The axial compressive failure of titanium reinforced with silicon carbide monofilaments

Abstract

Monofilament-reinforced titanium has been subjected to compressive loading, with a range of angles between the fibre axis and the loading direction. Under axial loading, the failure stress is about 4 GPa, which is well below levels predicted for kink band formation. It is proposed that compressive failure occurs under these circumstances by the crushing of individual fibres. A model is proposed for prediction of the composite strength as controlled by this mechanism. Observed strengths are consistent with monofilament crushing stresses of about 8–10 GPa. Composites were also studied after a post-consolidation heat treatment and with weak fibre–matrix interfacial bonding. In both cases, slightly higher compressive strengths were recorded than for the standard material. These increases are attributed to an enhanced matrix yield stress and to a higher monofilament compressive strength, respectively. Under off-axis loading, strengths fell from about 4 GPa at low misalignment angles to just above 1 GPa at an angle of 16°. A transition occurs between fibre crushing at low angles and kink band formation at higher angles. The transition range is around 3–4°, which is consistent with model predictions. Microstructural studies confirmed that the expected failure modes were operative in these two regimes.