Design method of three-dimensional gradient minimum curved surface sandwich structure and sandwich structure

Abstract

The invention discloses a design method of a three-dimensional gradient minimum curved surface sandwich structure and the sandwich structure, and belongs to the field of minimum curved surface sandwich structure design, and the design method comprises the following steps: S1, constructing a three-dimensional density distribution characteristic model; s2, constructing a modeling equation of the three-dimensional geometric model of the Gyandroid minimal curved surface structure; s3, obtaining a modeling equation of the three-dimensional gradient minimum curved surface structure; s4, obtaining a three-dimensional model of the three-dimensional gradient minimal curved surface structure through modeling software; s5, preparing a three-dimensional gradient minimum curved surface structure through an additive manufacturing technology; s6, obtaining a three-dimensional gradient minimum curved surface gradient sandwich structure; and S7, performing performance evaluation. By the adoption of the design method of the three-dimensional gradient minimum curved surface sandwich structure and the sandwich structure, the minimum curved surface with the dimension relative density being in gradient change in three directions is designed, the energy absorption performance of the structure is effectively improved, and meanwhile more effective protection on a target is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of minimal curved surface sandwich structure design, and in particular to a design method and a sandwich structure of a three-dimensional gradient minimal curved surface sandwich structure. Background Art

[0002] With the rapid development of military technology, the destructive effect of explosion shock waves on vehicles, armored vehicles and personnel in modern warfare is constantly increasing. Therefore, it is urgent to further improve the explosion resistance of protective structures to cope with the increasingly complex and severe battlefield environment. In this context, the minimal surface structure, as a new type of porous structure, has the following significant advantages: 1. Stable mechanical response: The minimal surface structure can maintain a relatively stable mechanical response when subjected to external impact, avoiding the brittle fracture or instability of traditional materials under impact loads; 2. Excellent energy absorption performance: Compared with traditional porous structures, the minimal surface structure can continuously absorb energy within a wider deformation range, thereby effectively reducing the impact of impact energy on the protected object; 3. Stable deformation behavior: The minimal surface structure exhibits a relatively uniform deformation characteristic when subjected to force, which helps to disperse the impact energy, reduce local stress concentration, and improve the overall protection effect. It can be seen that the minimal surface structure has gradually attracted widespread attention from researchers due to its stable mechanical response, excellent energy absorption performance and stable deformation behavior.

[0003] Existing studies have shown that the gradient design of the porous structure can significantly improve its energy absorption performance. Using the gradient porous structure as the core layer of the sandwich structure can not only significantly enhance the overall explosion resistance and protection effect 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 preparation of complex core layer structures. This advanced manufacturing technology can not only achieve high-precision and high-complexity structural molding, but also quickly adjust and optimize the design scheme according to actual needs, greatly shortening the R&D cycle and cost.

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

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

[0007] 2. Uneven platform stress: The platform stress of traditional materials under strong impact loads such as explosions is not stable enough, which is not conducive to providing reliable protection.

[0008] Compared with uniform structures, the minimal surface structure based on two-dimensional surface density distribution has significantly improved platform stress and energy absorption performance. However, under strong impact loads such as explosions, the platform stress of the structure that is too stable is not conducive to better protection of the protected object. Summary of the invention

[0009] The purpose of the present invention is to provide a design method and a sandwich structure of a three-dimensional gradient minimal surface sandwich structure to solve the above technical problems.

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

[0011] S1. Based on the two-dimensional saddle surface function combined with the linear function, a three-dimensional density distribution characteristic model is constructed;

[0012] S2. According to the Gyroid minimal surface equation, construct the modeling equation of the three-dimensional geometric model of the Gyroid minimal surface structure;

[0013] S3, combining the three-dimensional density distribution characteristic model constructed in step S1 with the three-dimensional geometric model modeling equation 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 minimal surface structure obtained in step S3, a three-dimensional model of the three-dimensional gradient minimal surface structure is obtained by modeling software;

[0015] S5, based on the three-dimensional model described in step S4, preparing a three-dimensional gradient minimum surface structure by additive manufacturing technology;

[0016] S6, using the three-dimensional gradient minimum surface structure obtained in step S5 as a core layer, arranging panels in the upper and lower planes of the core layer respectively, and combining the panels with the core layer to obtain a three-dimensional gradient minimum surface gradient sandwich structure;

[0017] S7, performing a performance evaluation on the three-dimensional gradient minimum surface gradient sandwich structure obtained in step S6, and determining a final three-dimensional gradient minimum surface gradient sandwich structure based on the performance evaluation result.

