A rapid layup design method for composite material structures based on shear stress field characteristics

Abstract

This invention discloses a rapid layup design method for composite material structures based on shear stress field characteristics, comprising the following steps: Step S1, establishing a solid finite element model of the target structure with material properties set to isotropic or equivalent orthotropic, applying loads and boundary conditions, and solving to obtain the three interlayer and / or internal shear stresses τ. ij The distribution field; Step S2: Calculate the shear stress threshold according to the following formula; Step S3: Extract the contour lines of shear stress equal to and , and select the area corresponding to the smallest contour line spacing as the risk area. Use the center line of the risk area as the design baseline, and make the fiber direction perpendicular to the design baseline. This invention has the characteristics of greatly reducing the modeling workload, convenient and quick extraction of the design baseline, avoiding over-design, and rapid layup.

Description

Technical Field

[0001] This invention relates to the field of composite material structure design technology, and specifically to a rapid layup design method for composite material structures based on shear stress field characteristics. Background Technology

[0002] Traditional methods for composite material layup design typically require establishing detailed finite element models of the layup, defining the material orientation, layup sequence, and contact relationships for each layer, and iteratively modifying them under multiple operating conditions until strength requirements are met. This "modeling-analysis-modification-reanalysis" cycle is lengthy, computationally costly, and highly dependent on engineer experience. Current improved methods include two approaches: one uses the principal stress tracing method, which requires calculating the angles of principal stresses point-by-point to obtain the local loading direction of the material. However, since the principal stress angles may vary discontinuously in complex stress fields, directly integrating the point-by-point calculation results into a continuous layup orientation field often presents difficulties. Therefore, in practical applications, smoothing methods or optimization algorithms may be needed to address the continuity of the orientation field. The second approach uses the Mises stress contour method, primarily for region partitioning. However, this method does not establish a direct geometric relationship between stress contours and fiber orientation, failing to provide clear guidance for fiber orientation design. Furthermore, Mises stress is a comprehensive stress index that cannot distinguish between normal stress in the fiber direction and shear stress within the matrix. Therefore, using this method for layup design may lead to under-optimization or over-design. Summary of the Invention

[0003] This invention aims to provide a rapid layup design method for composite material structures based on shear stress field characteristics. This method enables rapid layup, simple modeling, and efficient analysis. It addresses the problems of current methods, such as the principal stress trace method, which requires point-by-point calculation of principal stress angles, making it difficult to directly convert the results into a continuous layup direction field; and the Mises stress contour method, which is only used for region division and does not establish a direct geometric relationship between contour lines and fiber directions. Furthermore, the Mises stress method cannot distinguish between fiber direction normal stress and matrix shear stress, which can easily lead to over-design.

[0004] Therefore, the technical solution adopted in this invention is a rapid layup design method for composite material structures based on shear stress field characteristics, comprising the following steps:

[0005] Step S1: Establish a solid finite element model of the target structure with material properties set to isotropic or equivalent orthotropic, apply loads and boundary conditions, and solve for the three interlayer and / or internal shear stresses τ. ij (i represents the normal direction of the surface acting, j represents the direction of stress, ij=12, 13, 23) distribution field;

[0006] Step S2: Calculate the shear stress threshold according to the following formula. ,

[0007] ;

[0008] ;

[0009] Where α is the threshold coefficient, λ is the material aging strength retention rate, β is the fatigue allowable coefficient, and S is the shear strength of the composite resin matrix or rubber material.

[0010] Step S3, under shear stress τ ij In the distribution field (ij=12, 13, 23), for each shear stress component, the shear stress is extracted as equal to... , The contour lines are selected, and the area corresponding to the smallest interval between the contour lines is selected as the risk area. The center line of the risk area is used as the design baseline, and the fiber direction is perpendicular to the design baseline.

[0011] As a preferred embodiment of the above scheme, in step S2, the material aging strength retention rate λ≥0.5 is reasonably selected for the polymer material industry.

[0012] More preferably, in step S2, the allowable fatigue coefficient β is determined based on the fatigue life of the target material. When the target material has an infinite low-cycle fatigue life, the allowable fatigue coefficient β is 0.30 to 0.50; when the target material has a finite high-cycle fatigue life, the allowable fatigue coefficient β is 0.10 to 0.30; and when the target material has zero cracks, the allowable fatigue coefficient β is 0.01 to 0.05. The range is reasonably selected.

[0013] More preferably, in step S3, when laying multi-layer materials in a stacked manner, the stacking direction is parallel to the design baseline, the fiber direction of each layer of material is perpendicular to the design baseline, and the lamination direction of adjacent layers, that is, the normal direction of the surface where the layer is located, must be parallel to the design baseline, thereby ensuring that the layup material is perpendicular to the design baseline direction, and that the area between the design baselines is continuous and without breaks, and the design is reasonable.

