Effect of viscous flow on the thermal residual stresses in a monofilament SiC/borosilicate glass composite

Abstract

Residual strains of SiC (SCS-6) single fibres embedded between borosilicate slides were measured by comparing their post-fabricated in situ lengths with their original lengths as a function of processing temperature and load in an open die. If cooled without load the residual strains agreed with the values one would expect if the stress-free temperature was taken to be the strain point of the glass. However, if cooled under load, the residual strains were found to be significantly enhanced, and increased linearly with the applied load, but were insensitive to processing temperature. A hydrodynamic model, where glass flow normal to the vertically applied pressure entrains the embedded fibres and results in the enhanced residual strains, is proposed. The implications of these results in calculating thermal residual stresses in viscous media are discussed. At higher applied loads, the fibre edges broke into smaller fragments. The fragment length distribution was measured and analysed using Weibull statistics. Heat treatment of the fibres at 1600 °C for 4 h in vacuum, resulted in approximately a 50% decrease in their strength and critical length as compared to the as-received fibres. The Weibull moduli, however, were not affected by the heat treatment.