Mechanical modeling of granite subjected to contact loading
Time: Fri 2019-11-29 10.15
Location: Seminarierummet Hållfasthetslära, Teknikringen 8D, KTH, Stockholm (English)
Subject area: Solid Mechanics
Doctoral student: Hossein Shariati , Hållfasthetslära (Avd.)
Opponent: Dr. Timo Saksala, Department of Civil Engineering, Tampere University of Tecknology, Tampere, Finland
Supervisor: Professor Per-Lennart Larsson, Hållfasthetslära (Avd.); Professor Francois Hild, University of Paris-Saclay, Paris, France; Dr. Mahdi Saadati, Hållfasthetslära (Avd.)
The mechanical properties of Bohus granite subjected to contact loading is investigated based on experimental and numerical results. An elasto-plastic constitutive material model combined with a damage description is employed. The material model parameters are determined based on experimental results. Any kind of inelastic deformation except the tensile failure is described by a linear Drucker-Prager (DP) plasticity model with variable dilation angle. As for the damage description, an anisotropic damage model (DFH model) is considered to account for the tensile failure (i.e. mode I fracture). The resulting constitutive model is implemented numerically to simulate the mechanical behavior of the material under indentation loading up to its load capacity. In paper A, the DP material model parameters are calibrated based on quasioedometric tests performed in an earlier work. It is described how the yield surface and dilation angle are determined from this test. The calibrated material model is implemented numerically in a commercial finite element software. The numerical model is validated based on quasi-static spherical indentation tests performed in this work. The force-penetration (P-h) response of the material is recorded during the indentation tests. Moreover, a high speed camera is utilized to observe the specimen surface around the contact area during the indentation test. It is detected that the observed load-drops in the P-h response correspond to material removals on the specimen surface. The tested specimens are also scanned by X-ray tomography to investigate the fracture pattern. In paper B, the anisotropic DFH damage model is employed in order to predict the fracture pattern observed in the indentation test. The chosen damage model considers the heterogeneity in the material tensile strength. It is described how the statistical distribution of the tensile strength is calibrated. The calibrated DFH model is combined with the DP model and the resulting DP-DFH model is utilized to simulate the P-h response and the fragmentation process of Bohus granite subjected to quasi-static contact loading.