Brittle fracture propagation in rock under compression

Abstract

The results of studies of the initiation and propagation of fracture from a single Griffith crack in a biaxial compressive stress field are repe~ted, It is concluded that Griffith's theory of brittle fracture offers a reliable prediction of the fracture initiation stress but that the resulting fracture propagation from a single crack cannor account for the macroscopic fracture of a specimen. Some preliminary results of studies on crack arrays and on the effects of crack closure ha compression are presented. The applicability of these results to the prediction of rock fracture in predominantly compressive stress fields is discussed.

Experiments on 3-D crack growth in uniaxial compression

“…The mechanical properties evaluated during the tests are: Young's modulus _=_4GPa; uniaxial compressive strength _=_ 140MPa; fracture toughness _=_0.6MPa-m 1/2. Two methods of modelling the internal initial disk-like cracks were adopted: (1) embedding a thin disk-like inclusion into the resin block during casting. The inclusion consisted of two aluminium foil disks greased and put together and held within the sample by two cotton threads; (2) cutting two semi-circular slots of 0.3 mm thickness in two halves of the sample and then gluing the halves together (this method was used in [4]). In order to ensure the contact between the opposite faces of the crack, teflon or greased foil disks were inserted into the slots (According to the 2-D analysis [9], the initial cracks, i.e.…”

On some general properties of strength criteria

“…These cracks are oriented along the compression direction. This kind of fracture was addressed both in some theoretical models (Martin [37], Sammis and Ashby [38], Nikitin and Odintsev [39], Dyskin et al [40]) and experimentally (Martin [37], Sammis and Ashby [38], Hoek and Bieniawski [41], Gol'dshtein et al [42]). Let us consider the problem that serves as basis for some models of fracture in a porous material under biaxial loading ( [38], [42] and [43]).…”

“…4. This follows from the fact that in a homogeneous material an inclined crack grows stably under compression, being oriented along the compression axis (Hock and Bieniawski [41], Horii and Nemat-Nasser [46], Brace and Bombolakis [56]) and unstably under tension oriented perpendicular to the tension axis (Erdogan and Sih [57]). Consequently, in this case we have a fold-type catastrophe.…”

An assessment of the state of the art in predicting the failure of ceramics: Final report

“…Criteria that account for sliding friction between opposite faces of a closed crack have been proposed [McClintock (1963);Swedlow (1976A)], but have not been firmly established [Hoek (1965)]. Comparison and discussion of various criteria when applied to biaxial stress states have been presented by Shetty and coworkers (1981Shetty and coworkers ( , 1983.…”

“…Hoek (1965) studied crack arrays and coalescence in compression because coalescence precedes failure in compression. Cooke (1982) found that microcracking precedes fracture under other conditions, as well.…”