Optimization design method for wing rib through holes

Abstract

The invention provides a rib through hole optimization design method, and belongs to the field of airplane rib strength design. According to the rib through hole optimization design method, finite element software is utilized to simulate rib load, structural internal force is extracted, optimal geometric parameters of rib through holes are determined by referring to a mature engineering algorithm and wing surface design requirements through a parameterization means on the basis of meeting strength and rigidity from the aspect of process manufacturing, and the rib through hole with low manufacturing cost and high design efficiency is designed. And the light-weight structure product is simple in process molding. According to the method, on the premise that process manufacturing factors are considered in the design of the rib through hole structure, rapid iterative calculation is carried out, a lightweight configuration is obtained, and the overall safety, economy and reliability of the structure are guaranteed, the use performance potential of materials is fully excavated, the design period is shortened, and the cost is saved.

Description

Technical Field

[0001] The present invention belongs to the field of aircraft rib strength design, and relates to an optimized design method for rib through-holes, and particularly to an optimized design method for T-shaped longeron through-holes of ribs in an aircraft wing box section. Background Art

[0002] In the conventional box section structures of civil aircraft wings and tails, multiple longerons and stiffeners are usually arranged along the span direction of the skin and beams. In this way, when arranging ribs in the chord direction, multiple through-holes need to be designed at the surrounding boundaries of the box section to ensure that the longeron webs and stiffener webs pass through the ribs continuously, so as to strengthen the skin and wing beams. Therefore, the design of the rib through-hole body and the surrounding rib webs, flanges, and stiffener structures is particularly important. In the previous research and development of rib structures, limited by the low design and process levels, the overall structure was overweight, resulting in low material utilization efficiency and high R & D and maintenance costs. Summary of the Invention

[0003] The present invention provides an optimized design method for rib through-holes. Based on finite element simulation software, the actual load on the rib is simulated, the internal force of the element is extracted, and with reference to mature engineering algorithms and wing surface design requirements, through parametric means, on the basis of meeting strength and stiffness, from the perspective of process manufacturing, the optimal geometric parameters of the rib through-hole are determined, and a lightweight structural product with low manufacturing cost and simple process forming is designed.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0005] An optimized design method for rib through-holes, the design method uses finite element software to simulate the load on the rib, extracts the internal force of the structure, and with reference to mature engineering algorithms and wing surface design requirements, through parametric means, on the basis of meeting strength and stiffness, from the perspective of process manufacturing, determines the optimal geometric parameters of the rib through-hole, and designs a lightweight structural product with low manufacturing cost and simple process forming. The specific steps are as follows:

[0006] Step 1: Perform finite element simulation modeling on the wing box; specifically as follows:

[0007] (1.1) Considering that in the actual aircraft wing surface wing box structure, the front and rear beams, ribs, and skins jointly participate in load transfer, and the aerodynamic load and inertial load are diffused to the fuselage through hinge joints and connecting angle plates, so the design analysis of the rib through-hole is based on the finite element model of the overall rib structure in the wing box;

[0008] (1.2) The reference coordinate system for finite element modeling of the wing box needs to be consistent with the digital model coordinate system of the structural electronic prototype, and the same unit system as the actual product is adopted;

[0009] (1.3) In order to quickly extract the load and process the internal force, the node and element numbers should be selected as numbers with certain rules during modeling;

[0010] (1.4) According to the characteristics of the transmitted load, the structure needs to be reasonably simplified. The simplified element of the rib web is CQUAD4, and the through-hole stiffeners and stringers are simplified as CROD.

[0011] Step 2: Apply boundary conditions, aerodynamic loads, and inertial loads to the established finite element model; specifically as follows:

[0012] After the finite element model of the wing box is established, constraints are applied at the root, inertial loads are applied at the rib station nodes, and aerodynamic loads are applied on the aerodynamic surface elements; ensure that the structure accurately simulates the external loads during the flight of the aircraft.

[0013] Step 3: Calculate the finite element model of the wing box, and extract the internal forces of the rib through-holes and the surrounding structural elements according to the output result file; specifically:

[0014] (3.1) The rib webs around the through-holes are simplified as CQUAD4, and the corresponding element force flows Nx, Ny, and shear flow Nxy are extracted;

[0015] (3.2) The through-hole stiffeners and the surrounding stringers are simplified as CROD, and the corresponding element force Fx is extracted.

