A review of fatigue strength improvement methods

Abstract

Improving the fatigue strength of welded joints may be economically interesting in many situations, especially in those cases where high-strength steels are used. However, widespread use of a method is, in many cases, restricted by a lack of knowledge of its reliability. Previous work has focused only on the effectiveness of improvement methods to increase fatigue strength; cost studies and quality control instructions are rarely given.In this report, several methods for structural steel are summarized. A review of existing test results shows that improved connections made from a high yield strength steel reveal a higher percentage improvement than mild steel connections using the same improvement method. In addition, improved joints may be sensitive to the applied stress ratio. Finally, the most efficient method depends on the type of welded joint.Residual stress methods have relatively inexpensive application costs whereas some grinding methods are very costly. Quality control depends upon fabrication, loading, and environmental conditions. Examination of four types of fillet-welded joints has identified several methods that require further research. A three-dimensional finite element study of these joints predicts that at crack locations, under service loading, a very small plastic zone is formed. Therefore, residual stress methods may remain effective under variable-amplitude load conditions. Key words: structural steel, welded joints, fatigue, improvement methods, fillet welds, finite element analysis.