Estimation of Dynamic Interlaminar Fracture Toughness of CFRP by ENF Test Using SHPB Method

Abstract

To obtain the dynamic Mode II interlaminar fracture toughness of CFRP under impact loading, an impact bend test using split Hopkinson pressure bar (SHPB) method was applied to the end notched flexure (ENF) specimen, and the estimation of G_II was investigated. The dynamic behavior of the ENF specimen during impact bending was analysed by the finite element method, and the history of the energy release rate G_II of the specimen was calculated using the crack-closure method. The energy release rate G_II^CC calculated by the crack-closure method was compared with the energy release rate G_II^ST estimated by the formula for the static ENF test and the load history of the output bar of SHPB.
The results obtained are as follows. For the step input loading, the ratio G_II^ST/G_II^CC oscillates strongly around unity and the oscillation continues after considerably long time, while for the ramp input loading with a finite rise-time, the oscillation is damped more quickly and the ratio G_II^ST/G_II^CC approaches to unity more gradually as the rise-time increases. Therefore, the dynamic Mode II fracture toughness can be estimated by the formula for the static ENF test if the ramp input loading wave with an appropriate rise time is applied.