A Ply Optimization Method for a Composite Laminate with Delamination Layers

Abstract

The present invention belongs to the technical field of composite material structure design, and particularly relates to a method for optimizing the layup of a composite laminate with missing layers. The present invention provides an optimization framework that connects the geometric modeling, finite element calculation, and layup sequence optimization of the composite laminate with missing layers. In geometric modeling, the model is divided into regions according to the missing layer boundaries, and the overall complex structure is divided into discrete regions. The layup parameters of each region are set in an interlayer insertion manner to obtain the layup sequence, and it can be ensured that the layup sequence obtained by this method satisfies the layer-removability. The optimization process transforms the layup sequence optimization problem into an interlayer insertion position and angle optimization problem, making the optimization more efficient.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite material structure design, and particularly relates to a method for optimizing the layup of a composite laminate with missing layers. Background Art

[0002] Due to the requirement of aircraft structure lightweighting, it is often necessary to divide the composite skin into regions and design different thicknesses for each region. Compared with the optimization problem of general composite laminates, the layup optimization problem of composite laminates with missing layers has stronger designability, more layup sequence groups, and greater optimization difficulty.

[0003] Some theories have been proposed in the prior art. The analytical results of simple examples show that the layup optimization design of composite laminates with missing layers is feasible. However, at present, our layup optimization design for complex aircraft structures is still not accurate enough because the optimization theory has not been combined with finite element analysis. How to combine these optimization ideas with finite element software to solve the layup optimization of complex panels needs further research. Summary of the Invention

[0004] Object of the present invention: The present invention provides a method for optimizing the layup of a composite laminate with missing layers. The main purpose of this method is to complete the layup optimization with missing layers by combining finite element analysis software. This method is general and can optimize conventional layups. This method is no longer limited to the layup optimization of simple structures and is also applicable to the layup optimization of complex aircraft structures. It can obtain multiple sets of feasible solutions and relatively optimal solutions, providing a reference for composite material layup design and having certain practical value.

[0005] Technical solution of the present invention: A method for optimizing the layup of a composite laminate with missing layers, comprising the following steps:

[0006] Step S1: In finite element software, divide the model into n regions according to the missing layer boundary, and each region is denoted as Q i ——i = 1, 2... n;

[0007] Step S2: In finite element software, set the given initial layup quantity L(Q i ) for each divided region and the initial layup sequence parameters of each region, and the initial layup sequence parameters of each region are all 0;

[0008] Step S3: In finite element software, establish constraint conditions to fix or simply support the selected geometric boundaries of the structure, apply loads to the selected geometric elements of the structure, and set output targets such as stress, strain, and displacement; submit the established model for calculation to generate a grid model INP file containing complete layup information;

[0009] Step S4: For each divided region, establish a relationship with the layup quantity L(Qi )Equal {S i (x) —— x = 1, 2... L(Q i )} i＝1...n As the ply - stacking sequence parameter for each region;

[0010] Step S5: Set the determined ply - stacking sequence parameter S1(x) —— x = 1, 2... L(Q1) for the region with the minimum number of plies;

[0011] Step S6: Set the ply - stacking sequence parameters of the remaining regions in the order of increasing number of plies in an interleaving manner;

[0012] Step S7: Map the ply - stacking sequence parameters of each region determined in Step S6 to the initial ply - stacking sequence parameters of each region in the INP file of Step S3 one by one, and input the mapped INP file into the finite - element software for calculation to obtain the output target result;

[0013] Step S8: According to the output target result calculated in Step S7, transform the ply - optimization problem into an interleaving - optimization problem and assign new values to the ply - stacking sequence parameters;

[0014] Step S9: Repeat Steps S5 - S8 until the calculation result meets the requirements.

[0015] In a possible embodiment, the precise regional division of the model according to the layer - dropping boundary in Step S1 means that the model must be divided into n regions Q —— i = 1, 2... n according to all layer - dropping boundaries, and the regions are numbered in order according to the increasing number of plies: For There is L(Q i ) < L(Q i+1 ).

