Fatigue of Ship Structural Details—Technical Development and Problems

Abstract

During the past five years, a joint industry-government sponsored research project titled the Ship Structural Maintenance Project (SMP) has been conducted at the Department of Naval Architecture & Offshore Engineering, University of California at Berkeley. As a part of this project, the fatigue damage of ship structural details has been extensively studied. This paper summarizes the technical development in fatigue assessment of ship structural details developed during this project. In the fatigue resistance model, the fatigue damage evaluation of structural details was based on a stress range/number-of-cycles-to-failure (SN) approach in which the nominal stress procedure and the hot spot stress procedure were employed. The fatigue assessment of cracked structural details was based on a cracked SN approach developed by a hybrid SN-FM (fracture mechanics) methodology. This cracked SN approach was further developed to incorporate load-shedding effects. In the fatigue loading model, a new formula for the damage correction factor associated with a wide-banded load process was developed. The random loading sequence for ship service was addressed. Fatigue reliability models were then reviewed and the different fatigue reliability updating procedures were evaluated. These techniques were employed in the fatigue analysis of structural details in three tankers. Analysis results from these three ships were presented to illustrate the technical developments and problems associated with fatigue assessment of ship structural details.