Degree Type


Date of Award


Degree Name

Master of Science


Mechanical Engineering


Mechanical Engineering

First Advisor

Sriram Sundararajan


Many newly manufactured components are subject to a run-in procedure. It is commonly accepted that performing running-in at a fraction of the target load is beneficial due to a reduction in the surface roughness of the interacting surfaces. During this process, many changes take place within the surface layer including transformations in surface roughness, chemistry, and microstructure. These transformations can contribute to changes in the surface mechanical behavior of the components. The objective of this study was to understand how the surface hardness of 16MnCr5 bearing steel evolved during running-in and how varying contact pressure and initial composite roughness affected this evolution. The evolution of the tribofilm formed by zinc dialkyl dithiophosphate (ZDDP) and how it contributed to the measured hardness was also analyzed. The results indicated a higher initial composite roughness led to greater gains in hardness as compared to higher contact pressure during the running-in process. Tribofilm growth appeared to have little to no significant effect on the measured surface hardness increase during running-in and the primary contributor to the observed hardness increase was work hardening. The results of this study can inform engineers and manufacturers in their efforts to optimize running-in procedures, thereby increasing the efficiency and durability of their service components.


Copyright Owner

Alexander David-Arthur Jenson



File Format


File Size

65 pages