The Research Of The Longitudinal Vibration In Cone Bits-rock System

During drilling, the performance of cone bits directly effects the drilling process mainly in the form of operating efficiency, quality and cost, in which the longitudinal vibration of the drill string is most harmful and frequent. As a result of the longitudinal vibration, pressure is not evenly applied to cone bits so that it could be disconnected with the well because of pressure fluctuation, which could cause premature failure of bearings and teeth with impact loads and affect service life of cone bits. Therefore, dynamic analysis of cone bits is important both theoretically and practically.In this paper, the mechanism for breaking rocks is discussed and based on studies in geometry and kinetics, cone bits is regarded as elastic solid and rocks plastic and brittle body with differernt characters in different directions. The structure of rocks is established by using the elastic-plastic model, Drucker一Prager. Moreover, the finite element modelling for the longitudinal vibration of cone bits-rocks system is bulit.By introducing contact boundary condition and judgement, the process of breaking rocks is simulated by ABAQUS software, by which impact force, longitudinal vibration speed and acceleration as well as recovery coefficient are obtained. For analyzing craching, cracking modelling is established on the basis of stress-strain relations, where differences in the shap and volume of cracking between different rocks and teeth are discussed. Eventually, the optimum teeth space and cracking efficiency are available, which is meaningful both theoretically and practically to study kinetic rules, performance of cone bits in line with the state of rocks.