[0016] Step 4: According to the simplification principle, perform secondary distribution calculation of the loads to determine the loads of the through-hole stiffeners and the surrounding webs and stringers; specifically as follows:

[0017] (4.1) The rib webs are divided into different regions by longitudinal and transverse stiffeners. Each region contains N CQUAD4 elements. When calculating the web region near the through-hole, the force flows of the N elements in one region need to be averaged, and then the failure mode calculation is performed; the specific formula is as follows:

[0018]

[0019] Where, N x is the force flow in the x direction in one region, N / mm; N xi is the force flow in the x direction corresponding to the i-th element, N / mm; N y is the force flow in the y direction in one region, N / mm; N yi is the force flow in the y direction corresponding to the i-th element, N / mm; N xy is the shear flow in one region, N / mm; N xy is the shear flow corresponding to the i-th element, N / mm; n is the number of elements in one region;

[0020] (4.2) The stiffeners on the left and right sides of the rib through-holes are simplified as bar elements in the finite element and discretized into m elements longitudinally. When performing the check analysis of the unilateral stiffeners, the axial forces of the m elements are extracted, and the maximum axial force is used as the total load of the left and right side stiffeners. The specific formula is as follows:

[0021]

[0022] Among them, P m is the axial force of the m-th unit, N; P 0 is the total axial force of the stiffeners on the left and right sides, N; P is the axial force of a single-sided stiffener, N.

[0023] Step 5: Calculate the safety margins corresponding to the failure modes of the through-hole stiffeners and the surrounding webs and flanges according to the load. When all the safety margins are greater than 0, it indicates that the structural design meets the strength and stiffness requirements; when the safety margin is less than 0, it is necessary to adjust the geometric dimensions of the through-hole stiffeners, webs, and flanges to ensure that all the structural safety margins are greater than 0; specifically as follows:

[0024] (5.1) Conduct a stress failure analysis on the web around the through-hole;

[0025] Calculate the working stresses of the web in each direction:

[0026]

[0027] In the formula, σ x is the stress of the web in the X direction, MPa; N x is the force flow of the web in the x direction, N / mm; t is the thickness of the web, mm. σ y is the stress of the web in the y direction, MPa; N y is the force flow of the web in the y direction, N / mm; τ xy is the shear stress of the web, MPa; N xy is the shear flow of the web, N / mm.

[0028] Calculate the equivalent stress σ v of the web:

[0029]

[0030] Calculate the maximum shear stress τ max of the web:

[0031]

[0032] Safety margin calculation of the web:

[0033] Tension:

[0034] Shear: In the formula, k is the nail hole weakening coefficient; σ v is the maximum Von Mises equivalent stress, MPa; [σ tu is the allowable tensile stress of the web material, MPa; τ max is the maximum shear stress, MPa; [σsu is the allowable shear stress of the web material, MPa.

[0035] (5.2) Conduct shear stability failure analysis on the web around the through-hole;

[0036] The critical shear buckling stress τ of the web under in-plane shear load cr Calculation:

[0037]

[0038] In the formula, t is the web thickness, mm; b is the length value of the short side, mm; E is the elastic modulus of the material, MPa; μ is the Poisson's ratio of the material; η s is the plastic correction coefficient. When the buckling stress is higher than the proportional limit stress, η needs to be used s for correction; k s is the shear buckling coefficient.

[0039] Plastic correction coefficient η s Calculation:

[0040]

[0041] τ sy =0.55σ cy

[0042] In the formula: G is the shear modulus, MPa; σ cy is the yield stress of the material, MPa; n is the material property parameter in the Ramber-Osgood equation.

[0043] The shear buckling safety margin M.S. is calculated as follows.

[0044]

[0045] (5.3) Conduct compressive stability failure analysis on the web around the through-hole;

[0046] The critical compressive buckling stress σ of the web under in-plane axial compressive load cr :

[0047]

[0048] In the formula: t is the web thickness, mm; b is the length value of the loading side, mm; E is the elastic modulus of the material, MPa; μ is the Poisson's ratio of the material; η c is the plastic correction coefficient. When the buckling stress is higher than the proportional limit stress, η needs to be used c for correction; k c is the compressive buckling coefficient.

[0049] Plastic correction coefficient ηc The calculation is as follows.

[0050]

[0051] In the formula: σ cy is the material yield stress, MPa; n is the material property parameter in the Ramber-Osgood equation.

[0052] The safety margin M.S. of the web in axial compression buckling is calculated as follows.

[0053]

[0054] (5.4) Conduct a failure analysis of the combined compression-shear stability of the web around the through-hole;

[0055] The web is subjected to both compressive and shear loads, and the stability margin under the combined compression-shear load needs to be calculated;

[0056]

[0057]

[0058] In the formula: R c is the compressive stress ratio; R s is the shear stress ratio; τ xy is the working shear stress, σ is the working compressive stress, MPa.

