Direct Tension Tests of Intact Rocks Using Compression-to-Tension Load Converter

Abstract

Direct tensile strength and stiffness are determined from dog-bone shaped specimens of intact sandstone, limestone and marble.  A compression-to-tension load converter is developed to allow a of the elastic modulus and Poisson’s ratio under tensile and compressive loadings on the same specimen.  A series of finite difference analyses are performed to obtain the most suitable specimen configurations.  For all rock types the direct tensile strengths are clearly lower than the Brazilian and ring tensile strengths.  The elastic moduli and Poisson’s ratios under uniaxial tensile stress are lower than those under uniaxial compressive stress, probably because the effort required to dilate the pore spaces and fissures in the rocks under tensile loading is lower than that to contract them under compressive loading.  As a result these rocks tend to be stiffer under compression than under tension.