Degree
Doctor of Philosophy (PhD)
Department
Mechanical Engineering
Document Type
Dissertation
Abstract
Lubricating grease is an ideal lubricant for many devices such as roller bearings, journal bearings, slide bearings, gears, and many types of joints due to its simplicity. Once grease is put in place, it can often provide adequate lubrication for extended periods of time without the need for a complex supply system that would generally be needed for oil lubrication. However, during prolonged use, various degradation mechanisms change the physical and chemical properties of grease, possibly leading to inadequate performance and machinery failure.
In order to succinctly quantify the degradation of grease, it is essential to have robust, meaningful test methods. Development of such test methods is a key focus of this work. Numerous methods were considered, and the most suitable among these were selected for further use to quantify grease degradation. Unlike existing standardized methods, these identified techniques have the capacity to describe the structural integrity of a very small sample of grease. Thus, samples can be taken from machinery and analyzed in terms of the widely recognized method of cone penetration.
Using these techniques, degradation in standardized tools was analyzed and modeled with reasonable accuracy. In addition, the overall theory describing mechanical degradation was investigated in detail, showing that mechanical degradation at low shear rates is not well understood. However, by considering a restricted, practical range of shear rates, the mechanical degradation of grease can be modeled using the concept of entropy with reasonable accuracy on a useful time scale.
A key contribution of this work is the identification of useful correlations between rheological properties and cone penetration. Due to the ubiquity of cone penetration measurements, the ability to estimate this property using a substantially smaller sample represents an important advancement in used grease sample analysis. Another important contribution is an identification of various time scales of mechanical stability and how they must be understood in order to properly measure a grease sample and isolate permanent degradation from temporary microstructural arrangement. Finally, it was shown that a simplified version of entropic theory may be applied to the degradation of grease within a restricted, yet practical region.
Date
11-17-2024
Recommended Citation
Gurt, Alan, "Measuring and Modeling Grease Degradation" (2024). LSU Doctoral Dissertations. 6610.
https://repository.lsu.edu/gradschool_dissertations/6610
Committee Chair
Khonsari, Michael