Time-dependent fracture of epoxy resin under mixed-mode I/III loading

Abstract

In this study, fracture behavior of epoxy resin under mixed-mode loading between opening mode (mode I) and out-of-plane shearing mode (mode III) was investigated using an adjustable loading fixture set with a single-edge notched tension (SENT) specimen. Effects of specimen thickness and loading rate were investigated. Two different thicknesses of specimen were employed (4 and 8 mm) And, the fracture toughness tests were performed at two different loading rates of 0.1 and 1000 mm/min. Fracture toughnesses of epoxy resin were calculated using finite element (FE) analysis based on both linear-elastic fracture mechanics (LEFM) and elastic–plastic fracture mechanics (EPFM). It was found that under mixed-mode I/III and pure mode III loadings, fracture occurred in a ductile manner with severe plastic deformation. Therefore, LEFM is no longer valid, and EPFM approach was applied in this study to characterised fracture behavior of epoxy resin under mixed-mode I/III loading. Two different fracture mechanics parameters based on EPFM, e.g. critical J-integral (Jc) and critical crack-tip displacement, were calculated. Jc results revealed that the effect of specimen thickness was significant at low loading rate. However, at high loading rate the effect of specimen thickness was marginal. While, critical crack-tip displacement results indicated that fracture occurred at the same level of crack-tip displacements regardless of specimen thickness. An observation of fracture surfaces agreed with the crack-tip displacement results, i.e., a similar fracture surface topology for both thick and thin specimens tested at the same loading rate.