Abstract

Jacketed cylindrical specimens of pure, homogeneous, anisotropic Hasmark dolomite have been deformed dry under a constant confining pressure of 5000 atm at a strain rate of 1 per cent per minute. Uniaxial compression and extension experiments were carried out on cylinders oriented parallel and perpendicular to the direction of the optic-axis maximum of the fabric, and tests were conducted at room temperature and at 300°C for each orientation. All tests ended in fracture along a shear surface inclined at about 60° to the least principal stress axis, at a strain of less than 10per cent. The stress-strain curves obtained suggest (1) little or no strength anisotropy beyond the yield points, (2) little or no effect of temperature on strength or ductility, (3) a marked dependence of strength on normal stress.

The grain orientation of the deformed specimens was investigated by standard U-stage methods. After deformation at 300°C the principal visible change in the fabric is a moderate development of forumla twins. Measurements indicate that these have a negative1 direction sense of gliding, thus conforming with the recent lattice analysis of Bradley et al. (1953) and the recent experimental work of Turner et al. (1954). Observed results compare favorably with predicted deformed fabrics based on the assumption of twin-glide on forumla in a negative sense, a mechanism further supported by lamellae-spacing index data. No unequivocal evidence for translation-glide on the base {001} or for any other mechanisms was found. However, preliminary results of single crystal experiments confirm Johnsen's (1902) discovery of basal translation.

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