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The subject of this work is the experimental investigation and the mathematical modeling of the impact force behavior in a vibro-impact system, where a hammer is mounted on a cart that imposes a prescribed displacement. By changing the hammer stiffness and the impact gap it is possible to investigate the impact force behavior under different excitation frequencies. The experimental data will be used to validate the mathematical model. The hammer behavior is studied in more detail using a nonlinear analysis, which shows the various responses of the hammer, such as dynamical jumps, bifurcations and chaos.

The present paper proposes a novel hysteretic (non-reversible) bit/rock interaction model for the torsional dynamics of a drill string. Non-reversible means that the torque-on-bit depends not only on the bit speed, but also on the bit acceleration, producing a type of hysteretic cycle. The continuous drill string system is discretized by means of the finite element method and a reduced-order model is constructed using the normal modes of the associated conservative system. The parameters of the proposed hysteretic bit/rock interaction model is fitted with field data. The non-linear torsional vibration and the stability map of the drill string system are analyzed employing the proposed bit/rock interaction model and also a commonly used reversible model (without hysteresis). It turns out that the hysteretic model affects the stability region of the system.

The purpose of this work is the experimental investigation and the mathematical modeling of the impact force behavior in a vibro-impact system, where an impact pendulum is mounted on a cart that moves with a prescribed displacement. The dynamics of the system will be evaluated considering different excitation frequencies and changing the impact gap. Experimental data are used to validate the mathematical model. The mathematical model allows a detailed nonlinear analysis, showing the rich response of the system, which includes dynamical jumps, bifurcations and chaos. In impact systems, discrepancies between numerical results and experimental measurements are common due to the difficulty in describing all factors that influence the resulting impact force profile. The use of wires to suspend the impacting body has the purpose to limit these uncertainties.

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