It is very important to evaluate the fatigue life for multiaxial loading because almost all structures are subjected to multiaxial loading rather than uniaxial loading. In this regards, a study on development of the life prediction system for fatigue crack initiation under multiaxial loadings is performed. For this study, several multiaxial fatigue life prediction theories proposed so far, like maximum principal strain theory, maximum shear strain theory, maximum distortion energy theory, Sines model, Brown and Miller theory, Lohr and Ellison theory, Socie model, are used. And, a engine mount bracket of passenger car and three road load histories measured in proving ground are used for validation of this study. Also, static finite element analysis using MSC/NASTRAN for Windows is carried out to investigate the location of highest stress fields and to get data on stresses and strains in that loaction. Uniaxial equivalent strain histories for each theories are obtained by means of computer program coded by using the C language, which is based on the life prediction equations of proposed theries and finite element analysis data. Finally, these obtained uniaxial equivalent histories are used in fatigue life prediction software FatiCis Ver.1.0 based on uniaxial strain history, which has been developed by preceding researchers of Strength Design and Database Laboratory, to estimate fatigue crack initiation life under multiaxial loading. The estimated life results are evaluated and compared with each other. And the results are also compared with the result by using the P/FATIGUE commercial software. The predicted fatigue life results of maximum shear strain theory(Tresca theory), Sines model and Socie model are most conservative and are consistent well with P/FATIGUE result considerably.
It is thought that this exemplary procedure is quite useful in the stage of preliminary fatigue design and evaluation for vehicle components.