Interfacial debonding and fibre pull-out stresses - Part V A methodology for evaluation of interfacial properties

Based on a theoretical model developed previously by the authors in Part II of this series for a single fibre pull-out test, a methodology for the evaluation of interfacial properties of fibre-matrix composites is presented to determine the interfacial fracture toughness Gc, the friction coefficient μ, the radial residual clamping stress qo and the critical bonded fibre length zmax. An important parameter, the stress drop Δσ, which is defined as the difference between the maximum debond stress σd*and the initial frictional pull-out stress σfr, is introduced to characterize the interfacial debonding and fibre pull-out behaviour. The maximum logarithmic stress drop, In(Δσ), is obtained when the embedded fibre length L is equal to the critical bonded fibre length zmax. The slope of the In(Δσ)-L curve for L bigger than zmax is found to be a constant that is related to the interfacial friction coefficient μ. The effect of fibre anisotropy on fibre debonding and fibre pull-out is also included in this analysis. Published experimental data for several fibre-matrix composites are chosen to evaluate their interfacial properties by using the present methodology.