High Frequency Elastic Wave Emission Caused by a Single Elastohydrodynamically Lubricated Contact Fundamental sources and Principles

Elastohydrodynamically lubricated (EHL) contacts are fundamental for several rotating machine elements. For example gears, rolling element bearings and lubricated chain drives work due to the principle of EHL. All of these machine elements require maintenance and, as condition based maintenance has increased in industry, the need for monitoring techniques has also increased. In order to avoid incorrect condition indications, since the 60’s researchers have improved signal processing of existing monitoring tools and developed new techniques as a complement to these existing tools. In the past two decades acoustic emission has been identified as a new complementary tool for monitoring of rolling element bearings and investigated intensively by several research groups. However, most of the investigations were carried out at low rotational speeds. Furthermore, most of the investigations used simple signal processing methods like activation counts (AC) or trend analysis of the root mean square signal (RMS). One reason for using simple experimental conditions and signal processing methods is the complexity of a rolling element bearing itself. A rolling element bearing consists of several EHL contacts and each contact has different operational conditions (film thickness, slide to roll ratio, contact pressure, entrainment speed). The measured signal is the summation of all EHL contacts. This complexity is one reason why the high frequency emissions of an EHL contact are still not fully understood. Therefore, an investigation of the acoustic emission of a single EHL contact was here carried out within the framework of a PhD project. In this thesis simplified experiments were used to represent either a single EHL contact or elements of an EHL contact. Both acoustic emissions of tensile tests and ball impacts on a solid plate were studied and analyzed with respect to their significance for EHL contacts. For all investigations carried out in this thesis an absolute calibration method developed by McLaskey and Glaser was used. This calibration method was validated for boundary restricted systems, where a good agreement for zero frequencies was found, however, unsatisfying