[0014] The beneficial effects of this invention are:

[0015] (1) Compared with the current principal stress trace method which requires point-by-point calculation of principal stress angles, and the Mises stress contour method which is only used for region division, this scheme does not require the establishment of a complex ply detail model. Instead, a solid finite element model is established for the target structure, and the material properties are set to isotropic or equivalent orthotropic. This not only simplifies modeling but also allows for reasonable and efficient finite element analysis of complex target structures, obtaining the three interlayer and / or internal shear stresses τ. ij The modeling workload is greatly reduced, and the entity model has simple contact definition and good convergence.

[0016] (2) Under shear stress τ ij In the distribution field (ij=12, 13, 23), the maximum shear stress is selected, and the shear stress is equal to... Using contour lines as design baselines, the design baselines can be extracted through a single finite element analysis, directly determining the ply direction. This completely avoids the complex process of repeated iterations in traditional methods, reducing calculation time by more than 80%. When composite materials are subjected to in-plane or out-of-plane shear loads, the weak shear resistance of the matrix easily leads to composite material failure. This solution addresses this failure phenomenon by designing a threshold that is quantitatively correlated with the material shear strength S, the material aging strength retention rate λ, and the fatigue allowable factor β. By a two-step reduction (first considering the aging retention rate λ, then considering the fatigue allowable factor) The shear stress threshold applicable to fatigue / aging conditions is obtained from the original shear strength S. This effectively avoids over-design caused by blindly increasing the thickness due to the high stress of the Mises.

[0017] (3) The shear stress is equal to The contour lines are used as the design baseline, and fiber layup is carried out in the direction perpendicular to the design baseline. The design baseline is a geometric curve, and the layup direction is based on the geometric curve, which can be easily converted into a partitioned constant angle layup or variable angle layup process to achieve rapid layup and achieve better structural performance.

[0018] In summary, this invention features significantly reduced modeling workload, convenient and quick extraction of design baselines, avoidance of over-design, and rapid layering. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of the present invention.

[0020] Figure 2 Shear stress threshold A schematic diagram of a pressure of 0.3 MPa.

[0021] Figure 4 This is a schematic diagram showing the layup direction perpendicular to the design baseline in an embodiment of the present invention.

[0022] Figure 3 Shear stress threshold A schematic diagram of a pressure of 0.1 MPa.

[0023] Figure 5 This is a schematic diagram of layup continuity control in an embodiment of the present invention. Detailed Implementation

[0024] The present invention will be further described below with reference to the embodiments and accompanying drawings:

[0025] Combination Figure 1 — Figure 5 As shown, 1. A rapid layup design method for composite material structures based on shear stress field characteristics, the specific implementation steps are as follows:

[0026] Step S1: Establish a solid finite element model of the target structure with material properties set to isotropic or equivalent orthotropic, apply loads and boundary conditions, and solve for the three interlayer and / or internal shear stresses τ. ij (i represents the normal direction of the surface acting, j represents the direction of stress, ij=12, 13, 23) distribution field;

[0027] Interlaminar shear stress is the main failure mode of composite materials.

[0028] Step S2: Calculate the shear stress threshold according to the following formula. ,

[0029] ;

[0030] ;

[0031] Where α is the threshold coefficient, λ is the material aging strength retention rate, β is the fatigue allowable coefficient, and S is the shear strength of the composite resin matrix or rubber material.

[0032] In step S2, the material aging strength retention rate λ ≥ 0.5.

[0033] In step S2, the fatigue allowable factor β is determined based on the fatigue life of the target material. When the target material has an infinite low-cycle fatigue life, the fatigue allowable factor β is 0.30 to 0.50. When the target material has a finite high-cycle fatigue life, the fatigue allowable factor β is 0.10 to 0.30. When the target material has zero cracks, the fatigue allowable factor β is 0.01 to 0.05.

[0034] When the target material has an infinite life of low-cycle fatigue, the range of α is calculated according to the following formula: 0.5×(0.3~0.5)=0.15~0.25.

[0035] When the target material has a high-cycle fatigue finite life, the range of α is calculated according to the following formula: 0.5 × (0.1~0.30) = 0.05~0.15.

[0036] When the target material has zero cracks, the range of α is calculated according to the following formula: 0.5×(0.01~0.05) =0.005~0.025.

[0037] Step S3, under shear stress τ ijIn the distribution field (ij=12, 13, 23), for each shear stress component, the shear stress is extracted as equal to... , The contour lines are selected, and the area corresponding to the smallest interval between the contour lines is selected as the risk area. The center line of the risk area is used as the design baseline, and the fiber direction is perpendicular to the design baseline.

