A novel progressive optimization method for thin rods based on additive manufacturing technology

Abstract

The present invention discloses a novel progressive optimization method for thin rods based on additive manufacturing technology. First, the geometric model of the thin rod is meshed; then, various parameters of the model are initialized; then, the finite element software is used to calculate the material replacement standard J value of the set test; finally, the material replacement rate RR is updated to achieve the optimization goal. The key steps included in the present invention are: ① establishment and meshing of the thin rod model; ② initialization of thin rod parameters; ③ correction of material parameters; ④ judgment of the optimization target according to the standard threshold K; ⑤ thin rods with complex material distribution are formed by additive manufacturing technology. In view of the large deformation and uneven deformation of thin rods in impact and collision tests, the present invention cleverly reduces and corrects the yield limit of the material in the inefficient or invalid area to replace the continuous deletion of inefficient or invalid units in the traditional progressive optimization method, thereby solving the practical problems of large deformation and uneven deformation of thin rods in impact and collision tests, and combining additive manufacturing technology to ensure the practicality of the method of the present invention.

Description

Technical Field

[0001] The present invention relates to the technical field related to novel progressive structural optimization methods, and more specifically, to a novel progressive optimization method for thin rods based on additive manufacturing technology. Background Art

[0002] Structural topology optimization is to optimize the material distribution according to the load conditions, constraints and performance indicators in the design domain, and to seek the best force transmission path of the structure. In the past few decades, various optimization methods have been successfully applied to the topology optimization design of various engineering structures, including homogenization method, variable density method, progressive structural optimization method, independent continuous mapping method and level set method. Among them, the progressive structural optimization method is simple in principle, has good convergence, strong versatility and is easy to program and implement, so it is very popular.

[0003] The incremental structural optimization method was first proposed in the early 1990s. Its design idea is to gradually delete invalid or inefficient material units in the material, and finally present the best force transmission method of the structure. It is mainly aimed at the continuum topology optimization design. In addition, the incremental structural optimization method is based on the linear elastic theory, and the continuous change of its structural topology will bring about the problem of structural applicability. Once the geometric or material nonlinearity appears in the structure, such as impact / collision, the solution process of the traditional incremental structural optimization method will be unstable and non-convergent, which usually leads to deviations in the transient collision dynamics calculation. Therefore, there is an urgent need for a method to solve the instability problem of the traditional incremental structural optimization method. Summary of the invention

[0004] 1. In view of the instability problem of the above-mentioned traditional progressive structural optimization method, the present invention proposes a new progressive optimization method based on additive manufacturing technology in combination with the impact test of thin rods.

[0005] 2. A novel progressive optimization method for thin rods based on additive manufacturing technology includes the following steps:

[0006] Step 1: Model meshing: Establish a thin bar geometry model and mesh the thin bar geometry model to obtain the unit number of the thin bar geometry model. The total number of units is H.

[0007] Step 2: Parameter initialization: Initialize material replacement rate RR, evolution rate ER and material properties; select material replacement standard J.

[0008] Step 3: Finite element calculation of unit J value: Use finite element software to simulate the set test, calculate the J value of all units, and obtain the maximum J value of all units, that is, J max . Compare the J values ​​of all cells with J max For comparison:

[0009] J i ≤RR*J max

[0010] Where i represents the unit number, i=1,2,,,H;

[0011] If there are some units that satisfy the above comparison formula, the material-related parameters U of these units are corrected, that is, the material-related parameters U are multiplied by a number less than 1, and step 3 is repeated until a stable state is reached; if no unit satisfies the above formula, go to step 4. The correction formula of the material-related parameters U is as follows:

[0012] U=U*β

[0013] Where β<1; β is used to control the correction speed of the material-related parameter U. If it is too large, the material-related parameter U cannot find a suitable value, and if it is too small, the number of iterations will increase.

[0014] Step 4: Optimization target judgment: Determine whether the set optimization target is achieved based on the standard threshold K.

[0015] The optimization objectives are as follows: ① maximizing the energy absorption capacity of the structure; ② maximizing the plastic strain energy; and ③ uniformly distributing the plastic strain within the design area.

