A strength analysis method for variable gradient composite panels

Abstract

The present application belongs to the technical field of structural strength analysis, and particularly relates to a strength analysis method for a variable gradient composite material wall panel, the strength analysis method comprising: solving the shear stress and compression stress of the variable gradient composite material wall panel based on the external load and structural parameters of the variable gradient composite material wall panel; calculating the allowable shear stress, allowable axial compression stress, and allowable bending stress based on the structural parameters; calculating the safety margin through the shear stress, the compression stress, the allowable shear stress, the allowable axial compression stress, and the allowable bending stress; the iterative safety margin is 0; and the stability strength design of the trapezoidal composite material wall panel with a variable gradient of the rudder surface can be performed, and finally the lightest wall panel structural parameters that meet the constraint conditions are obtained.

Description

Technical Field

[0001] The present application belongs to the technical field of structural strength analysis, and in particular relates to a strength analysis method for variable gradient composite material wall panels. Background Art

[0002] The wing control surfaces of large aircraft are typical variable gradient trapezoidal cross-section structures. The trapezoidal structure causes obvious non-uniformity in the stress of the composite panel and complex instability modes of the panel. It is necessary to study the instability characteristics of the panel with a trapezoidal structure with large stress gradient changes. Summary of the Invention

[0003] In order to solve the above problems, a strength analysis method of variable gradient composite wall panels was proposed.

[0004] A strength analysis method for variable gradient composite panels.

[0005] The variable gradient composite material wall panel includes: an upper wall panel and a lower wall panel, the front and rear ends of the upper wall panel and the lower wall panel are connected by a front beam and a rear beam respectively, and the upper wall panel and the lower wall panel are connected on both sides by side ribs; the upper wall panel, the front beam, the rear beam, the side ribs and the lower wall panel form a trapezoidal box structure; the cross-section of the box structure along the front-to-back direction is trapezoidal, and the strength analysis method includes:

[0006] Step 1: Determine the stress form of the upper wall panel of the box structure: determine the bending load M and torsional moment T applied to the box structure, determine the compressive normal stress generated by the bending load M on the upper wall panel and the tensile normal stress generated by the bending load M on the lower wall panel, and determine the shear stress generated by the torsional load T on the box structure;

[0007] Step 2: Based on the force form of the upper wall panel, determine the shear stress τ of the upper wall panel under the torsional load T; determine the distribution form of the compressive stress σ of the upper wall panel under the bending load M and the stress magnitude at the characteristic point;

[0008] Step 3: Based on the distribution form of the upper wall plate compressive stress σσ and the stress magnitude at the characteristic point, the axial compressive stress σ of the upper wall plate is calculated. C and bending stress σ b Stress equivalent to determine the axial compressive stress σ C and bending stress σ b size;

[0009] Step 4: Based on the dimensional parameters of the upper wall panel of the variable gradient trapezoidal composite material, determine the allowable shear stress [τ] and allowable axial compressive stress [σ C ]、Allowable bending stress [σ b ];

[0010] Step 5: According to shear stress τ, axial compressive stress σ C , bending stress σb and allowable shear stress [τ], axial compressive stress [σ C ]、Allowable bending stress [σ b ], taking the composite safety margin MS of shear stability, axial compression stability and bending stability as the preset threshold Ra as the constraint condition, and aiming at minimizing the weight of the panel structure, the buckling-related equations were used to optimize the iterative solution to determine the lightweight structural parameters of the upper panel under composite loading.

[0011] Preferably, the calculation formula of the shear stress τ is:

[0012] τ=T / 2Ωt2

[0013]

[0014] Where Ω is the area enclosed by the midline of the cross-section of the box structure formed by the wall panels, front beams, rear beams, side ribs, and lower wall panels; H is the height of the front beam, h is the height of the rear beam; t1 is the thickness of the front beam, t2 is the thickness of the upper wall panel, t3 is the thickness of the lower wall panel, t4 is the thickness of the rear beam, and L is the chordal length of the box structure.

