A multi-level nested thin-wall energy absorbing structure and manufacturing process

Abstract

The invention discloses a manufacturing process of a multi-level nested thin-wall energy absorbing structure, comprising the following steps: S1, material selection of a variable density lattice structure; S2, constructing a variable density lattice structure model on a computer; S3, setting a laser scanning mode and process parameters, and printing to obtain a variable density lattice structure according to corresponding parameters; S4, heat treating the obtained variable density lattice structure; S5, removing the variable density lattice structure from a printed substrate through a wire cutting process; S6, preparing a multi-cellular thin-wall tube; S7, cutting out a variable density lattice structure of the same size according to the size of the prepared multi-cellular thin-wall tube; S8, making a multi-level nested thin-wall energy absorbing structure. The invention adopts a parameterized interpolation method to design and prepare a lattice structure, and the lattice structure is glued to the multi-cellular thin-wall tube to obtain a multi-level nested thin-wall energy absorbing structure, so as to improve the energy absorption efficiency of the variable density lattice-enhanced multi-cellular thin-wall structure. The preparation process is simple, and the produced multi-level nested thin-wall energy absorbing structure has high energy absorption efficiency.

Description

Technical Field

[0001] The invention relates to the field of impact resistance technology, and in particular to a multi-level nested thin-wall energy absorption structure and a manufacturing process. Background Art

[0002] As a representative of structural and functional integration, variable density lattice structure has been gradually applied in various fields such as rail transportation, aerospace, etc. in recent years due to its light weight, high specific stiffness, and especially excellent energy absorption performance. However, due to its high porosity and inevitable manufacturing defects, variable density lattice structure has low strength, can withstand small loads when used alone, and is prone to instability and collapse, thus limiting its engineering application as a load-bearing structure. At the same time, as a traditional energy-absorbing structure, thin-walled single-cell tube has the advantages of high axial bearing capacity and long stroke utilization, but its energy absorption efficiency is not high. Summary of the invention

[0003] In order to solve the problem of low energy absorption efficiency of thin-walled single-cell tubes in the prior art, the present application proposes a multi-level nested thin-walled energy absorption structure and a manufacturing process. The specific technical scheme is as follows: A manufacturing process of a multi-level nested thin-walled energy absorption structure comprises the following steps:

[0004] S1. Material selection of variable density lattice structure;

[0005] S2. Constructing a variable density lattice structure model on a computer;

[0006] S3, setting the laser scanning mode and process parameters, and printing according to the corresponding parameters to obtain a variable density dot matrix structure;

[0007] S4, heat treating the obtained variable density lattice structure;

[0008] S5, removing the variable density lattice structure from the printed substrate by a wire cutting process;

[0009] S6, preparing multi-cell thin-walled tubes by wire cutting process;

[0010] S7, cutting out variable density lattice structures of the same size according to the size of the prepared multicellular thin-walled tube;

[0011] S8. Make a multi-level nested thin-wall energy absorbing structure.

[0012] Preferably, in S2, the design steps of the variable density lattice structure model are as follows:

[0013] S2-1. Construct a parametric variable density lattice structure, extract relative density as the design variable, use the energy homogenization method for macro prediction, and establish a parametric material interpolation model;

[0014] S2-2, define the initial design domain, mesh the initial design domain, apply boundary conditions and external force loads, and establish a finite element model;

[0015] S2-3. Define the relative density design variable in the macrostructure design domain, assign values ​​to it, and calculate the unit stiffness matrix k i and the overall stiffness matrix K of the assembled structure, and finite element analysis is performed on the three-dimensional multi-scale variable density lattice structure to obtain the structural response information;

[0016] S2-4, construct a variable density lattice structure optimization model, perform sensitivity analysis on relative density design variables, and iteratively update the design variables to determine the optimal layout of the lattice microstructure;

[0017] S2-5. Determine the convergence of the design variables. When the change of the objective function in two consecutive iterations is less than 1×10 -3 , or when the maximum number of iterations set is 50, the optimization converges by default and the iteration process terminates; otherwise, the design variables are updated and the next iteration is continued.