[0059] (5.5) Conduct a failure analysis of the shear fracture strength of the web around the through-hole;

[0060] After considering the stability of the web, the shear fracture strength still needs to be checked and should satisfy the following formula:

[0061]

[0062] Shear fracture safety margin:

[0063]

[0064] In the formula: τ * is the allowable shear stress, MPa; τ is the working shear stress, MPa; λ is the correction factor, taking 0.9 - 1 for bolt connections; K is the correction factor, generally taking 1; σ 0.2 is the material tensile yield limit, MPa; σ b is the material tensile strength limit, MPa; τ b is the material shear strength limit, MPa.

[0065] (5.6) Conduct a failure analysis of the tensile-compressive strength of the through-hole stiffener or flange;

[0066] Calculate the working stress and the safety margins of tension and compression of the stiffeners or stringers.

[0067] (5.7) Failure analysis of the through-hole stiffener under compression loss;

[0068] The web provides support for the stiffeners in the plane, so the overall buckling failure of the stiffeners generally does not occur. Check the calculation of the stiffener compression loss failure:

[0069]

[0070] Safety margin of compression loss:

[0071]

[0072] In the formula: b is the length of the stringer, in mm; t is the thickness of the stringer, in mm; c is the boundary correction coefficient; E is the elastic modulus of the material, in MPa; σ cy is the compressive yield strength of the material, in MPa; σ cc is the stress of compression loss, in MPa; σ x is the working compressive stress, in MPa.

[0073] (5.8) Failure analysis of the local stability of the through-hole stiffener;

[0074] When the stiffener is subjected to a compressive load, column buckling will occur. The buckling problem of the column can be divided into overall buckling and local buckling of the column. When the column undergoes a combined buckling failure of overall and local buckling, the Johnson-Euler equation is used to calculate the critical buckling stress of the column.

[0075] Step 6: For the integrally machined rib structure, when meeting the requirements of strength and stiffness, the optimized size of the structural hole should consider the requirements of process manufacturing and the minimum opening size; specifically as follows:

[0076] (6.1) Requirements for the design size of the structural hole: Among them, the thickness of the stiffener is considered, and the minimum machining thickness should not be less than 1.5 mm; the width dimension of its through-hole is defined as follows:

[0077] A = t web + 2×(R str + δ str + δ rib + δ 机加 )

[0078] In the formula, A is the width of the rib through-hole, in mm; t web is the thickness of the longeron web, in mm; R str is the bottom corner radius of the longeron, in mm; δ rib is the rib positioning tolerance, in mm; δ 机加 is the machining tolerance, in mm; δ str is the longeron tolerance, in mm;

[0079] (6.2) The total tolerance of stringers takes into account the positioning error, thickness tolerance, and R - angle tolerance of stringers;

[0080] The height H of the rib through - hole is as follows:

[0081]

[0082] Where h is the height of the stringer web, in mm;

[0083] (6.3) In order to reduce the clamping and processing costs, the flange and stiffeners of the part are designed on one side of the web, and the stiffeners are designed to be perpendicular to the web as much as possible. If it cannot be designed perpendicular, a constant angle is adopted.

[0084] (6.4) Select the ratio p of the thickness to height of the stiffeners and flanges of the aluminum alloy part as required. For high - speed milling, p ≤ 1:20, and at the same time, the web thickness t ≥ 1.2 mm; for non - high - speed milling, p ≤ 1:10, and at the same time, the web thickness t ≥ 1.8 mm.

[0085] Step 7: The design of the rib through - hole structure needs to meet the weight index requirements. If the initially designed dimensions do not meet the weight requirements, steps 1 to 6 need to be cycled through to adjust the dimensions of the stiffeners, webs, and flanges at the hole edges until the structural weight requirements are met.

[0086] The present invention has the following advantages and beneficial effects:

[0087] In the design of the rib through - hole structure of the present invention, process manufacturing factors are considered, rapid iterative calculations are carried out, a lightweight configuration is obtained, and while ensuring the overall safety, economy, and reliability of the structure, the potential of material usage performance is fully explored, the design cycle is shortened, and costs are saved. Brief Description of the Drawings

[0088] Figure 1 is the flow chart of the design method of the present invention;

[0089] Figure 2 is the schematic diagram of the rib finite - element model;

[0090] Figure 3 is the load distribution diagram of the stiffeners;

[0091] Figure 4 is the schematic diagram of the rib through - hole structure product. Detailed Embodiments

[0092] The following further describes the detailed embodiments of the present invention in combination with the drawings and technical solutions.

