Fatigue in SiC fibre reinforced titanium metal matrix composites

The fatigue and interfacial characteristics of a unidirectional, SiC (SCS 6), fibre reinforced Ti 6Al 4V metal matrix composite have been investigated using a series of fatigue crack propagation, total life, and interfacial characterisation techniques. A room temperature crack arrest to catastrophic failure (CA/CF) transition was quantified using the initial stress intensity factor range ΔKapp. This transition occurred between 21 and 18 MPa√m in the three point bend geometry, and was found to be dependent on volume fraction of intact fibres bridging the crack. Increasing the test temperature to 300˚C had different effects on the resistance to fatigue crack growth depending on crack opening displacements and test piece stiffness. Total life fatigue tests revealed that the dominant failure mechanism was matrix fatigue cracking and fibre bridging. The extent of fatigue crack growth and fibre bridging was dependant on the applied stress and test temperature. The introduction of a dwell period at maximum load resulted in a small reduction in the total fatigue life. Post fatigue fibre push out tests identified that fatigue caused a reduction of interfacial properties below the as received levels. This reduction of interfacial properties was dependent on fatigue test temperature and initial loading conditions.