Stress non-uniformity in a hollow cylinder torsional sand specimen

Abstract

The hollow cylinder torsional apparatus (HCTA) facilitates more generalized stress path testing although it has been criticized on account of the level of stress non-uniformity that may develop because of the curvature of the test specimen wall. The stress non-uniformity which may develop in dense sand specimens (inner radius, 35.5 mm; outer radius, 50.0 mm; height, 200 mm) over small to medium strain levels in the HCTA was studied using an isotropic linear elastic stress analysis. The stress non-uniformity, quantified in terms of the stress non-uniformity coefficient , increased in proportion to the stress ratio , and was generally acceptable throughout the stress space for < 1.5. Regions where unacceptable stress non-uniformity may develop were identified in the vicinity of (,) equal to (1,0°) and (0,90°) and for all values of the parameter in the vicinity of = 45°. It was found that placing restrictions on the difference in the confining pressures which may be applied across the specimen wall thickness reduced the stress non-uniformity but also limited the regions in stress space that could be probed.