Effects of grain size on the initiation and propagation thresholds of stress-induced brittle fractures

Citation
E. Eberhardt et al., Effects of grain size on the initiation and propagation thresholds of stress-induced brittle fractures, ROCK MECH R, 32(2), 1999, pp. 81-99
Citations number
31
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Geological Petroleum & Minig Engineering
Journal title
ROCK MECHANICS AND ROCK ENGINEERING
ISSN journal
0723-2632 → ACNP
Volume
32
Issue
2
Year of publication
1999
Pages
81 - 99
Database
ISI
SICI code
0723-2632(199904/06)32:2<81:EOGSOT>2.0.ZU;2-Y
Abstract
The microstructure of rock is known to influence its strength and deformati on characteristics. This paper presents the results of a laboratory investi gation into the effects of grain size on the initiation and propagation thr esholds of stress-induced brittle fracturing in crystalline rocks with simi lar mineralogical compositions, but with three different grain sizes. Strai n gauge and acoustic emission measurements were used to aid in the identifi cation and characterization of the different stages of crack development in uniaxial compression. Results indicate that grain size had only a minor ef fect on the stress at which new cracks initiated. Crack initiation threshol ds were found to be more dependent on the strength of the constituent miner als. Grain size did have a significant effect, however, in controlling the behaviour of the cracks once they began to propagate. The evidence suggests that longer grain boundaries and larger intergranular cracks, resulting fr om increased grain size, provide longer paths of weakness for growing crack s to propagate along. This promoted degradation of material strength once t he longer cracks began to coalesce and interact. Thus, rock strength was fo und to decrease with increasing grain size, not by inducing crack initiatio n at lower stresses, but through a process where longer cracks propagating along longer planes of weakness coalesced at lower stresses.