Constant Amplitude and Variable Load History Fatigue Test Results and Predictions for Cruciform Weld

Cruciform welds were fatigue tested under constant amplitude axial load and variable load history conditions.Fatigue cracks generally initiate at the root but may initiate at the toe if higher bending stresses are induced by joint distortion.This study attempts to interrelate the parameters that influence the fatigue life of weldments and to predict accurately the fatigue lives of complex weldments using an initiation-propagation model developed by author.The model for the predictions assumes that the fatigue crack initiation period(N_I) is the number of cycles for the initiation of a fatigue crack and its early growth and coalescence into a dominant fatigue crack.N_I is estimated using strain-controlled fatigue data and the Palmgren-Miner linear damage cumulation rule through Knowledge of the local stress and strain response at the tip of the notch.The fatigue crack propagation period(N_I) is estimated using fatigue propagation data and the power law of Paris.The fatigue test results were compared with predictions made using the analytical model and good agreement between experiment and theory was observed.Moreover,the study indicated that the fatigue crack initiation period is the main portion of the total fatigue life at long lives.