The use of peak stresses for fatigue strength assessments of welded lap joints and cover plates with toe and root failures

In its original formulation the Peak Stress Method (PSM) was adopted to assess the fatigue strength when only mode I stresses are singular (for example at the toe of fillet-welds) or significant (for example at the root of load-carrying fillet welded cruciforms). Nevertheless in welded lap joints and cover plates both mode I and mode II stresses are singular at the weld root, where fatigue cracks are likely to initiate. In the present paper the PSM is extended to mode II loading conditions and then an equivalent peak stress is derived, which is used to assess either weld toe or weld root fatigue failures.