[0018] Preferably, in step S1, mathematical software is used to construct a two-dimensional surface of the structural density distribution based on the two-dimensional saddle surface function, and the value of each point in the two-dimensional surface of the structural density distribution is adjusted by changing the parameter value of the two-dimensional saddle surface function, so that the relative density value presents a saddle surface distribution in the xy plane. At the same time, a linear function is combined to make the relative density change linearly in the z direction, so as to obtain a three-dimensional density gradient distribution model.

[0019] Preferably, the two-dimensional curved surface of the structural density distribution 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] Wherein, z1, x and y represent the z-axis coordinate value, x-axis coordinate value and y-axis coordinate value in three-dimensional space respectively; a represents a constant term used to adjust the height variation amplitude of the two-dimensional surface in the z direction; b represents a constant term used to adjust the width variation amplitude of the two-dimensional surface in the x and y directions; 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 constants;

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

[0026] γ(x,y,z)=z1z2 (3);

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

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

[0029]

[0030] In the formula, It describes the density of the Gyroid structure at the original coordinates (x, y, z); (X, Y, Z) represents the standardized coordinates of the period length α, and X = 2απx, Y = 2βπy, Z = 2γπz, where α, β and γ are all 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 characteristic model is introduced into the Gyroid minimal surface equation, so that the relative density of the Gyroid minimal surface structure in the plane is distributed according to the characteristics of the three-dimensional density distribution characteristic model, and a modeling equation of a three-dimensional gradient minimal surface structure is obtained, and the expression of the modeling equation of the three-dimensional gradient minimal surface structure is as follows:

[0032]

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

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

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

[0036] S71, performing a quasi-static compression test on the three-dimensional gradient minimal surface structure specimens with multiple specification parameters obtained in S5, obtaining the stress-strain curve and force-displacement curve of the three-dimensional gradient minimal surface structure specimen, and then calculating the platform stress and energy absorption of the three-dimensional gradient minimal surface gradient sandwich structure, wherein the specification parameters include size parameters and weight parameters;

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

[0038]

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

[0040] The expression of 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 minimal surface structure;

[0043] S72. Based on the calculation results of formula (6) and formula (7) described in S71, the final three-dimensional gradient minimum surface gradient sandwich structure is screened.

[0044] A sandwich structure is designed by a design method of a three-dimensional gradient minimum 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 a three-dimensional gradient minimum surface structure and panels arranged on both sides of the core layer, wherein the three-dimensional gradient minimum surface structure has the following characteristics: the relative density in the xy plane is distributed in a two-dimensional curved gradient, and the relative density in the z direction is distributed in a linear gradient.

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

[0047] 1. Uniform and controllable density distribution: Through the combination of saddle surface function and linear function, the density is precisely controlled in different directions, so that the structure has different mechanical properties in different areas to meet various application requirements;

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

[0049] 3. Gradient density design: A linear gradient change of 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 gradient mechanical properties;

[0050] 4. Efficient 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 by quasi-static compression test, the structure has high platform stress and energy absorption, can effectively absorb and disperse energy during the force process, and reduce the damage to the system caused by impact;

[0052] 6. Lightweight design: The minimal curved surface structure itself has a lower 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 three-dimensional gradient minimal surfaces described in the present invention uses the 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, and through precise mathematical modeling and advanced manufacturing technology, it achieves precise control of the structural density and significant improvement of the mechanical properties, thereby improving the energy absorption and explosion-proof and impact-resistant performance of the sandwich structure. Its unique advantages make it have broad application potential in multiple fields, especially in application scenarios that require high performance, lightweight and good energy absorption capacity.

[0054] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0056] Figure 2 It is a structural schematic diagram of the sandwich structure of the present invention;

[0057] Figure 3 It is a two-dimensional saddle surface diagram of the sandwich structure of the present invention;

[0058] Figure 4 A relative density distribution diagram of the xy plane minimal surface structure of the sandwich structure of the present invention;

[0059] Figure 5 The density distribution patterns of the three samples of the embodiment are shown in FIG. 1 , wherein (a) is a density distribution pattern diagram of a uniform Gyroid model, (b) is a density distribution pattern diagram of a three-dimensional density gradient distribution model, and (c) is a density distribution pattern diagram of a Gyroid model in which the relative density in the z direction changes linearly with a gradient;

