ULTRASONIC CHARACTERIZATION OF THE FIBER-MATRIX INTERPHASE INTERFACE FOR MECHANICS OF CONTINUOUS FIBER-REINFORCED METAL-MATRIX AND CERAMIC-MATRIX COMPOSITES

This paper presents a novel approach to evaluate the elastic propertie s and the behavior of the interphase region formed by a chemical react ion between the matrix and the fiber materials in metal matrix and cer amic matrix composites. Contrary to the traditional approach which doe s not allow any relative displacement at the interface without fractur e, this paper considers elastic deformation of the interphase zone bet ween the matrix and the fiber by replacing the zone by an ''equivalent elastic interface''. The elastic behavior of the equivalent elastic i nterface describes the local elastic rigidity and deformation of the i nterphase zone and can be quantified by a mechanics parameter called ' 'shear stiffness coefficient'' which is proportional to the ratio of t he shear modulus to the local thickness of the interphase material. Th is paper also outlines an ultrasonic reflectivity modeling that can be used for the experimental measurement of the interfacial shear stiffn ess coefficient along the length of an embedded fiber. Further, an exp erimental method of measurement of the shear stiffness coefficient is presented and experimentally measured values are tabulated. The signif icance of the quantification of such a parameter is that the elastic p roperty of the interface obtained can be used as a common basis among material scientists designing and developing the composite systems, an d groups studying material behavior for life prediction. Also, the par ameter can be used by production engineers to assure that the designed properties of the composite are being achieved, and by the end users to ensure that the designed and produced properties are being retained in use.