Modeling the ultimate tensile strength of unidirectional glass-matrix composites

The ultimate tensile strengths of a unidirectional glass-matrix composite w ere measured as a function of fiber volume fraction. The results were compa red with predictions, using a refined solution of the stress field generate d by an axisymmetric damage model, which incorporated the effect of stress concentration in the fiber caused by the presence of a matrix crack both be fore and after deflection at the fiber/matrix interface. Two possible locat ions for the fiber failure were considered: (1) at a transverse matrix crac k, near a bonded fiber/coating interface and (2) at the tip of a debond, at the fiber/coating interface. At low fiber volume fractions, the measured u ltimate tensile strength matched the prediction calculated, assuming no cra ck deflection. For higher volume fractions, the predictions calculated for a debonded crack matched the observed values. The model results were relati vely insensitive to debond length and interfacial shear stress for the rang e of values in this study. In comparison, the global load-sharing model, wh ich does not account for the stress singularity at the fiber/matrix interfa ce, was found to overpredict the values of the ultimate tensile strength fo r all fiber volume fractions, An important contribution of the present work was to introduce the use of fiber volume fraction as a parameter for testi ng theoretical predictions of the mode of fiber failure.