Fatigue check of welded joints based on local deformation measures

Fatigue resistance of welded joints represents an interesting and challenging studying field from a scientific point of view, with valuable and important practical consequences. In the specific, the main target is to establish in general the proper quantitative verification and design procedures, based on theoretical achievements. The actual procedures and standard codes are extremely useful for most engineering applications, in which elevated safety factors have to be used. On the other hand the mechanical behavior of welded material is different from the base metal; the weld bead material has different mechanical characteristics because of microstructural changes and other local effects, due to extremely variable weld toe geometry, resulting in notch effects and coupled with relevant residual stresses not to be ignored. In this work, a brief resume of the principal design methods is primarily reported for the estimation of residual life expectancies of welded joints, leading to different engineering approaches; among them, the method based on local deformations measurements is presented as reliable verification tool, already analyzed and modified by several authors in the past. The local deformation approach has been deeply applied and verified by the authors and the main advantage and characteristics are explained, as well as the present limitations to be observed in the frame of many experimental fatigue testing activities.