Slow crack growth resistance and bridging stress determination in alumina-rich magnesium aluminate spinel/tungsten composites

摘要

The slow crack growth (SCG) resistance (V-K_I diagrams) of magnesium aluminate spinel and its tungsten composites with different metallic content (7, 10, 14 and 22 vol. percent) is reported. It is found that tungsten plays a crucial role in the composite by increasing crack resistance: the higher the W content, the higher the stress intensity factor needed for crack extension at a given rate. The reinforcement is due to the bridging mechanism performed by metal particles, as it strongly affects the compliance of cracked specimens. Its magnitude is estimated by a compliance function PHI (a) from a double torsion test. From the compliance function, R-curve behaviour is predicted for: the composite with highest tungsten content. It explains the effect of metal particles on SCG curves. The W-MgAl_2O_4 interface is believed to influence the reinforcement mechanism.