Low-cycle fatigue analysis of a web frame corner in ship structures

Abstract

Ship structures are subjected to cyclic loads which may lead to fatigue failures particularly at welded joints. In addition to loads induced by waves and structural vibrations, which contribute to high-cycle fatigue, various structural details are also subjected to a limited number of high-stress cycles caused by changing loading conditions, which may lead to low-cycle fatigue. Thus, appropriate procedures are required for the shipbuilding industry, which are missing in the existing design codes. Experimental investigations and numerical analyses were performed to validate a procedure for the design of ship structures in the low-cycle fatigue regime. Three large-scale fatigue tests were carried out with high bending moments on test models of web frame corners in order to initiate fatigue cracks after few hundred cycles. Different cracks occurred; however, a crack at the cruciform joint has shown to determine the failure of the connection. An extension of the effective notch stress approach was applied to this joint to assess the low-cycle fatigue life, considering the elastic–plastic strain, evaluated by nonlinear finite element analyses, in the notch of the weld toe. This practical method offers promising possibilities to assess the fatigue life of welded joints in the low-cycle fatigue regime.