The Influence Of Residual Stress On The Fatigue Strength Of Butt Welded Joints Containing Slag Defects

TWI Industrial Member Report Summary 33/1977

By C F Boulton

Background

Fatigue tests have been carried out on butt welded joints which were fabricated by the MMA process and contained buried slag-line defects. One series of joints contained continuous defects and the other intermittent defects. An attempt was made to introduce high tensile residual stresses in the region of the defect by spot heating. The joints were tested under axial pulsating tension loading to establish S-N relationships, and hence to determine the influence of residual stress on the fatigue behaviour of the defective joints.

The test results appeared to indicate that residual stress had no effect upon the fatigue strength of slag-bearing butt welds. However, there is some doubt as to whether the spot-heating technique was effective in introducing the required distribution of residual stresses. Nevertheless the test results were found to be consistent with comparable data obtained from other sources, and could be adequately quantified using a proposed method of determining acceptable defect sizes for fatigue service.