Mode II Cyclic Delamination Growth

Abstract

The end notched flexure (ENF) specimen is employed in an investigation of the inter laminar fracture of unidirectional graphite/epoxy, graphite/polyimide, and graphite/PEEK composites subjected to Mode II fatigue loading. Fatigue crack growth rates are deter mined for the stable delamination growth observed under fully reversed cyclic loading. Within the crack driving force range studied, cyclic crack growth data obeyed a power law dependency on the cyclic strain energy release rate. The response of the various material systems is compared to crack growth under static loading. The importance of the data re duction scheme for the crack growth resistance is discussed. Friction is examined as a potential energy absorbing mechanism in the test by finite element analysis. Suggestions for appropriate experimental geometries minimizing frictional effects are presented. Finally, fatigue fracture surfaces are analyzed with scanning electron microscopy to identify crack growth mechanisms.