LIMITATIONS OF THE UNCOUPLED, RVE-BASED MICROMECHANICAL APPROACH IN THE ANALYSIS OF FUNCTIONALLY GRADED COMPOSITES

A new class of materials, called functionally graded composites, has r ecently evolved in which the microstructure is tailored to meet specif ic applications. This is accomplished by distributing the reinforcemen t phase in a nonuniform manner, resulting in statistically inhomogeneo us composites. The standard micromechanical approach used to analyse t he response of this class of materials is to decouple the local and gl obal effects by assuming the existence of a representative volume elem ent at every point within the composite. Recently, a new micromechanic al theory, which couples the local and global effects, has been develo ped and applied to functionally graded composites. Herein, this theory is used to assess the limits of applicability of the standard microme chanical approach in predicting local stresses in the fiber and matrix phases of functionally graded composites subjected to a thermal gradi ent. It is shown that the simplified uncoupled approach is inaccurate when the dimension of the reinforcement phase is large relative to the dimension of the composite.