The use of the J V parameter in welded joints: Stress analysis and fatigue assessment

Abstract

This paper investigates the use of the J V parameter, a path-independent integral, for the evaluation of the elastic local stress parameters in welded details and for the estimation of their fatigue life. First, the stress intensity factors (SIF) of an embedded crack lying along the bisector of a sharp V-notch is calculated by means of the J V without modelling the crack and by keeping the same external load and boundary conditions of the cracked model. Furthermore, the notch stress intensity factors (NSIFs) of the welds can be calculated after a post processing procedure of FE analysis with the advantage of using coarse meshes. Second, a correlation between the fatigue life of welded details and the J V parameter is shown. In fact, careful analysis of the fracture surface of fillet welds taken from literature and of new fatigued joints indicates that the first stage of fatigue crack propagation follows the bisector line of the local V-notch as only mode I would be present. Therefore, since the J V evaluated on a suitable integration path represents the SIF of an embedded crack lying along the bisector, the J V is used for the fatigue life assessment of welded details. The critical characteristic length of a suitable integration path for welded joints made of steel and aluminium alloys has been calculated. These critical characteristic lengths were used for the evaluation of two fatigue general scatter bands, mainly based on fatigue data of non-load-carrying cruciform joints characterised by a V-notch angle of 135°. Further, fatigue life data of steel and aluminium alloy welded connections have also been investigated when both mode I and mode II loadings are singular.