[0016] In a possible embodiment, the INP file mentioned in Step S3 contains complete regional - division information, sufficient loading, and constraint conditions.

[0017] In a possible embodiment, Step S4 must group the sequence parameters according to the regional - division result of Step S1. The number of groups of sequence parameters is equal to the number of divided regions and a corresponding relationship is established between them. The number of elements included in each group of sequence parameters is consistent with the number of plies in the corresponding region.

[0018] In a possible embodiment, in Step S6, except for the sequence parameters of the region with the least number of plies set in Step S5, the corresponding sequence parameters of the remaining regions are all obtained in an interleaving manner: Considering a laminated plate with a total of n regions, the i - th region is written as Q i —— i = 1, 2... n, L(Q i ) represents Q iThe number of plies in the region, obtained according to the rule of arranging the numbers from small to large: For there is L(Q i ) < L(Q i+1 ); S i (x) —— x = 1, 2... L(Q i ) represents the angle of the x-th ply in the i-th region; the adjacent situation of all regions is represented by the n×n matrix U:

[0019]

[0020]

[0021] If all S i (x) —— x = 1, 3... L(Q i ) of the i-th region are known, then for the i + 1-th region:

[0022]

[0023] where p i (m) —— m = 1, 2... (L(Q i+1 ) - L(Q i )) represents the newly created ply sequence parameter, with the initial value taking any real number, and the subsequent values are controlled by the optimization algorithm. The symbol represents the intercalation operation, represents the sequence of the i-th region in which a newly created ply sequence parameter p i (x) is inserted between any adjacent elements S i (x) and S i (x + 1) to form a new sequence {S i (1), S i (2), p i (1)... p i (L(Q i+1 ) - L(Q i ))}, p i (L(Q i ))}, the new sequence has L(Q i+1 ) elements, and the new sequence is assigned values according to the element pair S i (x + 1) as follows:

[0024]

[0025] The above steps obtain all the ply sequence parameters S i+1 (x) of the i + 1-th region. Considering the i + 2-th region, there are 8 adjacent situations:

[0026] Case 1: U(i, i + 1) = 1, U(i, i + 2) = 1, U(i + 1, i + 2) = 1

[0027] Case 2: U(i, i + 1) - 1, U(i, i + 2) - 1, U(i + 1, i + 2) = 0

[0028] Case 3: U(i, i + 1) = 1, U(i, i + 2) = 0, U(i + 1, i + 2) = 1

[0029] Case 4: U(i, i + 1) = 1, U(i, i + 2) = 0, U(i + 1, i + 2) = 0

[0030] Case 5: U(i, i + 1) = 0, U(i, i + 2) = 1, U(i + 1, i + 2) = 1

[0031] Case 6: U(i, i + 1) = 0, U(i, i + 2) = 0, U(i + 1, i + 2) = 1

[0032] Case 7: U(i, i + 1) = 0, U(i, i + 2) = 1, U(i + 1, i + 2) = 0

[0033] Case 8: U(i, i + 1) = 0, U(i, i + 2) = 0, U(i + 1, i + 2) = 0

[0034] For Cases 1, 3, 4, 5, 6, 7, 8:

[0035]

[0036] For Case 2, any one of the following formulas can be used to determine S i+2 (x):

[0037]

[0038] In a possible embodiment, step S7 maps the ply sequence parameter S i (x) - where x = 1, 2... L(Q i ) to the numerical values representing the ply angles in the corresponding region of the INP file, and the mapping method can be manual change or script change.

[0039] In a possible embodiment, step S8 transforms the problem of optimizing the laminate with missing plies into an interlayer optimization problem, and the design variables change from the ply sequences of each region to the ply sequence S1(x) of the region with the fewest plies - where x = 1, 2... L(Q1), and the interlayer situation p i (m) - where m = 1, 2... (L(Q i+1 ) - L(Q i)) According to whether the target results of finite element calculations such as stress, strain, and displacement meet the design requirements, for S1(x), p i (m), use optimization algorithms such as genetic algorithms and simulated annealing algorithms for unconstrained optimization to generate new S1(x), p i (m).

