The main objective of the present thesis was to study how composite patches can reduce the stress intensity in cracked steel plates, and how these patches, by reducing the stress intensity, can limit the extent of fatigue crack growth.
Two different cases have been analysed using the finite element software Abaqus; a single-edge notched tension steel plate and a ship manhole experiencing fatigue crack growth. The former has been modelled and analysed with a number of patch configurations with varying thickness, width and placement along the crack line. The latter has been modelled and analysed with two patch repair alternatives; first, with double sided CFRP strengthening of the cracked deck and then a single CFRP patch inside the rim of the manhole. For both alternatives fatigue life calculations has been made.
The results shows that composite patch repair solutions are, when applied in the right manner, well suited for preventing fatigue crack growth and extending the fatigue life of cracked plates. Additionally, it is shown that the composite thickness and especially the width have considerable influence on the performance of the patches.