CN116186880A - Method for calculating and analyzing fatigue life of welding spot of aircraft structure - Google Patents

Method for calculating and analyzing fatigue life of welding spot of aircraft structure Download PDF

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CN116186880A
CN116186880A CN202211537983.3A CN202211537983A CN116186880A CN 116186880 A CN116186880 A CN 116186880A CN 202211537983 A CN202211537983 A CN 202211537983A CN 116186880 A CN116186880 A CN 116186880A
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邱春图
隋福成
解放
于淼
张宝才
单兴业
李金明
邓永先
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Shenyang Aircraft Design and Research Institute Aviation Industry of China AVIC
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Abstract

The invention belongs to the field of calculation and analysis of fatigue life of an airplane structure, and relates to a calculation and analysis method of fatigue life of welding spots of an airplane structure, which comprises the following steps of S1: calculating the structural stress of the welded structure by a finite element method; taking the main stress with the maximum absolute value of the structural stress as a damage parameter; step S2: based on the damage parameters, acquiring S-N curves of a weld core and a base metal through a material fatigue performance test; step S3: determining a stress spectrum of the welded structure based on the S-N curve; step S4: and acquiring the damage and service life distribution conditions of all the welding structures based on the stress spectrum. According to the method and the device, the fatigue life of the welding spots can be predicted by calculation in the initial stage of design, the distribution condition of the welding spots on the whole structure is known, and therefore the number and the distribution mode of the welding spots in the actual process can be guided to be reasonably adjusted, the fatigue performance of the aircraft structure is improved, and the manufacturing cost can be reduced.

