THERMAL RESIDUAL-STRESSES IN CERAMIC-MATRIX COMPOSITES .1. AXISYMMETRICAL MODEL AND FINITE-ELEMENT ANALYSIS

The residual stresses induced in composites when cooling down from the processing temperature were determined using a cylinder model and usi ng a finite element computer program. Various specimen geometries were examined: microcomposites, unidirectional composites and flat substra tes coated with one or two layers. Various combinations were investiga ted involving MoSi2 as an interphase, SiC as a fiber, a matrix, a subs trate of an external coating layer and C as a fiber, a substrate, an i nterphase or an intermediate coating layer. The influence of factors s uch as interphase thickness and uncertainty in interphase properties ( including Young's modulus and coefficient of thermal expansion) was an alyzed. It was shown that trends in distribution of thermal residual s tresses (TRS) prevailing in 1D composites can be satisfactorily predic ted using the analytical cylinder model. The presence of a MoSi2 inter phase induces the highest interfacial stresses but it relieves stresse s in the matrix. The presence of a C interphase essentially reduces th e interfacial stresses.