Mechanics and physics of quasibrittle fracture of polycrystalline metals under conditions of stress concentraiton. III. Toughness of metals and alloys

We consider new characteristics of toughness based on the fundamental ideas concerning the micromechanism of quasibrittle fracture of metals and taking into account the specific features of fracture under the conditions of stress concentration. Unlike the existing characteristics of toughness (e.g., impact toughness), these characteristics can be directly used in the numerical analysis of load-carrying structural elements. By analogy with the safety margin, we introduce the concept of the "safety margin of toughness" of a metal. We propose analytic relations for the evaluation of the safety factor of toughness of a metal in products containing structural stress concentrators and macrocracks. For these types of concentrators, we deduce the relationships between the ordinary safety factor and the safety factor of toughness. We analyze the values of toughness for low-, medium-, and high-strength steels and propose opitmal combinations of the strength and toughness characteristics of metals. The relationships between the new characteristics of toughness and K sub IC are also established. (Example materials include iron, alloys 40Kh and 30KhGSA, among others.)