Understanding the mechanism of acoustic emission generation due to surface asperity interaction in mixed lubrication conditions

当它们啮合在一起时，齿轮齿被置于非常高的负载下，并被通常只有几微米厚的润滑剂薄膜分开。高温和压力在齿轮齿之间的油膜内发展。真正的齿轮，特别是在航空航天传动中，可能有精细加工的表面，看起来很光滑，但在微观的润滑膜上，它们是粗糙的。这些粗糙表面的尖峰（称为凹凸不平）经常相互接触。这些情况会导致润滑油膜本身的失效、磨损、表面损伤和逐渐开裂（疲劳），这些在飞机发动机中都是不可取的！当材料发生变形时（例如当粗糙的表面进入加载接触时），会以瞬态弹性波的形式快速释放能量，称为声发射（AE）。这些波可以用安装在材料上的传感器记录下来，声发射方法已被广泛用于监测结构，在那里它们已被证明优于其他方法。在齿轮系统中，粗糙的接触、磨损、表面损伤或开裂会导致声发射的发生。该项目的重点是开发一种先进的计算模型，以预测由于润滑接触内的粗糙相互作用而产生的声发射水平，例如在齿轮齿之间发现的那些。先前的研究人员发现，这种粗糙相互作用是一对啮合齿轮声发射信号的重要组成部分。这项工作将成为长期目标的关键部分，即开发高速、重载动力传动齿轮的声发射监测技术。这项工作将包括基于应变能计算和润滑油膜内压力和剪切应力的高级模拟的计算模型的开发，以及一个全面的实验计划。

When they mesh together, gear teeth are placed under very high loads and separated by thin films of lubricant often only a few microns thick. High temperatures and pressures develop within the oil film between the gear teeth. Real gears, particularly in aerospace transmissions, may have finely machined surfaces and appear smooth but on the microscopic scale of the lubricant film they are rough. The peaks of these rough surfaces (known as asperities) often come into contact with each other. These conditions can lead to failure of the lubricant film itself, wear, surface damage and gradual cracking (fatigue), none of which are desirable in an aircraft engine for example!When a material undergoes deformation (such as occurs when rough surfaces come into loaded contact) a rapid release of energy in the form of transient elastic waves occurs, known as Acoustic Emission (AE). These waves can be recorded using sensors mounted on the material, and AE methods have been widely used in monitoring structures where they have been shown to out-perform other methods. In gear systems, asperity contact, wear, surface damage or cracking causes acoustic emissions to occur. This project focusses on the development of an advanced computational model to predict the levels of AE generation due to asperity interaction within a lubricated contact, such as those found between gear teeth. This asperity interaction has been found by previous researchers to be a significant part of the AE signal from a pair of meshing gears. The work will form a key part of a long-term aim of developing the use of AE monitoring techniques for high speed, heavily loaded power transmission gearing.The work will include both the development of the computational models, which are based on strain energy calculations and advanced simulations of pressures and shear stresses within the lubricant film, together with a comprehensive experimental programme.