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The research deals with the effect of welding residual stresses on fatigue crack growth in medium strength low alloy steel weldments. Three kinds of flat specimens have been used—unwelded specimens, specimens with butt perpendicular welds, and specimens with butt longitudinal welds. Residual stress distributions were others in both kinds of welded specimens. All specimens were tested under constant and variable amplitude load with stress ratios R > 0. Forman's equation and Wheeler's model of crack retardation were used for theoretical analysis of fatigue crack growth under constant and variable amplitude load, respectively. The theoretical results were more realistic when effective stress ratio Reff and effective stress intensity range ∇Keff, which compensated for residual stresses, were used. It was found that the tensile residual stresses increased the fatigue crack growth rate and compressive stresses reduced it. The lower the applied load, the higher the residual stress effect. This paper presents both experimental results and an analytical method of fatigue crack growth prediction in steel weldments on the basis of results obtained from parent material properties.
fatigue (materials), crack propagation, residual stresses
Research engineer, Institute of Cranes and Building Machinery, Warsaw Technical University, Warsaw, Poland