On the analysis of the end-notched flexure specimen for measuring mode II fracture toughness of composite materials

Abstract

This paper deals with the correction of mode II strain energy release rate, G II, of composite laminates measured with the end-notched flexure (ENF) specimen. A derivation is given of the expressions for compliance and strain energy release rate, in which the asymmetric flexure of the specimen and the shear deformations are considered. The results are compared with finite element results. It is shown that the expression for compliance based on the shear deformation beam theory may result in some errors when it is used to calculate G II even though it gives an accurate prediction of compliance. By considering the deformation at the crack root, an improved expression for strain energy release rate is obtained. The values of G II obtained from the improved expression are almost the same as those obtained from the finite element method. A test procedure for determining G II by using the ENF specimen is suggested.