Characterisation and Modelling of Mechanical Properties for Granite and Diabase

This report describes the Master thesis done by one student at the Mechanical Engineering program, Engineering Mechanics at Luleå University of Technology. The aim of the project was to characterise the mechanical impact properties of granite and diabase and to calibrate a constitutive model using the FEM-software LS-Dyna.To characterise the granite and diabase, three different experiments were performed; uniaxial compression, Brazilian disc and Split-Hopkinson pressure bar (SHPB). The uniaxial compression and Brazilian disc were performed under quasi-static condition in Luleå, while the Split-Hopkinson pressure bar test was performed under high strain rates at Nagoya Institute of Technology. Two types of rocks were used, Bohus granite and Diabase. Diabase was chosen as it has similar mechanical properties as granite but less micro cracks and defects.To choose a constitutive model suitable for granite a survey on what has been done in research before was made. The material models that were chosen were 096_MAT_BRITTLE_DAMAGE and 110_MAT_JOHNSON_HOLMQUIST_CERAMICS from the material library in LS-Dyna. They had both been used for simulating rocks and concrete before [1]. Brittle damage is a simple model with a few material parameters to define while Johnson-Holmquist ceramics is more complicated with a strain rate dependency and a lot of parameters to define.The experiments were virtually reproduced with the software LS-Dyna and the uniaxial compression and Brazilian disc experiments were solved using implicitly integration while the SHPB was solved using explicitly integration. In the implicit simulations, tests were performed with the tools both as rigid and as elastic material.It showed no difference in using different material in the tools. For the uniaxial compression the granite failed at an average stress level of 149 MPa. The results for granite in Brazilian disc showed an average tensile stress at failure of 12.2 MPa. For diabase the average stress at failure in uniaxial compression was 254 MPa. The results from the Brazilian disc gave an average tensile stress at failure for diabase of 22.2 MPa. The numerical model was also able to predict when the two rock type failed in a good and promising way.Conclusions from this work are that an experimental characterisation of Bohus granite and Diabase has been completed for quasi-static conditions. The characterisation for the rock types during dynamic conditions has started, but more experiments have to be performed. Also numerical models of the mechanical systems have been constructed to further calibrate and validate the constitutive models.Validerat; 20160325 (global_studentproject_submitter