Completing the hollow cylinder methodology for testing of transversely isotropic rocks: torsion testing

The paper presents the completion of the hollow cylinder methodology in the determination of elastic parameters for the mechanical description of transverse isotropic rocks. The application of a torsional stress to hollow cylinder specimens of transversely isotropic rock allows the direct determination of the shear modulus. Previously presented studies have shown how uniaxial compression and radial compression stress conditions, when applied to hollow cylinder specimens, can be used in the determination of the other four required material elastic parameters. A short description of the design and capabilities of the testing apparatus is given. Testing of an isotropic, aircraft aluminum has illustrated the reliability of the experimental system, procedures and methodology. Tests on several rock types have led to an improved empirical relationship for the approximation of the shear modulus of transverse isotropic rocks wizen no direct measurements are available. Torsion of a highly micro-cracked granite has illustrated the effect of small normal stress on the development of volumetric strains, and nonlinear stress-strain behavior resulting from small shear stresses. (C) 1999 Elsevier Science Ltd. All rights reserved.