A calculation method for allowable shear stress of aircraft rectangular web

Abstract

A method for calculating the allowable shear stress of an aircraft rectangular web is firstly to calculate the critical stress τ of elastic instability of the rectangular web under uniform shear load. cr ; Secondly, the actual shear stress τ of the rectangular web and the critical stress τ of elastic instability cr The ratio is the load ratio c of the rectangular web, and the calculation formula of the load ratio c is obtained; then, according to the different ranges of the load ratio c, the tensile yield limit σ of the rectangular web material is calculated. 0.2 , tensile strength limit σ b , shear strength limit τ b And the load ratio c gives the allowable shear stress τ of the rectangular web all Finally, let the actual shear stress in the load ratio c calculation formula be equal to the allowable shear stress τ all , combined with the calculation formula of load ratio c and allowable shear stress τ all The calculation formula is solved to obtain the allowable shear stress of the rectangular web. The invention can calculate the allowable shear stress of the rectangular web more conveniently, quickly and accurately.

Description

Technical Field

[0001] The invention belongs to the field of aircraft structure strength design, and in particular relates to a method for calculating the allowable shear stress of an aircraft rectangular web. Background Art

[0002] The wing is one of the important parts of the aircraft. It is installed on the fuselage. Its main function is to generate lift and form good stability and maneuverability together with the tail. The wing is usually composed of components such as spar, stringer, rib and skin. The spar web and rib web are usually considered to be pure shear rectangular webs in engineering.

[0003] In the current strength verification, the allowable shear stress of the wing spar web and the rib web is calculated according to the following method: the calculated shear stress of the web is calculated based on the overall finite element model of the whole aircraft, and then the elastic instability critical stress of the rectangular web under uniform shear load is obtained based on the web shear critical stress coefficient, the length and width, thickness, material elastic Poisson's ratio and material elastic modulus of the web, and then the tension field coefficient is determined according to the load ratio. Finally, the allowable shear stress of the web is calculated based on the tension field coefficient, the tensile yield limit, tensile strength limit, shear strength limit and correction factor of the web material.

[0004] For the webs of wing beams and ribs, once the web size, material and boundary support conditions are determined, the allowable shear stress of the web is a constant, and should not be related to the calculated shear stress of the web calculated by the overall finite element model of the entire aircraft. The results obtained according to the formula listed in the "Aircraft Design Manual" (Volume 9) are of low accuracy. Therefore, it is necessary to explore a new calculation method to conveniently, quickly and accurately calculate the allowable shear stress of the aircraft rectangular web. Summary of the invention

[0005] The present invention provides a method for calculating the allowable shear stress of an aircraft rectangular web, and further calculation is performed based on the formula listed in the Aircraft Design Manual (Volume 9), in order to improve the calculation accuracy of the allowable shear stress of a pure shear rectangular web.

[0006] The present invention provides a method for calculating the allowable shear stress of a rectangular web of an aircraft, wherein the rectangular web is a metal plate of equal thickness and is riveted to surrounding structures on all sides, and comprises the following steps:

[0007] 1) According to the formula listed in the Aircraft Design Manual (Volume 9), calculate the critical stress τ of elastic instability of the rectangular web under uniform shear load cr , elastic instability critical stress τ cr The calculation formula is:

[0008]

[0009] Where:

[0010] τcr —Critical stress for elastic instability;

[0011] b—length of the short side of the rectangular web;

[0012] E—Young's elastic modulus of the rectangular web;

[0013] μ e —Poisson's ratio of elasticity of the rectangular web material;

[0014] δ—thickness of rectangular web;

[0015] K S —The shear critical stress coefficient should be selected according to the specific connection form between the rectangular web and the surrounding structure.

[0016] 2) The actual shear stress borne by the rectangular web is the actual shear stress τ. The ratio of the actual shear stress to the critical stress of elastic instability is the load ratio c of the rectangular web. The calculation formula of the load ratio is:

[0017] τ=cτ cr

[0018] 3) When the load ratio c is greater than or equal to 1 and less than 2, the allowable shear stress τ of the rectangular web is all The calculation formula is:

[0019]

[0020] When the load ratio c is greater than or equal to 2, the allowable shear stress τ of the rectangular web all The calculation formula is:

[0021]

[0022] Where: 0.2 is the tensile yield limit of the web material; σ b is the tensile strength limit of the web material; τ b is the shear strength limit of the web material;

[0023] 4) When the actual shear stress of the rectangular web reaches the allowable shear stress, the rectangular web fails in shear. Therefore, the actual shear stress in step 2) is equal to the allowable shear stress in step 3). The load ratio calculation formula in step 2) and the allowable shear stress calculation formula in step 3) are combined to obtain the allowable shear stress of the rectangular web.

[0024] The beneficial effects of the present invention are:

[0025] 1) The method provided by the present invention can accurately calculate the allowable shear stress of the rectangular web, meeting the static strength calculation requirements of the wing spar web and rib web structure.

[0026] 2) Compared with the traditional web shear stress calculation method, it reflects the inherent characteristics of the allowable shear stress and improves the calculation accuracy.