[0040] In a possible embodiment, if the calculation result described in step S7 is less than the threshold specified by the design, then step S9 terminates the optimization and outputs the layup sequence corresponding to the settlement result; if the calculation result described in step S7 is greater than the threshold specified by the design, then step S9 iterates the new layup sequence parameters generated in step S8 back to step S5 for a new round of optimization process.

[0041] Advantages of the present invention: The method of the present invention has a concise logic and flexible and easy-to-implement specific operations. It divides a whole complex composite laminate into discrete regions according to the layer-discarding boundary, replaces the original layer-discarding process of the composite material from more to less with an interlayer insertion method from less to more. The interlayer insertion method also considers the adjacent situation of each region and adds rules, thereby giving a more specific layup sequence. More importantly, the layup sequence ensures the layer-discarding property of the structure; the optimization space is changed from the layup sequence to the interlayer insertion position and angle. Optimization algorithms such as genetic algorithms and simulated annealing algorithms can be used to optimize the interlayer insertion position and angle, which can reduce the time cost of layup design, obtain a more efficient layup sequence, and provide a reference for the layup design of composite laminates with layer discarding. Description of the Drawings

[0042] Figure 1 It is a schematic diagram of layer-discarding layup of a preferred embodiment of the present invention Detailed Embodiments

[0043] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0044] Perform the following steps using the ABAQUS software.

[0045] Step 1: As Figure 1 shown, divide it into four regions A, B, C, and D according to the layer-discarding boundary of the laminate

[0046] Step 2: Set the ply stacking sequences for the four regions A, B, C, and D. The initial values can be arbitrarily taken. In this example, the initial sequences are A: [0 / 0 / 0 / 0 / 0], B: [0 / 0 / 0 / 0 / 0 / 0 / 0], C [0 / 0 / 0 / 0 / 0 / 0 / 0 / ], D: [0 / 0 / 0 / 0 / 0 / 0 / 0 / 0];

[0047] Step 3: The laminate is simply supported on all four sides and a uniform pressure is applied on the surface. Output the maximum deformation of the entire model. Submit the model to the finite element software for calculation, generate an INP file, and obtain the maximum deformation of the model;

[0048] Step 4: Establish the order parameter sequences S1(x), S2(x), S3(x), and S4(x) for the four regions A, B, C, and D respectively;

[0049] Step 5: Since SA is the order parameter with the least number among the four order parameters, first set the ply stacking sequence for region A: S1(1) = a1, s1(2) = a2, S1(3) = a3, S1(4) = a4, s1(5) = a6, a i is a real number, representing a specific angle;

[0050] Step 6: In the present invention, the ply stacking sequence of region B is determined by the interlayer method: In this example, it corresponds to case 3, that is, U(i, i + 1) = 1, U(i, i + 2) = 0, U(i + 1, i + 2) = 1. The ply stacking sequence of region B is determined by the ply stacking sequence of region A and the interlayer position and interlayer angle of region B. The ply stacking sequence of region C is determined by the ply stacking sequence of region B and the interlayer position and interlayer angle of region C. The ply stacking sequence of region D is determined by the ply stacking sequence of region C and the interlayer position and interlayer angle of region D. S2(1) = a1, S2(2) = a2, S2(3) = a6, S2(4) = a3, S2(5) = a4, S2(6) = a6; The same applies to regions C and D; Ultimately, the ply stacking sequences of regions B, C, and D are all determined by the ply stacking sequence of region A and the interlayer positions and interlayer angles of their respective regions;

