Investigation of fatigue crack bridging in Ti/SiC composites by X-ray microtomography and diffraction

• Main Author: Hung, Yu-Chen
• Published: University of Manchester 2009
• Subjects: 620.1126
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.499131

Fatigue resistance by crack bridging in pre-cracked Ti-6Al-4V/SCS-6 composites has been investigated experimentally using in-situ synchrotron X-ray microtomography and diffraction strain mapping techniques. Measurements were performed at room temperature and, in the ter case, at elevated temperatures. This was carried out using qualitative observation of the crack growth morphology and quantitative measurements of the ply-by-ply fibre and matrix strain distributions in the vicinity of the crack, both as a function of crack growth and distance from the crack plane. Qualitative tomographic observations showed that the crack front bowed out between fibres and eventually reconnected further downstream. This led to some matrix bridging the crack even when the crack front was some way past a given fibre and to a more tortuous non-planar crack path, both of which could increase the fatigue resistance. The rate of crack growth slowed somewhat near the fibres, but the magnitude of crack opening displacements was relatively insensitive to the actual locations of the fibres. This was associated with the crack bridging traction being applied by each fibre extending over a large interfacial sliding distance of the order of 0.8-1 mm from the crack plane. The effectiveness of crack bridging was demonstrated through the reduction of more than 70% of the nominally applied stress intensity factor at the crack tip.