[0015] Preferably, the specific method of converting the compressive stress into axial compressive stress and bending stress includes:

[0016] calculating the compressive stress;

[0017] The upper wall plate located at the rear beam and the upper wall plate located at the front beam are selected as the characteristic points;

[0018] Calculating the compressive stress of the upper wall panel at the rear beam and the compressive stress of the upper wall panel at the front beam based on the compressive stress;

[0019] The axial compressive stress and bending stress are calculated based on the compressive stress of the upper wall plate at the rear beam and the compressive stress of the upper wall plate at the front beam.

[0020] Preferably, the compressive stress σ of the upper wall panel under the bending load M is a typical linear trapezoidal distribution, and the compressive stress σ is calculated as follows:

[0021]

[0022]

[0023]

[0024] Where I is the bending stiffness of the trapezoidal structure enclosed by the centerline of the box structure section, y is the distance from the bending neutral layer, and Y is the linear equation of the centerline of the upper wall panel.

[0025] Preferably, the axial compressive stress σ C and bending stress σ bThe calculation formula is:

[0026] σ C =(σ1+σ2) / 2;

[0027] σ b =(σ1-σ2) / 2;

[0028]

[0029]

[0030] σ1 is the compressive stress of the upper wall panel at the rear beam, and σ2 is the compressive stress of the upper wall panel at the front beam.

[0031] Preferably, the specific method for calculating the allowable shear stress, allowable axial compressive stress, and allowable bending stress based on the structural parameters includes:

[0032] Based on the dimensional parameters of the upper wall panel of the variable gradient trapezoidal composite material, the allowable shear stress [τ] and the allowable axial compressive stress [σ C ]、Allowable bending stress [σ b ];

[0033] The calculation formula for allowable shear stress is:

[0034]

[0035] The calculation formula for the allowable axial compressive stress is:

[0036]

[0037] The calculation formula for allowable bending stress is:

[0038]

[0039] Where [τ] is the allowable shear stress of the upper wall plate, [σ C ] is the allowable axial compressive stress, [σ b ] is the allowable bending stress, D 11 、D 12 、D 22 、D 66 is the bending stiffness coefficient of the rudder panel compared with the composite laminate, t2 is the thickness of the upper panel, L is the chord length of the upper panel, B is the distance between the left rib and the right rib; m is the directional instability half-wave of the rudder panel composite laminate, K s is the shear instability coefficient.

[0040] Preferably, the calculation formula for the composite margin of shear stability, axial compression stability, and bending stability of the upper wall plate is:

[0041]

[0042] R s =τ / [τ], R c =σ c / [σ c ]、R b =σ b / [σ b ];

[0043] Among them, MS is the composite safety margin, R s is the shear coefficient, R c is the compression coefficient, R b is the bending coefficient.

[0044] Preferably, in step 5, a loop method is used to optimize the iterative solution to determine the lightweight structural parameters of the upper wall panel under composite load. When the composite safety margin MS is greater than the preset threshold Ra, the size parameters of the upper wall panel are optimized according to the size of MS, and steps 1 to 4 are repeated until the composite safety margin MS is equal to the preset threshold Ra.

[0045] Preferably, the preset threshold Ra is set to 0. This application uses a certain structural shape and a certain design load as constraints, meets aircraft stability and strength requirements as a prerequisite, and minimizes the panel structure weight as an objective function to develop a set of strength analysis methods for the stability of composite panels under combined compression, shear, and bending loads. This application can perform stability and strength design on trapezoidal composite panels with variable gradients on rudder surfaces, ultimately obtaining the lightest panel structural parameters that meet the constraints.

[0046] This application is based on certain structural shapes and certain design loads as constraints, and on the premise of meeting the aircraft stability and strength conditions. It takes minimizing the weight of the panel structure as the objective function to form a set of strength analysis methods for the stability of composite panel under compression, shear, and bending combined loads. It creatively uses structural shape constraints and stability and strength constraints to design a lightest structure for trapezoidal composite materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 This is a schematic diagram of the force on the variable gradient composite material box structure;

[0048] Figure 2 It is a cross-sectional view of the variable gradient composite material box structure;

[0049] Figure 3 This is a schematic diagram of the laminate structure of the rudder composite upper wall panel;

[0050] Figure 4 is the shear stress diagram of the upper wall panel;

[0051] Figure 5 The force diagram of the upper wall panel under trapezoidal compression load;

[0052] Figure 6 The decomposition diagram of the bending and axial compression of the upper wall panel under trapezoidal compression load;

[0053] Figure 7 This is the cross-sectional parameter diagram of the variable gradient composite material box.

