Mechanics and physics of quasibrittle fracture of polycrystalline metals under the conditions of stress concentration. Part I. Experimental results

In the present work, which consists of three parts, we make an attempt to formulate the fundamental ideas of the theory of quasibrittle fracture of polycrystalline metals and structural alloys on the macroscopic and microscopic levels. Within the framework of the usual approach, we consider physical aspects of the problem of analysis of the elementary acts of fracture of the crystal lattice and regularities of macroscopic fracture under conditions of stress concentration in connection with the problem of structural integrity. We propose simple and convenient practical criteria of quasibrittle fracture under conditions of stress concentration and formulate physically substantiated concepts of the ductility of metals. In the first part of the work, we present the results of the experimental investigation of the fracture of specimens with stress concentrators of various geometries and fatigue cracks, establish the regularities of changes in the local characteristics of fracture, and analyze the principal factors affecting the value of the critical cleavage stress σ_f. Institute of Physics of Metals, National Academy of Sciences of Ukraine, Kiev, Ukraine. Translated from Problemy Prochnosti, No. 4, pp. 5–16, July–August, 1997.