Time-dependent interfacial debonding propagation in single fiber composite

Interfacial debonding propagation is one of the most important problems for long-term creep in unidirectional composites because the strength of the unidirectional composites decreases with increase of the interfacial debonding length. In this study, time-dependent interfacial failure was investigated by using the Micro Raman Spectroscopy. The specimen was single fiber composite consisting of one carbon fiber embedded in the vinylester resin. It was subjected to a constant strain to assume the long-term creep in the unidirectional composites. To discuss the timedependent interfacial debonding propagation behavior, a time-dependency of a criterion for interfacial debonding propagation in the SFC must be determined. In this paper, the time-dependent boundary condition of the interfacial debonding was obtained from experimental results, and the interfacial debonding propagation was formulated. Here, the compression stress applied to the interface in the fiber radius direction was formulated as a function of time on the consideration of Poisson contraction and thermal residual stress. The interfacial debonding propagation and variation of the fiber axial strain distribution as a function of time were formulated by using the following three parameters: a relaxation of the frictional stress, an interfacial shear viscoelastic behavior and the time-dependent boundary condition at the interfacial debonding tip. These formulations showed a good agreement with the corresponding experimental results.