[0054] Figure 8 Optimization iterative diagram for a variable gradient composite panel. DETAILED DESCRIPTION

[0055] In order to make the purpose, technical solutions and advantages of the implementation of this application clearer, the technical solutions in the implementation of this application will be described in more detail below in conjunction with the drawings in the implementation of this application. In the drawings, the same or similar numbers throughout represent the same or similar elements or elements with the same or similar functions. The described implementation is a part of the implementation of this application, not all of the implementations. The implementation described below with reference to the drawings is exemplary and is intended to be used to explain this application, and should not be understood as a limitation on this application. Based on the implementation in this application, all other implementations obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application. The implementation of this application is described in detail below in conjunction with the drawings.

[0056] In order to solve the above problems, the present application provides a strength analysis method for a variable gradient composite material wall panel, which includes:

[0057] Based on the external load and structural parameters of the variable gradient composite wall panel, the shear stress and compressive stress of the variable gradient composite wall panel are solved;

[0058] Calculate the allowable shear stress, allowable axial compressive stress, and allowable bending stress based on structural parameters;

[0059] Calculating a safety margin using the shear stress, the compressive stress, the allowable shear stress, the allowable axial compressive stress, and the allowable bending stress;

[0060] The iterative safety margin is 0.

[0061] Specifically: Figure 1-Figure 3As shown, the variable gradient composite material wall panel includes: an upper wall panel 1 and a lower wall panel 4, the distance between the upper wall panel 1 and the lower wall panel 4 gradually increases from front to back, the front and rear ends of the upper wall panel 1 and the lower wall panel 4 are connected by a front beam and a rear beam, and the left and right sides of the upper wall panel 1 and the lower wall panel 4 are connected by side ribs 3; the upper wall panel 1, the front beam, the rear beam, the side ribs 3 and the lower wall panel 4 form a trapezoidal box structure, that is, the cross-section of the box structure along the front and back directions is trapezoidal; determine the compressive positive stress generated by the bending load M on the upper wall panel 1 and the tensile positive stress generated on the lower wall panel 4, determine the shear stress formed by the torsional load T in the box structure, the external load includes the bending load M and the torsional moment T, wherein the compressive positive stress of the upper wall panel 1 and the tensile positive stress of the lower wall panel 4 under the bending load M are balanced, and the torsional load T is balanced by the shear stress formed by the box structure.

[0062] The strength analysis method includes:

[0063] Step S1: Determine the force form of the box structure Figure 1 The shear stress of the upper wall panel 1 of the variable gradient trapezoidal composite material under torsional load T is Figure 4 Distribution form, based on the external load and structural parameters of the variable gradient composite material wall panel, the shear stress τ of the variable gradient composite material wall panel is calculated:

[0064] τ=T / 2Ωt2

[0065]

[0066] Wherein, Ω is the area enclosed by the center line of the cross section of the box structure formed by the wall panel 1, front beam, rear beam, side ribs 3 and lower wall panel 4; Figure 7 As shown, H is the height of the front beam, h is the height of the rear beam; t1 is the thickness of the front beam, t2 is the thickness of the upper wall panel 1, t3 is the thickness of the lower wall panel 4, t4 is the thickness of the rear beam, and L is the chord length of the box structure.

[0067] Step S2: Figure 5-Figure 6 As shown, under the bending load M: the compressive stress caused by the bending of the upper wall panel is Figure 5 The typical linear trapezoidal distribution shown in the figure shows the compressive stress of the upper wall plate. The compressive stress includes axial compressive stress and bending stress. That is, based on the linear trapezoidal compressive stress distribution form of the upper wall plate of the box body, it is Figure 6 The decomposition of axial compressive working stress and bending stress is shown.