[0038] In step S3, when laying multi-layer materials in a stacked manner, the stacking direction is parallel to the design baseline, and the fiber direction of each layer of material is perpendicular to the design baseline.

[0039] Example 1

[0040] First, a solid model of the I-shaped ring bearing component is created using an isotropic elastic material solid model. Solid elements are then divided, and the working load is applied. The model is as follows: Figure 1 As shown.

[0041] Then, the shear strength of the epoxy vinyl resin was set to S = 60 MPa, according to... Calculate threshold coefficient =0.005, substitute Calculate the shear stress threshold =0.3 MPa.

[0042] Then extract the shear stress τ 12 The contour lines are ±0.3 MPa, measured + and- The width of the region between pairs of contour lines. In this embodiment, the width of this region is approximately 10–15 mm, such as… Figure 2 As shown.

[0043] When the width of this region is greater than or equal to the ply thickness, there is no risk of shear stress concentration throughout the thickness, and no special ply design is required; a conventional homogeneous ply can be used. When the width of this region is less than the ply thickness, there is a risk of shear stress concentration in this region; the centerline of this region should be used as the design baseline, such as... Figure 3 As shown by the dashed line, the fiber direction of each layer of material is perpendicular to the design baseline, that is, it is laid along the normal direction of the baseline.

[0044] If the risk area is large and a single layer cannot completely cover it, a multi-layer stacked material can be used: the stacking direction is parallel to the design baseline, and the fiber direction of each layer is perpendicular to the design baseline. In this case, the total coverage width of the multi-layered ply is the sum of the thicknesses of each layer. By adjusting the number of layers, the total coverage width is made not less than the width of the risk area, ensuring that the risk area is completely covered, thereby effectively inhibiting crack initiation and propagation.

[0045] When the material's aging strength retention rate λ or shear strength decreases to 1 / 3 of its original value, the shear stress threshold is adjusted to 1 / 3 of its original value, which means... =0.1 MPa, τ is automatically measured by computer software. 12 The width of the area between the ±0.1 MPa contour lines is approximately 3–5 mm. If the thickness of a single layer is greater than this width, the area is risk-free; if the thickness is less, a multi-layer stacked layer is required to ensure the total coverage width is not less than the width of the area. In this embodiment, the material layer thickness is 3–5 mm, and a single layer is sufficient to completely cover the risk area. Figure 4 As shown.

[0046] The entire design cycle was shortened from two weeks using the traditional method to three days. Figure 5 To demonstrate the actual layup effect, the fiber direction is perpendicular to the design baseline in this cross-section.

[0047] The "10-15 mm" and "3-5 mm" mentioned above are exemplary data for specific embodiments of the present invention and do not constitute a limitation on the scope of application of this method.

Claims

1. A rapid layup design method for composite material structures based on shear stress field characteristics, characterized in that, Includes the following steps: Step S1: Establish a solid finite element model of the target structure with material properties set to isotropic or equivalent orthotropic, apply loads and boundary conditions, and solve for the three interlayer and / or internal shear stresses τ. ij The distribution field of (ij=12, 13, 23); Step S2: Calculate the shear stress threshold according to the following formula. , ； ； Where α is the threshold coefficient, λ is the material aging strength retention rate, β is the fatigue allowable coefficient, and S is the shear strength of the composite resin matrix or rubber material. Step S3, under shear stress τ ij In the distribution field (ij=12, 13, 23), for each shear stress component, the shear stress is extracted as equal to... , The contour lines are selected, and the area corresponding to the smallest interval between the contour lines is selected as the risk area. The center line of the risk area is used as the design baseline, and the fiber direction is perpendicular to the design baseline.

2. The rapid layup design method for composite material structures based on shear stress field characteristics according to claim 1, characterized in that: In step S2, the material aging strength retention rate λ ≥ 0.

5.

3. The rapid layup design method for composite material structures based on shear stress field characteristics according to claim 1, characterized in that: In step S2, the fatigue allowable factor β is determined based on the fatigue life of the target material. When the target material has an infinite low-cycle fatigue life, the fatigue allowable factor β is 0.30 to 0.

50. When the target material has a finite high-cycle fatigue life, the fatigue allowable factor β is 0.10 to 0.

30. When the target material has zero cracks, the fatigue allowable factor β is 0.01 to 0.

05.

4. The rapid layup design method for composite material structures based on shear stress field characteristics according to claim 1, characterized in that: In step S3, when laying multi-layer materials in a stacked manner, the stacking direction is parallel to the design baseline, and the fiber direction of each layer of material is perpendicular to the design baseline.

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