[0051] Step 7: Map the order parameters S1(x), S2(x), S3(x), and S4(x) one by one to the sequence representing the ply angles in the finite element input file: The ply angles of the four regions A, B, C, and D are all 0, that is, A: [0 / 0 / 0 / 0 / 0], B: [0 / 0 / 0 / 0 / 0 / 0 / 0], C [0 / 0 / 0 / 0 / 0 / 0 / 0 / ], D: [0 / 0 / 0 / 0 / 0 / 0 / 0 / 0]. After mapping:

[0052] A: [S1(1) / S1(2) / S1(3) / S1(4) / S1(5)], B: [S2(1) / S2(2) / S2(3) / S2(4) / S2(5) / S2(6)], C: [S3(1) / S3(2) / S3(3) / S3(4) / S3(5) / S3(6) / S3(7)], D: [S4(1) / S4(2) / S4(3) / S4(4) / S4(5) / S4(6) / S4(7) / S4(8)];

[0053] Step 8: Perform finite element calculation on the mapped finite element input file (INP) and output the maximum deformation of the laminated plate; According to the maximum displacement condition, in this example, the genetic algorithm is used to adjust the ply sequence in area A and the ply insertion positions and angles in the other areas. After the adjustment, a new ply sequence in area A and the ply insertion positions and angles in the other areas are generated;

[0054] Step 9: If the maximum deformation of the laminated plate is less than the maximum deformation threshold required by the design, terminate the optimization. If the maximum deformation is greater than the threshold required by the design, go to Step 5.

[0055] As described above, only the specific embodiments of the present invention are described in detail, and the unelaborated parts are conventional techniques. However, the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention. The protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A method for optimizing the layup of a delamination-containing composite laminate, characterized in that, It includes the following steps: Step S1: In the finite element software, divide the model into n regions according to the delamination boundary, and each region is denoted as Q i ——i = 1, 2... n; Step S2: In the finite element software, set the given initial ply number L(Q i ) for each divided area respectively, and the initial ply sequence parameters for each area, where the initial ply sequence parameters for each area are all 0; Step S3: In the finite element software, establish constraint conditions to fix or simply support the selected geometric boundaries of the structure, apply loads to the selected geometric elements of the structure, and set output targets such as stress, strain, and displacement; Submit the model established above for calculation to generate an INP file of the mesh model containing complete ply information; Step S4: For each divided area, establish {S i}(x)——x = 1, 2... L(Q i i)) that is equal to the number of plies L(Q i＝1...n ) of this area as the ply sequence parameter for each area; Step S5: Set the determined ply sequence parameter S1(x) for the area with the minimum number of plies — x = 1, 2... L(Q1); Step S6: Set the ply sequence parameters of the remaining areas in ascending order of the number of plies in an interleaved manner; In step S6, except that the sequence parameters of the area with the least number of plies are set in step S5, the sequence parameters corresponding to the remaining areas are all obtained by the way of intercalation: Considering a laminate with a total of n areas, the i-th area is written as Q i ——i = 1, 2... n, L(Q i ) represents the number of plies in the Q i area, and is obtained according to the arrangement rule from small to large: For there is L(Q i ) < L(Q i+1 ); S i (x)——x = 1, 2... L(Q i ) represents the angle of the x-th ply in the i-th area; the adjacent situation of all areas is represented by an n×n matrix U: If all S in the i-th region are known i (x) —— where x = 1, 2... L(Q i ), then for the (i + 1)-th region: where p i (m)——m=1,2...(L(Q i+1 )-L(Q i )) represents the newly created ply sequence parameter, the initial value is any real number, and the subsequent value is controlled by the optimization algorithm; symbol represents the interpolation operation, Represents the sequence of the i-th region Any adjacent element S i (x), S i Insert the new ply order parameter p between (x+1) i (m), forming a new sequence {S i (1) S i (2) p i (1)...p i (L(Q i+1 )-L(Q i )), p i (L(Q i ))}, the new sequence has L(Q i+1 ) elements, and the new sequence is element-wise S i The assignment of (x+1) is: All the ply sequence parameters S of the (i + 1)-th region are obtained through the above steps i+1 (x). Considering the (i + 2)-th region, there are eight adjacent cases: Case 1: U(i, i + 1) = 1, U(i, i + 2) = 1, U(i + 1, i + 2) = 1 Case 2: U(i, i + 1) = 1, U(i, i + 2) = 1, U(i + 1, i + 2) = 0 Case 3: U(i, i + 1) = 1, U(i, i + 2) = 0, U(i + 1, i + 2) = 1 Case 4: U(i, i + 1) = 0, U(i, i + 2) = 0, U(i + 1, i + 2) = 0 Case 5: U(i, i + 1) = 0, U(i, i + 2) = 1, U(i + 1, i + 2) = 1 Case 6: U(i, i + 1) = 0, U(i, i + 2) = 0, U(i + 1, i + 2) = 1 Case 7: U(i, i + 1) = 0, U(i, i + 2) = 1, U(i + 1, i + 2) = 0 Case 8: U(i, i + 1) = 0, U(i, i + 2) = 0, U(i + 1, i + 2) = 0 For Cases 1, 3, 4, 5, 6, 7, 8: For Case 2, any one of the following formulas can be arbitrarily used to determine S i+2 (x): Step S7: Map the ply sequence parameters of each area determined in Step S6 to the initial ply sequence parameters of each area in the INP file of Step S3 one by one, input the mapped INP file into the finite element software for calculation, and obtain the output target results; Step S8: According to the output target results calculated in Step S7, transform the ply optimization problem into an interleaving optimization problem, and assign new values to the ply sequence parameters; Step S9: Repeat Steps S5 - S8 until the calculation results meet the requirements.

