S-N and IEFM combined fatigue life analysis for welded structures

According to the evolution of fatigue cracks in welded structures, the fatigue life of welded structures was defined as the sum of crack initiation life Ni and crack propagation life N_p, and the SN curve and fracture mechanics combined with fatigue life evaluating method was proposed. Equivalent structural stress method and the lower 99% boundary of master SN curve were utilized to evaluate the crack initiation life, and cracks at the end of the initiation stage was regarded as semi-elliptical surface crack. Paris Equation and the stress intensity factor range of semi-elliptical surface cracks were utilized to evaluate the crack propagation life. Fatigue test data of 5 crane runway girder specimens from a reference were utilized to the comparisons and Validation investigation. Result showed that equivalent structural stress can characterize the crack initiation state of complex welded structures well, and there is a good consistency between the calculating fatigue life and the test life.