Study On Fatigue Property Of Automobile Sheets

Fatigue fracture damage is the most common phenomenon in engineering,especially in the vehicle industry,the fatigue damage is the main form of structure and component failure in cars,fatigue damage in automobile industry can cause a lot of personal and property losses.Automobile sheet suffer fatigue damage under cyclic loading when car runs,analyze fatigue life and damage mechanism of automobile sheet under cyclic loading which is of great importance to the safety design of automobile structure.In this paper,experiment study of fatigue property was conducted on two kinds of automobile sheet.The research contents are as follows:In the first aspect,uniaxial tensile test and high & low cycle fatigue tests are conducted on specimen with equal-section area made of SAPH440 steel,uniaxial tensile stress-strain curve and cyclic stress-strain curve are obtained.High cycle fatigue curve(S-N curve),low cycle fatigue curve(E-N curve)and relevant fatigue parameters are obtained after calculation.Preliminary mechanism of fatigue crack propagation is discussed through fracture morphology analysis.Second aspect: Fatigue crack propagation rate experimental with stress ratio R equal 0.1,0.3,0.5 are conducted on compact tension specimen made of SAPH440.Crack propagation rate is described with Paris law,results show that crack propagation rate increased with the increase of stress ratio under equal stress intensity factor amplitude.Third aspect: Relevant fixtures are designed and made to conduct fatigue crack propagation rate experiment of DP780 thin sheet under mixed loading.Effect of torsional load(controlled by torsional angle)on fatigue crack propagation was discussed,torsion loading effect reduced crack propagation rate,increased fatigue crack propagation life.?and ? mixed mode crack propagation rate experiment was conducted.