[0016] Step 4.a: Maximize the energy absorption capacity of the structure: that is, verify the minimum collision force F in all units min Whether the standard threshold F is reached K If the specified optimization target is not reached, the material replacement rate RR is updated and steps (3)-(4) are repeated; if the specified optimization target is reached, the cycle ends. Standard threshold F K The formula for the specified optimization objective is as follows:

[0017] F min <F K

[0018] Step 4.b: Maximize plastic strain energy: verify whether the total plastic strain energy E reaches the standard threshold E K If the specified optimization target is not reached, the material replacement rate RR is updated and steps (3)-(4) are repeated; if the specified optimization target is reached, the cycle ends. Standard threshold E K The formula for the specified optimization objective is as follows:

[0019] E <E K

[0020] Step 4.c: Plastic strain in the uniformly distributed design area: verify whether the equivalent plastic strain of all units reaches the optimization target specified by the standard threshold K. If the specified optimization target is not reached, update the material replacement rate RR and loop through steps 3-4; if the specified optimization target is reached, end the loop. The formula for the optimization target specified by the standard threshold K is as follows:

[0021] (1-α)*K≤J i ≤(1+α)*K

[0022] Where i represents the unit number, i = 1, 2,,, H; α is the correction factor, which is a number less than 1. The update formula of the material replacement rate RR is as follows:

[0023] RR=RR+ER

[0024] The evolution rate ER is used to control the evolution speed of the material substitution rate RR; after the material substitution rate is updated, the finite element calculation is repeated until the structure reaches another stable state.

[0025] Step 5: Use additive manufacturing technology to form thin rods with complex material distribution. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the implementation cases of the present invention, the drawings required for use in the implementation cases will be briefly introduced below. Obviously, the drawings described below are only some implementation cases of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0027] Figure 1 is a flow chart of the method of the present invention;

[0028] Figure 2 is the part geometry model;

[0029] Figure 3 It is a thin bar mesh model;

[0030] Figure 4 is the equivalent plastic strain diagram of the thin bar;

[0031] Figure 5 is the evolution diagram of plastic strain of thin bar with the number of iterations;

[0032] Figure 6 This is the equivalent plastic strain diagram of the optimized thin bar;

[0033] Figure 7 This is the material distribution diagram of the optimized thin rod;

[0034] Figure 8 It is the overall flow chart of the present invention; DETAILED DESCRIPTION

[0035] Some specific implementation cases are given below for the technical solution adopted by the present invention. It should be pointed out that the described implementation cases are only intended to facilitate the understanding of the present invention and do not have any limiting effect thereon.

[0036] Specific implementation case: Combined with the finite element software Radioss, the thin rod is progressively optimized. The flow chart of this new progressive optimization method is as follows: Figure 1 shown.

[0037] (1) Model meshing: Establish a thin bar geometry model (such as Figure 2 ), and mesh the thin bar geometry model (as shown Figure 3 The total number of elements is 10000. The material replacement criterion J is the equivalent plastic strain.

[0038] (2) Parameter initialization: Initialize material replacement rate RR = 0.15, evolution rate ER = 0.01, elastic modulus E = 117 GPa, Poisson's ratio μ = 0.35, yield strength σ y =400MPa, shear modulus E T =100.08Mp, standard threshold E K =0.5.

[0039] (3) Finite element calculation unit J value: According to the impact test, the finite element analysis of the thin rod is performed to calculate the equivalent plastic strain value of all units (such as Figure 4 As shown), and obtain the maximum J value of all units, that is, J max . Compare the J values ​​of all cells with J max For comparison:

[0040] J i ≤RR*J max

[0041] Where i represents the unit number, i=1,2,,,10000.

[0042] If there are some units that satisfy the above comparison formula, the yield limit U of these units will be corrected, that is, the yield limit of the material is multiplied by a number less than 1, here we take U = 0.9, and loop step (3) until a stable state is reached; if no unit satisfies the above formula (that is, a stable state is reached), go to step (4). The correction formula of the material-related parameter U is as follows:

[0043] U=U*β

[0044] Where β<1; β is used to control the correction speed of the material-related parameter U. If it is too large, the material-related parameter U cannot find a suitable value, and if it is too small, the number of iterations will increase. Here we take β=0.9.