Description

Method for calculating and analyzing fatigue life of welding spot of aircraft structure
Technical Field
The invention belongs to the field of calculation and analysis of fatigue life of an airplane structure, and relates to a calculation and analysis method of fatigue life of welding spots of an airplane structure.
Background
Spot welding is widely applied to the manufacturing process of aircraft parts as an efficient connection mode, so that the number of rivets or screw connections is reduced to a great extent, and meanwhile, certain structural weight is also reduced. However, due to the nature of the weld, numerous tests have also shown that: compared with the base metal, the welded connection can greatly reduce the fatigue failure resistance of the whole structure, so that the structure connected by spot welding often fails and breaks at the welded part during service, thereby causing accidents. Therefore, if the fatigue life of the welding spots can be predicted by calculation in the initial stage of design, the distribution situation of the welding spots on the whole structure is known, so that the reasonable adjustment of the number and distribution modes of the welding spots in the actual process can be guided, the fatigue performance of the structure can be improved, and the manufacturing cost can be reduced. However, there is currently no very effective method for analyzing the fatigue life of a solder joint.
Disclosure of Invention
In order to solve the problems, the application provides a method for calculating and analyzing the fatigue life of welding spots of an aircraft structure,
step S1: calculating the structural stress of the welded structure by a finite element method; taking the main stress with the maximum absolute value of the structural stress as a damage parameter;
step S2: based on the damage parameters, acquiring S-N curves of a weld core and a base metal through a material fatigue performance test;
step S3: determining a stress spectrum of the welded structure based on the S-N curve;
step S4: and acquiring the damage and service life distribution conditions of all the welding structures based on the stress spectrum.
Preferably, the method for calculating the structural stress specifically comprises the following steps: and simulating the welding core of the welding structure through the equivalent rigid beam unit, and calculating the structural stress around the welding core and the connecting plate through calculating the force and the moment transmitted by the equivalent rigid beam unit.
Preferably, the method for calculating the force and moment transferred by the equivalent rigid beam unit specifically comprises the following steps: taking a plurality of points on the equivalent rigid beam unit as calculation points: and taking two end points of the equivalent rigid beam unit as a calculation point 1 and a calculation point 2, taking the intersection point of two structural interfaces welded by a welding structure and the equivalent rigid beam unit as a calculation point 3, and respectively calculating the axial force and the bending moment in the three-phase mutually perpendicular directions of the calculation point 1, the calculation point 2 and the calculation point 3.
Preferably, the method for calculating the structural stress around the weld core and the connecting plate comprises the following steps: and calculating the structural stress of the inner surfaces of the two parts welded by the welding structure and the structural stress of the welding core at the joint point between the welding core and the two parts based on the force and the moment transmitted by the equivalent rigid beam unit.
Preferably, the specific method for determining the stress spectrum comprises the following steps:
and calculating the effective stress history of each calculation point by a quasi-static method, and then determining a stress spectrum by a rain flow cycle count.
Preferably, the fatigue damage is calculated by the damage accumulation rule to obtain the damage and life distribution of all welded structures.
The advantages of the present application include: a welding spot fatigue life calculation model and an analysis method suitable for engineering application are provided. The fatigue life of the welding spots can be predicted by calculation in the initial stage of design, and the distribution condition of the welding spots on the whole structure is known, so that the number and distribution modes of the welding spots in the actual process can be guided to be reasonably adjusted, the fatigue performance of the aircraft structure is improved, and the manufacturing cost can be reduced. By the method, the welding spot damage and service life calculation analysis of a certain airplane structure are finished for the first time in China.
Drawings
FIG. 1 is a schematic illustration of a typical solder joint connection;
FIG. 2 is an S-N curve of a nugget and a base material.
Detailed Description
For the purposes, technical solutions and advantages of the present application, the following describes the technical solutions in the embodiments of the present application in more detail with reference to the drawings in the embodiments of the present application. In the drawings, the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The described embodiments are some, but not all, of the embodiments of the present application. The embodiments described below by referring to the drawings are exemplary and intended for the purpose of explaining the present application and are not to be construed as limiting the present application. All other embodiments, based on the embodiments herein, which would be apparent to one of ordinary skill in the art without undue burden are within the scope of the present application. Embodiments of the present application will be described in detail below with reference to the accompanying drawings.
The application provides a calculation and analysis method for the fatigue life of welding spots of an aircraft structure, and an example of calculation for the service life of a welding structure of a certain high-mobility aircraft is given below:
step S1: calculating the structural stress of the welding structure of the aircraft by a finite element method, and calculating the structural stress of the welding structure by a finite element method; taking the main stress with the maximum absolute value of the structural stress as a damage parameter; the calculation method of the structural stress specifically comprises the following steps: simulating a welding core of a welding structure through the equivalent rigid beam unit, and calculating structural stress around the welding core and the connecting plate through calculating force and moment transmitted by the equivalent rigid beam unit; the method for calculating the force and moment transferred by the equivalent rigid beam unit specifically comprises the following steps: taking a plurality of points on the equivalent rigid beam unit as calculation points: taking two end points of the equivalent rigid beam unit as a calculation point 1 and a calculation point 2, taking the intersection point of two structural interfaces welded by a welding structure and the equivalent rigid beam unit as a calculation point 3, and respectively calculating the axial force and bending moment in the three-phase mutually perpendicular directions of the calculation point 1, the calculation point 2 and the calculation point 3; the method for calculating the structural stress around the welding core and the connecting plate comprises the following steps: and calculating the structural stress of the inner surfaces of the two parts welded by the welding structure and the structural stress of the welding core at the joint point between the welding core and the two parts based on the force and the moment transmitted by the equivalent rigid beam unit.
