Fatigue behaviour of stitched GRP laminates

This paper examines the effect of through-thickness stitching on the in-plane fatigue performance and fatigue damage mechanisms of a glass-reinforced polymer (GRP) laminate under zero-to-tension cyclic loading The influence of stitching orientation and stitching density on the S-N curve of the laminate has also been investigated. The fatigue resistance was reduced considerably by stitching, particularly at relatively low fatigue stresses. Both the non-stitched and stitched laminates experienced similar types of fatigue damage, i.e. cracking of the vinyl ester resin matrix and glass fibres, and debonding between the matrix and fibres. However, the stitched laminates also suffered fatigue failure between the stitches and surrounding laminate, which contributed to the reduction in the fatigue lives of these materials. Their fatigue resistance was also reduced by damage to the glass fibres caused when the laminates were stitched. It was concluded that while stitching improved the interlaminar fracture properties of the GRP, it seriously degraded the fatigue performance. (C) 1996 Published by Elsevier Science Limited