This paper describes an investigation of the dynamics of contact systems that exhibit nonlinear stiffness characteristics. A dynamic contact model that accommodates normal motions with either analytical or empirical descriptions of nonlinear interface compliance has been formulated. Other joint nonlinearities, such as play and discontinuous changes in friction, which have been considered previously, are avoided in this study. The interface friction is related to the normal motion through the adhesion theory of friction. Numerical analyses of the model using common joint component materials and interface finishes under dynamic loads reveal that chaotic joint motion and, by implication, chaotic friction can occur over a significant range of contact parameters and operating conditions. Even though the chaotic motions are found to be on the order of microns, the instantaneous friction force is found to fluctuate considerably in the presence of such micro-scale normal motions.

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