On welding residual stresses near fatigue crack tips

Abstract

Residual stresses in steel plates with longitudinal fillet welded gussets have been experimentally determined by means of neutron diffraction. The redistribution of the residual stresses due to fatigue crack growth has been studied. The residual stress fields determined have been related to experimental fatigue strength data in terms of constant amplitude fatigue testing data (S-N data). Further, the fatigue crack region has been characterized by means of metallographic investigations such as micrographs, Vickers hardness measurements and computerized tomography. The presented work is on welded specimens, made of unalloyed fine grained carbon steel, with different fatigue crack lengths. The results of the diffraction measurement show that the initial tensile residual stresses near the weld toe are, caused by phase transformation at low temperatures, below the base material's yield strength. Tensile residual stresses in the order of the yield strength can be found below the material's surface. These areas of high residual stresses move with the propagating crack tip through the specimen during fatigue loading. © (2014) Trans Tech Publications, Switzerland.