Morphological aspects of fatigue crack propagation Part II—effects of stress biaxiality and welding residual stress

Abstract

In order to maintain structural integrity of welded structures, it is of great importance to evaluate the fitness for serviceability of the structural components, in which fatigue cracks are found during in-service inspections. Crack propagation paths are sometimes prerequisite for the proper estimation of fatigue crack propagation, because curved crack paths and sharp crack turning could occur at the intersections of structural members mainly due to stress biaxiality of repeated loads. In order to investigate this fatigue crack-growth behavior, fatigue crack-propagation tests and numerical simulation are carried out under various biaxial stress range ratios. Morphological mode transitions of fatigue failures are observed in experiments and also by computer simulation. Although simulated modes of failures are in fairly good agreement with the experimental results, discrepancies are sometimes observed for the crack-propagation lives. In order to investigate this problem, the welding residual stresses in the test specimens are measured, and the fatigue crack-propagation lives are quantitatively examined in terms of the combined effects of residual stress distribution and crack paths.