[0068] The calculation formula of the compressive stress σ is:

[0069]

[0070]

[0071]

[0072] Where I is the bending stiffness of the trapezoidal structure enclosed by the centerline of the box structure section, y is the distance from the bending neutral layer, and Y is the linear equation of the centerline of the upper wall panel; Figure 2 As shown, Y is Figure 2 The equation of the straight line L1 of the trapezoidal upper wall panel;

[0073] Axial compressive stress σ C and bending stress σ b The calculation formula is:

[0074] σ C =(σ1+σ2) / 2;

[0075] σ b =(σ1-σ2) / 2;

[0076]

[0077]

[0078] σ1 is the compressive stress of the upper wall panel at the front beam, and σ2 is the bending stress of the upper wall panel at the front beam.

[0079] Step S3: Based on the size parameters of the variable gradient trapezoidal composite upper wall panel, determine the allowable shear stress [τ], allowable axial compressive stress [σ C ]、Allowable bending stress [σ b ];

[0080] The calculation formula for allowable shear stress is:

[0081]

[0082] The calculation formula for the allowable axial compressive stress is:

[0083]

[0084] The calculation formula for allowable bending stress is:

[0085]

[0086] Where [τ] is the allowable shear stress of the upper wall plate, [σ C ] allowable axial compressive stress, [σ b ] Allowable bending stress, D 11 、D 12 、D 22 、D 66is the bending stiffness coefficient of the rudder panel compared with the composite laminate, t2 is the thickness of the upper panel, L is the chord length of the upper panel, B is the distance between the left rib and the right rib; m is the directional instability half-wave of the rudder panel composite laminate, K s is the shear instability coefficient.

[0087] Step S4: According to the obtained shear stress τ and axial compressive stress σ C , bending stress σ b and allowable shear stress [τ], axial compressive stress [σ C ]、Allowable bending stress [σ b ], taking the composite safety margin of shear stability, axial compression stability and bending stability as the constraint conditions, the stability safety margin of the variable gradient trapezoidal composite upper wall panel is determined:

[0088]

[0089] R s =τ / [τ], R c =σ c / [σ c ]、R b =σ b / [σ b ];

[0090] Among them, MS is the safety margin, R s is the shear coefficient, R c is the compression coefficient, R b is the bending coefficient.

[0091] Step S5: Optimize and iterate the structural parameters of the upper wall panel, repeating steps 1 to 4 until the composite material upper wall panel's stability composite safety margin MS is 0, thereby obtaining the lightest structural parameters of the upper wall panel.

[0092] This application uses a certain structural shape and a certain design load as constraints, and takes meeting the aircraft stability and strength conditions as a prerequisite. It takes minimizing the panel structure weight as the objective function to form a set of strength analysis methods for the stability of composite panel under compression, shear, and bending combined loads. This application can perform stability and strength design on the gradient-variable trapezoidal composite panel of the rudder surface, and ultimately obtain the lightest panel structure parameters that meet the constraints. The iterative flow chart is as follows: Figure 8 .

[0093] In practice, the aforementioned analysis technique was used to determine the critical buckling load of a large aircraft's variable-gradient trapezoidal composite structure, with airfoil heights of 360mm at the front and 80mm at the rear beams, effectively reducing the panel weight by 16.8%. Comparison of critical buckling results from stability tests of the variable-gradient trapezoidal composite panel revealed a mere 2% error in the analysis.

