TWI Industrial Member Report Summary 161/1981
By S J Maddox and B J Fitzpatrick
Previous work established that the fatigue strength of fillet welded joints in steel could be increased by controlled shot peening. Further tests were carried out on transverse non-load-carrying joints in a structural steel to investigate some factors which might influence the beneficial effect. They included applied stress ratio (R), stress-relief and variation in the shot peening conditions.
It was found that compared with results obtained under R = 0, there was a small increase in fatigue strength for R = -1 but a large reduction for R = 0.5. Results obtained from shot peened and stress-relieved joints were slightly higher than those for as-welded joints indicating that the treatment improves
the weld geometry as well as introducing compressive residual stresses. There was little influence of the peening conditions in the present work but comparison with previous results obtained from similar joints shot peened using the same conditions demonstrated that there could be a wide Cariation in fatigue strength even for nominally identical shot peening conditions.
Residual stress measurements showed that shot peening introduced compressive residual stresses similar in magnitude to the tensile yield strength of the steel and that they were partly relaxed by cycling and fully relaxed by thermal stress-relief. Based on a simplified analysis, the fatigue test results also indicated that fatigue cycling caused some relaxation of the residual stress.