[0093] The entire optimization design method of the present invention is integrated in the flow chart shown in Figure 1 . The specific implementation process is as follows:

[0094] Step 1: Use finite element software to establish a finite element model of the wing box structure. The finite element model of the wing rib is shown in Figure 2 . The model modeling criteria are as follows:

[0095] (1.5) Considering that in the actual aircraft wing box structure, the front and rear beams, ribs, and skins jointly participate in load transfer, and the aerodynamic load and inertial load are diffused to the fuselage through hinge joints and connecting angle plates, the design analysis of the rib through-hole is based on the finite element model of the overall structure of the wing rib in the wing box;

[0096] (1.6) The reference coordinate system for finite element modeling of the wing box needs to be consistent with the digital model coordinate system of the structural electronic prototype, and the same unit system as the actual product is adopted;

[0097] (1.7) In order to quickly extract loads and process internal forces, the node and element numbers should be selected as numbers with certain rules during modeling;

[0098] (1.8) According to the load transfer characteristics, the structure needs to be reasonably simplified. The wing rib web is simplified to the CQUAD4 element, and the through-hole stiffeners and flanges are simplified to the CROD;

[0099] Step 2: Apply loads and boundary conditions to the overall finite element central wing box section model established in Step 1. Specifically:

[0100] After the finite element of the wing box is established, constraints are applied at the root, and inertial loads are applied at the wing rib station nodes and aerodynamic loads are applied on the aerodynamic surface elements; ensure that the structure accurately simulates the external loads during aircraft flight;

[0101] Step 3: Use finite element software to calculate the overall wing box finite element model, and extract the internal loads of the structure according to the output result file. Specifically:

[0102] (3.1) The rib web around the through-hole is simplified to the CQUAD4, and the corresponding element force flows Nx, Ny, and shear flow Nxy are extracted;

[0103] (3.2) The through-hole stiffeners and the surrounding flanges are simplified to the CROD, and the corresponding element force Fx is extracted;

[0104] Step 4: After extracting the loads from the web and stiffened structure, perform load processing as follows:

[0105] (4.1) The rib web is divided into different regions by longitudinal and transverse stiffeners. Each region contains N CQUAD4 elements. When calculating the web region near the through-hole, the force flows of the N elements in one region need to be averaged, and then the failure mode calculation is performed; the specific formula is as follows:

[0106]

[0107] Among them, N x is the x-direction force flow in a region, N / mm; N xi is the x-direction force flow corresponding to the i-th unit, N / mm; N y is the y-direction force flow in a region, N / mm; N yi is the y-direction force flow corresponding to the i-th unit, N / mm; N xy is the shear flow in a region, N / mm; N xy is the shear flow corresponding to the i-th unit, N / mm; n is the number of units in a region;

[0108] (4.2) The stiffeners on the left and right sides of the rib through-hole are simplified into bar elements in the finite element, discretized into m units longitudinally. When performing the checking analysis of the unilateral stiffeners, the axial forces of the m units are extracted, as shown in Figure 2 . Among them, the maximum axial force is used as the total load of the left and right side stiffeners. The specific formula is as follows:

[0109]

[0110] Among them, P m is the axial force of the m-th unit, N; P 0 is the total axial force of the left and right side stiffeners, N; P is the axial force of the unilateral stiffeners, N;

[0111] Step Five: Determination of the loads on the web and stiffening structure around the through-hole: Based on the load data calculated by the finite element obtained in Step Four, and for the requirements of calculating the initial dimensions of the structural units and different failure modes, perform strength and stability calculations on the structure; specifically as follows:

[0112] (5.1) Conduct stress failure analysis on the web around the through-hole;

[0113] Calculate the working stresses in each direction of the web:

[0114]

[0115] In the formula, σ x is the stress in the X direction of the web, MPa; N x is the x-direction force flow of the web, N / mm; t is the thickness of the web, mm. σ y is the stress in the y direction of the web, MPa; N y is the y-direction force flow of the web, N / mm; τ xy is the shear stress of the web, MPa; N xy is the shear flow of the web, N / mm.

