Delamination growth during fatigue of advanced polymer matrix composites

Abstract

Advanced polymer matrix composites such as carbon fibre reinforced polymers (CFRP), offer many advantages over more traditional materials such as metals. Usually, CFRP have greater strength/weight and stiffness/weight ratios than traditional engineering materials, which makes them ideal for use in many weight sensitive applications, especially in the aerospace sector. To maximise the use of these materials there is a need to gain a better understanding of how CFRP, and more generally FRPs, behave under fatigue load conditions. This work investigates the fatigue response and damage mechanisms found in a CFRP. Previous work has highlighted that fatigue with a compressive element is more damaging than pure tensile fatigue and that delamination is the dominant damage mechanism in both cases. However, in the tensile fatigue tests the primary delamination was on a different interface from the primary delamination found in the compression fatigue tests. The cause of this trend to delaminate along a particular interface has been investigated using mixed mode bend tests. These tests have been used to investigate the response of the interface to both static and fatigue loads. Initial tests have been carried out on the 0°/45° interface. Delamination growth was monitored at three levels of mode mixity, ratios of MI/MII of 1:1, 1:3 and 3:1. PRC/1848