SIC FIBER BOROSILICATE GLASS COMPOSITE .3. THERMAL-SHOCK BEHAVIOR/

The influence of thermal stresses on the mechanical properties of ther mal-shocked Nicalon SiC fibre/Pyrex composites has been analysed by co nsidering the effect of thermal-mismatch stress on the mechanical prop erties of composite constituents. The thermal-mismatch stresses develo ped between devitrified cristobalite, and fibre and glass matrix were calculated using the values of material parameters obtained from exper iment. This shows that the high thermal mismatch stresses originating from larger coefficient of thermal expansion of devitrified cristobali te extended the preexisting matrix crack, and caused fibre debonding. Thus, the reductions in the modulus and the interfacial stress of ther mal-shocked composites in comparison with those of as-fabricated compo sites resulted from the matrix devitrification. The lower proportional limit of thermal-shocked composite was attributed to the lower interf acial stress and larger pre-existing cracks compared with those of as- fabricated composite, The reduction in ultimate strength of thermal-sh ocked composite was correlated with the decreases of fiber hardness an d interfacial stress.