[0116] Calculate the equivalent stress σ v of the web:

[0117]

[0118] Calculate the maximum shear stress τ of the web max :

[0119]

[0120] Calculation of the safety margin of the web:

[0121] Tension:

[0122] Shear: In the formula, k is the hole weakening coefficient. The holes in the structure will reduce the allowable tensile stress. For the 2000 series aluminum alloy, the hole weakening coefficient is taken as 0.88, and for the 7000 series aluminum alloy, it is taken as 0.95; σ v is the maximum VonMises equivalent stress, MPa; [σ tu is the allowable tensile stress of the web material, MPa; τ max is the maximum shear stress, MPa; [σ su is the allowable shear stress of the web material, MPa.

[0123] (5.2) Conduct a shear stability failure analysis on the web around the through hole;

[0124] The critical shear buckling stress τ of the web under in-plane shear load cr Calculation:

[0125]

[0126] In the formula, t is the web thickness, mm; b is the length value of the short side, mm; E is the elastic modulus of the material, MPa; μ is the Poisson's ratio of the material; η s is the plastic correction coefficient. When the buckling stress is higher than the proportional limit stress, η s needs to be used for correction; k s is the shear buckling coefficient.

[0127] Plastic correction coefficient η s Calculation:

[0128]

[0129] τ sy = 0.55σ cy

[0130] In the formula: G is the shear modulus, MPa; σ cy is the yield stress of the material, MPa; n is the material property parameter in the Ramber-Osgood equation.

[0131] The shear buckling safety margin M.S. is calculated as follows.

[0132]

[0133] (5.3) Conduct a compressive stability failure analysis on the web around the through-hole;

[0134] The critical compressive buckling stress σ of the web under in-plane axial compressive load cr :

[0135]

[0136] where: t is the web thickness, in mm; b is the length value of the loading side, in mm; E is the elastic modulus of the material, in MPa; μ is the Poisson's ratio of the material; η c is the plastic correction factor. When the buckling stress is higher than the proportional limit stress, η c needs to be used for correction; k c is the compressive buckling coefficient.

[0137] The plastic correction factor η c is calculated as follows.

[0138]

[0139] where: σ cy is the yield stress of the material, in MPa; n is the material property parameter in the Ramber-Osgood equation.

[0140] The safety margin M.S. of the web under axial compression buckling is calculated as follows.

[0141]

[0142] (5.4) Conduct a combined compression-shear stability failure analysis on the web around the through-hole;

[0143] The web is subjected to both compressive and shear loads, and the stability margin under combined compression-shear loads needs to be calculated

[0144]

[0145] where: R c is the compressive stress ratio; R s is the shear stress ratio; τ xy is the working shear stress, and σ is the working compressive stress, in MPa.

[0146] (5.5) Conduct a shear fracture strength failure analysis on the web around the through-hole;

[0147] After considering the stability of the web, the shear fracture strength still needs to be checked and should satisfy the following formula.

[0148]

[0149] Shearing fracture safety margin:

[0150]

[0151] Where: τ * is the allowable shear stress, MPa; τ is the working shear stress, MPa; λ is the correction factor, for bolt connection, it is taken as 0.9 - 1; K is the correction factor, generally taken as 1; σ 0.2 is the tensile yield limit of the material, MPa; σ b is the tensile strength limit of the material, MPa; τ b is the shear strength limit of the material, MPa.

[0152] (5.6) Failure analysis of the tensile and compressive strength of stiffeners or stringers with through - holes;

[0153] Calculate the working stress and the tensile and compressive safety margins of the stiffeners or stringers.

[0154] Calculation of working stress:

[0155]

[0156] If σ x > 0, tensile margin:

[0157]

[0158] If σ x > 0, compressive margin:

[0159]

[0160] Where: t is the thickness of the stiffener or stringer, mm; b is the length of the stiffener or stringer, mm; σ ty is the tensile ultimate strength of the material, MPa; σ cy is the compressive ultimate strength of the material, MPa; K is the correction factor, if there are nail holes on the stringer or column, take 0.8, otherwise take 1; σ x is the working stress, MPa.

[0161] (5.7) Failure analysis of the compressive loss of stiffeners with through - holes;

[0162] The web provides support for the stiffeners in the plane, so the stiffeners generally do not undergo overall instability failure. Check the calculation of the compressive loss failure of the stiffeners:

[0163]

[0164] Compressive loss safety margin:

[0165]

[0166] where: b is the length of the flange, in mm; t is the thickness of the flange, in mm; c is the boundary correction factor, taking 0.565 for one end free and 1.427 for no free end; E is the elastic modulus of the material, in MPa; σ cy is the compressive yield strength of the material, in MPa; σ cc is the crushing stress, in MPa; (if σ cc > 0.9σ cy , then take σ cc = 0.9σ cy ), in MPa; σ x is the working compressive stress, in MPa.

