Elucidation of the various mechanisms responsible for fracture in different materials was the general subject of the Fourth Annual Symposium on Fundamental Phenomena in the Materials Sciences held January 31 and February 1, 1966, in Boston and sponsored by the Ilikon Corporation of Natick, Massachusetts. In an analysis of the brittle-to-ductile transition in polycrystalline metals, T. L. Johnston (Ford Motor Company) placed major emphasis on factors related to the plastic resistance associated with grain boundaries and the effects of plastic anisotropy. Utilizing a generalized form of the...