Thermal cracks in unconfined sioux quartzite : Friedman, M; Johnson, B Proc 19th US Symposium on Rock Mechanics, Stateline, Nevada, 1–3 May 1978, V1, P423–430. Publ Reno: University of Nevada, 1978

Abstract

The morphology, orientation, and abundance of thermal cracks are characterized in unconfined specimens of Sioux quartzite subjected to (1) slow thermal cycling (< 2 C/min) to 385, 560 and 685 C; and (2) slow heating at the same rate followed by quenching from 400 C. In both, all the thermal cracks are microscopic in size and occur primarily along grain boundaries and secondarily as intragranular microfractures. The latter intersect parted grain boundaries. In the slowly cycled specimens the intragranular cracks are strongly oriented at 60 to 90 to the axis of the greatest principal elongation (100 x 10/sup -6/, elongations counted positive) of the average state of residual elastic strain in the rock prior to thermal treatment, as measured by x-ray diffractometry. This geometry suggests a genetic relation between the cracks and the net stresses resulting from superposition of the residual stresses and the thermoelastic stresses developed from differential expansions of anisotropic nearest-neighboring grains. 17 references.