[0018] Preferably, in S2-1, the parameterized material interpolation model is as follows:

[0019] D ij =a0+a1η+a2η 2 +a3η 3 +a4η 4 +a5η 5

[0020] Among them, D ij is the equivalent elastic parameter, a k (k=0-5) is the coefficient of the corresponding term of the fitting polynomial curve equation, and η is the relative density of the parameterized variable density lattice structure.

[0021] Preferably, in S2-3, the unit stiffness matrix k i And the calculation formula of the overall stiffness matrix K of the assembled structure is as follows:

[0022]

[0023]

[0024] Where B is the strain matrix of the unit, Ω i is the integration domain of the i-th unit, and the material elasticity matrix corresponding to unit i is D i H (η i );

[0025] Preferably, in S2-4, the variable density lattice structure optimization model is as follows:

[0026] find:X={η1,η2,…,η n} T

[0027] min:

[0028] st:KU=F

[0029]

[0030] 0<η min ≤η i ≤η max ≤1,i=1,2,…,n

[0031] Among them, X is the design variable vector, which contains n relative density variables η; C is the objective function, which is the overall compliance function of the variable density lattice structure; st is the constraint condition, K and k i are the overall stiffness matrix of the structure and the stiffness matrix of element i, U and u respectively. i are the displacement field of the entire structure and the displacement field of unit i respectively, and F is the external force exerted on the entire structure.

[0032] Preferably, the Stripes scanning method is adopted, the rotation angle of each layer is 67°, the printing layer thickness is 0.02-0.10 mm, the laser power is 80-500 W, the laser scanning speed is 500-2000 mm / s, and the scanning interval is 0.17-0.23 mm.

[0033] Preferably, in S1, the material of the variable density lattice structure is AlSi10Mg aluminum alloy, and the material of the multi-cellular thin-walled tube in S6 is 6061 aluminum alloy.

[0034] Preferably, in S8, the multi-cellular thin-walled tubes and the variable density lattice structure are bonded by epoxy resin to form a multi-level nested thin-walled energy absorbing structure.

[0035] A multi-stage nested thin-walled energy absorbing structure is manufactured using a manufacturing process for a multi-stage nested thin-walled energy absorbing structure, including a thin-walled tube structure and a variable density lattice structure. The thin-walled tube structure is centrally symmetrical and has multiple layers of tube walls. Multiple cavities are provided in the thin-walled tube structure, and the variable density lattice structure is filled in the cavity. Multiple constraint ribs are provided between the thin tube wall structures for connection.

[0036] Preferably, the thin-walled tube structure is, from inside to outside, an inner wall, a middle wall and an outer wall, and the wall thickness of the inner wall, the middle wall, the outer wall and the restraining rib plate are all 1 mm.

[0037] The present invention adopts a parametric interpolation method to design and prepare a lattice structure, adopts a wire cutting process to prepare a multi-cellular thin-walled tube, and glues the lattice structure and the multi-cellular thin-walled tube together through epoxy resin to obtain a multi-level nested thin-walled energy absorbing structure, thereby improving the energy absorption efficiency of the variable-density lattice-reinforced multi-cellular thin-walled structure. The preparation process is simple and can be mass-produced, and the produced multi-level nested thin-walled energy absorbing structure has high energy absorption efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a cross-sectional view of a multi-cellular thin-walled tube of the present invention.

[0039] Figure 2 It is a flow chart of the design of the variable density lattice structure of the present invention.

[0040] Figure 3 It is a schematic diagram of the initial design domain subjected to external loads in Example 1 of the present invention.

[0041] Figure 4 It is a schematic diagram of the iterative curve of structural compliance and structural volume fraction in Example 1 of the present invention.

[0042] Figure 5 It is a three-dimensional diagram of the variable density lattice structure obtained in Example 1 of the present invention.