[0060] Figure 6 The mechanical response and platform stress curves of six samples of the embodiment; (a) is the stress-strain curve of the six samples, (b) is the platform stress distribution diagram of the six samples; (c) is the energy absorption bar graph of the six samples;

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

[0062] Reference numerals

[0063] 1. Core layer; 2. Panel. DETAILED DESCRIPTION

[0064] In order to make the purpose, technical scheme and advantages disclosed in the embodiments of the present invention clearer, the embodiments of the present invention are further described in detail in combination with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the embodiments of the present invention and are not used to limit the embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application. Examples of the embodiments are shown in the accompanying drawings, where the same or similar reference numerals throughout represent the same or similar elements or elements with the same or similar functions.

[0065] It should be noted that the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or server that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units that are not explicitly listed or inherent to these processes, methods, products or devices.

[0066] The embodiments of the present invention are described in detail below in conjunction with the accompanying drawings.

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

[0068] S1. Based on the two-dimensional saddle surface function combined with the linear function, a three-dimensional density distribution characteristic model is constructed;

[0069] In step S1, mathematical software is used to construct a two-dimensional surface of structural density distribution based on the two-dimensional saddle surface function. The value of each point in the two-dimensional surface of structural density distribution is adjusted by changing the parameter value of the two-dimensional saddle surface function, so that the relative density value presents a saddle surface distribution in the xy plane. At the same time, the linear function is combined to make the relative density change linearly in the z direction, so as to obtain a three-dimensional density gradient distribution model.

[0070] The two-dimensional curved surface of the structural density distribution 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] Wherein, z1, x and y represent the z-axis coordinate value, x-axis coordinate value and y-axis coordinate value in three-dimensional space respectively; a represents a constant term used to adjust the height variation amplitude of the two-dimensional surface in the z direction; b represents a constant term used to adjust the width variation amplitude of the two-dimensional surface in the x and y directions; 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 constants;

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

[0077] γ(x,y,z)=z1z2 (3);

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

[0079] S2. According to the Gyroid minimal surface equation, construct the modeling equation of the three-dimensional geometric model of the Gyroid minimal surface structure;

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

[0081]

[0082] In the formula, It describes the density of the Gyroid structure at the original coordinates (x, y, z); X, Y, Z) represents the standardized coordinates of the period length α, and X = 2απx, Y = 2βπy, Z = 2γπz, where α, β and γ are all 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 recorded in (b) has a relative density that changes gradiently in all three dimensions. Figure 2 (c) The Gyroid minimal surface structure recorded has a linear gradient change in relative density only in the Z direction. The relative density and surface value of each point position of the Gyroid minimal surface structure in the XY plane correspond one to one.

[0084] S3, combining the three-dimensional density distribution characteristic model constructed in step S1 with the three-dimensional geometric model modeling equation 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 characteristic model is introduced into the Gyroid minimal surface equation, so that the relative density of the Gyroid minimal surface structure in the plane is distributed according to the characteristics of the three-dimensional density distribution characteristic model, and the modeling equation of the three-dimensional gradient minimal surface structure is obtained, and the expression of the modeling equation of the three-dimensional gradient minimal surface structure is as follows:

[0086]

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

[0088] S4, based on the modeling equation of the three-dimensional gradient minimal surface structure obtained in step S3, a three-dimensional model of the three-dimensional gradient minimal surface structure is obtained by modeling software;

[0089] S5, based on the three-dimensional model described in step S4, preparing a three-dimensional gradient minimum surface structure by additive manufacturing technology;

[0090] In step S5, SLM additive manufacturing technology is used to perform additive manufacturing using aluminum alloy powder or titanium alloy powder as a base material.

[0091] S6, using the three-dimensional gradient minimum surface structure obtained in step S5 as a core layer, arranging panels in the upper and lower planes of the core layer respectively, and combining 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 by bonding.

[0093] S7, performing a performance evaluation on the three-dimensional gradient minimum surface gradient sandwich structure obtained in step S6, and determining a final three-dimensional gradient minimum surface gradient sandwich structure based on the performance evaluation result.

[0094] Step S7 specifically includes the following steps:

[0095] S71, performing a quasi-static compression test on the three-dimensional gradient minimal surface structure specimens with multiple specification parameters obtained in S5, obtaining the stress-strain curve and force-displacement curve of the three-dimensional gradient minimal surface structure specimen, and then calculating the platform stress and energy absorption of the three-dimensional gradient minimal surface gradient sandwich structure, wherein the specification parameters include size parameters and weight parameters;

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

[0097]

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

[0099] The energy absorption E is expressed 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 minimal surface structure;

[0102] S72. Based on the calculation results of formula (6) and formula (7) described in S71, the final three-dimensional gradient minimum surface gradient sandwich structure is screened.

