Borosilicate glass reinforced with continuous silicon carbide fibres: a new engineering ceramic

Abstract

Silicon carbide fibre-reinforced glass and glass-ceramic composites are under development at Harwell where current research is concerned with the whole spectrum of activities from optimization of fabrication processes, through detailed properties assessment to fabrication of components. For the case if SiC fibre-reinforced borosilicate glass, a detailed account of a powder-infiltration-hot-pressing route to composite fabrication is given, and the effects of the variation of key fabrication parameters on composite properties are discussed. A comparison of energy balance and fracture mechanics approaches to the problem of matrix cracking in composites under tension is shown to yield equivalent expressions for the matrix failure strain and the stress to propagate a crack. It is then inferred that for this composite system the stress at the tip of a crack is independent of crack length once the crack is longer than a certain equilibrium length. For aligned fibre composites the tensile strengths of material with fibres at various angles to the stressing direction are shown to fit Tsai's theoretical model for the strength of resin matrix composites. The tensile and flexural strengths of the various composite structures considered differ by approximately a factor 2. Attempts are made to reconcile these differences by discussion of classical theories of fibre bundle failure, stressed volume effects and theories of the influence of matrix cracking on bending moment. Examples of components fabricated to nett shape are shown.