Dynamics of Rolling Friction in Soft-rigid Interface

该研究项目旨在全面了解软滚动接触的非线性动力学，以便能够预测局部摩擦干扰引起的不稳定性。目前关于软接触动力学建模的知识状态仍然基于一个有300年历史的摩擦系数的概念，该概念是为了表示硬粗糙表面的整体摩擦行为而发展起来的。这个概念忽略了局部粘滑不稳定性，它是任何涉及摩擦的动力系统的重要激励来源。通过放弃Amonton和Coulomb为刚体力学制定的原理，并将软胶接触行为的现代认知引入动力学分析，这一努力将有助于理解软-刚性界面中滚动摩擦的动力学。从汽车轮胎到皮带传动中的动力传动，再到软机器人抓取，软滚动运动在无数的工程应用中无处不在。如果成功，这项工作将显著增加目前对这些系统的了解，导致分析和设计将减少与动态效应相关的能量损失、噪音污染、精度损失、磨损等。这项研究的成功完成还将引入一种在柔性动力学模拟中解决接触问题的替代方法，这将显著扩展计算动力学研究社区的能力。该项目包括通过K-12实习和研究人员实验室的培训机会增加未被充分代表的群体参与工程的外联活动。这项研究将探索新发现的与软滚动接触相关的非线性动力学和不稳定性，目的是提出新的/纳入基于分子间(粘性)和原子间(粘性)相互作用的适当第一原理模型。该方法不采用摩擦系数的概念，也不采用与实验观测直接冲突的局部滑动假设，而是将重点放在引入滚动系统的确定性动态响应与与局部随机法向(粘性)分离和脱离接触的切向运动相关的相对接触位移的耦合上。从这一概念背景中，将出现观察到的非线性动力学和全球不稳定性。预测方法的结果将与复杂的实验进行比较，这些实验包括动态测量滚动摩擦、观察接触面积变化和检查近接触区的变形，同时使用具有不同粘性和粘性的材料。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.