Dynamics of Rolling Friction in Soft-rigid Interface

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This research project addresses the need for a comprehensive understanding of the nonlinear dynamics of soft rolling contact to enable prediction of instabilities arising from local frictional interference. The current state-of-knowledge regarding the modeling of soft contact dynamics is still based on a 300-year-old concept of a coefficient of friction, which was developed to represent global frictional behavior of hard rough surfaces. This concept ignores local stick-slip instabilities that represent an important source of excitation for any dynamic system involving friction. The effort will contribute to the understanding of dynamics of rolling friction in soft-rigid interfaces by abandoning the principles formulated by Amontons and Coulomb for rigid body mechanics, and by introducing the modern perception of soft adhesive contact behavior into dynamics analysis. Soft rolling motion is ubiquitous in countless engineering applications ranging from vehicle tires to power transmission in belt drives, to soft robotic grasping. If successful, the effort will significantly increase the current understanding of these systems, leading to analysis and design that will reduce energy losses, noise pollution, loss of accuracy, wear, etc. associated with dynamic effects. Successful completion of the research will also introduce an alternative way of addressing contact problems in flexible dynamics simulation, which will significantly expand the capabilities of the computational dynamics research community. The project includes outreach activities to increase participation of underrepresented groups in engineering through K-12 internship and training opportunities in the investigators' labs.This research will explore newly-uncovered nonlinear dynamics and instabilities associated with soft rolling contact, with the objective of posing new/incorporating appropriate first-principle models based on intermolecular (adhesive) and interatomic (viscous) interactions. Without employing the concept of a friction coefficient nor the assumption of local sliding, which are both long-held and in direct conflict with experimental observations, the approach will focus on introducing a coupling of the deterministic dynamic response of the rolling system to relative contact displacements associated with a local stochastic normal (adhesive) separation and out-of-contact tangential motion. From this conceptual context will emerge the observed nonlinear dynamics and global instabilities. Results from the predictive approach will be compared to elaborated experiments involving dynamic measurements of rolling friction, observation of contact area evolutions, and examination of deformations in the near-contact zone, while using materials having different adhesive and viscous properties.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.