NONSINGULAR TOUGHENING AND R-CURVE BEHAVIOR IN NOMINALLY PURE ALUMINA

More interferometry is employed to study toughening in medium to large grain size nominally pure alumina. The fracture scale length, which i s characterized by the grain size of the alumina, is systematically va ried from 35 to 102 mum. R curves are derived from bulk mode I complia nce calculations for the differing grain sizes and from the near tip m oire fringes. The level of material toughening that arises from the no nsingular processes of crack bridging and grain boundary friction are found by comparing the bulk and near tip moire R curves.