Significance of Fracture Extension Resistance (R-Curve) Factors in Fracture-Safe Design for Nonfrangible Metals

摘要

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 factors 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 presented for the mutual consideration of metal-type 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 interaction of these factors cannot be overstated, and considerable emphasis is placed on introductory aspects. Data presentation of R-curve research is limited to illustrative examples, which document the reality of fracture extension processes in determining conditions for structural failure. The report is intended as a precursor to topical reports on the subject. A rationale is presented for the use of the Dynamic Tear test in standard and modified configurations, which provide for definition of R-curve features. Indexing of the R-curve features to the Ratio Analysis Diagram (RAD) adds new dimensions to analytical capabilities of this system. (Author)