CRACK GROWTH ASSESSMENT IN SHIP STRUCTURES

Cyclic loads represent a typical demand on ship structures, and all the stress concentration zones (hot spots) are potential sources of fatigue cracking. Experience shows which are the most critical structural details that need to be regularly inspected. Periodic surveys, which are normally carried out to assess the serviceability of ship structures throughout their lifetime, should obviously be especially directed to the inspection of such details. Once a crack has been detected, Fracture Mechanics is a suitable tool for assessing the residual fatigue life of the structure in question, so that sound decisions can be taken about repairing or replacing it. This paper deals with the problem of setting up a procedure for predicting the growth of fatigue cracks, so that the time remaining before failure may be properly estimated. The proposed procedure is focused on the assessment, by means of finite element models, of the stress intensity factors that play the main role in determining the crack growth rate. The whole procedure is illustrated with reference to a welded joint that is typical in ship structures, and which also has been the subject of full-scale tests. This example can help in drawing general guidelines for other practical applications.