The effect of sliding interfaces and inhomogeneous interphases on thermal and elastic properties of composites.

摘要

The transition zone between the matrix and the inclusion plays an important role in the transfer of loads, and it is a key factor affecting local stresses, displacement fields, and elastic and thermal properties of composites. In literature, this transition zone is assumed to be either the surface between matrix and inclusion called "interface" or an additional phase existing between matrix and inclusion called "interphase". In this dissertation these two cases are investigated by considering the following two problems.; In the first problem, a composite containing either aligned or randomly oriented short fibers of spheroidal shape is studied. The interface between matrix and fiber allows sliding such that shear tractions are specified to vanish. The fiber interaction is accounted for by using a Mori and Wakashima's (1990) successive iteration method based on a Mori-Tanaka's (1973) average field theory. In this problem thermal stresses and thermal expansion coefficients of composites are determined by taking the matrix and the fiber to be isotropic in stiffness and transversely isotropic in thermal expansion coefficients. The effect of interface on thermal stresses and properties is investigated by comparing the results for the sliding case with the results for perfectly bonded case.; In the second problem, a composite containing aligned long fibers of cylindrical shape, which are distributed uniformly in the matrix, is studied. The interphase between matrix and inclusion is assumed to be inhomogeneous. Few functional forms are chosen to simulate the radial variation of the thermal and elastic properties in this region. The effect of this interphase on the local elastic fields and the overall thermal and elastic properties is studied. The thermal and elastic properties are assumed to be isotropic in the interphase and the matrix, and transversely isotropic in the inclusion. The perfect bonding is assumed at the matrix/interphase interface and the interphase/inclusion interface. The effective elastic constants and thermal expansion coefficients are derived by using the composite cylinders assemblage model (Hashin and Rosen, 1964) and the generalized self-consistent scheme (Kerner, 1956; Christensen and Lo, 1979).