Requirements for new directions in fracture research emerge from considerations of the basic lack of applicability of K parameters for definition of the fracture extension resistance of nonfrangible metals. New research is required into fact@ors relating to the increase in plastic work energy resistance defined by R curves. The urgency of such studies evolves from the increasing use of metals of low-intensity plane stress (low-shelf low-tearing-energy) characteristics in structures of high-compliance features. A case is presenkd for the mutual consideration of metaltype structure-type relationships in fracture-safe design. Present fracture-safe design practices do not include a rational approach to this question. The report provides an introduction to these considerations in terms of extension of fracture mechanics concepts@ as well as metallurgical factors and engineering practices. The importance for understanding the interact@ion of these factors cannot be overstated@ and considerable emphasis is placed on introductory aspects. Data presentation of 11 curve research is limted to illustrative examples@ which document the reality of fracture extension processes in determining conditions for structure failure. The report is intended as a precursor to topical reports on the subject.