Determination of mechanical properties of fiber–matrix interface from pushout test

For ceramic matrix composites, the pushout test is the most widely used test for finding the two mechanical properties of the fiber–matrix interface – (1) the coefficient of friction and (2) the residual radial stress. Experimental measurements from the pushout test do not directly give the values of these two mechanical properties of the fiber–matrix interface, but need to be regressed to theoretical models. Currently, approximate theoretical models based on shear–lag analysis are used for regression. In this paper, the adequacy of the shear–lag analysis model in accurately finding the mechanical properties of the fiber–matrix interface is discussed. An elasticity solution of the pushout test based on boundary element method is developed. Regressing one set of available experimental data from a pushout test to both shear–lag analysis and boundary element method models gives values differing by 15% for the coefficient of friction but similar values for the residual radial stress. Parametric studies were also conducted to show the difference between the shear–lag analysis and boundary element method results for factors such as fiber to matrix elastic moduli ratios, coefficient of friction and fiber volume fractions.