[0043] Figure 6 It is a schematic diagram of the assembly of the multi-level nested thin-wall energy absorbing structure in Example 1 of the present invention.

[0044] Figure 7 It is a three-dimensional diagram of the multi-level nested thin-wall energy absorbing structure in Example 1 of the present invention.

[0045] Figure 8 It is a comparison diagram of displacement curves of the multi-stage nested thin-wall energy absorbing structure in Example 1 of the present invention.

[0046] Fig. 9 It is a schematic diagram of the initial design domain subjected to external loads in Example 2 of the present invention.

[0047] Fig.10 It is a schematic diagram of the iterative curve of structural compliance and structural volume fraction in Example 2 of the present invention.

[0048] Fig.11 It is a front view of the variable density lattice structure obtained in Example 2 of the present invention.

[0049] Fig.12 It is a schematic diagram of the assembly of the multi-level nested thin-wall energy absorbing structure in Example 2 of the present invention.

[0050] Fig.13 It is a three-dimensional diagram of the multi-level nested thin-wall energy absorbing structure in Example 2 of the present invention.

[0051] Fig.14It is a comparison diagram of displacement curves of the multi-stage nested thin-wall energy absorbing structure in Example 2 of the present invention.

[0052] In the figure: 1. inner wall; 2. middle wall; 3. outer wall; 4. restraining rib plate; 5. variable density lattice structure. DETAILED DESCRIPTION

[0053] The following is a further detailed description of the embodiments of the present invention in conjunction with the accompanying drawings and examples. Figures 1 to 14 It can be seen that a manufacturing process of a multi-level nested thin-walled energy absorbing structure of the present invention comprises the following steps:

[0054] S1. Material selection for variable density lattice structure: AlSi10Mg aluminum alloy.

[0055] S2. According to the topology optimization process, a variable density lattice structure model is constructed on the computer, the digital model is converted into STL format in UG software, and then imported into Magics software for subsequent file repair, placement, support addition, slicing and other data processing.

[0056] S3, using Stripes scanning method, the rotation angle of each layer is 67°, the printing parameter settings are: the printing layer thickness is 0.02-0.10mm, the laser power is 80-500W, the laser scanning speed is 500-2000mm / s, the scanning spacing is 0.17-0.23mm, and the variable density dot matrix structure is obtained by printing.

[0057] S4. The obtained variable density lattice structure is heat treated. Under high vacuum conditions, the heat treatment temperature of the aluminum alloy variable density lattice structure is 200-300° C., and the heat treatment is maintained for 1 hour, followed by rapid cooling with argon gas.

[0058] S5. Remove the variable density lattice structure from the printed substrate through a wire cutting process.

[0059] S6. Prepare multi-cell thin-walled tubes by wire cutting process, using 6061 aluminum alloy material

[0060] S7. Cut the printed variable density lattice structure into several parts according to the cross-sectional configuration of the multicellular tube.

[0061] S8. Use epoxy resin to glue the cut variable density lattice structure to the multi-cellular thin-walled tube to form a variable density lattice reinforced multi-cellular thin-walled energy absorbing structure.

[0062] The topology optimization process of the variable density lattice structure in S2 includes the following processes:

[0063] S2-1. Construct a parametric variable density lattice structure, extract the relative density as the design variable, use the energy homogenization method for macro prediction, and establish a parametric material interpolation model.

[0064] S2-2. Define the initial design domain, mesh the initial design domain, apply boundary conditions and external force loads, and establish a finite element model.

[0065] S2-3. Define the relative density design variable in the macrostructure design domain, assign values ​​to it, and calculate the unit stiffness matrix k i As well as the overall stiffness matrix K of the assembled structure, finite element analysis is performed on the three-dimensional multi-scale variable density lattice structure to obtain the structural response information.

[0066] S2-4. Construct a variable density lattice structure optimization model, perform sensitivity analysis on the relative density design variables, and iteratively update the design variables to determine the optimal layout of the lattice microstructure.