[0167] (5.8) Analysis of the local stability failure of the through-hole stiffener;

[0168] When the stiffener is subjected to a compressive load, column instability will occur. The instability problem of the column can be divided into overall column instability and local instability. When the column undergoes combined instability failure of overall and local instability, the Johnson-Euler equation is used to calculate the critical instability stress of the column. Stiffener slenderness ratio:

[0169] λ = L' / ρ

[0170] where: (L' / ρ) is the slenderness ratio, dimensionless; L' is the effective length, dimensionless; ρ is the radius of gyration, in mm;

[0171]

[0172] where: (L' / ρ) t is the demarcation point between medium-length columns and long columns, dimensionless.

[0173] According to different slenderness ratios, the critical instability stress of the column is calculated as follows:

[0174] When 0 < λ < 12.5

[0175] σ c = σ cc

[0176] When 12.5 < λ < λ E

[0177]

[0178] Here:

[0179]

[0180] When λ > λ E

[0181] ​​

[0182] In the formula: σ c is the critical buckling stress of the column, MPa; σ cc is the pressure loss stress, MPa;

[0183] Safety margin for column buckling:

[0184]

[0185] Step 6: The design dimensions of the structural through-holes also need to consider the process manufacturing and the minimum dimension requirements. Specifically as follows:

[0186] (6.1) Requirements for the design dimensions of the structural holes: The thickness of the stiffener should be considered such that the minimum machining thickness should not be less than 1.5 mm; the width dimension of the through-hole is defined as follows:

[0187] A = t web + 2×(R str + δ str + δ rib + δ 机加 )

[0188] In the formula, A is the width of the rib through-hole, mm; t web is the thickness of the stringer web, mm; R str is the bottom corner radius of the stringer, mm; δ rib is the rib positioning tolerance, mm; δ 机加 is the machining tolerance, mm; δ str is the stringer tolerance, mm;

[0189] (6.2) The total tolerance of the stringer considering the stringer positioning error, thickness tolerance and R-angle tolerance;

[0190] The height H of the rib through-hole is as follows:

[0191]

[0192] In the formula, h is the height of the stringer web, mm;

[0193] (6.3) In order to reduce the clamping and processing costs, the flange and stiffener of the part are designed on one side of the web, and the ribs are designed to be perpendicular to the web as much as possible. If it cannot be designed perpendicular, a constant angle is adopted. For the minimum web thickness requirement of the machined part, medium-thick aluminum plate material is selected. It is preferred to use a minimum thickness of 1.8 ± 0.3 mm, and the acceptable minimum thickness is 1.2 ± 0.2 mm; for aluminum forging material, it is preferred to use a minimum thickness of 2.5 ± 0.3 mm, and the acceptable minimum thickness is 2.2 ± 0.2 mm.

[0194] (6.4) Select the ratio p of the thickness to the height of the stiffeners and flanges of the aluminum alloy parts as required. For high-speed milling, p ≤ 1:20, and at the same time, the web thickness t ≥ 1.2 mm; for non-high-speed milling, p ≤ 1:10, and at the same time, the web thickness t ≥ 1.8 mm.

[0195] Step 7: During the design process of the through-hole structure of the rib, on the basis of ensuring the safety and reliability of the structure, the weight parameter index should also be considered. If the structural safety margin is large when the strength and stiffness requirements are met, it will make the design weight too large. In order to better meet the design index corresponding to the weight, the above steps need to be cycled, and the relevant dimensional parameters of the structure are adjusted until the weight index requirements are met, and then the product drawing is completed, as Figure 4 shown.

[0196] The above embodiments only represent the implementation modes of the present invention, but should not be construed as limiting the scope of the present invention patent. It should be noted that for those skilled in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention.

Claims

1. A rib through hole optimization design method, characterized in that: The design method comprises the following steps: Step 1: Conduct finite element simulation modeling on the wing box; Step 2: Apply boundary conditions, aerodynamic loads, and inertial loads to the established finite element model; Step 3: Calculate the finite element model of the wing box and extract the internal forces of the rib through-hole and surrounding structural units based on the output result file; Step 4: According to the principle of simplification, the load is secondary distributed and calculated to determine the loads of the through-hole reinforcement and the surrounding web and flange; Step 5: Calculate the safety margins corresponding to the failure modes of the through-hole reinforcement and the surrounding webs and flanges according to the load. When the safety margins are all greater than 0, it means that the structural design meets the strength and stiffness requirements. When the safety margin is less than 0, it is necessary to adjust the geometric dimensions of the through-hole reinforcement, webs, and flanges to ensure that the safety margins of all structures are greater than 0. The details are as follows: Step 6: For the integrally machined wing rib structure, the optimized size of the structural hole should take into account the process manufacturing and minimum opening size requirements while meeting the strength and stiffness requirements; Step 7: The rib through-hole structure design needs to meet the weight index requirements. If the initial size of the design does not meet the weight requirements, it is necessary to loop through steps 1 to 6 to adjust the hole edge reinforcement, web, and flange dimensions until the structural weight requirements are met.

