Determination of fiber-matrix interphase moduli from experimental moduli of composites with multi-layered fibers

摘要

In this paper we report a method for inverse determination of effective elastic moduli of fiber-matrix interphases from experimentally measured composite moduli. Multi-phase micromechanical models and simplified spring approximations are used for inversion. An analytical expression for the transverse shear modulus of a composite with multi-layered fibers is derived using a multi-phase generalized self-consistent (MGSC) model, which forms the theoretical basis for inversion. This method has been used to determine the moduli of fiber-matrix interphases in ceramic and intermetallic matrix composites with similar SiC fibers and carbon fiber coating using the composite moduli measured ultrasonically. We find that the calculated moduli of interphasial carbon in the intermetallic matrix composite, after considering differences in microstructure, are very close to those available in the literature. The interphasial moduli obtained for the ceramic matrix composite are smaller than those published. We have found that this difference can be well explained by considering imperfect contact between the interphasial carbon and the matrix due to excessive matrix porosity at the interfacial region. Special emphasis is placed on error propagation in the inversion process and interpretation of experimental results. The results show that the interphasial moduli in intermetallic matrix composites are more sensitive to measurement error than those in ceramic matrix composites due to higher interphase-to-matrix stiffness ratio in intermetallic matrix composites. For both types of composites the calculated interphasial moduli are most sensitive to error in measurements of composite and matrix moduli and less sensitive to error in fiber moduli.