Influence of Life Improvement Techniques on Different Steel Grades Under Fatigue Loading

ABSTRACT Different fatigue life improvement techniques were applied to test specimens with a non-load carrying fillet weld. These test specimens were then tested under both constant amplitude and variable amplitude fatigue loading. For the as-welded specimens fatigue lives have been related to weld flaws, mainly cold laps, detected at the fracture surfaces. The size and distribution of cold laps, which are a direct function of plate surface quality, have shown a consistent influence on fatigue lives. TIG-dressing of weld toe region has shown a fatigue life improvement ranging from 60% to 120% of applied stress range. Steel grades with higher yield strength have shown larger improvement than ordinary structural steels. The influence of blast-cleaning on fatigue properties is addressed. Mechanisms of improvement are discussed and X-ray diffraction measurements of initial residual stress distributions and relaxation due to fatigue loading are used to explain part of the life extension obtained. The paper also includes fractographic studies of the broken fatigue specimens.