Abstract
In the previous papers [1], authors clarified that the crack generation time, the crack length and the crack propagation speed can be detected by the strain information obtained from a strain gauge bonded on the indentation surface, in the case of single spot-welded joint specimens of tensile-shear type. Thereupon, by developing further this technique, authors have tried to estimate or detect in process the crack generation time, the crack depth, the fatigue life, etc. in the multi-spot-welded structure, when the direction of the main load axis and/or the load type which act in each spot weld are unknown. For this purpose, authors developed a new type strain gauge (Authors call it "SA-gauge"). This SA-gauge has a special gauge pattern in which eight sectorial gauge elements are radially arranged at angle intervals of 45°, and can be bonded on the indentation surface of nearly 5 mm in diameter.
In this paper, the specifications of SA-gauge and the basic experiment results obtained are described as the first step of a research for the prediction method of the fatigue strength and/or life of multi-spot-welded structure using SA-gauge. The specimen material used is mild steel sheet of 0.8 mm in thickness. The test specimens used are three types of single spot-welded joint specimen of tensileshear type, cross-tension type and L-tension type.