2. The rib through hole optimization design method according to claim 1, characterized in that: The step 1 is specifically as follows: (1.1) In the actual aircraft wing box structure, the front and rear beams, ribs, and wall panels jointly participate in load transmission, and the aerodynamic loads and inertial loads are diffused to the fuselage through hinge joints and connecting corner pieces. The rib through-hole design analysis is based on the finite element model of the overall structure of the wing rib in the wing box; (1.2) The reference coordinate system of the finite element modeling of the wing box should be consistent with the digital model coordinate system of the structural electronic prototype, and the same unit system as the actual product should be used; (1.3) When modeling, the node and unit numbers should be selected with certain rules; (1.4) According to the characteristics of the transferred load, the structure needs to be reasonably simplified. The rib and web are simplified by CQUAD4, and the through-hole reinforcement and flange are simplified by CROD.

3. The rib through hole optimization design method according to claim 1, characterized in that: The step 2 is specifically as follows: after the wing box finite element is established, constraints are applied at the root, and inertial loads are applied to the wing rib station nodes and aerodynamic loads are applied to the aerodynamic surface units; ensuring that the structure accurately simulates the external loads during the flight of the aircraft.

4. The rib through hole optimization design method according to claim 1, characterized in that: The step 3 is as follows: (3.1) The rib web around the through hole is simplified into CQUAD4, and the corresponding unit force flow Nx, Ny, and shear flow Nxy are extracted; (3.2) The through hole reinforcement and the peripheral edge strips are simplified to CROD, and the corresponding unit force Fx is extracted.

5. The rib through hole optimization design method according to claim 1, characterized in that: The step 4 is specifically as follows: (4.1) The rib web is divided into different areas by longitudinal and transverse reinforcements. Each area contains N CQUAD4 units. When calculating the web area near the through hole, it is necessary to average the force flow of the N units in one area, and then perform the failure mode calculation; the specific formula is as follows: Among them, N x is the force flow in the x direction within a region, N / mm; N xi is the x-direction force flow corresponding to the i-th unit, N / mm; N y is the force flow in the y direction within a region, N / mm; N yi is the force flow in the y direction corresponding to the i-th unit, N / mm; N xy is the shear flow in a region, N / mm; N xy is the shear flow corresponding to the ith unit, N / mm; n is the number of units in a region; (4.2) The left and right side reinforcements of the rib through hole are simplified into bar units in the finite element method and discretized into m units in the longitudinal direction. When performing the single-side reinforcement verification analysis, the axial forces of the m units are extracted, and the largest axial force is taken as the total load of the left and right side reinforcements. The specific formula is as follows: Among them, P m is the axial force of the mth unit, N; P0 is the total axial force of the left and right reinforcements, N; P is the axial force of the unilateral reinforcement, N.

6. The rib through hole optimization design method according to claim 1, characterized in that: The step 5 is specifically as follows: (5.1) Perform stress failure analysis on the web around the through hole, including calculation of the working stress in all directions of the web, calculation of the web equivalent stress, calculation of the maximum shear stress of the web, and calculation of the web safety margin; (5.2) Perform shear stability failure analysis on the web around the through hole, including calculating the critical shear instability stress τ of the web under in-plane shear load cr , Calculate the plasticity correction factor η s , calculate the shear buckling safety margin; (5.3) Perform compression stability failure analysis on the web around the through hole, including analysis of the critical compression instability stress σ of the web under in-plane axial compression load cr , Calculate the plasticity correction factor η c , calculate the safety margin of web plate under axial compression buckling; (5.4) Perform compression-shear composite stability failure analysis on the web around the through hole; (5.5) Perform shear fracture strength failure analysis on the web around the through hole; (5.6) Failure analysis of the tensile and compressive strength of through-hole reinforcement or flanges; calculation of the working stress and tensile and compressive safety margin of the reinforcement or flanges; (5.7) Analysis of the effectiveness of through hole reinforcement compression loss; (5.8) Analysis of local stability failure of through-hole reinforcement; when the column suffers combined instability failure of global instability and local instability, the Johnson-Euler equation is used to calculate the critical instability stress of the column.

