Interplay of fretting wear, fatigue and damping: Influence of contact shape and mode of loading

微动磨损和微动疲劳在使用经受振动的摩擦接触的应用中代表了相当大的和长期存在的问题，例如热交换器中的管、骨科中的接头或燃气涡轮机的燕尾叶片根部的微动磨损。微动的物理原因是摩擦接触边界附近的局部滑动。这是由于曲面接触时，接触边界上的法向压力为零。这种局部滑动和由此产生的微动磨损只能通过使用与锋利边缘的接触来防止（例如，平端圆柱体）。然而，在这种情况下，法向和切向应力在边界处都将是奇异的，并且高振荡应力将导致微动疲劳。因此，振动下摩擦接触的应用程序应该找到一个最佳路径之间的Scylla微动磨损和Charybdis微动疲劳。避免微动损伤的一种方法可能是在不同的振荡模式之间引入相移，这导致移动的滑动区，并可能定性地改变磨损和疲劳的特性。另一种方法可以是完全抑制振动。然而，在许多结构中，这种抑制只能由于微滑移引起的阻尼而发生。然而，高结构阻尼由于摩擦（不损坏接触表面）也可以是一个积极的建设性的目标本身（如在空间应用）。在本项目中，我们研究这三位一体的“磨损疲劳阻尼”的钢对钢的微动接触。我们将研究从微动磨损到微动疲劳的过渡，通过不断改变形状从抛物线到平顶，并考虑叠加的正常和切向振荡与各种振幅和相移。预期的研究工作旨在减少微动损伤，从而增加摩擦学系统的寿命。该项目将包括广泛的经验研究，从短期模型实验到非常长期的耐久性和疲劳测试。实验研究将得到物理模型和基本接触力学及控制损伤机制的数值模拟的支持。柏林工业大学的“系统动力学和摩擦物理”系是开展该项目的所在地，该系在摩擦学领域拥有出色的研究经验，是研究动态接触问题的世界领先机构之一。

Fretting wear and fretting fatigue represent a considerable and long standing problem in applications using frictional contacts subjected to vibrations as e.g. fretting of tubes in heat exchangers, joints in orthopaedics, or dovetail blade roots of gas turbines. The physical reason for the fretting is partial sliding in the vicinity of boundary of a frictional contact. It is due to the vanishing normal pressure at the contact boundary in contacts with curved surfaces. This partial slip and the resulting fretting wear can only be prevented by using a contact with sharp edges (as e.g. a flat-ended cylinder). However, in this case, both normal and tangential stresses will be singular at the boundary, and the high oscillating stress will lead to fretting fatigue. Thus, applications with frictional contacts under vibrations should find an optimal path between Scylla of fretting wear and Charybdis of fretting fatigue. One way to avoid fretting damage could be the introduction of phase shifts between different oscillation modes which leads to a moving slip zone and may qualitatively change the character of wear and fatigue. Another way could be to completely suppress vibrations. However, in many structures this suppression can only occur due to damping caused by micro slip. Nevertheless, high structural damping due to friction (without damaging the contacting surfaces) can also be a positive constructive goal for itself (as e.g. in space applications).In the present project we study this triad “wear-fatigue-damping” for the fretting contact of steel-on-steel. We will study the transition from fretting wear to fretting fatigue by continually changing the shape from parabolic to flat-ended and by considering the superposition of normal and tangential oscillations with various amplitudes and phase shifts. The intended research work aspires to reduce fretting damages and thereby increase the life span of tribological systems. The project will comprise extensive empiric investigations, ranging from short-term model experiments to very-long-term endurance and fatigue tests. The experimental investigations will be supported by physical models and numerical simulations of the underlying contact mechanics and the governing damage mechanisms.The department "System Dynamics and Friction Physics" of Technische Universität Berlin, where the project is to be carried out, has excellent research experience in the field of tribology and is one of the world's leading institutions in the investigation of dynamic contact problems.