Finite element modelling of fatigue crack initiation in SiC-fibre reinforced titanium alloys

In the present investigation, fatigue crack initiation in SiC fibre (SCS-6) reinforced titanium has been analysed on the basis of a finite element (FE) model. In this composite material after processing a complicated interfacial zone exists, consisting of the remains of the carbon coating and the reaction zone. This reaction zone usually causes the initiation of a fatigue crack as it fails at a low stress. The growth of a fatigue starting at a reaction layer crack is analysed for different thick reaction layers (from 0.5 to 3 μm). The conditions under which a fatigue crack can be arrested and the influence of additional fibre failure on fatigue crack growth have been analysed. The results show that the formation of the matrix crack largely depends on the applied stress and reaction layer thickness. Under an applied stress, σ_max<800MPa, a crack in 1-μm-thick reaction layer cannot extend into the matrix. For higher applied stress a matrix crack can grow form the cracked reaction layer but after an extension of several microns it can be arrested. A mechanism of ΔK-reduction is found to be responsible for the crack arrest. The thickness of the reaction layer up to 3 μm has no significant influence on fatigue crack growth rate for larger fatigue cracks (>10 μm).