CN113051784A

CN113051784A - Method for judging fatigue dangerous part of lug hole edge

Info

Publication number: CN113051784A
Application number: CN201911387422.8A
Authority: CN
Inventors: 彭航; 张彦军; 赵天娇; 王�锋
Original assignee: Xian Aircraft Design and Research Institute of AVIC
Current assignee: Xian Aircraft Design and Research Institute of AVIC
Priority date: 2019-12-27
Filing date: 2019-12-27
Publication date: 2021-06-29

Abstract

A method for judging fatigue dangerous parts at the edge of a lug hole is characterized in that the structural parameters of the lug are known, and a finite element model and a local cylindrical coordinate system are established for the lug structure; converting the stress value of the lug structure in the global coordinate system into a tangential stress value under a cylindrical coordinate system, and obtaining the tangential stress of each grid unit at the edge of the lug hole through finite element analysis; and selecting the position where the lug hole is most easy to crack according to the magnitude of the tangential stress value, wherein the position is the fatigue dangerous part of the lug hole edge under the load condition.

Description

Method for judging fatigue dangerous part of lug hole edge

Technical Field

The invention belongs to the field of design of airplane structural strength, and relates to a method for judging dangerous positions of lug hole edges in the field of design of airplane structural strength.

Background

The lug structure is a common connecting structure in an airplane structure and is also a key part for fatigue and damage tolerance of the airplane structure, and when the damage tolerance of the lug structure is analyzed, the crack initiation position is a key factor for crack propagation analysis of the lug structure. The cracking position of the lug hole edge depends on the maximum stress of the hole edge, and the maximum stress position of the lug hole edge is directly determined by adopting which criterion to calculate the stress of the hole edge, so that the cracking position for judging the lug crack is determined.

At present, the damage tolerance analysis of the ear is usually focused on the analysis under the condition that the straight ear and the symmetrical oblique ear are subjected to the straight load, the maximum Mises stress is taken as a cracking criterion to determine the most possible cracking position, and the maximum Mises stress is taken as the cracking criterion to be no longer applicable under the condition that the straight ear is subjected to the oblique load and the oblique ear is subjected to the straight load and the oblique load under other oblique cutting angles, so that the determination of the cracking criterion suitable for determining the cracking position of the ear under the condition that different ear types are subjected to different directional loads is the core for solving the problem.

Disclosure of Invention

The method aims to accurately judge the cracking position of the lug structure hole edge under the action of the fatigue load, and provides a method for judging the fatigue dangerous part of the lug structure hole edge.

A method for judging fatigue dangerous parts at the edge of an ear hole is known, and the method is characterized by comprising the following steps: 1) carrying out grid division on the lug structure in finite element analysis software, establishing a finite element model, and establishing a local cylindrical coordinate system at the center of a lug hole; 2) applying boundary conditions and loads to the lug structure in finite element analysis software to obtain a stress value of the lug structure under the loads in a global coordinate system; 3) converting the stress value of the lug structure in the global coordinate system into a tangential stress value under a cylindrical coordinate system, and obtaining the tangential stress of each grid unit at the edge of the lug hole through finite element analysis; 3) and sequencing the tangential stress of the lug hole edges, wherein the lug hole edges corresponding to the grid units with larger stress values have higher possibility of cracking, and selecting the position where the lug holes are most prone to cracking according to the magnitude of the tangential stress values, wherein the position is the fatigue dangerous part of the lug hole edges under the load condition.

The beneficial effect of this application lies in: the method is simple and reliable, easy to popularize and calculate, and suitable for distinguishing the fatigue dangerous parts of the lug hole edge comprising the straight lugs, the symmetrical oblique lugs and the asymmetrical oblique lugs.

The present application is described in further detail below with reference to the accompanying drawings of embodiments.

Drawings

Fig. 1 is a schematic view of a tab structure.

Fig. 2 is a schematic diagram of a tab hole stress coordinate transformation.

Fig. 3 is a schematic diagram of a finite element model of a tab structure.

Figure 4 is a graph of the stress distribution at the edge of the tab hole for a tab construction under a 0 ° load, showing the parameters used in the practice.

Figure 5 is a graph of the stress distribution at the edge of the tab hole for a tab construction under a 45 ° load, showing the parameters used in the practice.

Figure 6 is a graph of the stress distribution at the edge of the tab hole for a 90 ° load for the tab construction, showing the parameters used in the practice.

Figure 7 is a graph of the stress distribution at the edge of the straight tab hole under a 135 ° load for the tab construction showing the parameters used in the practice.

Figure 8 is a graph of the stress distribution at the edge of a straight tab hole under a 180 ° load for a tab construction showing the parameters used in the practice.

