Nonsingular toughening and R-curve behavior in nominally pure alumina

Moire interferometry is employed to study toughening in medium to large grain size nominally pure alumina. The fracture scale length, which is characterized by the grain size of the alumina, is systematically varied from 35 to 102 p,m. R curves are derived from bulk mode I compliance calculations for the differing grain sizes and from the near tip moire fringes. The level of material toughening that arises from the nonsingular processes of crack bridging and grain boundary friction are found by comparing the bulk and near tip moire R curves.