Design method of hybrid composite structure with variable thickness based on ply continuity criterion

Abstract

The present invention discloses a design method for a variable thickness hybrid composite structure based on a ply continuity criterion. For a variable thickness hybrid composite structure, sub-regions are divided and the number of layers and load conditions of each sub-region are determined; the initial region is selected according to the load, and the ply structure of the initial region is optimized by a genetic algorithm, and the constraint module is nested to meet the actual production conditions; the remaining sub-regions are optimized according to the ply structure of the initial region combined with the load conditions, and the target value is calculated, and the optimal ply structure of the remaining sub-regions that meets all manufacturing constraints is obtained according to the target value combined with the manufacturing constraints; the final ply structure scheme is obtained to manufacture a variable thickness hybrid composite structure. The present invention incorporates a variety of manufacturing constraints, enhances the manufacturability of the structure, can effectively reduce the overall mass of the structure, and at the same time the structural integrity will not be damaged, while minimizing the mass and cost of the entire structure, it also achieves the optimal overall performance of the composite structure, and enhances the applicability of the optimization results.

Description

Technical Field

[0001] The invention relates to a composite product structure design method, in particular to a variable thickness hybrid composite structure design method based on a ply continuity criterion. Background Art

[0002] Composite structures have a series of advantages such as high specific strength, high specific stiffness and light weight, and are widely used in aerospace, shipbuilding and automotive fields. Compared with conventional composite structures, variable thickness hybrid composite structures have significant advantages such as improved material properties, reduced costs and flexible design. For the design of variable thickness hybrid composite structures, there are many problems with existing design methods, such as the lack of addition of manufacturing constraints, the inability to guarantee the optimality of the layup results, and the lack of consideration of the continuity of the layups between adjacent regions. This will lead to inconsistent layups between adjacent regions, causing stress concentration in the layup transition zone of the structure, resulting in matrix cracking and delamination.

[0003] At present, composite structures are often optimized with a single material, especially in the design of variable thickness composite structures, most of which are made of carbon fiber reinforced composite materials. However, this optimization technology has many defects:

[0004] The performance of a single material is insufficient, so the overall performance of the structure cannot meet the requirements;

[0005] Carbon fiber reinforced composites are expensive to manufacture and difficult to reuse and dispose of.

[0006] By incorporating the ply continuity criterion into the design of variable thickness hybrid composite structures, the stress concentration phenomenon in the transition zone can be significantly avoided. In addition, the introduction of hybrid multi-materials into variable thickness composite structures can effectively make up for the defects between materials. Taking carbon fiber and glass fiber as examples, the former has a high modulus and low elongation and is relatively expensive; the latter has a low modulus and high elongation and is relatively cheap. If the two are effectively combined, the overall performance of the structure can be improved. Therefore, variable thickness hybrid composite structures that take into account the consistency of plies between adjacent regions have great advantages. Summary of the invention

[0007] In view of the problems existing in the existing composite structure design, the present invention provides a variable thickness hybrid composite structure design method based on the ply continuity criterion, which solves some of the problems mentioned in the above background by incorporating more manufacturing constraints and multi-material distribution.

[0008] To achieve the above object, the technical solution of the present invention is as follows:

[0009] S1. For the variable thickness hybrid composite structure, divide the sub-regions and determine the number of layers and load conditions of each sub-region;

[0010] The specific implementation is to establish an optimization model to divide the sub-regions and determine the number of layers and load conditions of each sub-region according to the different thicknesses of the variable thickness hybrid composite structure.

[0011] S2. Optimization of initial area:

[0012] According to the number of sub-regions divided as above, the optimization processing order of each sub-region is determined according to the order of load from small to large, and the sub-region with the smallest load is selected as the initial region. The ply structure of the initial region is optimized by using a genetic algorithm. The ply structure includes the ply sequence and ply material distribution. At the same time, a constraint module is embedded in the genetic algorithm so that the ply sequence and ply material distribution generated each time meet the actual production conditions.

[0013] Each sub-region is composed of multiple layers of anisotropic materials, such as fibers. The materials of each layer can be different, and the arrangement angles and directions of the materials of each layer can also be adjusted differently.

[0014] The ply sequence refers to the composition of the arrangement angle direction of the materials in each layer, and the ply material distribution refers to the composition of the materials used in each layer.