Referring to fig. 1, wherein the welding parts are respectively a plate 1 and a plate 2, and a calculation point 1 calculates a point 2 and a calculation point 3 is respectively a point 1, a point 2 and a point 3 in the diagram; the specific implementation mode of the step S1 is as follows:
when the structural stress is calculated by a finite element method, an equivalent rigid beam unit simulating a welding core is adopted, the length of the rigid beam unit simulating the welding core is 0.5 (s1+s2), wherein s1 and s2 are the thicknesses of a plate 1 and a plate 2 respectively, points 1 and 2 are the endpoints of the beam unit on two layers of shell units respectively, and point 3 is the intersection point of the central line of the welding core and the connecting surface of the two plates. The forces and moments transferred by the equivalent rigid beam units are used to calculate structural stresses around the weld nuggets and the connecting plates, a detailed finite element model of the welded structure is established, the structural stresses are calculated by a finite element method, the axial forces Fx, fy, fz and x, y, z of the points 1, 2 and 3 are extracted from the calculated data result file, and the bending moments Mx, my and Mz of the directions of z are calculated according to the structural stresses of the inner surfaces of the plates 1 and 2 and the weld nuggets at the junction points with the two plates (the structural stresses are calculated by taking a point every 15 degrees along the circumferential direction of the weld nuggets). The forces and moments at points 1 and 2 are those applied to the plate by the weld nugget, while the forces and moments at point 3 are those applied to the lower plate by the upper plate. The structural stress is calculated as follows:
σ v1 ＝-σ max (F x1 )cosθ-σ max (F y1 )sinθ+σ(F z1 )+σ max (M x1 )sinθ
-σ max (M y1 )cosθ(1)
wherein: d is the diameter of the weld core, sigma v1 Is equivalent stress of point 1, F x1 Is the axial force F of point 1 in the x direction y1 Axial force F of Point 1 in the y-direction z1 The axial direction of point 1 in the z-directionForce, M x1 Moment of bending M in x-direction at point 1 y1 Bending moment of point 1 in y direction; the stress calculation formula described above takes into account empirical factors obtained through extensive experimentation, where λ=0.6 s 0.5 (as compensation for bending stress gradient effects);
σ max (F x1 )＝F x1 /πds 1 ；σ max (F y1 )＝F y1 /πds 1 ；σ(F z1 )＝λ(1.744F z1 /s 1 2 ),
when F z1 At > 0; sigma (F) z1 ) =0, when F z1 At less than or equal to 0, only the tensile component in the axial force of the welding core causes damage, and simultaneously:
σ max (M x1 )＝λ(1.872M x1 /ds 1 2 )；σ max (M y1 )＝(1.872M y1 /ds 1 2 )。
the structural stress calculation at point 2 is similar to that at point 1.
The absolute maximum principal stress is used as a damage parameter for calculating the structural stress of the point 3, and is as follows:
τ＝τ max (F x3 )sin 2 θ+τ max (F y3 )cos 2 θ (2)
σ＝σ(F z3 )cosθ+σ max (N X3 )sinθ-σ max (M y3 )cosθ (3)
wherein:
τ max (F x3 )＝16F x3 /(3πd 2 )；τ max (F y3 )＝16F y3 /(3πd 2 )；σ(F z3 )＝4F z3 /(πd 2 ) When F z3 At > 0;
σ(F z3 ) =0, when Fz3 is less than or equal to 0. Sigma (sigma) max (M x3 )＝32M x3 /(πd 3 )；
σ max (M y3 )＝32M y3 /(πd 3 )；
τ is the shear stress, F x3 Is the axial force F of point 3 in the x direction y3 Axial force F of point 3 in y-direction z3 Axial force of point 3 in z direction, M x3 Bending moment of point 3 in x direction, M y3 Bending moment of point 3 in y direction;
the principal in-plane stress can be found from the shear and normal stresses in the nugget:
Figure BDA0003976092580000051
the principal stress with the largest absolute value of stress in the formula (4) is taken as the damage parameter
Step S2: based on the damage parameters, acquiring S-N curves of a weld core and a base metal through a material fatigue performance test;
step S3: determining a stress spectrum of the welded structure based on the S-N curve;
the specific implementation mode is as follows: for example, a basic spectrum block of the random spectrum of the aircraft consists of 15 typical subjects, 142 total take-off and landing, representing 186.52 flight hours. To ensure the integrity of the basic spectrum blocks, a spectrum with 13258 flight hours as one complete cycle is constructed, comprising 73 basic spectrum blocks, with a load cycle number of 237439.
And extracting complete load circulation by a rain flow counting method, and according to a principle and a method for selecting a standard constant-amplitude load circulation, selecting peak load of the equivalent constant-amplitude load circulation by R=0.1 of the equivalent constant-amplitude load stress ratio R=0.1 of the machine body structure, and calculating effective stress histories of each calculation point by a quasi-static method to determine the stress of the welding structure corresponding to the peak load up and down so as to form a stress spectrum of the welding structure.
The stress level corresponding to 1g overload of the welded structure is 57.53MPa (obtained by calculation), so the maximum stress sigma of equivalent constant-amplitude load max ＝137.62MPa。
Step S4: and acquiring the damage and service life distribution conditions of all the welding structures based on the stress spectrum.
The specific implementation manner of the step S4 is as follows:
after structural stresses at the weld core and the connecting plate are calculated according to the above formula, the fatigue characteristics of the weld core and the base material are combined, and then the fatigue damage can be calculated according to Miner damage accumulation rule formula (5). This gives a distribution of all solder joint damage and life.
Figure BDA0003976092580000061
Wherein D is i Damage produced under load of each stage, n i Number of cycles per stage load, N i，f The number of fatigue limit times corresponding to each stage of load.
The life values of the first four dangerous welds and their locations where failure may occur are calculated and output as shown in table 1.
TABLE 1 calculation of weld fatigue damage
Figure BDA0003976092580000062
The application provides a welding spot fatigue life calculation model and an analysis method suitable for engineering application. The fatigue life of the welding spots can be predicted by calculation in the initial stage of design, and the distribution condition of the welding spots on the whole structure is known, so that the number and distribution modes of the welding spots in the actual process can be guided to be reasonably adjusted, the fatigue performance of the aircraft structure is improved, and the manufacturing cost can be reduced. By the method, the welding spot damage and service life calculation analysis of a certain airplane structure are finished for the first time in China.
The foregoing is merely specific embodiments of the present application, but the scope of the present application is not limited thereto, and any changes or substitutions easily conceivable by those skilled in the art within the technical scope of the present application should be covered in the scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims (6)