[0045] (4) Optimization target judgment: Select the plastic strain in the uniformly distributed design area as the optimization target. Verify whether the equivalent plastic strain of all units reaches the standard threshold E K If the specified optimization target is not reached, the material replacement rate RR is updated and steps (3)-(4) are repeated; if the specified optimization target is reached, the cycle ends. Standard threshold E K The formula for the specified optimization objective is as follows:

[0046] 0.6E K ≤J i ≤1.4E K

[0047] The update formula of material replacement rate RR is as follows:

[0048] RR=RR+ER

[0049] The evolution rate ER is used to control the evolution speed of the material replacement rate RR. Here we take ER = 0.01. After the material replacement rate is updated, the finite element calculation is repeated until the structure reaches another stable state.

[0050] (5) Save the calculation results: Obtain the evolution diagram of plastic strain with the number of iterations (such as Figure 5 ) and the plastic strain diagram of the optimized thin rod (as shown in Figure 6 As shown in Figure 2), and the material distribution diagram of the optimized thin rod (as shown in Figure 2 Figure 7 As shown in the figure), finally, additive manufacturing technology is used to form thin rods with complex material distribution.

Claims

1. A novel progressive optimization method for thin rods based on additive manufacturing technology, characterized in that: Step 1: Model meshing: Establish a thin bar geometry model, mesh the thin bar geometry model, obtain the unit number of the thin bar geometry model, and the total number of units is H; Step 2: Parameter initialization: Initialize material replacement rate RR, evolution rate ER and material properties; select material replacement standard J; Step 3: Finite element calculation of unit J value: Use finite element software to simulate the set test, calculate the J value of all units, and obtain the maximum J value of all units, that is, J max； Compare the J values ​​of all cells with J max For comparison: I i ≤RR*J max Where i represents the unit number, i=1,2,,,H; If there are some units that satisfy the above comparison formula, the material-related parameters U of these units are corrected, that is, the material-related parameters U are multiplied by a number less than 1, and step 3 is repeated until a stable state is reached; if no unit satisfies the above formula, step 4 is entered; the correction formula of the material-related parameters U is as follows: U=U*β Where β<1; β is used to control the correction speed of the material-related parameter U. If it is too large, the material-related parameter U cannot find a suitable value, and if it is too small, the number of iterations will increase. Step 4: Optimization target judgment: judge whether the set optimization target is achieved based on the standard threshold K; The optimization objectives include: ① maximizing the energy absorption capacity of the structure; ② maximizing the plastic strain energy; ③ uniformly distributing the plastic strain in the design area; Step 4.a: Maximize the energy absorption capacity of the structure: that is, verify the minimum collision force F in all units min Whether the standard threshold F is reached K The specified optimization target; if the specified optimization target is not reached, the material replacement rate RR is updated and steps (3)-(4) are looped; if the specified optimization target is reached, the loop is terminated; the standard threshold F K The formula for the specified optimization objective is as follows: F min <F K Step 4.b: Maximize plastic strain energy: verify whether the total plastic strain energy E reaches the standard threshold E K The specified optimization target; if the specified optimization target is not reached, the material replacement rate RR is updated and steps (3)-(4) are looped; if the specified optimization target is reached, the loop is terminated; the standard threshold E K The formula for the specified optimization objective is as follows: AND <E K Step 4.c: Plastic strain in the uniformly distributed design area: verify whether the equivalent plastic strain of all units reaches the optimization target specified by the standard threshold K; if the specified optimization target is not reached, update the material replacement rate RR and loop steps 3-4; if the specified optimization target is reached, end the loop; the formula for the optimization target specified by the standard threshold K is as follows: (1-a)*K≤J i ≤(1+α)*K Where i represents the unit number, i = 1, 2,,, H; α is the correction factor, which is a number less than 1. The update formula of material replacement rate RR is as follows: RR=RR+ER The evolution rate ER is used to control the evolution speed of the material replacement rate RR; after the material replacement rate is updated, the finite element calculation is repeated until the structure reaches another stable state; Step 5: Use additive manufacturing technology to form thin rods with complex material distribution.

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