Direct tensile strength measurement of granite by the universal tensile testing machine

Abstract

The direct tensile strength of a typical hard rock like granite is measured by a novel apparatus known as compression-to-tensile load transfer (CTLT) device. The rock specimen is prepared in form of a slab containing a central hole and placed in the universal testing machine where the direct tensile stress can be applied to this specimen by implementing a special type of load transferring device which converts the applied compressive load to that of the tensile during the test. In the present work, some typical hard rock specimens of granite are specially prepared and tested in the laboratory to measure their direct tensile strengths. Then, a new load converting device implemented in the universal tensile testing machine is used to cause the rock specimen to be subjected to a direct tensile loading during the test. The compressive load was applied to the transferring device at the rate of 0.02 MPa/s. Numerical modeling of the tested specimens were accomplished using the discrete element method (DEM) and the higher order displacement discontinuity method (HODDM). The tensile failure of granite rock mainly occurs along the horizontal axis. The experimental results were in a good accordance with DEM results and HODDM outputs.