1. A calculation and analysis method for the fatigue life of welding spots of an aircraft structure is characterized by comprising the following steps of:
step S1: calculating the structural stress of the welded structure by a finite element method; taking the main stress with the maximum absolute value of the structural stress as a damage parameter;
step S2: based on the damage parameters, acquiring S-N curves of a weld core and a base metal through a material fatigue performance test;
step S3: determining a stress spectrum of the welded structure based on the S-N curve;
step S4: and acquiring the damage and service life distribution conditions of all the welding structures based on the stress spectrum.
2. The method for calculating and analyzing the fatigue life of the welding spot of the aircraft structure according to claim 1, wherein the method for calculating the structural stress is specifically as follows: and simulating the welding core of the welding structure through the equivalent rigid beam unit, and calculating the structural stress around the welding core and the connecting plate through calculating the force and the moment transmitted by the equivalent rigid beam unit.
3. The method for calculating and analyzing the fatigue life of welding spots of an aircraft structure according to claim 2, wherein the method for calculating the forces and moments transferred by the equivalent rigid beam unit comprises the following steps: taking a plurality of points on the equivalent rigid beam unit as calculation points: and taking two end points of the equivalent rigid beam unit as a calculation point 1 and a calculation point 2, taking an intersection point of an interface of two parts welded by a welding structure and the equivalent rigid beam unit as a calculation point 3, and respectively calculating axial forces and bending moments in three mutually perpendicular directions of the calculation point 1, the calculation point 2 and the calculation point 3.
4. A method of aircraft structural weld fatigue life calculation analysis as claimed in claim 3, wherein the method of structural stress calculation around the weld nuggets and the connection plates comprises: and calculating the structural stress of the inner surfaces of the two parts welded by the welding structure and the structural stress of the welding core at the joint point between the welding core and the two parts based on the force and the moment transmitted by the equivalent rigid beam unit.
5. The method for calculating and analyzing the fatigue life of the welding spot of the aircraft structure according to claim 3, wherein the specific determining method of the stress spectrum is as follows:
and calculating the effective stress history of each calculation point by a quasi-static method, and then determining a stress spectrum by a rain flow cycle count.
6. A method of analyzing the fatigue life of a weld of an aircraft structure according to claim 3, wherein the fatigue damage is calculated by a damage accumulation algorithm to obtain the damage and life distribution of all welded structures.
CN202211537983.3A 2022-12-01 2022-12-01 Method for calculating and analyzing fatigue life of welding spot of aircraft structure Pending CN116186880A (en)

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