formula, E V The integral of the stress-strain curve of a three-dimensional gradient-minimum surface structure specimen; ε D This represents the dense strain of a three-dimensional gradient minimum surface structure; The expression for energy absorption E is as follows: In the formula, σ(ε) represents the stress-strain relationship function; dε represents the strain increment; V represents the volume of the three-dimensional gradient minimum surface structure; S72. Based on the calculation results of formulas (6) and (7) mentioned in S71, the final three-dimensional gradient minimum surface gradient sandwich structure is obtained by screening.

7. A sandwich structure, characterized in that: The design method of the three-dimensional gradient minimal curved surface sandwich structure described in claim 6 is used to obtain the structure.

8. A sandwich structure according to claim 7, characterized in that: The sandwich structure is a three-dimensional gradient minimum surface gradient sandwich structure, which includes a core layer formed by the three-dimensional gradient minimum surface structure and panels disposed on both sides of the core layer. The three-dimensional gradient minimum surface structure has the following characteristics: the relative density in the xy plane is distributed in a two-dimensional surface gradient, and the relative density in the z direction is distributed in a linear gradient.

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