[0067] S2-5. Determine the convergence of the design variables. When the change of the objective function in two consecutive iterations is less than 1×10 -3 , or when the maximum number of iterations set is 50, the optimization converges by default and the iteration process terminates; otherwise, the design variables are updated and the next iteration is continued.

[0068] The relative density η in S2-1 is used to describe the proportion of the area where the material distribution exists in the microstructure unit cell to the entire unit cell domain; its calculation formula is as follows:

[0069]

[0070] Among them, V strut represents the total volume of all the rods in the microstructure unit cell, V lattice Represents the total volume enclosed by the entire microstructure unit cell.

[0071] The energy homogenization method is used to predict the macroscopic properties, and the fifth-order polynomial curve is used to describe the relative density η and the equivalent elastic constant D. ij The display relationship between them, the mathematical expression of its parameterized material interpolation model is as follows:

[0072] D ij =a0+a1η+a2η 2 +a3η 3 +a4η 4 +a5η 5

[0073] where a k (k=0~5) is the coefficient of the corresponding term of the fitting polynomial curve equation.

[0074] In S2-3, the relative density design variable on the macroscopic structure design domain is defined and assigned a value. The equivalent elastic matrix D of the microscopic unit is calculated using the parametric interpolation method at the microscopic scale. H , according to the equivalent elastic matrix DH Solve the element stiffness matrix k i As well as the overall stiffness matrix K of the assembled structure, finite element analysis is used to solve the displacement field U, which is calculated as follows:

[0075] U=K -1 F

[0076] Among them, F is the external force on the entire structure;

[0077] Equivalent elastic matrix D H The expression is as follows:

[0078]

[0079] in, and are the equivalent stress and equivalent strain of the equivalent homogeneous body, respectively, then the unit stiffness matrix k i And the calculation formula of the overall stiffness matrix K of the assembled structure is as follows:

[0080]

[0081]

[0082] Where B is the strain matrix of the unit, Ω i is the integration domain of the i-th unit, and the material elasticity matrix corresponding to unit i is D i H (η i );

[0083] In S2-4, according to the displacement field U solved in S3, the objective function C in the three-dimensional variable density lattice structure optimization model is calculated, and its calculation formula is as follows:

[0084] C=U T KU

[0085] The variable density lattice structure optimization model is as follows:

[0086] find:X={η1,η2,…,η n} T

[0087] min:

[0088] st:KU=F

[0089]

[0090] 0<η min ≤η i ≤η max ≤1,i=1,2,…,n

[0091] Among them, X is the design variable vector, which contains n relative density variables η; C is the objective function, which is the overall compliance function of the variable density lattice structure; st is the constraint condition, K and k i are the overall stiffness matrix of the structure and the stiffness matrix of element i, U and u respectively. i are the displacement field of the entire structure and the displacement field of unit i respectively, and F is the external force acting on the entire structure.

[0092] In S2-5, sensitivity analysis is performed on the design variables to solve the sensitivity analysis of the objective function and constraint function relative to the design variables, and the overall flexibility C of the structure and the material consumption V with respect to the relative density design variable η are derived. i The derivative of

[0093] The sensitivity analysis of the overall flexibility of the structure with respect to the relative density design variable is carried out on both sides of the static equilibrium equation with respect to the relative density design variable η. i Taking the derivative, the expression is as follows:

[0094]

[0095] According to the principle of independence of design variables, the above expression is simplified as follows:

[0096]

[0097]

[0098] According to the relevant theory of finite element analysis, the overall flexibility C of the structure is related to the relative density design variable η i The sensitivity expression of is as follows:

[0099]

[0100] The volume of material used is related to the relative density design variable η i The sensitivity expression of is as follows:

[0101]

[0102] The multi-level nested thin-walled energy absorbing structure made by the above manufacturing process includes a thin-walled tube structure and a variable density lattice structure 5. The thin-walled tube structure is centrally symmetrical and has a multi-layer tube wall. A plurality of cavities are arranged inside the thin-walled tube structure, and the variable density lattice structure 5 is filled into the cavity. The thin tube wall structure is, from the inside to the outside, an inner wall 1, a middle wall 2 and an outer wall 3. A plurality of constraint ribs 4 for connection are arranged between the inner wall 1, the middle wall 2 and the outer wall 3. The wall thickness of the inner wall 1, the middle wall 2, the outer wall 3 and the constraint ribs are all 1 mm. The size of the thin-walled tube structure is the same as that of the variable density lattice structure 5, to ensure that when epoxy resin is used to bond the multi-cellular tube to the internal lattice structure, there is no excess gap between the components and they are fully bonded.

