The use of the JV parameter in welded joints: stress analysis and fatigue assessment

This paper investigates the use of the JV parameter, a crack 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 JV parameter 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. Both SIF and NSIF can be evaluated with the advantage of using coarse meshes in the FE analysis. Second, a correlation between the fatigue life of welded details and the JV parameter is shown. In fact, a 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 JV parameter represents the SIF of an embedded crack lying along the bisector, the JV is used for the fatigue life assessment of welded details. The critical size of JV for welded joints made of steel and aluminium alloys has been calculated. These critical radii 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 singula