Failure cause analysis of welded joints

Failure of welded structures/machine components lead to various direct losses such as the cost of repair work, the cost of the work to prevent future failure and accident compensation, and indirect losses such as decrease in production and a damage to company's image. Joints being the weakest elements in any structure/machine are likely to fail first. It is, therefore, imperative to understand the failure of these joints. Understanding a failure occurrence and its propagation will lead to a better appreciation of welded joints from reliability point of view. It may be possible that a few cause events or failure causes may be crucial and could be minimized at design or fabrication stage leading to failure minimization of such joints. In this paper, a procedure based on digraph modeling and matrix approach is suggested for failure analysis of welded joints. The failure logic digraph for welded joint (WLFLD) is defined which considers contributing cause events and their interrelations. The digraph is analysed using connection and reachability matrices. Welded joint failure connection matrix (WJFCM) is obtained for the welded joint failure logic digraph and welded joint failure reachability matrix (WJFRM) is derived from it which helps in identifying the stage relationship among various cause events and evaluate the importance of the cause events for the failure modes. It, therefore, provides direction for appropriate action for minimization of failure mode thus improving the reliability of the joints.