[0103] The present invention will be further described below in conjunction with embodiments:

[0104] Example 1: In this example, the properties of the three-dimensional lattice structure define elastic modulus E = 100 MPa, Poisson's ratio μ = 0.3. The initial design domain is as follows Figure 3 As shown in the figure, the length of the axial anti-collision structure is 100 mm, the cross section is a 60 mm × 60 mm square, the vertical uniform force F is applied to the right end face of the structure, and the total load is 300 N; the left end face of the structure is the constraint area; the entire design domain uses an eight-node hexahedron unit with a unit size of 10 mm × 10 mm × 10 mm. Considering the design requirements and the additive manufacturing process constraints, the upper and lower limits of the relative density of the parameterized lattice material in this embodiment are set as η max =0.60 and η min =0.10. In the optimization process, the optimization goal is to minimize the structural compliance, and the upper limit of the material allowable is set to 20%. Figure 4 is the iteration curve of the objective function C. It can be seen from the curve that the objective function converges rapidly, and the convergence speed gradually slows down after 20 iterations. This method can converge rapidly and reach a stable value. Figure 5 This is a three-dimensional image of the optimized variable density lattice structure.

[0105] The optimized variable density lattice structure was prepared by laser powder bed melting method. The material used was AlSi10Mg. The preparation process parameters included laser power of 325W, scanning speed of 1200mm / s, slice thickness of 30μm, scanning spacing of 140μm, substrate preheating temperature of 80℃, Stripes scanning method, and rotation angle of each layer of 67°. After heat treatment at 230℃, it was cut from the substrate by wire cutting after one hour of insulation. Then, the multi-cellular thin-walled tube was prepared by wire cutting process. The material was 6061 aluminum alloy with a wall thickness of 1mm. The printed lattice structure was cut into several parts according to the cross-sectional configuration of the multi-cellular tube. Finally, epoxy resin was used to glue the cut lattice structure to the multi-cellular thin-walled tube to form a variable density lattice reinforced multi-cellular thin-walled energy-absorbing structure. The structure length L was 100mm, and epoxy resin was used for bonding. The assembly process is as follows: Figure 6 As shown, Figure 7 The three-dimensional diagram of the obtained nested thin-wall energy absorbing structure is shown in FIG. Figure 8 This is a comparison diagram of the quasi-static axial compression force-displacement curve of the multi-level nested thin-walled energy-absorbing structure based on variable density lattice reinforcement of the present invention. The quasi-static axial compression test of the multi-level nested thin-walled structure reinforced by the variable density lattice shows that for this composite structure, the lattice structure provides sufficient lateral support for the multi-cellular tube, so that the buckling mode of the thin-walled tube becomes a shorter wavelength. It is precisely because of this interaction mechanism between the lattice and the multi-cellular tube that the energy absorption efficiency of the composite structure is further improved than that of the multi-cellular thin-walled empty tube, and even greater than the sum of the multi-cellular tube and the lattice tested separately.

