Analysis and experimental characterization of the Center Notch Flexural test specimen for Mode II interlaminar fracture

The interlaminar Mode II critical strain energy release rates of unidirec tional graphite/epoxy, graphite/polyetheretherketone (PEEK), and graphite/epoxy with interleaf material were characterized using the End Notch Flexural (ENF) and Center Notch Flexural (CNF) test specimens. The CNF test method was developed specifically for this study. Compliance and strain energy release rate expressions of the CNF are derived and are in good agreement with finite element results for a wide range of crack lengths. Mode II critical energy release rates for both test methods were found to be in quite good agreement.