[0015] S3, according to the ply structure of the initial area, select the sub-area of ​​the second load size in S1 as the second sub-area; optimize the second sub-area in combination with the load condition of the second sub-area, specifically, based on the ply structure scheme of the initial area, add layers in sequence according to the number of layers in the second sub-area and then use a genetic algorithm to optimize the whole after the ply adding operation, obtain the target value of the ply gap during the ply adding operation, and obtain the optimal ply structure of the second sub-area that meets all manufacturing constraints according to the target value and the manufacturing constraints;

[0016] S4. Repeat the above step S3 and perform the same processing on the remaining sub-areas. The ply structure scheme of each sub-area is calculated based on the ply structure scheme of the original initial area, that is, the ply structure of all sub-areas is finally formed into a final scheme, and then a variable thickness hybrid composite structure is manufactured according to the ply structure scheme.

[0017] The step S2 is specifically as follows:

[0018] The initial area is optimized using a genetic algorithm to obtain the optimal ply sequence and material distribution, specifically:

[0019] 2.1) The ply order and material distribution in the initial area are mixed and encoded to obtain the initialized population, and then the genetic algorithm is used for optimization and iteration;

[0020] That is, the material arrangement angle direction and the material in each layer are considered simultaneously, and all possible arrangements and combinations of the material arrangement angle direction and the material in each layer are encoded.

[0021] Before the crossover mutation process in each iteration of the genetic algorithm, the manufacturing constraints are set, and all possible ply sequences under the number of plies in the initial area are tested according to the manufacturing constraints using a traversal program, and the plies that do not meet the constraints are eliminated to obtain all ply structure solutions that meet the manufacturing constraints.

[0022] 2.2) All the above-mentioned ply structure solutions that meet the manufacturing constraints are used to calculate the target value f of all possible ply structure solutions in the initial area according to the following formula: obj :

[0023]

[0024] In the formula, f obj (λ i ,x j ) represents the target value of the jth material in the i-th layer, λ i is the buckling value of the i-th layer, x ij is the cost of using the jth material in the i-th layer, i represents the layer number in the initial region, j represents the material number in the i-th layer, and N represents the total number of layers in the initial region; w i is the weight factor of the i-th layer, w ij is the weight factor of the jth material in the i-th layer;

[0025] 2.3) Finally, select the maximum target value f obj The corresponding ply structure scheme is taken as the optimization result of the initial area.

[0026] In step S3, at each layer adding operation, the ply plan corresponding to the maximum target value obtained in the above step is constrained, and the manufacturing constraints are set by nesting the constraint module, and the maximum target value of all gaps between two adjacent layers before the layer adding operation is calculated, and the maximum target value is judged according to the manufacturing constraints:

[0027] When the manufacturing constraints are violated, the ply structure of the second sub-region corresponding to the maximum target value is deleted, and the ply addition operation and genetic algorithm are repeated again in sequence by adding a penalty factor until all manufacturing constraints are met, thereby obtaining the optimal ply structure of the second sub-region that meets all manufacturing constraints;

[0028] In a specific implementation, when a manufacturing constraint is violated, a penalty factor is applied to the target value of the laminate structure so that it is eliminated during the evolution process until a laminate structure that satisfies all constraints is found, which is the optimal laminate structure for the second sub-region.

[0029] Otherwise, the ply structure of the second sub-region corresponding to the maximum target value is retained as the optimal ply structure of the second sub-region.

[0030] The step S3 is specifically as follows:

[0031] 3.1) Selecting a sub-region with a second load size as the second sub-region;

[0032] 3.2) Taking the ply structure of the initial area as the basis of the ply structure of the second sub-area, an additional layer is added on the ply structure of the initial area, and the additional layer can only be located in the gap between two adjacent layers. All possible positions of the additional layer and the material arrangement angle direction and material in the additional layer determined by the position of the additional layer are traversed, and all possible angles are added to the additional layer. Each time a ply angle is added, its material properties are transformed to obtain all possible positions of the additional layer and the material arrangement angle direction and material in the additional layer. The overall ply structure scheme of all possible second sub-areas under all possible positions of the additional layer and the material arrangement angle direction and material in the additional layer is composed of the material arrangement angle direction and material of each layer in the second sub-area, and includes the basis of the ply structure of the initial area;

[0033] 3.3) Then, all possible ply structure schemes of the second sub-region as a whole are used to calculate the target value of each ply structure scheme in the same way as the initial region, and the ply structure scheme corresponding to the maximum target value is taken as the optimization result after the second sub-region is added with the current added layer;

