Fatigue Damage Analysis by Use of Cyclic Strain Approach

A number of cracks were reported in a bulk carrier (approx. 300m long) after 23 years of trade. The ship was still in good condition, no significant corrosion was found by inspection. The trade routes of the vessel were in the North Atlantic, usually one voyage in fully loaded condition followed by one in ballast condition.

Some of the reported cracks had their origins in holes in the longitudinals (the holes were probably made for mounting purposes) located at the upper deck close to the midship section Fig. 1. The cracks began at the upper edge of the holes and propagated in the direction of the deck. The initiation of the cracks was probably due to fatigue damage.

In this paper the cracks will be investigated using the cyclic strain approach, and the obtained results will be compared with fatigue lives estimated by the S-N approach.