Room temperature tensile tests are reported on two low-cost ceramic matrix composite materials, comprised of matrices of Blackglas(R) and a proprietory glass composition each reinforced with Nicalon(R) SiC-based fibers. The measured mechanical behaviors, supplemented by post-fracture analysis of fiber pullout and fiber fracture mirrors, are compared in derail to the performance predicted theoretically. This allows for an assessment of the roles of the matrix, fiber srength, residual stresses, fiber geometry, and the fiber/matrix interfacial properties in determining mechanical response. Tile Blackglas(R) matrix cracks extensively during processing, and so the mechanical response is controlled by the deformation and fracture of the fiber bundle. The interfacial sliding resistance, tau, is determined to be approximate to 17 MPa and the in-situ (post-processed) fiber characteristic strength, sigma(c) is found to be approximate to 2.0 GPa, both similar to values reported in the literature for Nicalon(R)/CAS-glass systems. For the glass matrix, the unidirectional and cross-ply materials show marked differences in mechanical behavior. In the cross-ply composites, tau approximate to 14 MPa and sigma(c)-2.9 GPa; in the unidirectional variants, these values were 1.7 MPa and 1.6 GPa, respectively. With these data and other derived micromechanical parameters, the stress-strain and failure point of these materials was predicted using existing models, and excellent agreement with the experiments was obtained. These materials thus perform as expected given the in-situ fiber and interface properties. Notably, the cross-ply glass matrix composites exhibit high fiber strength retention and hence show tensile strengths that are better than other Nicalon(R)-based materials tested to date. (C) 1997 Acta Metallurgica Inc.