Influence of ENF Specimen Geometry and Friction on the Mode II Delamination Resistance of Carbon/PEEK

Abstract

Unidirectional carbon/polyetheretherketone (PEEK) composites were tested under mode II (shear) loading conditions. Three ENF (end notched flexure) specimen thicknesses have been tested, allowing a range of span length-to-thickness ratios to be examined. Analysis of the results from a first series of tests indicated a strong influence of specimen thickness on G,,, values. However, a second series of tests was then performed on similar specimens under identical loading conditions but with a folded layer of PTFE film inserted between the crack faces to reduce friction. These test results were independent of specimen thickness except for the thickest specimens at the shortest span length. It is concluded that friction can cause overestimation of G,, C values by up to 20%. A standard mode II test method must include steps to reduce this friction component.