An Engineering Strength Checking Method for the Chamfer Region of a Composite Material Structure

Abstract

An engineering strength checking method for the chamfered area of a composite material L-shaped structure. The chamfered area is a sector arc segment. Given the design data of the composite material L-shaped structure, the sector arc segment of the chamfered area is divided into multiple checking sections; according to the design data of the composite material L-shaped structure and the section angles corresponding to the checking sections, the remaining strength coefficients of each checking section are calculated; the remaining strength coefficients of all the checking sections are compared, and the minimum remaining strength coefficient is selected as the remaining strength coefficient of the chamfered area of the composite material L-shaped structure.

Description

Technical Field

[0001] The present invention belongs to the field of composite material design and relates to an engineering strength checking method for composite materials in the chamfer area of aircraft structures. Background Art

[0002] Advanced composite materials are increasingly widely used in aircraft structures and have begun to appear in main load-bearing structures such as the central wing box section and the wing. However, the interlaminar performance of composite materials is weak, resulting in low strength in the thickness direction. Especially for components with large curvatures, there may be a high stress level in the thickness direction. In practical applications, it has been found that in the fillet area of the beam or the chamfer area at the root of the rib, composite materials are extremely prone to delamination failure, posing a serious threat to the safety of the structure. It is difficult to conduct strength checking on the chamfer area at the initial stage of aircraft structure design. In the design, it is necessary to analyze the stress level and failure conditions in these areas to determine their safety. Research has found that the stress in the thickness direction of the composite laminate L-shaped component is the main cause of delamination in the fillet area. Currently, there is a technical gap in the strength checking of the composite material chamfer area. There is an urgent need for a means or method to analyze the stress level and failure conditions in these areas at the initial stage of aircraft structure design to determine their safety. Summary of the Invention

[0003] The purpose of this application is to provide an engineering strength checking method for the chamfer area of composite material structures, aiming to establish an engineering approximation method that can quickly calculate the stress in the fillet area and judge its failure state. The accuracy of the load input, or rather the accuracy of this method, depends on the discretization degree and mesh size of the finite element model.

[0004] An engineering strength checking method for the chamfer area of a composite material L-shaped structure, where the chamfer area is a sector arc segment. Given the design data of the composite material L-shaped structure, it is characterized by the following: 1) Divide the sector arc segment of the chamfer area into multiple checking sections; 2) Calculate the remaining strength coefficient of each checking section according to the design data of the composite material L-shaped structure and the section angle corresponding to the checking section; 3) Compare the remaining strength coefficients of all the checking sections and select the smallest remaining strength coefficient as the remaining strength coefficient of the chamfer area of the composite material L-shaped structure.

[0005] The engineering strength checking method for the chamfer area of the composite material L-shaped structure is characterized in that when calculating the remaining strength coefficient of each checking section, the calculation method is as follows: 1) Calculate the bending moment force flow m r (α) and the tangential force flow s r (α) of the L-shaped structure of each checking section according to the design data of the composite material L-shaped structure; 2) According to the bending moment force flow m r (α) and the tangential force flow s r(α) Calculate the normal stress and shear stress of each check section; 3) Calculate the remaining strength coefficient of the check section according to the normal stress and shear stress of each check section.

[0006] For the engineering strength check method of the chamfered area of the composite material L-shaped structure described above, it is characterized in that in step 3), the out-of-plane failure remaining strength coefficient and in-plane failure remaining strength coefficient of the check section are calculated respectively according to the normal stress and shear stress of each check section, and the smaller remaining strength coefficient of the two is selected as the remaining strength coefficient of the check section.

[0007] Compared with the prior art, the advantages of the present invention are as follows: 1) By using an engineering method to check the strength of the chamfered area, the problem of difficult strength analysis in the initial stage of aircraft structure design is solved; 2) Fill the blank of composite material strength analysis in the field of aircraft structure design; 3) Greatly improve the efficiency of strength analysis of the chamfered area of the aircraft composite material structure and simplify the analysis process.

[0008] The following further describes the present invention in detail with reference to the accompanying drawings of the embodiments. Description of the Drawings

[0009] Figure 1 It is a schematic cross-sectional view of the chamfered area of the composite material structure

[0010] Figure 2 It is a schematic view of the check section of the chamfered area of the composite material structure.

[0011] Description of the numbers in the figure: 1 L-shaped structure, 2 chamfered area, 3 upper end face of the chamfered area, 4 lower end face of the chamfered area, 5 check section. Specific Embodiments

[0012] Referring to the accompanying drawings, for the engineering strength check method of the chamfered area 2 of the composite material L-shaped structure 1 of the present application, the chamfered area 2 is a fan-shaped arc segment. Given the design data of the composite material L-shaped structure 1, when performing the engineering strength check on the chamfered area 2, the fan-shaped arc segment of the chamfered area 2 needs to be divided into multiple check sections 5. Figure 2 In the embodiment, eight check sections 5 are divided between the upper end face 3 of the chamfered area and the lower end face of the chamfered area; according to the design data of the composite material L-shaped structure 1 and the section angle corresponding to the check section 5, the remaining strength coefficient of each check section is calculated; the section angle here refers to the included angle between the check section 5 and the upper end face 3 of the chamfered area. Compare the remaining strength coefficients of all the check sections, and select the smallest remaining strength coefficient as the remaining strength coefficient of the chamfered area of the composite material L-shaped structure.

