Proposed means for fabrication of weldments with high fatigue strength

Summary

During evaluation of the weld fatigue strength, a major difference has been found between large welded beam specimens and small welded specimens. To overcome this problem, the maximum stress standard fatigue life test method (σ_max = σ_y test) has been proposed. This test method involves small welded specimens being subjected to the stress serving as the fatigue design requirement, i.e. a stress such that the maximum stress is equal to the yield strength, as the working stress. This test method is confirmed as being useful even for specimens containing high tensile residual stresses of yield strength order. The basic yield strength decreases with the increasing yield strength of the material. Based on this result, the following proposals are made to increase the fatigue strength of welded structures by reducing the tensile residual stresses:

1. use of low yield ratio materials preventing any loss of tensile strength;

2. use of low transformation temperature steels or welding materials;

3. use of weld metal with a lower yield strength than the base metal for the passes involved in fatigue crack initiation;

4. use of welding methods (electroslag welding, electron beam welding, submerged‐arc welding with forced cooling giving early cooling of the plate surface