Fracture toughness measurements on igneous rocks using a high-pressure, high-temperature rock fracture mechanics cell

Abstract

How to cite:Balme, M.R.; Rocchi, V.; Jones, C.; Sammonds, P.R.; Meredith, P.G. and Boon, S. (2004). Fracture toughness measurements on igneous rocks using a high-pressure, high-temperature rock fracture mechanics cell. Journal of Volcanology and Geothermal Research, ABSTRACTA sound knowledge of mechanical properties of rocks at high temperatures and pressures is essential for modelling volcanological problems such as fracture of lava flows and dike emplacement. In particular, fracture toughness is a scale invariant material property of a rock that describes its resistance to tensile failure. A new fracture mechanics apparatus has been constructed enabling fracture toughness measurements on large (60mm diameter) rock core samples at temperatures up to 750°C and pressures up to 50 MPa. We present a full description of this apparatus and, by plotting fracture resistance as a function of crack length, show that the size of the samples is sufficient for reliable fracture toughness measurements. A series of tests on Icelandic, Vesuvian and Etnean basalts at temperatures from 30-600 o C and confining pressures up to 30 MPa gave fracture toughness values between 1.4 and 3.8 MPam 1/2 . The Icelandic basalt is the strongest material and the Etnean material sampled from the surface crust of a lava flow the weakest. Increasing temperature does not greatly affect the fracture toughness of the Etnean or Vesuvian material but the Icelandic samples showed a marked increase in toughness at around 150 o C, followed by a return to ambient toughness levels. This material also became tougher under moderate confining pressure but the other two materials showed little change in toughness. We describe in terms of fracture mechanics probable causes for the changes in fracture toughness and compare our experimental results with values obtained from dike propagation modelling found in the literature.

Interpretation and analysis of planetary structures

“…As discussed by Olson (2003) and others, there are several possible causes for the larger than expected values of K Ic for the Ship Rock dikes. These include the temperature dependent behavior of K Ic (DeGraff and Aydin, 1993;Balme et al, 2004;Schultz et al, 2008a), mechanical interaction between adjacent segments (Delaney and Pollard, 1981), and the effects of process zones surrounding fractures (Pollard, 1987). The Candor joints lack evidence of thermal alteration, thus temperature effects appear unlikely, but are not completely ruled out.…”

Geomechanical rock properties of a basaltic volcano

“…Only recently have laboratory studies begun to systematically investigate the microstructural, physical, and mechanical properties of volcanic rocks, a material infamously known for its formation under disequilibrium conditions, thereby rich in heterogeneities at all scales. These include experiments on a range of material under relevant volcanic conditions such as thermal stressing (Vinciguerra et al, 2005;Kendrick et al, 2013a;Heap et al, 2014a), cyclic inflation-deflation cycles by intrusions (Heap et al, 2009(Heap et al, , 2010Kendrick et al, 2013a), fragmentation (Spieler et al, 2004;Kueppers et al, 2006;Scheu et al, 2008), and flow or fracture at high temperatures and/or pressures (Balme et al, 2004;Rocchi et al, 2004;Smith et al, 2005;Lavallée et al, 2007Lavallée et al, , 2008Benson et al, 2008;Cordonnier et al, 2009;Loaiza et al, 2012;Kendrick et al, 2013b).…”

Experimental and theoretical fracture mechanics applied to fracture of the crust of Venus

“…Note the decrease in stiffness of the sample; stiffness serves as a proxy for crack length because crack advance decreases the stiffness of the sample in a known fashion. After Balme et al [2004]. T is the sample temperature; P is the confining pressure; N s is the number of samples; K c is the weighted mean of the level II fracture toughness; DK c is the weighted error on the weighted mean of the fracture toughness.…”

“…The test apparatus developed to solve these problems is shown in Figure 11 (a detailed description is given by Balme [2001] and Balme et al [2004]). It is basically a high-pressure vessel (maximum confining pressure 70 MPa using inert gases, carbon dioxide, oil, water or even brine) containing a furnace system (maximum sample temperature 700°C) and an actuator and housing to deform the sample.…”

“…All components are made from Hastelloy C22, a highly corrosion resistant nickel alloy. After Balme et al [2004]. applicable to the Venusian surface; the results are summarized in Table 2.…”