The numbering in the figures illustrates: 1 lug structure and 2 lug holes

DETAILED DESCRIPTION OF EMBODIMENT (S) OF INVENTION

Referring to the attached drawings, the method for distinguishing the fatigue dangerous part at the edge of the lug hole of the application, knowing the structural parameters of the lug, is characterized by comprising the following steps: 1) carrying out grid division on the lug structure 1 in finite element analysis software, establishing a finite element model, dividing the lug hole edge into not less than 360 grid units in the finite element model during implementation, and establishing a local cylindrical coordinate system at the center of the lug hole 2; 2) applying boundary conditions and loads to the lug structure 1 in finite element analysis software to obtain a stress value of the lug structure 1 under the loads in a global coordinate system, wherein the tangential stress of each grid unit at the edge of the lug hole is a tangential component of the stress on the hole wall; 3) converting the stress value of the lug structure 1 in the global coordinate system into a tangential stress value under a cylindrical coordinate system, and obtaining the tangential stress of each grid unit at the edge of the lug hole through finite element analysis; 3) and sequencing the tangential stress of the lug hole edges, wherein the lug hole edges corresponding to the grid units with larger stress values have higher possibility of cracking, and selecting the position where the lug holes 2 are most easy to crack according to the magnitude of the tangential stress values, wherein the position is the fatigue dangerous part of the lug hole edges under the load condition.

According to the above method for determining a fatigue risk site on the ear hole edge, the embodiment provided by the present application is an example of the ear structure in fig. 1, and the fatigue risk sites on the hole edge that are subjected to loads of 0 °, 45 °, 90 °, 135 °, and 180 ° (counterclockwise along the axis of symmetry of the ear) are respectively shown in table one determination and comparison results when the outer/inner diameter ratio Ro/Ri of the ear hole 2 is 1.5, 2.0, 2.5, and 3.0, respectively.

In table one, according to the method for determining a fatigue dangerous part at an ear hole edge of the present application, a first fatigue dangerous part and a second fatigue dangerous part at the ear hole edge, which are obtained by an ear hole under different angular loads with different outer diameters and inner diameters, are more accurate and reliable in result compared with the existing maximum Mises stress position, and the method is simple.

In another embodiment, the distribution of the maximum Mises stress and the maximum shear stress (tangent stress) of the ear configuration parameters in the load directions of 0 °, 45 °, 90 °, 135 ° and 180 ° is shown in fig. 4 to 8, respectively, taking as an example that the ratio Ro/Ri of the outer diameter to the inner diameter of the ear hole 2 is 2.5.

FIG. 4 reflects the maximum Mises stress and maximum shear stress (tangent stress) distribution of the ear outer diameter ratio Ro/Ri of 2.5 in the 0 load direction;

FIG. 5 reflects the maximum Mises stress and maximum shear stress (tangent stress) distribution of the ear outer diameter ratio Ro/Ri of 2.5 in the 45 load direction;

FIG. 6 reflects the maximum Mises stress and maximum shear stress (tangent stress) distribution of the ear outer diameter ratio Ro/Ri of 2.5 in the 90 load direction;

FIG. 7 reflects the maximum Mises stress and maximum shear stress (tangent stress) distribution of the ear outer diameter ratio Ro/Ri of 2.5 in the 135 load direction;

fig. 8 reflects the maximum Mises stress and maximum shear stress (tangent stress) distribution of the ear outer inner diameter ratio Ro/Ri 2.5 in the 180 ° load direction.

Table one: judging the comparison result

Claims

1. A method for judging fatigue dangerous parts at the edge of an ear hole is known, and the method is characterized by comprising the following steps: 1) carrying out grid division on the lug structure in finite element analysis software, establishing a finite element model, and establishing a local cylindrical coordinate system at the center of a lug hole; 2) applying boundary conditions and loads to the lug structure in finite element analysis software to obtain a stress value of the lug structure under the loads in a global coordinate system; 3) converting the stress value of the lug structure in the global coordinate system into a tangential stress value under a cylindrical coordinate system, and obtaining the tangential stress of each grid unit at the edge of the lug hole through finite element analysis; 3) and sequencing the tangential stress of the lug hole edges, wherein the lug hole edges corresponding to the grid units with larger stress values have higher possibility of cracking, and selecting the position where the lug holes are most prone to cracking according to the magnitude of the tangential stress values, wherein the position is the fatigue dangerous part of the lug hole edges under the load condition.

2. The method for determining a fatigue risk portion of a tab hole edge as claimed in claim 1, wherein in the step 1), the tab hole edge is divided into not less than 360 mesh cells.

3. The method for determining the fatigue risk portion of the tab hole edge as claimed in claim 1, wherein in step 2), the tangential stress of each grid cell of the tab hole edge is a tangential component of the stress on the hole wall.

4. The method for determining a fatigue risk portion at the edge of a tab hole according to claim 1, wherein the tab includes a straight tab, a symmetrical oblique tab, and an asymmetrical oblique tab.