Fracture Toughness and Fracture Roughness Interrelationship in Thermally treated Westerly Granite

Abstract

This paper presents an experimental work aimed at assessing the correlation between fracture toughness (K IC ) and fracture roughness for a series of Westerly granite specimens thermally treated up to 850°C. Mode I fracture toughness as a function of thermal treatment is determined using Cracked Chevron Notched Brazilian Disc specimens. The degree of roughness of the resultant fracture surfaces is analyzed with the aid of a high accuracy, high precision stereo-topometric measurement system. Roughness and toughness values display a negative correlation as a function of temperature. Fracture toughness decreases with increasing temperature due to the gradual opening of grain-grain boundaries in response to thermal stresses. Mode I fractures preferentially follow these weakened grain-grain boundaries, which in addition to the thermal expansion of individual grains, result in rougher failure profiles with increasing temperature. At low temperature, a distinct anisotropy in roughness was observed in all fracture surfaces with higher roughness values perpendicular to the direction of fracture propagation. However, higher treatment temperatures resulted in the homogenization of fracture roughness in all directions. These results confirm the important link among petrofabric analysis, fracture toughness, and fracture roughness in response to thermal treatment.

Fracture Mechanical Properties of Damaged and Hydrothermally Altered Rocks, Dixie Valley‐Stillwater Fault Zone, Nevada, USA

“…We observed both increases and decreases in K IC , SCI, UCS, and elastic properties in damaged, altered, and cemented fault zone material. Mean K IC in relatively unaltered granodiorite from the Box Canyons is similar to reported values of K IC from Westerly granite (1.74 MPa√m, Atkinson, ; 1.79 ± 0.02 MPa√m, Meredith & Atkinson, ; 1.43 ± 0.05 MPa√m, Nasseri et al, ). SCI is similar to reported values for Lac du Bonnet granodiorite (55.9, 58.5, Wilkins, ; 56, Lajtai & Bielus, ) and Westerly granite (35.9–39, Atkinson, ; 69, Swanson, ).…”

Influence of thermal treatment on mode I fracture toughness of certain Indian rocks

“…If this induced stress due to thermal treatment exceeds the tensile or the shear strength of rocks, either new cracks will develop along those boundaries, or existing cracks will migrate, resulting in irreversible structural damage (Somerton, 1992;Tian et al, 2012). The findings of this experiment are in accordance with the results of Nasseri et al (2009), who evaluated the fracture toughness of thermally treated Westerly granite up to a temperature range of 850°C and observed a decreasing trend in the fracture toughness from untreated specimen to specimens treated at 850°C. This is possibly due to a variation in the thermal coefficient of expansion of minerals such as quartz, feldspar and mica, as a result of grain-grain boundary opening and increased micro-crack density.…”

Thermal Cracking in Westerly Granite Monitored Using Direct Wave Velocity, Coda Wave Interferometry, and Acoustic Emissions

“…Assuming that thermal microcracking in Westerly Granite is isotropic and homogeneous (Nasseri, Tatone, et al, ; and also shown to be the case in La Peyratte granite by C. David et al, ), and ignoring thermal strain effects, the relative time shift in the arrival times of scattered waves may be equated to a change in the velocity of the rock. We expect the coda to contain surface waves and multiple‐reflected waves, which are both sensitive mostly to changes in v S (Grêt et al, ; Snieder, ).…”