[0034] 3.4) Repeating steps 3.2)-3.3) to process each of the remaining added layers in the second sub-region, obtain the final optimization result of the second sub-region, that is, obtain the preliminary ply structure plan of the second sub-region;

[0035] 3.5) At the same time, manufacturing constraints are added to the preliminary ply structure scheme of the second sub-area obtained in step 3.4), specifically:

[0036] It is set that the layup structure scheme cannot have more than 4 consecutive layers of materials with the same arrangement angle direction, and thus each layer in the layup structure scheme obtained in step 3.3) is searched and judged: if there is a violation of the manufacturing constraint, the preliminary layup structure scheme is deleted, and steps 3.2)-3.4) are repeated to obtain a new preliminary layup structure scheme after excluding the preliminary layup structure scheme, as the optimal layup structure for the second sub-area that meets the manufacturing constraint; otherwise, the layup structure scheme is retained as the optimal layup structure for the second sub-area that meets the manufacturing constraint.

[0037] The manufacturing constraints include symmetry, balance, maximum drop number, and the manufacturing constraints that the innermost layer and the outermost layer are not allowed to drop.

[0038] The variable thickness hybrid composite structure is specifically a variable thickness product, such as a blade or wing of a wind turbine, but is not limited thereto.

[0039] The beneficial effects of the present invention are:

[0040] In the design of the variable thickness hybrid composite structure, the present invention takes into account more design guidelines and incorporates multiple manufacturing constraints, so that the entire structural layup is more in line with actual production conditions and the manufacturability of the structure is enhanced.

[0041] The use of variable thickness hybrid composite structures can effectively reduce the overall mass of the structure while maintaining structural integrity, thereby minimizing the mass and cost of the entire structure while achieving optimal overall performance of the composite structure.

[0042] Based on the consideration of manufacturing constraints, a variety of specific coding strategies are proposed here, and the constraints are embedded in the design program, so that the entire program does not need to be manually changed or added with manufacturing constraints, which greatly reduces the workload and further enhances the applicability of the optimization results.

[0043] In summary, the variable thickness hybrid composite structure optimization method proposed in the present invention can not only effectively improve the defects of insufficient performance of a single material and improve the overall performance of the structure; it also makes the optimized variable thickness hybrid composite structure more complete and more in line with actual production conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a schematic diagram of a variable thickness hybrid composite structure model implemented in the present invention;

[0045] Figure 2 It is a schematic diagram of the hybrid composite structure model of the present invention. DETAILED DESCRIPTION

[0046] To make the description clearer, the present invention is further described with reference to the accompanying drawings and embodiments, but the protection scope of the present invention is not limited thereto:

[0047] The specific details of the embodiments of the present invention are as follows:

[0048] 1) Specific implementation: The entire area is divided into 18 sub-areas according to the load size of each sub-area, such as Figure 1 shown.

[0049] choose Figure 1 The 18-panel composite structure with different loads is used as an alternative model for the variable thickness hybrid composite structure (N x1 、N Y1 / N x2 、N Y2 / ……N xn 、N Yn ), where N x1 Indicates the load magnitude in the first sub-area in the X direction, N Y1 Indicates the load magnitude in the y direction of the first sub-region, Nxn Indicates the load magnitude in the X direction of the nth sub-region, N Yn Indicates the load magnitude in the y direction of the nth sub-region.

[0050] The length of each region boundary is (a 1 、b 1 / a 2 、b 2 / ……a n 、b n ), where a n represents the length of the nth sub-region along the x direction, b n Indicates the length of the nth sub-region along the y direction.

[0051] 2) The initial area is optimized using genetic algorithms to obtain the optimal ply sequence and material distribution, specifically:

[0052] The initial area is optimized using a genetic algorithm to obtain the optimal ply sequence and material distribution, specifically:

[0053] 2.1) The ply order and material distribution in the initial area are mixed and encoded to obtain the initialized population, and then the genetic algorithm is used for optimization and iteration;

[0054] Before the crossover mutation process in each iteration of the genetic algorithm, manufacturing constraints are set, including symmetry, balance, maximum drop number, and manufacturing constraints that the innermost layer and the outermost layer are not allowed to drop. At the same time, all possible ply sequences under the number of plies in the initial area are checked according to the manufacturing constraints using a traversal program, and the plies that do not meet the constraint conditions are eliminated to obtain all ply structure solutions that meet the manufacturing constraint conditions.