[0103] Example

[0104] In this embodiment, the SLM additive manufacturing technology is used to prepare the gradient Gyroid minimal surface structure, and the base material of the Gyroid minimal surface structure is 316L metal powder provided by Guangzhou Leijia Additive Technology Co., Ltd. The parameters of the parameter sample obtained by additive manufacturing are shown in Table 1.

[0105] Table 1 Parameters of the sample

[0106] Sample No. 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 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, three structures (each structure corresponds to two specimens, a total of six specimens) were subjected to static pressure tests, that is, the six specimens included two three-dimensional gradient lattice structures (SWTD-1-1#, 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 on a quasi-static test machine and calculate the platform stress σ based on the experimental results combined with formula (6) and formula (7) m And the energy absorption E. The results are as follows Figure 6 As shown by Figure 6 (a) and (b) show that the yield stress of the two gradient lattice structures is lower than that of the uniform Gyroid minimal surface structure. The average yield stress of the three-dimensional gradient lattice structure is 64.32MPa, which is 19.11% lower than that of the uniform Gyroid minimal surface structure. In addition, it can be seen that the yield stress of the linear gradient minimal surface and the three-dimensional gradient minimal surface is basically the same.

[0109] Depend on Figure 6 (c) It can be seen that the gradient minimal surface structure based on the surface density distribution described in the present invention has higher energy absorption performance under the condition of the same relative density, and realizes the improvement of the mechanical properties of the structure. The lattice structure based on the three-dimensional gradient has a lower yield stress than the uniform Gyroid minimal surface structure, but the overall energy absorption performance is higher. Compared with the traditional uniform Gyroid lattice, the energy absorption is improved by 17.04%. Not only that, the energy absorption of the three-dimensional gradient lattice structure is improved by 11.74% compared with the traditional linear gradient lattice structure. This shows that the three-dimensional gradient lattice structure based on the saddle surface has better energy absorption performance. At the same time, the yield stress of the three-dimensional gradient lattice structure is lower, which means that when facing the same impact load, the present invention can undergo plastic deformation earlier to achieve the purpose of protecting the protected object in advance.

[0110] Depend on Figure 7It can be seen that based on the deformation process of the three-dimensional gradient minimal surface structure as the structure with the best mechanical properties when subjected to compressive load, it can be seen that the deformation of the structure shows an obvious gradient yield effect, which proves that the three-dimensional gradient minimal surface sandwich structure designed by the present invention can yield and deform earlier to protect the protected target when facing impact loads, thereby proving the effectiveness of the present invention.

[0111] like Figure 2-Figure 4 As shown, a sandwich structure is designed by a design method of a three-dimensional gradient minimum curved surface sandwich structure. The sandwich structure is a three-dimensional gradient minimum curved surface gradient sandwich structure, which includes a core layer 1 formed by a three-dimensional gradient minimum curved surface structure and panels 2 arranged on both sides of the core layer 1, and the positions of the upper and lower panels 2 are perpendicular to the z direction of the core layer 1, wherein the three-dimensional gradient minimum curved surface structure has the following characteristics: the relative density in the xy plane is distributed in a two-dimensional curved surface gradient, and the relative density in the z direction is distributed in a linear gradient.

[0112] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A design method for a three-dimensional gradient minimal surface sandwich structure, characterized in that: The following steps are involved: S1. Based on the two-dimensional saddle surface function combined with the linear function, a three-dimensional density distribution characteristic model is constructed; S2. According to the Gyroid minimal surface equation, construct the modeling equation of the three-dimensional geometric model of the Gyroid minimal surface structure; S3, combining the three-dimensional density distribution characteristic model constructed in step S1 with the three-dimensional geometric model modeling equation of the Gyroid minimal surface structure constructed in step S2 to obtain the modeling equation of the three-dimensional gradient minimal surface structure; S4, based on the modeling equation of the three-dimensional gradient minimal surface structure obtained in step S3, a three-dimensional model of the three-dimensional gradient minimal surface structure is obtained by modeling software; S5, based on the three-dimensional model described in step S4, preparing a three-dimensional gradient minimum surface structure by additive manufacturing technology; S6, using the three-dimensional gradient minimum surface structure obtained in step S5 as a core layer, arranging panels in the upper and lower planes of the core layer respectively, and combining the panels with the core layer to obtain a three-dimensional gradient minimum surface gradient sandwich structure; S7, performing a performance evaluation on the three-dimensional gradient minimum surface gradient sandwich structure obtained in step S6, and determining a final three-dimensional gradient minimum surface gradient sandwich structure based on the performance evaluation result.