[0013] When calculating the remaining strength coefficient of each check section 5, the calculation method is as follows: According to the design data of the composite material L-shaped structure, calculate the bending moment force flow m of the L-shaped structure of each check section 5 r(α) and tangential force flow s r (α); bending moment force flow m of the L-shaped structure according to each checking section 5 r (α) and tangential force flow s r (α) Calculate the normal stress and shear stress of each checking section 5; calculate the out-of-plane failure remaining strength coefficient and in-plane failure remaining strength coefficient of the checking section according to the normal stress and shear stress of each checking section 5 respectively, and select the smaller remaining strength coefficient of the two as the remaining strength coefficient of the checking section.

[0014] In implementation, for an L-shaped member 1 connected by bolts, due to the existence of fasteners and free edges, there is local stress concentration. We can consider an empirical coefficient, such as the force flow concentration coefficient (γ), to amplify the forces (Nx, Nz and My) extracted from the GFEM model as the external forces during the chamfer area analysis.

[0015] Nx, Nz and My consider the coefficient γ:

[0016]

[0017]

[0018] Such as Figure 1 As shown, an L-shaped member 1 is connected to a rigid support.

[0019] It is known that the thickness of the two side walls of the L-shaped member 1 remains unchanged, t h = 4mm, the cross-section width w = 80mm, and the chamfer radius r i = 6mm. The external force application point is at a distance h = 50mm from the rigid support surface.

[0020] Divide the fan-shaped arc section of the chamfer area 2 into ten equal parts of 10°, and divide it into ten checking sections 5. The upper end face 3 of the chamfer area is the first checking section, and the lower end face 4 of the chamfer area is the last checking section. The section angle of the checking section is the included angle α between the checking section and the upper end face 3 of the chamfer area.

[0021] Calculate the bending moment force flow m r (α) and tangential force flow s r (α)

[0022] F z (h) = -2000N

[0023] F x (h) = -50N

[0024] Q y (h) = -3000Nmm

[0025] The concentration coefficient of the force flow needs to be considered:

[0026]

[0027]

[0028]

[0029] Therefore, from the force flow derivation, the forces at the chamfer starting position are f, s, and m. For any angle α, the corresponding forces and bending moments are different. Therefore, it is necessary to calculate the remaining strength coefficients at different angles. Only the calculation results for α = 20° are listed below.

[0030] Bending moment force flow:

[0031] m r (α = 20°) - 110.8 N

[0032] Tangential force flow:

[0033] s r (α = 20°) - 11.1 N

[0034] According to the bending moment force flow m r (α) and tangential force flow s r (α) of the L-shaped structure 1 at each verification section, the normal stress and shear stress of each verification section 5 are calculated. Only the calculation results for the section angle α = 20° are listed below:

[0035] The stress calculation shows:

[0036] τ 13 (α) = -4.2 MPa

[0037] σ 33 (α) == 5.4 MPa

[0038] According to the normal stress and shear stress of each verification section 5, the remaining strength coefficient stress allowable value f 33 t = 44 MPa, f 13 = 58 MPa, the failure coefficient h(α) is calculated as:

[0039] h(α) = 0.14

[0040] The B-reference value coefficient is taken as 0.81, and the environmental impact factor is taken as 0.75. Therefore, when α = 20°, the remaining strength coefficient RF is:

[0041] RF(α) = 4.3

[0042] The remaining strength coefficients of ten verification sections are obtained by the above method, as shown in Table 1.

[0043] Table 1 Stress, bending moment, force flow and remaining strength coefficient of ten checking sections

[0044] α <![CDATA[m r (α)]]> <![CDATA[t r (α)]]> <![CDATA[σ 33 (α)]]> <![CDATA[τ 13 (α)]]> h(α) RF 0 -94 -1 4.5 -0.4 0.10 5.9 10 -99 -6 4.8 -2.3 0.12 5.3 20 -111 -11 5.4 -4.2 0.14 4.3 30 -130 -16 6.3 -5.9 0.18 3.5 40 -155 -20 7.5 -7.5 0.21 2.8 50 -185 -24 9.0 -8.8 0.25 2.4 60 -220 -26 10.7 -9.9 0.30 2.0 70 -259 -29 12.5 -10.7 0.34 1.8 80 -300 -30 14.5 -11.1 0.38 1.6 90 -341 -30 16.5 -11.3 0.42 1.4

[0045] The remaining strength coefficient RF of the chamfered area is as follows:

[0046] RF = Min α-0→90o (RF(α)) = 1.4, where α = 90°.

Claims

1. An engineering strength verification method for the chamfered area of a composite material L-shaped structure. The chamfered area is a fan-shaped arc segment. Given the design data of the composite material L-shaped structure, it is characterized in that It includes the following: 1) Divide the sector arc segment of the chamfered area into multiple checking sections; 2) Calculate the remaining strength coefficient of each checking section according to the design data of the composite L-shaped structure and the section angle corresponding to the checking section; 3) Compare the remaining strength coefficients of all the checking sections, and select the minimum remaining strength coefficient as the remaining strength coefficient of the chamfered area of the composite L-shaped structure. When calculating the remaining strength coefficient of each checking section, the calculation method is as follows: 1) Calculate the bending moment force flow m r (α) and tangential force flow s r (α) of the L-shaped structure of each checking section; 2) Calculate the normal stress and shear stress of each checking section according to the bending moment force flow m r (α) and tangential force flow s r (α) of the L-shaped structure of each checking section; 3) Calculate the remaining strength coefficient of the checking section according to the normal stress and shear stress of each checking section. In step 3), calculate the out-of-plane failure remaining strength coefficient and in-plane failure remaining strength coefficient of the checking section respectively according to the normal stress and shear stress of each checking section, and select the smaller remaining strength coefficient of the two as the remaining strength coefficient of the checking section.

2. The engineering strength verification method for the chamfered area of a composite material L-shaped structure according to claim 1, characterized in that Divide the sector arc section of the chamfered area into no less than eight checking sections.

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