2. The method for optimizing the layup of a delamination-containing composite laminate according to claim 1, characterized in that, The precise regional division of the model according to the layer loss boundaries described in step S1 means that the model must be regionally divided into n regions Q according to all the layer loss boundaries i --For i = 1, 2... n, number the regions in ascending order of the number of laying layers in sequence: For There is L(Q i ) < L(Q i+1 ).

3. The method for optimizing the layup of a delamination-containing composite laminate according to claim 2, characterized in that, The INP file mentioned in Step S3 contains complete regional division information, sufficient loading, and constraint conditions.

4. The method for optimizing the layup of a delamination-containing composite laminate according to claim 3, characterized in that, In Step S4, the sequence parameters must be grouped according to the regional division results of Step S1. The number of groups of sequence parameters is equal to the number of divided regions, and a corresponding relationship is established between them. The number of elements contained in each group of sequence parameters is the same as the number of plies in the corresponding region.

5. The optimized layup method for a delamination-containing composite laminate according to claim 4, wherein, Step S7 maps the sequential parameter S i (x)--where x = 1, 2... L(Q i ) to the values in the corresponding area of the INP file that characterize the ply angles. The mapping method can be manual modification or script modification.

6. The optimized layup method for a delamination-containing composite laminate according to claim 5, wherein, Step S8 has transformed the optimization problem of the ply-drop composite laminate into an interlayer optimization problem. The design variables have changed from the ply sequence of each region to the ply sequence S1(x) of the region with the fewest plies — x = 1, 2... L(Q1), and the interlayer condition p i (m) — m = 1, 2... (L(Q i+1 ) - L(Q i )); According to the target results of the finite element calculation, such as whether the stress, strain, and displacement meet the design requirements, unconstrained optimization is performed on S1(x) and p i (m) using optimization algorithms such as genetic algorithms and simulated annealing algorithms to generate new S1(x) and p i (m).

7. The optimized layup method for a delamination-containing composite laminate according to claim 6, wherein, If the calculation result described in Step S7 is less than the threshold specified by the design, Step S9 terminates the optimization and outputs the ply sequence corresponding to this calculation result; if the calculation result described in Step S7 is greater than the threshold specified by the design, Step S9 iterates the new ply sequence parameters generated in Step S8 back to Step S5 for a new round of optimization process.

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