TWI Industrial Member Report Summary 212/1983
By R M Rivett and G Slater
The work covered in this report details the development of rational dynamic 'type tests' for determining the quality of resistance spot welds in low carbon and high strength steels. The effect of specimen width on the shear fatigue properties of welds in 2 and 4mm low carbon and HSLA [ high strength low alloy] steels has been studied. The specimen width significantly influenced the test results with fatigue endurance increasing with specimen width. An empirical formula has been proposed which links specimen width and load for a fatigue life of 106 cycles. The results of this analysis suggest that minimum widths of 120 and 175mm are required for testing welds in 2 and 4mm steels respectively, if the test results are to be independent of specimen width. The effect of specimen width and restraint on the shear impact properties of welds in 2 and 4mm low car on steels was studied for impact velocities in the range 1-14m/sec. It was established that there was a difference of up to x2 obtained in the failure energy and failure forces of unrestricted samples compared to results obtained using restricted samples. This difference in results decreased with increasing specimen width such that eventually there would be no difference in the results obtained using the two test techniques. It was recommended that the specimen widths given in the IIW document for the static shear testing of welds (Doc. III-616-79) be employed for impact shear welds using unrestricted samples. The influence of specimen width on the impact cross-tension properties of welds in 2 and 4mm low carbon and HSLA steels was examined. The impact failure energy was directly proportional to specimen widths in the range 30-80mm. In contrast, the failure force was independent of specimen width. Consequently, it was not possible to suggest a critical specimen width and therefore the figures recommended by the IIW for the static cross-tension testing (Doc. III-615-79) should be employed.