2. The design method of a three-dimensional gradient minimal surface sandwich structure according to claim 1, characterized in that: In step S1, mathematical software is used to construct a two-dimensional surface of structural density distribution based on the two-dimensional saddle surface function. The value of each point in the two-dimensional surface of structural density distribution is adjusted by changing the parameter value of the two-dimensional saddle surface function, so that the relative density value presents a saddle surface distribution in the xy plane. At the same time, the linear function is combined to make the relative density change linearly in the z direction, so as to obtain a three-dimensional density gradient distribution model.

3. The design method of a three-dimensional gradient minimal surface sandwich structure according to claim 2, characterized in that: The two-dimensional curved surface of the structural density distribution 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); Wherein, z1, x and y represent the z-axis coordinate value, x-axis coordinate value and y-axis coordinate value in three-dimensional space respectively; a represents a constant term used to adjust the height variation amplitude of the two-dimensional surface in the z direction; b represents a constant term used to adjust the width variation amplitude of the two-dimensional surface in the x and y directions; 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 constants; The three-dimensional density gradient distribution model expression is as follows: γ(x,y,z)=z1z2 (3); Where γ(x,y,z) represents the density at the coordinate (x,y,z) in three-dimensional space.

4. The design method of a three-dimensional gradient minimal surface sandwich structure according to claim 3, characterized in that: The modeling equation expression of the three-dimensional geometric model of the Gyroid minimal surface structure described in step S2 is as follows: In the formula, It describes the density of the Gyroid structure at the original coordinates (x, y, z); (X, Y, Z) represents the standardized coordinates of the period length α, and X = 2απx, Y = 2βπy, Z = 2γπz, where α, β and γ are all constants used to control the number of unit cells of the Gyroid minimal surface structure along the three directions of x, u and z.

5. The design method of a three-dimensional gradient minimal surface sandwich structure according to claim 4, characterized in that: In step S3, a three-dimensional density distribution characteristic model is introduced into the Gyroid minimal surface equation, so that the relative density of the Gyroid minimal surface structure in the plane is distributed according to the characteristics of the three-dimensional density distribution characteristic model, and the modeling equation of the three-dimensional gradient minimal surface structure is obtained, and the expression of the modeling equation of the three-dimensional gradient minimal surface structure is as follows:

6. The design method of a three-dimensional gradient minimal surface sandwich structure according to claim 5, characterized in that: In step S5, SLM additive manufacturing technology is used to perform additive manufacturing using aluminum alloy powder or titanium alloy powder as a base material.

7. The design method of a three-dimensional gradient minimal surface sandwich structure according to claim 6, characterized in that: In step S6, the panel and the core layer are bonded together by bonding.

8. The design method of a three-dimensional gradient minimal surface sandwich structure according to claim 7, characterized in that: Step S7 specifically includes the following steps: S71, performing a quasi-static compression test on the three-dimensional gradient minimal surface structure specimens with multiple specification parameters obtained in S5, obtaining the stress-strain curve and force-displacement curve of the three-dimensional gradient minimal surface structure specimen, and then calculating the platform stress and energy absorption of the three-dimensional gradient minimal surface gradient sandwich structure, wherein the specification parameters include size parameters and weight parameters; The platform stress σ m The calculation formula is as follows: In the formula, E V Represents the integral of the stress-strain curve of the three-dimensional gradient minimum surface structure specimen; ε D Represents the compact strain of three-dimensional gradient minimum surface structure; The energy absorption E is expressed 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 minimal surface structure; S72. Based on the calculation results of formula (6) and formula (7) described in S71, the final three-dimensional gradient minimum surface gradient sandwich structure is screened.

9. A sandwich structure, characterized in that: The structure is obtained by designing a three-dimensional gradient minimal surface sandwich structure as described in claim 8 above.

10. A sandwich structure according to claim 9, characterized in that: The sandwich structure is a three-dimensional gradient minimum surface gradient sandwich structure, which includes a core layer formed by a three-dimensional gradient minimum surface structure and panels arranged on both sides of the core layer, wherein 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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