Assessment of Fatigue Crack Growth in Imperfect Lap Joint (Crack Growth Analysis using Influence Function Method)

Abstract

The deck plates of single-deck floating roofs for large oil storage tanks are joined by continuous full-fillet welds on the upper side of lap plates. The deck plate area is subjected to cyclic deformation due to strong wind load. Fatigue cracks may occur at the lap welded joints. The objective of this study is to investigate the effect of the imperfect lap joints on the fatigue life. The fatigue life is predicted by the crack growth analysis. The stress intensity factors are analyzed using the influential function method established by Shiratori, and the crack growth is based on the Paris Law in this paper. In the influential function method, the stresses on the virtual cracked surface of the uncracked lap joints had been analyzed and were reported in the previous paper. Under the tensile load, the fatigue life of the joint decreases with increasing the gap size of the lap plates. On the other hand, the fatigue life is not related to the gap size under the bending load.