Criteria for Crack Initiation into a Matrix from the Ends of Partially Debonded Surfaces of a Flat Inclusion

Abstract

The interfacial debonding is observed in the earliest stage of damage in dispersed composite materials. The crack initiation into a matrix from the ends of partially debonded surfaces of dispersed inclusions plays an important role in the estimation of strength of dispersed composite materials. The criteria discussed in this paper are as follows : (1) the maximum hoop stress criterion, (2) the minimum strainenergy density criterion, (3) the maximum energy-release-rate criterion and (4) the maximum principal stress criterion. These criteria were based on the singular stress field at the ends of debonded surfaces. Tension tests were performed by using epoxy resin specimens containing a flat steel inclusion. By examining the experimental results, it was found that (1) the maximum hoop stress criterion, (2) the minimum strain-energy density criterion and (4) the maximum principal stress criterion are appropriate as the criteria for crack initiation when the matrix is subjected to tensile stress in the direction of the flat inclusion. However the maximum energy-release-rate criterion is invalid.