7. The rib through hole optimization design method according to claim 6, characterized in that: The (5.1) is specifically: Calculate the working stress in each direction of the web: In the formula, σ x is the stress in the web X direction, MPa; N x is the force flow in the x direction of the web, N / mm; t is the thickness of the web, mm; σ y is the stress in the y direction of the web, MPa; N y is the force flow in the y direction of the web, N / mm; τ xy is the web shear stress, MPa; N xy is the web shear flow, N / mm; Calculate the equivalent stress σ of the web v : Calculate the maximum shear stress τ of the web max : Calculation of web safety margin: Stretch: Cut: Where k is the nail hole weakening coefficient; σ v is the maximum Von Mises equivalent stress, MPa; [σ tu ] is the allowable tensile stress of the web material, MPa; τ max is the maximum shear stress, MPa; [σ su ] is the allowable shear stress of the web material, MPa.

8. The rib through hole optimization design method according to claim 6, characterized in that: The (5.2) mentioned above is specifically: the critical shear instability stress τ of the web under the in-plane shear load cr calculate: Where, t is the web thickness, mm; b is the length of the short side, mm; E is the elastic modulus of the material, MPa; μ is the Poisson's ratio of the material; η s is the plasticity correction factor. When the instability stress is higher than the proportional limit stress, η s Correction; k s is the shear instability coefficient; Plasticity correction factor η s calculate: t sy =0.55σ cy Where: G is the shear modulus, MPa; σ cy is the material yield stress, MPa; n is the material performance parameter in the Ramber-Osgood equation; The shear buckling safety margin MS is calculated as follows; 9. The rib through hole optimization design method according to claim 6, characterized in that: The above (5.3) is specifically: the critical compressive instability stress σ of the web under the in-plane axial compressive load cr : Where: t is the web thickness, mm; b is the length of the loading side, mm; E is the elastic modulus of the material, MPa; μ is the Poisson's ratio of the material; η c is the plasticity correction factor. When the instability stress is higher than the proportional limit stress, η c Correction; k c is the compression instability coefficient; Plasticity correction factor η c The calculation is as follows; Where: cy is the material yield stress, MPa; n is the material performance parameter in the Ramber-Osgood equation; The web axial compression buckling safety margin MS is calculated as follows; 10. The rib through hole optimization design method according to claim 6, characterized in that: In step 5: The above (5.4) is specifically: the web is subjected to compression and shear loads at the same time, and the stability margin under the combined compression and shear loads needs to be calculated; Where: R c is the compression stress ratio; R s is the shear stress ratio; τ xy is the working shear stress, σ is the working compressive stress, MPa; The specific content of (5.5) is: after considering the stability of the web, the shear fracture strength still needs to be checked and should satisfy the following formula: Shear fracture safety margin: Where: τ * is the allowable shear stress, MPa; τ is the working shear stress, MPa; λ is the correction factor, which is 0.9 to 1 for bolted connections; K is the correction factor, which is generally 1; σ 0.2 is the tensile yield limit of the material, MPa; σ b is the ultimate tensile strength of the material, MPa; τ b is the ultimate shear strength of the material, MPa; The (5.7) is specifically: The web provides support for the reinforcement in the plane, and the reinforcement does not suffer from overall instability failure. Then the reinforcement compression failure calculation is checked: Pressure loss safety margin: Where: b is the length of the edge strip, mm; t is the thickness of the edge strip, mm; c is the boundary correction coefficient; E is the elastic modulus of the material, MPa; σ cy is the compressive yield strength of the material, MPa; σ cc is the pressure loss stress, MPa; σ x is the working compressive stress, MPa.

11. The rib through hole optimization design method according to claim 1, characterized in that: The step 6 is specifically as follows: (6.1) Design dimension requirements for structural holes: The thickness of the reinforcement should be no less than 1.5 mm for minimum machining thickness; (6.2) Stringer tolerance is the total tolerance after considering stringer positioning error, thickness tolerance and R angle tolerance; (6.3) The flange and reinforcement of the parts are designed on one side of the web, and the ribs are designed to be perpendicular to the web as much as possible. If it is not possible to design it to be perpendicular, a constant angle is used; (6.4) Select the thickness and height ratio p of the reinforcement and flange of aluminum alloy parts as required. For high-speed milling, p≤1:20, and the web thickness t≥1.2mm; For non-high-speed milling, p≤1:10, and the web thickness t≥1.8mm.

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