Fatigue delamination growth behavior in composite materials under block loading

Abstract

Delamination is one of the most important damage in composite materials. It can propagate under fatigue loading and cause failures of composite structures. With the application of damage tolerance design philosophy in engineering and requirement of light weight structures in advanced aircrafts, how to characterize fatigue delamination growth behavior in composite materials and develop reliable prediction models become critical issues for the application of these materials. A large amount of studies have been conducted on the characterization of fatigue delamination growth under constant amplitude loading in composite materials. However, little attention has ever been put into the block loading sequence effect on delamination growth. Referring to fatigue crack growth in metals, shielding mechanism of plasticity deformation around the crack front plays a dominant role in the loading sequence effect. Fibre bridging, acting as the shielding mechanism, therefore can contribute to the loading sequence effect on fatigue delamination growth in composite materials. Double Cantilever Beam (DCB) specimens were designed and manufactured for the mode I fatigue delamination tests with HI-HI and LO-HI block loading sequences. Paris relation was subsequently used to interpret the experimental results. It demonstrates there is an obvious loading sequence effect on fatigue delamination growth in composite materials. The fatigue crack growth in the HI-HI block loading is slower than it in the LO-HI block loading.