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 tran sverse isotropic rocks. The application of a torsional stress to hollow cyl inder specimens of transversely isotropic rock allows the direct determinat ion of the shear modulus. Previously presented studies have shown how uniax ial compression and radial compression stress conditions, when applied to h ollow cylinder specimens, can be used in the determination of the other fou r required material elastic parameters. A short description of the design a nd 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 ro ck types have led to an improved empirical relationship for the approximati on of the shear modulus of transverse isotropic rocks wizen no direct measu rements are available. Torsion of a highly micro-cracked granite has illustrated the effect of sma ll normal stress on the development of volumetric strains, and nonlinear st ress-strain behavior resulting from small shear stresses. (C) 1999 Elsevier Science Ltd. All rights reserved.