局部応力集中と構造的応力集中を考慮した溶接止端部の疲労強度評価法

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Stress concentration at weld toe is one of the major factors influencing fatigue strength of welded structures. The stress concentration factor (SCF) K_t is expressed by K_t =K_w・K_s, where K_w is the local SCF depending upon the local geometry of a weld, and K_s is the structural SCF determined by the joint type of a structural member. The structural SCF is currently taken into account by some of fatigue design guidances. While the local SCF and K_t are considered as unknown factors and to be involved in the basic S-N curves. For a consistent fatigue evaluation of various types of joints, it is necessary to establish a unified method dealing with both local and structural SCFs quantitatively. In this study, a fatigue evaluation method has been studied based on the following phenomenon ; 1. Since local stress concentration is principally caused by a very small radius of weld toe, a high stress region is quite limited in a small area. Therefore, the local SCF affects fatigue crack initiation and growth of a very small crack. This means that even if K_w is as large as infinity, the fatigue strength is still greater than that for a crack propagation life. Namely, as K_w becomes large, the fatigue strength decreases from that for a small K_w to that for crack propagation life. 2. Whereas the affecting area of structural stress concentration is relatively large, the structural SCF influences not only crack initiation but also crack propagation until the crack becomes large. Thus, the K_s has the same effect as an increase in nominal applied stress. Eventually, a unified equation in which the local and structural SCFs are integrated has been proposed for fatigue strength estimation of welded structural members.
社団法人日本船舶海洋工学会の論文
1996-12-00

局部応力集中と構造的応力集中を考慮した溶接止端部の疲労強度評価法

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