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 properties and the behavior of the interphase region formed by a chemical reaction between the matrix and the fiber materials in metal matrix and ceramic matrix composites. Contrary to the traditional approach which does not allow any relative displacement at the interface without fracture, this paper considers elastic deformation of the interphase zone between the matrix and the fiber by replacing the zone by an “equivalent elastic interface”. The elastic behavior of the equivalent elastic interface describes the local elastic rigidity and deformation of the interphase zone and can be quantified by a mechanics parameter called “shear stiffness coefficient” which is proportional to the ratio of the shear modulus to the local thickness of the interphase material. This paper also outlines an ultrasonic reflectivity modeling that can be used for the experimental measurement of the interfacial shear stiffness coefficient along the length of an embedded fiber. Further, an experimental method of measurement of the shear stiffness coefficient is presented and experimentally measured values are tabulated. The significance of the quantification of such a parameter is that the elastic property of the interface obtained can be used as a common basis among material scientists designing and developing the composite systems, and groups studying material behavior for life prediction. Also, the parameter 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.