The mode transition from mild to severe wear - observation of the realistic contact area under shear stress -

Burwell和斯特朗在1952年提出的轻到重载荷条件下的临界值，作为从轻度磨损到严重磨损模式转变的概念，本文试图在考虑各向同性和高斯表面的情况下，对临界值进行估计，并通过直接观察加以验证。简而言之，阈值条件表示为标称接触面积完全被屈服面积覆盖时的临界压力。采用随机粗糙表面接触理论和约翰逊的弹塑性压痕模型，结合Chang-Etsion的分析，计算了该临界压力。粗糙微凸体的顶点被假定为球形，并且所有的粗糙微凸体都具有相同的半径。分析了滑动对粗糙表面接触的影响。采用滑移线场理论，将接触视为二维粗糙面与平面的接触，设计了微滑移机构，能够施加法向载荷和剪切载荷，观察真实接触点。在纳米驱动器的设计中，首先设计了压电扫描工作台，但由于其接触处的剪切变形很难减小，并且由于电机驱动滑块移动400 mm的末端磨损，很难观察到附着状态。机械特性（正常压力，剪切应力，杨氏模量，硬度和剪切强度的表面），几何特性（表面粗糙度和形状）的影响进行了研究的磨损模式的讨论。在不久的将来，计划直接观察实际接触面积，即接触微凸体的形状、数量和面积。

The threshold of load condition from light to heavy that Burwell and Strang proposed in 1952 as a concept of the mode transition from mild to severe wear, are tried to be estimated considering isotropic and Gaussian surface, and verification by direct observation. In brief, the threshold condition is expressed as the critical pressure at which the nominal contact area is wholly covered with the yielding area. This critical pressure has been calculated using stochastic rough surface contact theory and Johnson's Elastic Plastic Indentation model with Chang-Etsion's analysis. Individual summit of rough asperity has been assumed to be a sphericity and all of them to have the same radius. Analysis has been developed the effect of slip on rough surface contact. The contact is regarded as 2D and is assumed as that between rough surface and plane to apply the slip line field theory.Micro-sliding mechanism are designed for the system which is able to give the normal load and shearing load to observe the realistic contact points. At the beginning the piezo-scanning stage would be planned for nano-scaled actuator, but it is difficult to decrease the shear deformation at their contact, observe the status of adhesion due to wear of the end of the 400 mm traveling by motor actuated slider.In the experiments, normal force and tangential force are measured simultaneously. The effects of mechanical characteristics (normal pressure, shear stress, the Young's modulus, hardness and shear strength of surfaces) , geometric characteristics (surface roughness and shape) are investigated in the discussion of the wear mode. The direct observation of the realistic contact area, which mean the shape, number and area of contacted asperity is planed in the near future.