Elastic and Thermal Effects in the Interphase: Part I. Comments on Characterization Methods

Abstract

The complexity of the fiber-matrix interphase in a composite is largely due to the myriad of variables (material, processing, and design) that affect its formation. The interphase, thus formed, has to be characterized at several levels (microstructural, chemical, and mechanical) for one to understand fully the nature of the bond between the fiber and matrix and perform a stress analysis of the fiber-interphase-matrix assemblage. A cursory glance at the literature shows that great progress has been made in all of the three levels of characterization mentioned above for various composite systems. The progress in mechanical characterization is manifested in the development of several methods of interphasial shear strength measurement and a better understanding of the local failure process, which often initiates global composite failure. A thorough thermomechanical characterization of the interphase is difficult, at present, because of the necessity of studying the interphase in situ, its small dimension (usually on the order of a micrometer), and its general complexity. This article presents a brief review of the principal interphasial characterization methods (microstructural, chemical, and mechanical) and discusses several recent techniques for the physical characterization (evaluation of volume fraction, thickness, Young's modulus, shear modulus, and coefficient of thermal expansion) of the interphase.