Stress Distribution and Fatigue Strength of Multi-Spot Welded Joints (II)

Results of Fatigue Test

Abstract

In the previous paper, stress distribution analyses of single-spot welded joint and multi-spot welded joints arranged in perpendicular to load direction were carried out, under prediction that fatigue strength of spot welded joints corresponds with stress distribution on line including nugget front where fatigue crack may generate.
In this paper, fatigue tests of single-spot welded joint with various specimen widths and/or lap lengths and of multi-spot welded joints with various spot spaces and/or lap lengths were carried out. And, these experimental results were compared with the numerical results obtained from stress distribution analysis of single-and multi-spot welded joints in the previous paper. Main conclusions obtained in this investigation are as follows:
(1) The effects of specimen width and lap length on fatigue strength of single-spot welded joint become clear.
(2) The effects of spot space and lap length on fatigue strength of multi-spot welded joints become clear.
(3) It is experimentally, proved that the effect of spot space on fatigue strength of multi-spot welded joint is equivalent to the effect of specimen width of the same length on fatigue strength of singlespot welded joint.
(4) Moreover, it is found that at fatigue life of 2 × 10⁶ cycles dependency of fatigue strength on specimen width or spot space and lap length obtained in these experiments correspond very well with that obtained from stress distribution analysis, although at fatigue life of 1 × 10⁵ cycles do not so. Consequently, fundamental design data according to which prediction of fatigue strength of multi-spotwelded joints is possible without fatigue test of multi-spot welded joints from fatigue test results of single-spot welded joint with the same nugget diameter with nugget diameter of multi-spot welded joints, is obtained.