[0055] 2.2) All the above-mentioned ply structure solutions that meet the manufacturing constraints are used to calculate the target value f of all possible ply structure solutions in the initial area according to the following formula: obj :

[0056]

[0057] In the formula, f obj (λ i ,x j ) represents the target value of the jth material in the i-th layer, λ i is the buckling value of the i-th layer, x ij is the cost of using the jth material in the i-th layer, i represents the layer number in the initial region, j represents the material number in the i-th layer, and N represents the total number of layers in the initial region; w i is the weight factor of the i-th layer, w ij is the weight factor of the jth material in the i-th layer;

[0058] 2.3) Finally, select the maximum target value f obj The corresponding ply structure scheme is taken as the optimization result of the initial area.

[0059] 3) optimization of ply sequence and material distribution in the second sub-area;

[0060] 3.1) selecting the region with the second load magnitude in step 1) as the second sub-region;

[0061] 3.2) Based on the ply order and material distribution of the initial region, interpolation operations are performed on the second sub-region, specifically:

[0062] First, the stress condition N in the second sub-region is X2 、N y2 Based on the ply sequence and material distribution in the initial area, an additional layer is added on the basis of the ply structure in the initial area, and the additional layer is first placed in the gap between the first and second layers;

[0063] Next, all possible material arrangement angles and materials are added to the added layer, and each time a material arrangement angle is added, a different material is used to transform it, so as to obtain a layer structure with different material arrangement angles and different materials under the gap between the first and second layers.

[0064] After all the plying sequences and material distributions have been traversed, that is, after the traversal of the additional layer plan for the gap has been completed, the additional layer is deleted;

[0065] Then, the ply sequence and material distribution under all the above-mentioned ply structure schemes are taken as input information to calculate the target values ​​under all possible ply structure schemes;

[0066] Finally, the maximum target value max_1 of all layup structure schemes and its corresponding layup structure scheme are saved.

[0067] 3.3) Repeat the above 3.2) step to calculate the maximum target value max_2 under the gap between the second and third layers of the added layer and save it. According to this step, the maximum target values ​​max_1, max_2, ... max_n under the gaps of all layers are calculated;

[0068] 3.4) sorting the maximum target values ​​obtained in step 3.3) and selecting the ply order and material distribution corresponding to the maximum target value as the candidate distribution scheme for the second sub-area;

[0069] 3.5) Add manufacturing constraints to the maximum target value selected in step 3.4), specifically:

[0070] Set the constraint that there cannot be more than 4 layers of materials with the same angle arrangement direction, so as to retrieve and judge each layer in the ply structure scheme obtained in step 3.3), and specifically implement traversal with 4 layers as a group:

[0071] If there is a violation of the manufacturing constraints, the preliminary layup structure plan will be deleted, and steps 3.2)-3.4) will be repeated to obtain a new candidate preliminary layup structure plan after excluding the preliminary layup structure plan, as the optimal layup structure for the second sub-area that meets the manufacturing constraints; otherwise, the layup structure plan will be retained as the optimal layup structure for the second sub-area that meets the manufacturing constraints.

[0072] 4) Repeat step 3) to obtain the ply structure solutions for all remaining sub-areas.

[0073] The details are as follows:

[0074]

[0075]

[0076] Finally, the layup structure scheme of all layers of the variable thickness hybrid composite structure is obtained as follows: Figure 2 shown.

