Friction: The Tribology Enigma

摩擦在生活、运输、制造、工艺工程、医疗器械和日常人类活动中发挥着核心作用。摩擦引起了阿蒙顿、库仑和达芬奇的注意，他们简单化的经验定律一直是摩擦理论的基石。在概念和理论层面上，大量的现代摩擦文献揭示了即使是最简单的过程也是巨大的复杂性，以及早期摩擦定律的局限性。摩擦与粘着、接触几何形状和磨损密切相关，所有这些都需要了解在多个长度尺度上发生的高度非平衡和非线性过程。提出的挑战是，现实工程接触中的摩擦是无法预测的。了解接触界面的物理和化学过程是破解摩擦学之谜的唯一途径。这项计划拨款中涉及的研究差距与摩擦的精确实验和数值模拟的发展有关。我们认识到，寻找一个统一的摩擦预测模型是徒劳的，因为摩擦是系统相关的。然而，预测摩擦的目标是可以实现的。我们已经确定了4个关键领域，由于以下不同的复杂性，目前在理解摩擦起源方面存在挑战：-反应表面；在许多系统中，摩擦接触导致只能用非平衡热力学描述的化学反应。我们需要通过先进的现场化学分析--极端界面--才能提供的反应的准确的动力学速率数据；这些界面可以被描述为导致高应变率材料变形并与电化学反应相结合的任何界面。模拟和感知是提高理解的关键。-非线性材料；在工程和生物系统中，我们看到用于摩擦学应用的“软”材料的演变。预测这些系统中的摩擦依赖于对流变学/摩擦学相互作用的了解。-颗粒和第二相材料；对于材料加工或了解磨损颗粒在接触中的传输，我们需要了解发生断裂/变形的复杂接触条件下的颗粒-颗粒摩擦。

Friction plays a central role in life; in transport, in manufacturing, in process engineering, in medical devices and in everyday human activities. Friction has commanded the attention of Amontons, Coulomb and Da Vinci and their simplistic, empirical laws have been the cornerstone of friction theory. At the conceptual and theoretical levels the vast modern day friction literature has revealed the enormous complexity of even the simplest processes and the limitations of the early friction laws. Friction is intimately linked to both adhesion, contact geometry and wear and all require an appreciation of the highly non-equilibrium and non-linear processes occurring over multiple length scales. The challenge presented is that friction in realistic engineering contacts cannot be predicted. Understanding the physical and chemical processes at contacting interfaces is the only route to cracking the tribological enigma. The research gap addressed in this Programme Grant is linked to the development of accurate experimental and numerical simulations of friction. We appreciate that the search for a unified model for friction prediction is futile because friction is system dependent. However, the goal to predict friction is achievable. We have identified 4 key areas where there are current challenges in understanding the origins of friction because of different complexities as outlined below:- Reactive surfaces; in many systems the frictional contact brings about chemical reactions that can only be described by non-equilibrium thermodynamics. We need accurate kinetic rate data for reactions which can only be provided by advanced in-situ chemical analysis- Extreme interfaces; these can be described as any interfaces that are inducing high strain rate material deformation and combined with electrochemical or chemical reactions. Simulation and sensing are key to improving the understanding. - Non-linear materials; in engineering and in biological systems we see the evolution of "soft" materials for tribological applications. Predicting friction in these systems relies on understanding the rheology/tribology interactions. - Particles and 2nd phase materials; for materials processing or for understanding the transport of wear particles in a contact we need to understand particle-particle friction in complex contact conditions where fracture/deformation are occurring.