Material grain size and crack size influences on cleavage fracturing

• Published in: Philosophical transactions of the Royal Society of London. Series A: Mathematical, physical, and engineering sciences Vol. 373; no. 2038; pp. 1 - 18
• Main Author: Armstrong, Ronald W.
• Format: Journal Article
• Language: English
• Published: England THE ROYAL SOCIETY 28.03.2015; The Royal Society Publishing
• Subjects: Cleavage; Crack Size; Dislocation Pile-Up Mechanics; Ductile-Brittle Transition; Fracture Mechanics; Grain Size; ductile–brittle transition; cleavage; grain size; crack size; dislocation pile-up mechanics; fracture mechanics
• ISSN: 1364-503X; 1471-2962
• DOI: 10.1098/rsta.2014.0124

A review is given of the analogous dependence on reciprocal square root of grain size or crack size of fracture strength measurements reported for steel and other potentially brittle materials. The two dependencies have much in common. For onset of cleavage in steel, attention is focused on relationship of the essentially athermal fracture stress compared with a quite different viscoplastic yield stress behaviour. Both grain-size-dependent stresses are accounted for in terms of dislocation pile-up mechanics. Lowering of the cleavage stress occurs in steel because of carbide cracking. For crack size dependence, there is complication of localized crack tip plasticity in fracture mechanics measurements. Crack-size-dependent conventional and indentation fracture mechanics measurements are described also for results obtained on the diverse materials: polymethylmethacrylate, silicon crystals, alumina polycrystals and WC-Co (cermet) composites.