High‐Temperature Failure of Polycrystalline Alumina: III, Failure Times

High‐temperature failure data have been obtained for two polycrystalline aluminas, revealing a strongly stress‐dependent failure time. The observed stress dependence has been compared with the dependence predicted by models of the nucleation, growth, and coalescence stages of failure. Only models of the coalescence phase indicate sufficient nonlinearity to be a plausible explanation of the data. Further observations and measurements of coalescence, involving continuous crack nucleation and shear‐band formation, are identified as requirements for further understanding of the rupture process.