Stick–slips and jerks in an SDOF system with dry friction and clearance

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Presence of dry friction and clearance discontinuities in various dynamic systems, such as friction wedge dampers in a three-piece railway freight-vehicle bogie, centre buffer coupler connecting two coaches, originate significant jerks. While nonlinear dynamics of systems, with these individual and combined discontinuities has received some attention, behavior of jerks remains unexplored. This study investigates the stick–slip effects and sources of jerks in such systems, using a representative single degree of freedom system, featuring simultaneous presence of dry friction and clearance, subjected to harmonic excitation. Den Hartog’s analytical formulations Hartog (1930) of friction mode transitions are extended numerically, to include the combined effect of dry friction and clearance, for investigation of stick–slip and jerk characteristics. It is shown that jerks can be distinguished between those arising from stick–slip effects due to dry friction and those from soft spring impacts. Limiting values of the ratio of friction force to excitation force for stick–slip motion are obtained. These frequency dependent ratios are larger than those in systems with friction alone. Multiple-stick–slip events, within a cycle, are observed at lower excitation frequencies. At higher frequencies, instances of high amplitude jerks are more than at lower excitation frequencies. A parametric study is carried out with a view to obtain the optimum range of design parameters for jerk minimization. Effects of wear and tear on jerks have also been considered through modeling of deteriorated system parameters.