[0106] Example 2

[0107] In this example, the properties of the three-dimensional lattice structure define the elastic modulus E = 100 MPa and the Poisson's ratio μ = 0.3. The initial design domain is as follows Fig. 9 As shown in the figure, the length of the three-point bending beam structure is 200mm, and the cross section is a 60mm×60mm square; a uniformly distributed force F is applied vertically downward in the center area of ​​the upper end face of the structure, and the total load is 1000N; the area 20mm away from the left and right sides of the lower end face is the support surface, which constrains its vertical freedom. The entire design domain uses an eight-node hexahedral unit with a unit size of 10mm×10mm×10mm; considering the design requirements and additive manufacturing process constraints, the upper and lower limits of the relative density of the parameterized lattice material in this example are set as η max =0.60 and η min = 0.10. In the optimization process, the optimization goal is to minimize the structural compliance, and the upper limit of the material allowance is set to 20%. Fig.10 It is the iterative curve of the objective function C. It can be seen from the curve that the objective function converges rapidly. After 20 iterations, the convergence speed gradually slows down. This method can converge rapidly and reach a stable value. Fig.11 This is the front view of the optimized lattice structure.

[0108] The optimized lattice structure was prepared by laser powder bed melting method. The material used was AlSi10Mg. The preparation process parameters included laser power of 325W, scanning speed of 1200mm / s, slice thickness of 30μm, scanning spacing of 140μm, substrate preheating temperature of 80℃, Stripes scanning method, and rotation angle of each layer of 67°. After heat treatment at 230℃, it was cut from the substrate by wire cutting after one hour of insulation. Then, the multi-cellular thin-walled tube was prepared by wire cutting process. The material was 6061 aluminum alloy with a wall thickness of 1mm. The printed lattice structure was cut into several parts according to the cross-sectional configuration of the multi-cellular tube. Finally, epoxy resin was used to glue the cut lattice structure to the multi-cellular thin-walled tube to form a variable-density lattice-reinforced multi-cellular thin-walled energy-absorbing structure. The structure length L was 200mm, and epoxy resin was used for bonding. The assembly process is as follows: Fig.12 As shown, Fig.13 Schematic diagram of the multi-level nested thin-wall energy absorption structure. Fig.14 The figure is a comparison diagram of the force displacement curves of the multi-level nested thin-walled energy absorbing structure of the present invention under three-point bending conditions. The three-point bending test of the multi-level nested thin-walled structure reinforced by the variable density lattice shows that for this composite structure, due to the interaction mechanism between the lattice and the multi-cellular tube, the energy absorption efficiency of the composite structure is ultimately higher than that of the multi-cellular thin-walled empty tube, and higher than the sum of its single components.

[0109] The present invention adopts a parametric interpolation method to design and prepare a lattice structure, adopts a wire cutting process to prepare a multi-cellular thin-walled tube, and glues the lattice structure and the multi-cellular thin-walled tube together through epoxy resin to obtain a multi-level nested thin-walled energy absorbing structure, thereby improving the energy absorption efficiency of the variable-density lattice-reinforced multi-cellular thin-walled structure. The preparation process is simple and can be mass-produced, and the produced multi-level nested thin-walled energy absorbing structure has high energy absorption efficiency.

Claims

1. A manufacturing process for a multi-level nested thin-walled energy absorbing structure, characterized in that: The following steps are involved: S1. Material selection of variable density lattice structure; S2. Constructing a variable density lattice structure model on a computer; S3, setting the laser scanning mode and process parameters, and printing according to the corresponding parameters to obtain a variable density dot matrix structure; S4, heat treating the obtained variable density lattice structure; S5, removing the variable density lattice structure from the printed substrate by a wire cutting process; S6, preparing multi-cell thin-walled tubes by wire cutting process; S7, cutting out variable density lattice structures of the same size according to the size of the prepared multicellular thin-walled tube; S8. Make a multi-level nested thin-wall energy absorbing structure.