[0094] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A strength analysis method for variable gradient composite panels, The variable gradient composite material wall panel comprises: The upper wall panel (1) and the lower wall panel (4), and the front and rear ends of the upper wall panel (1) and the lower wall panel (4) are connected respectively by a front beam and a rear beam, and both sides of the upper wall panel (1) and the lower wall panel (4) are connected by side ribs (3); the upper wall panel (1), the front beam, the rear beam, the side ribs (3) and the lower wall panel (4) form a trapezoidal box structure; The cross-section of the box structure along the front-to-back direction is trapezoidal, and is characterized in that the strength analysis method includes: Step 1: Determine the stress form of the upper wall plate (1) of the box structure: determine the bending load M and the torsional moment T applied to the box structure, determine the compressive normal stress generated by the bending load M on the upper wall plate (1) and the tensile normal stress generated on the lower wall plate (4), and determine the shear stress generated by the torsional load T on the box structure; Step 2: Based on the stress form of the upper wall plate (1), determine the shear stress τ of the upper wall plate (1) under the torsional load T; determine the distribution form of the compressive stress σ of the upper wall plate (1) under the bending load M and the stress magnitude at the characteristic point; Step 3: Based on the distribution form of the compressive stress σ of the upper wall plate (1) and the stress magnitude at the characteristic point, the axial compressive stress σ of the upper wall plate (1) is calculated. C and bending stress σ b Stress equivalent to determine the axial compressive stress σ C and bending stress σ b size; Step 4: Based on the dimensional parameters of the variable gradient trapezoidal composite upper wall panel (1), determine the allowable shear stress [τ], allowable axial compressive stress [σ C ]、Allowable bending stress [σ b ]; Step 5: Use a cyclic method to optimize and iterate the solution to determine the lightweight structural parameters of the upper wall panel (1) under composite load. When the composite safety margin MS is greater than the preset threshold Ra, optimize the size parameters of the upper wall panel (1) according to the size of MS, and repeat steps 1 to 4 until the composite safety margin MS is equal to the preset threshold Ra. The calculation formula of the shear stress τ is: τ=T / 2Ωt2 Wherein, Ω is the area enclosed by the midline of the cross section of the box structure formed by the upper wall plate (1), the front beam, the rear beam, the side ribs (3) and the lower wall plate (4); H is the height of the front beam, h is the height of the rear beam; t1 is the thickness of the front beam, t2 is the thickness of the upper wall plate (1), t3 is the thickness of the lower wall plate (4), t4 is the thickness of the rear beam, and L is the chord length of the box structure; The specific method of converting the compressive stress into axial compressive stress and bending stress includes: calculating the compressive stress; The upper wall plate located at the rear beam and the upper wall plate located at the front beam are selected as the characteristic points; Calculating the compressive stress of the upper wall panel at the rear beam and the compressive stress of the upper wall panel at the front beam based on the compressive stress; Based on the compressive stress of the upper wall panel at the rear beam and the compressive stress of the upper wall panel at the front beam, the axial compressive stress and the bending stress are calculated respectively; The compressive stress σ of the upper wall plate (1) under the bending load M is a typical linear trapezoidal distribution. The calculation formula of the compressive stress σ is: Where I is the bending stiffness of the trapezoidal structure enclosed by the centerline of the box structure section, y is the distance from the bending neutral layer, and Y is the straight line equation of the centerline of the upper wall panel; Axial compressive stress σ C and bending stress σ b The calculation formula is: s C =(σ1+σ2) / 2; s b =(σ1-σ2) / 2; σ1 is the compressive stress of the upper wall panel at the rear beam, and σ2 is the compressive stress of the upper wall panel at the front beam.

2. The strength analysis method of the variable gradient composite material wall panel according to claim 1, characterized in that: The specific methods for calculating the allowable shear stress, allowable axial compressive stress, and allowable bending stress based on structural parameters include: Based on the dimensional parameters of the upper wall panel of the variable gradient trapezoidal composite material, the allowable shear stress [τ] and the allowable axial compressive stress [σ C ]、Allowable bending stress [σ b ]; The calculation formula for allowable shear stress is: The calculation formula for the allowable axial compressive stress is: The calculation formula for allowable bending stress is: Where [τ] is the allowable shear stress of the upper wall plate, [σ C ] is the allowable axial compressive stress, [σ b ] is the allowable bending stress, D 11 、D 12 、D 22 、D 66 is the bending stiffness coefficient of the rudder panel compared with the composite laminate, t2 is the thickness of the upper panel, L is the chord length of the upper panel, B is the distance between the left rib and the right rib; m is the directional instability half-wave of the rudder panel composite laminate, K s is the shear instability coefficient.

3. The strength analysis method of the variable gradient composite material wall panel according to claim 2, characterized in that: The calculation formula of the composite margin of shear stability, axial compression stability and bending stability of the upper wall plate (1) is: R s =τ / [τ]、R c =s c / [s c ]、R b =s b / [s b ]; Among them, MS is the composite safety margin, R s is the shear coefficient, R c is the compression coefficient, R b is the bending coefficient.

4. The strength analysis method of the variable gradient composite material wall panel according to claim 1, characterized in that: The preset threshold Ra is set to 0.

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