[0027] 3) The method provided by the present invention is simple to operate, realizes the standardization of calculation methods and processes, avoids the large errors in the results when different R&D personnel calculate, and provides a method for accurately solving the allowable shear stress of rectangular webs for dealing with deviations in similar parts. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram of the web structure of a certain aircraft wing beam.

[0029] Explanation of numbers in the figure: 1 web, 2 column, 3 rivet, 4 flange. DETAILED DESCRIPTION

[0030] Referring to the attached drawings, taking the web of a wing beam of an aircraft as an example, the web 1 is an aluminum alloy sheet with a thickness of 3 mm, which is connected to the flange 4 and the column 2 by a single row of rivets 3, respectively. The area surrounded by the flange 4 and the column 2 is a rectangle with a length of 400 mm and a width of 200 mm. The calculation method of the allowable shear stress of the rectangular web of the aircraft includes the following steps:

[0031] 1 According to the formula listed in the Aircraft Design Manual (Volume 9), calculate the critical stress τ of elastic instability of the rectangular web under uniform shear load cr , elastic instability critical stress τ cr The calculation formula is:

[0032]

[0033] Where:

[0034] τ cr —Critical stress for elastic instability;

[0035] b—length of the short side of the rectangular web;

[0036] E—Young's elastic modulus of the rectangular web;

[0037] μ e —Poisson's ratio of elasticity of the rectangular web material;

[0038] δ—thickness of rectangular web;

[0039] K S —The shear critical stress coefficient should be selected according to the specific connection form between the rectangular web and the surrounding structure.

[0040] Using the web size and material parameters, the elastic instability critical stress τ of the rectangular web is calculated according to the above formula: cr 91.4MPa;

[0041] 2 The actual shear stress borne by the rectangular web is the actual shear stress τ. The ratio of the actual shear stress to the critical stress of elastic instability is the load ratio c of the rectangular web. The calculation formula of the load ratio is:

[0042] τ=cτ cr

[0043] 3 When the load ratio c is greater than or equal to 1 and less than 2, the allowable shear stress τ of the rectangular web is all The calculation formula is:

[0044]

[0045] When the load ratio c is greater than or equal to 2, the allowable shear stress τ of the rectangular web all The calculation formula is:

[0046]

[0047] Where: 0.2 is the tensile yield limit of the web material; σ b is the tensile strength limit of the web material; τ b is the shear strength limit of the web material;

[0048] 4 When the actual shear stress of the rectangular web reaches the allowable shear stress, the rectangular web fails in shear. Therefore, let the actual shear stress in step 2) be equal to the allowable shear stress in step 3), and combine the load ratio calculation formula in step 2) and the allowable shear stress calculation formula in step 3) to solve and obtain the allowable shear stress of the rectangular web.

[0049] When the load ratio c is greater than or equal to 1 and less than 2:

[0050]

[0051] Obtain the tensile yield limit σ of the web material according to the material handbook 0.2 is 275MPa, and the tensile strength limit σ b is 405MPa, the shear strength limit τ b is 225MPa, and solving the equations yields: The allowable shear stress τ of the rectangular web all The load ratio c is 148.52MPa and 1.6255. The load ratio obtained by solving the equations meets the prerequisite of the equation group "the load ratio c is greater than or equal to 1 and less than 2", and the solution of this group is valid.

[0052] When the load ratio c is greater than or equal to 2:

[0053]

[0054] Solving the equations, we can obtain: The allowable shear stress τ of the rectangular web is allThe load ratio c is 148.53 MPa and 1.6256. The load ratio obtained by solving does not meet the prerequisite of the equation group "load ratio c is greater than or equal to 2", so this group of solutions is invalid.

[0055] Therefore, the allowable shear stress τ of the rectangular web is all It is 148.52MPa.

Claims

1. A method for calculating the allowable shear stress of a rectangular web of an aircraft, wherein the rectangular web is a metal plate of equal thickness and is riveted to the surrounding structure on all sides, characterized in that Contains the following: 1) Calculate the critical stress τ of elastic instability of rectangular web under uniform shear load cr ; 2) The actual shear stress borne by the rectangular web is the actual shear stress τ. The ratio of the actual shear stress to the critical stress of elastic instability is the load ratio c of the rectangular web. The load ratio calculation formula is τ = cτ cr ; 3) When the load ratio c is greater than or equal to 1 and less than 2, the allowable shear stress τ of the rectangular web is all The calculation formula is: When the load ratio c is greater than or equal to 2, the allowable shear stress τ of the rectangular web all The calculation formula is: Where: 0.2 is the tensile yield limit of the web material; σ b is the tensile strength limit of the web material; τ b is the shear strength limit of the web material; 4) Let the actual shear stress in step 2) be equal to the allowable shear stress in step 3), combine the load ratio calculation formula in step 2) and the allowable shear stress calculation formula in step 3), and solve to obtain the allowable shear stress of the rectangular web.

2. The method for calculating the allowable shear stress of an aircraft rectangular web according to claim 1, characterized in that: When calculating the critical stress of elastic instability, the boundary conditions of the rectangular web should be determined according to the specific connection form between the web and the surrounding structure.

3. The method for calculating the allowable shear stress of an aircraft rectangular web according to claim 1, characterized in that: The load ratio of the rectangular web that causes elastic instability should be greater than or equal to 1.

Images