2. The manufacturing process of a multi-level nested thin-walled energy absorbing structure according to claim 1, characterized in that: In S2, the design steps of the variable density lattice structure model are as follows: S2-1. Construct a parametric variable density lattice structure, extract relative density as the design variable, use the energy homogenization method for macro prediction, and establish a parametric material interpolation model; S2-2, define the initial design domain, mesh the initial design domain, apply boundary conditions and external force loads, and establish a finite element model; S2-3. Define the relative density design variable in the macrostructure design domain, assign values ​​to it, and calculate the unit stiffness matrix k i and the overall stiffness matrix K of the assembled structure, and finite element analysis is performed on the three-dimensional multi-scale variable density lattice structure to obtain the structural response information; S2-4, construct a variable density lattice structure optimization model, perform sensitivity analysis on relative density design variables, and iteratively update the design variables to determine the optimal layout of the lattice microstructure; S2-5. Determine the convergence of the design variables. When the change of the objective function in two consecutive iterations is less than 1×10 -3 , or when the maximum number of iterations set is 50, the optimization converges by default and the iteration process terminates; otherwise, the design variables are updated and the next iteration is continued.

3. The manufacturing process of a multi-level nested thin-walled energy absorbing structure according to claim 2, characterized in that: In S2-1, the parameterized material interpolation model is as follows: D ij =a0+a1η+a2η 2 +a3h 3 +a4h 4 +a5h 5 Among them, D ij is the equivalent elastic parameter, a k (k=0-5) is the coefficient of the corresponding term of the fitting polynomial curve equation, and η is the relative density of the parameterized variable density lattice structure.

4. The manufacturing process of a multi-level nested thin-walled energy absorbing structure according to claim 2, characterized in that: In S2-3, the unit stiffness matrix k i And the calculation formula of the overall stiffness matrix K of the assembled structure is as follows: Where B is the strain matrix of the unit, Ω i is the integration domain of the i-th unit, and the material elasticity matrix corresponding to unit i is 5. The manufacturing process of a multi-level nested thin-walled energy absorbing structure according to claim 2, characterized in that: In S2-4, the variable density lattice structure optimization model is as follows: find: X={η1,η2,…,η n } T st:KU=F 0<η min ≤η i ≤η max ≤1,i=1,2,…,n Among them, X is the design variable vector, which contains n relative density variables η; C is the objective function, which is the overall compliance function of the variable density lattice structure; st is the constraint condition, K and k i are the overall stiffness matrix of the structure and the stiffness matrix of element i, U and u respectively. i are the displacement field of the entire structure and the displacement field of unit i respectively, and F is the external force exerted on the entire structure.

6. The manufacturing process of a multi-level nested thin-walled energy absorbing structure according to claim 1, characterized in that: In S3, the Stripes scanning method is adopted, the rotation angle of each layer is 67°, the printing layer thickness is 0.02-0.10 mm, the laser power is 80-500 W, the laser scanning speed is 500-2000 mm / s, and the scanning interval is 0.17-0.23 mm.

7. The manufacturing process of a multi-level nested thin-wall energy absorbing structure according to claim 1, characterized in that: In S1, the material of the variable density lattice structure is AlSi10Mg aluminum alloy, and the material of the multi-cellular thin-walled tube in S6 is 6061 aluminum alloy.

8. The manufacturing process of a multi-level nested thin-walled energy absorbing structure according to claim 1, characterized in that: In the above S8, the multi-cellular thin-walled tubes and the variable density lattice structure are bonded by epoxy resin to form a multi-level nested thin-walled energy absorbing structure.

9. A multi-level nested thin-walled energy absorbing structure manufactured by the manufacturing process of a multi-level nested thin-walled energy absorbing structure according to claim 1, characterized in that: It comprises a thin-walled tube structure and a variable density lattice structure (5), wherein the thin-walled tube structure is centrally symmetrical and has a multi-layer tube wall, wherein a plurality of cavities are arranged inside the thin-walled tube structure, wherein the variable density lattice structure (5) is filled into the cavities, and a plurality of constraint ribs (4) for connection are arranged between the thin-walled tube structures.

10. The multi-level nested thin-wall energy absorbing structure according to claim 9, characterized in that: The thin-walled tube structure comprises, from the inside to the outside, an inner wall (1), an intermediate wall (2) and an outer wall (3), and the wall thickness of the inner wall (1), the intermediate wall (2), the outer wall (3) and the restraining rib plate (4) are all 1 mm.

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