The influence of three elastic contact models on the dynamics of the drilling module is studied by representing the percussive drilling process as a drifting oscillator. The Kelvin-Voigt, Hertz stiffness and nonlinear stiffness and damping models were considered. The local dynamics of the system were found to be almost identical for the three models. Hence the Kelvin-Voigt system adequately describes the local dynamics of the system. However, for larger frequency and higher damping the behaviour of the three models differed. Experimental indentation studies were carried out on sandstones samples using static and dynamic loading. A force penetration relation was obtained for the loading and unloading phases of the indentation using a conical and spherical indenter under quasi-static conditions. Conical indentation tests were carried out in dynamic conditions. Both experiments showed that the force penetration relationship that could describe the contact model were closer to that obtained for the elastic-plastic indentation of ductile materials. The dynamic model for the drilling module was developed using an elastic plastic model for conical and spherical indenter. In addition, the model’s parameters were modified to those obtained from the experiments and used for the comparison with the results obtained for the elastic plastic model. The result obtained suggested a topological similarity between the experimental and theoretical parameters. It was also noted that the results suggested that the conical indenter appeared to be more efficient of the two indenter types considered. Finally, the rock fracture as a result of its contact with the drill-bit insert was investigated. For simplicity, the inserts are considered as flat punch and the contact problem is treated as a plane strain problem. Experimental studies were also carried out to determine the crack initiation angle in sandstone.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:521152 |
| Date | January 2009 |
| Creators | Ajibose, Olusegun K. |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=61011 |
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