N12A-T010 TITLE: Developing and validating a model to understand mixed lubrication regions for fluid-film bearings

TECHNOLOGY AREAS: Materials/Processes

ACQUISITION PROGRAM: PMS 397 Ohio Replacement Program (ACAT I)

OBJECTIVE: This objective of this STTR is to develop and experimentally validate a model capable of simulating startup and shut-down of an elastohydrodynamic bearing.

DESCRIPTION: Innovative approaches are sought to model and simulate the startup and shut-down of an elastohydrodynamic (EHD) bearing. Inputs into the model should include critical film parameters during mixed and EHD lubrication transitions. Desired outcomes of this model are accurate torque and film thickness predictions throughout the mixed lubrication regime at which fully hydrodynamic conditions either occurs during startup or ceases during shutdown. The model must be experimentally validated.

Fluid-film bearings are used in several systems aboard ships. The improper design and usage of bearings can cause premature part and/or system failures leading to increased life cycle cost, decrease in mission capabilities and system availabilities. Hence, accurate understanding and modeling of these fluid-film layers are critical to the design, manufacturing, and maintainability of these bearing systems. Although fluid-film bearing modeling has advanced greatly over the past several decades and validated models for hydrodynamic and EHD regions have been demonstrated by several researchers [1,4], there is still a dearth of knowledge and validated modeling techniques to understand the operating regime between dry sliding and hydrodynamic/EHD conditions, called the mixed lubrication regime. The fluid characteristics in this region are constantly and rapidly changing, making it very difficult to understand and model. Furthermore, the focus for most of the current mixed lubrication research is on point [2, 3] and line [5] contact types (non-conformal contacts), rather than on conformal contact types, which is what bearings are and is the focus of this STTR.

PHASE I: Define and develop a concept model for the mixed lubrication region for rubber-lined bearings. Experimentally validate the concept model. Contractors may make use of public domain facilities operated by academic institutions.

PHASE II: After Phase 1 validation, further develop the model to enable combined hydrostatic, hydrodynamic, elastohydrodynamic, and mixed lubrication regions. Experimentally validate this expanded model.

PHASE III: Further develop the model to experimentally derived guidance for selection of critical film parameter for mixed-to-hydrodynamic lubrication transition. Continue to develop the model to commercially viable form or to a service provided for private sector and other government uses.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Fluid-film bearings are present in many systems, such as ships, aircrafts, automobiles, etc. A validated model for such bearings can benefit these industries during design, construction, and condition based maintenance.

REFERENCES:
[1] D. Dowson and P. Ehret. Past, present and future studies in elastohydrodynamics. Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology, 213(5):317�333, 1999.

[2] M. H. Hoeprich. Analysis of ehl circular contact start up: Part i�mixed contact model with pressure and film thickness results. Journal of tribology, 123:67, 2001.

[3] Y. Z. Hu and D. Zhu. A full numerical solution to the mixed lubrication in point contacts. Journal of tribology, 122(1):1�9, January 2000.

[4] H. A. Spikes. Sixty years of EHL. Lubrication Science, 18(4):265�291, 2006.

[5] J. Zhao and F. Sadeghi. The effects of a stationary surface pocket on ehl line contact start-up. Journal of Tribology, 126(4):672�680, 2004.

KEYWORDS: Fluid-film, bearing, elastohydrodynamic, mixed lubrication, hydrodynamic, model

Questions may also be submitted through DoD SBIR/STTR SITIS website.