Random Vibration Fatigue Life Prediction Of Spot-welded Structure Based On Finite Element Analysis

With the vigorous development of the automotive industry,high-speed car and lightweight have become the main tone of the industry,but it has brought many problems,vibration fatigue damage is one of the problems.As the road surface is uneven,the car driving on the road will be affected by the random load.This will not only affect the comfort of the guests riding the car,but also cause the car body spot-welded structure fatigue damage,affect the using life of the car.Therefore,it is very important to study the fatigue damage and life of the spot-welded structure under random vibration environment.In this paper,the single spot-welded samples made of ST 12 low-carbon steel plate are used as the research object.The fatigue damage and life span of the spot-welded joints under random vibration are analyzed from the experimental and finite element simulation.The paper mainly studies the following aspects:1.The Dirlik method and the NarrowBand method are used to estimate the random vibration fatigue life of spot-welded and the influence of different acceleration power spectrum on the fatigue life of the vibration of the spot welded structure is analyzed.The finite element model of the spot-welded structure is established by using Hypermesh software.Based on the modal test data of spot-welded structure,the solid finite element model of the spot-welded structure is modified.Based on the ANSYS Workbench software and nCode software,the fatigue life estimation of the spot-welded structure under different acceleration power spectrum is carried out by combining the empirical formula of the Dirlik rainstorm amplitude probability function and the NarrowBand method.2.Based on the simplified finite element model of the spot-welded,the difference between the random vibration fatigue life estimated by the same acceleration power spectrum and the random vibration life estimated by the solid model is analyzed.Construct finite element simplified model of spot-welded structure by using shell element and beam element.ANSYS Workbench software and nCode software are used to simulate,analyze and compare modal frequency difference between the finite element model of spot-welded established by shell beam element and the finite element model of spot-welded established by solid element.And compare the difference of two models between the random vibration fatigue life estimated under the same acceleration power spectrum.3.Based on the variation of the natural frequency under the crack initiation and expansion of the spot welded structure under random vibration,the cross-sectional area of the crack propagation is defined as the damage parameters to study random vibration life.Under the excitation of random vibration,the fatigue failure of the spot-welded structure is accompanied by the initiation and expansion of the crack.Based on the modal analysis of ANSYS Workbench,the relationship between the natural frequency variation and the crack propagation cross section was studied under the crack initiation and expansion of the spot-welded structure under random vibration.Use the nCode software to estimate the relationship between the residual life of the current random vibration and the propagation cross section of the crack initiation under the crack propagation,and the relationship between the lifetime loss of the random vibration and the propagation cross section of the crack initiation under the crack propagation.