Claims

1. A design method for variable thickness hybrid composite structures based on ply continuity criterion, It is characterized in that The steps include: S1. For the variable thickness hybrid composite structure, divide the sub-regions and determine the number of layers and load conditions of each sub-region; S2. Optimization of the initial area: According to the number of sub-areas divided above, the optimization processing order of each sub-area is determined according to the order of load from small to large, and the sub-area with the smallest load is selected as the initial area. The ply structure of the initial area is optimized by using a genetic algorithm. The ply structure includes the ply sequence and ply material distribution. At the same time, a constraint module is embedded in the genetic algorithm so that the ply sequence and ply material distribution generated each time meet the actual production conditions. S3. Optimizing the second sub-region according to the ply structure of the initial region and the load condition of the second sub-region. Specifically, based on the ply structure scheme of the initial region, plies are added in sequence according to the number of plies in the second sub-region, and then a genetic algorithm is used to optimize the whole after the ply addition operation, so as to obtain a target value of the ply gap during the ply addition operation, and according to the target value and the manufacturing constraints, an optimal ply structure of the second sub-region that satisfies all the manufacturing constraints is obtained; S4, repeating the above step S3, and performing the same processing on the remaining sub-areas, and calculating the ply structure scheme of all the remaining sub-areas based on the ply structure scheme of the original initial area, and then manufacturing the variable thickness hybrid composite structure according to the ply structure scheme; The step S2 is specifically as follows: The initial area is optimized using a genetic algorithm to obtain the optimal ply sequence and material distribution, specifically: 2.1) The ply order and material distribution in the initial area are mixed and encoded to obtain the initialized population, and then the genetic algorithm is used for optimization and iteration; Before the crossover mutation process in each iteration of the genetic algorithm, the manufacturing constraints are set, and all possible ply sequences under the number of plies in the initial area are tested according to the manufacturing constraints using a traversal program, and the plies that do not meet the constraints are eliminated to obtain all ply structure solutions that meet the manufacturing constraints. 2.2) All the above-mentioned ply structure solutions that meet the manufacturing constraints are used to calculate the target value f of all possible ply structure solutions in the initial area according to the following formula: obj : In the formula, f obj (λ i ,x j ) represents the target value of the jth material in the i-th layer, λ i is the buckling value of the i-th layer, x ij is the cost of using the jth material in the i-th layer, i represents the layer number in the initial region, j represents the material number in the i-th layer, and N represents the total number of layers in the initial region; w i is the weight factor of the i-th layer, w ij is the weight factor of the jth material in the i-th layer; 2.3) Finally, select the maximum target value f obj The corresponding ply structure scheme is used as the optimization result of the initial area; In step S3, during each layer adding operation, a constraint module is embedded to set manufacturing constraints, and the maximum target value of all gaps between two adjacent layers before the layer adding operation is calculated, and the maximum target value is judged according to the manufacturing constraints: When the manufacturing constraints are violated, the ply structure of the second sub-region corresponding to the maximum target value is deleted, and the ply addition operation and genetic algorithm are repeated again in sequence by adding a penalty factor until all manufacturing constraints are met, thereby obtaining the optimal ply structure of the second sub-region that meets all manufacturing constraints; Otherwise, the ply structure of the second sub-region corresponding to the maximum target value is retained as the optimal ply structure of the second sub-region; The step S3 specifically includes the following steps: 3.1) Selecting a sub-region with a second load size as the second sub-region; 3.2) Taking the ply structure of the initial area as the basis of the ply structure of the second sub-area, an additional layer is added on the ply structure of the initial area, and the additional layer can only be located in the gap between two adjacent layers. All possible positions of the additional layers and the material arrangement angles, directions and materials in the additional layers determined by the positions of the additional layers are traversed to obtain all possible overall ply structure solutions for the second sub-area under all possible positions of the additional layers and the material arrangement angles, directions and materials in the additional layers; 3.3) Then, all possible ply structure schemes of the second sub-region as a whole are used to calculate the target value of each ply structure scheme in the same way as the initial region, and the ply structure scheme corresponding to the maximum target value is taken as the optimization result after the second sub-region is added with the current added layer; 3.4) Repeating steps 3.2)-3.3) to process each of the remaining added layers in the second sub-region, obtain the final optimization result of the second sub-region, that is, obtain the preliminary ply structure plan of the second sub-region; 3.5) At the same time, manufacturing constraints are added to the preliminary layup structure scheme of the second sub-area obtained in step 3.4), specifically: it is set that the layup structure scheme cannot have more than 4 consecutive layers of materials with the same arrangement angle direction, thereby searching and judging each layer in the layup structure scheme obtained in step 3.3): if there is a violation of the manufacturing constraint, the preliminary layup structure scheme is deleted, and steps 3.2)-3.4) are repeated to obtain a new preliminary layup structure scheme after excluding the preliminary layup structure scheme, as the optimal layup structure for the second sub-area that meets the manufacturing constraints; otherwise, the layup structure scheme is retained as the optimal layup structure for the second sub-area that meets the manufacturing constraints.

2. A variable thickness hybrid composite structure design method based on ply continuity criterion according to claim 1, Features: The manufacturing constraints include symmetry, balance, maximum drop number, and the manufacturing constraints that the innermost layer and the outermost layer are not allowed to drop.

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