Stress transfer at a partially bonded fibre/matrix interface

This paper presents an approach for determining the stress transfer at a partially bonded fibre/matrix interface different from that used for shear lag analysis. It is based on minimization of the total complementary energy in the fibre and matrix. Analytical results for fibre debonding stresses in both fibre pull-out and push-out analyses which are in excellent agreement with shear lag analysis, establish the validity of the method. This approach, however, predicts an interfacial radial stress larger in magnitude than that obtained by shear lag analysis. For fibre pull-out where the interfacial radial stress is tensile, this suggests that continual fibre debonding takes place under a mixed rather than pure shear mode. The use of a single parameter-debonding criterion based on the interfacial shear stress reaching the interfacial shear strength appears inadequate. In the fracture mechanics approach to fibre debonding, a higher interfacial fracture toughness is obtained when the strain energy due to the radial and circumferential stresses in the matrix is included in evaluating the strain energy release rate.