Eureka! Institutional Repository

The aim of this thesis is the experimental investigation of hardness of intact rocks by the Brinell indentation method. This test consists of compressing, into the surface of a test piece, a steel spherical indenter of diameter D, with al load F for a certain period of time and measuring the diameter of the indentation d left in the surface after removal of the test force. The application of this test resulting useful conclusions for the effect of mineralogical composition and indentation load on hardness value as well as its correlation with other mechanical parameters such as uniaxial compressive strength and modulus of elasticity. The testing program consisted of a series of Brinell penetration tests on prismatic and cylindrical specimens formed from larger blocks of intact rocks. Twenty – one rocks from all three rock categories (igneous, sedimentary, metamorphic) were examined to cover the maximum possible hardness range. The total number of Brinell penetration tests was 263. All tests were performed applying a constant load of 500 kgf for 15 sec. After the tests were completed, photographs were taken and the diameter of the impression was measured using a Nikon SMZ25 microscope. From the set of penetration hardness tests the hardness of each rock was derived. Sedimentary rocks show lower Brinell hardness values than igneous rocks. The Brinell test projects the deterioration of the mechanical characteristics of rocks. Also, porosity significantly affects the hardness value. According to the results of the measurements of the impressions with the microscope, there are significant differences in the values of the depth of penetration measured with the recorder in relation to those calculated based on the diameter of the impression measured. Therefore, the Brinell hardness values obtained from the penetration depth measurement are lower than the hardness values calculated from the indentation diameter measurements, which are now considered reliable.