Interphase effects on the bend strength and toughness of an oxide fibre/oxide matrix composite

The effect of alumina–20 wt.% ZrO2 (PRD-166) fibre and SnO2 coating properties on the bending strength and toughness of alumina fibre/SnO2/glass matrix composites have been investigated. The mean strength of as-received alumina–20 wt.% ZrO2 fibres was 1380 MPa for a gage length of 17 mm and decreased with increase in heat treatment temperatures. It was also observed that as the SnO2 coating thickness increased, roughness of the coating increased and this decreased the strength of the fibres. This roughness effect had serious implications on the fracture characteristics of PRD-166/SnO2/glass and Saphikon/SnO2/glass matrix composites. PRD-166/SnO2/glass matrix composites exhibited non-planar failure with fiber bridging and fibre debonding as major toughening mechanisms. Saphikon/SnO2/glass matrix composites failed in a tough manner with extensive fibre pullout. The difference in the failure mode between PRD-166/SnO2/glass and Saphikon/SnO2/glass matrix composites was attributed to the clamping stress associated with fiber roughness at the PRD-166/SnO2 interface as compared to the smoother Saphikon/SnO2 interface.