Parametric Analyses of the Mixed-Lubrication Performance of Rolling/Sliding Contacts in High-Load and High-Speed Conditions

This article conducts a theoretical analysis of the mixed lubrication rolling/sliding contacts using a recently developed mathematical model that incorporates asperity-level mechanical, thermal, and tribochemical aspects into the bulk elastohydrodynamic setting. A systematic parametric analysis is carried out to study the mixed lubrication in high-load, high-sliding conditions. The parameters studied include contact size, surface roughness, surface hardness, surface boundary film property, and operating load and speed. The performance and the state of contact and lubrication of the system are measured by load sharing between fluid and solid, area of asperity contacts, fraction area of asperity contacts undergoing plastic flow, as well as experimentally measurable variables such as traction coefficient, friction power intensity, and temperature of the contact. The results show that the surface roughness, surface hardness, load, and sliding velocity are very important parameters affecting the state and severity of the mixed lubrication. The results also suggest that there may be an optimal range of surface hardness to achieve the best performance. A hardness that is too low is vulnerable to mechanical stress-induced plastic deformation, whereas a hardness that is too high may cause thermal stress-induced surface distress in high sliding. The authors hope that the model and the theoretical approach can be used in conjunction with experiments to gain more fundamental insights into the performance and failure of high-load, highspeed rolling/sliding contacts in mixed lubrication.