ESTIMATION AND FINITE ELEMENT ANALYSIS OF STRESS INTENSITY FACTORS IN SPOT-WELDED STRUCTURE

Abstract

Resistance spot Welding is a predominant method for sheet metal joining process in automobile and aerospace industries. These spot welds may be subjected to fatigue. Stress intensity factors (SIF) are used to predict fatigue crack propagation life of resistance spot welds. An essential part of the solution of a fracture problem in Linear Elastic Fracture Mechanics (LEFM) is the establishment of stress intensity factor for the crack problem under consideration. Actually stress intensity factor determines the stress field around the crack tip and provides energy available to propagate the crack. In RSW, notch at nugget edge acts as an initial crack. Actually, in RSW stress intensity factor and `J' integral are functions of sheet thickness and nugget diameter. The equations of stress intensity factor and `J' integral are derived on the basis of simple bending theory. Two types of samples are taken i.e. Tensile-shear (TS) and Modified coach-peel (MCP). In TS membrane load dominates whereas in MCP bending load dominates. Stress intensity factors and `J' integral (Crack initiation energy) are calculated. It is observed that KI, Kn and `J'integral are most affected by welding current, weld time and least affected by electrode force. As sheet thickness is increased, K1, K11 and `J'integral value increases. In case of MCP spot-welds, the loads comes less in comparison to tensile shear specimens. Finite Element analysis has been also done to calculate the stress intensity factors