Optimum Design of Spot Weld Joints and Nondestructive Measurement of Weld Quality for Light Weight Structures

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Resistance spot welding has been widely used for the construction of thin sheet metal structures. In these structures, the spot welds are distributed in various direction and with different intervals, which are determined by the empirical data. However, the number and location of spot joints have significant technical and economical effects in the design and manufacturing processes. Especially, the assessment of strength is an important tool for the optimum design of spot welded structures. Nevertheless, the assessment of strength for multi-spot welded structures is not always established even in the static loading.In order to develop the assessment of strength and the method for optimum design of spot welded structures, in this study, the stress-strain analysis and the tensile-shear test were performed on three types of specimens, which are constitutive elements of spot welded structures. In addition, a nondestructive measurement was tried to develop their in-process assurance of stre … More ngth.According to the stress-strain analyses, the location of spot joints affects the stress distribution which is related to the axial force and bending moment induced in the tensile-shear test. In the specimens with spot welds in the transverse direction to the applied force, no mutual effect appeared in the stress distribution, from which it was shown that the strength was given by the summation of strength of constitutive spot welds. In the specimens with spot welds in the parallel direction to applied force, on the other hand, large difference appeared in the stress distribution between outer and inner surfaces. This difference is related to the bending moment and affects the strength of specimen. It was shown from the comparison of strength with single spot welds that this effect was given by the generalized curve, which was peculiar to the materials and was independent of the plate thickness and width. The experimental results showed that the strength of specimens was estimated by this generalized curve. In the specimen with spot welds in the oblique direction, the strength was shown to be given by the combined effect of two specimens above mentioned. The assessment of strength based on three types of specimens was available to the optimum design for the determination of number and location of spot welds. The displacement of electrode was clarified to be a useful in-process measurement for the nondestructive evaluation of weld size and for the detection of expulsion. Less