Browse Topic: Tribology
Bench-level tribological experiments were utilized to evaluate material, coating, and lubricant formulation effects on the loss-of-lubricant survivability of tapered roller end and cone rib contacts. Cone rib and roller end contacts were simulated using a single rotating roller and rotating flat disk. The applied load and rotational speeds of the roller and disk were controlled to simulate representative rotorcraft gearbox bearing operating conditions. The contacts were lubricated for an initial period before the lubricant supply was shut off, and the supply tube was then removed. Tests continued to run, without additional oil, until the measured friction force reached a predetermined cutoff value. Weibull-based statistical analysis was used to compare the loss-of-lubrication runtimes.
ABSTRACT Loss of the primary lubrication in a helicopter gearbox can result in a very rapid or immediate failure of the transmission system due to drastic reduction in heat removal and the degrading tribological performance of the highly loaded gear contacts. Current methods for predicting the gearbox life and performance under loss-of-lubrication condition are largely experimental and experience-based and thus provide limited insights into the underlying physics of the evolving tribology of gears and bearings. One of the major technical barriers that currently constrain the physics-based predictive capability is the limited understanding and quantitative modeling of the thermomechanical response of tooth surface after the loss of lubrication. The experimental portion of the effort described in this paper is a systematic study of the temperature rise and tooth surface evolution for a generic gearbox under loss-of-lubrication conditions. The overall thermal conditions of the gearbox are
ABSTRACT The development of a Wedeven Associates Machine (WAMmp) for micro-pitting utilizes an advanced gearbox design and other support components to apply high loads and precision surface velocities while measuring traction under incipient sliding conditions. It is intended to evaluate oil and material pairs for specific performance characteristics related to high cycle fatigue and micropitting. Testing and modeling from WAMmp data creates the opportunity to predict the performance of bearing/gear materials, surface processing, and lubricants during the component design phase. Wedeven Associates, Inc. (WAI) has developed surface finishing processes to axially hone test articles to represent gear tooth finishing. The development of this method provides a meaningful tool for evaluation of new technologies and for predictive modeling for advanced gearbox and drive system designs.
ABSTRACT The current status of an ongoing effort to develop a comprehensive gearbox aero-thermodynamics and tribology simulation tool, named PSULOL, applicable to both well-lubricated and loss-of-lubrication operation is presented. PSULOL employs a multi-scale approach, wherein various physical effects including: meshing tribology, convection heat transfer within the system and to the environment, high-frequency thermodynamic effects induced by the gear meshing frequency, and the long-time response of the overall gearbox temperature to a net imbalance of heat generation and transfer to the environment are simulated separately and coupled with one another iteratively through appropriate boundary and initial conditions. As established in 2014, the first-generation version of PSULOL was the first computational fluid dynamics-based (CFD-based) tool coupled with an all-lubrication regime tribology model capable of simulating transient loss-of-lubrication failure of high-speed gearboxes
ABSTRACT Loss of the primary lubrication in a helicopter gearbox can result in a very rapid or even immediate failure of the system due to the much-reduced heat removal and the degrading tribological performance of the highly loaded gear contacts. While a limited understanding of this topic may be an acceptable risk for ground vehicles, however, a properly functioning gearbox is flight safety critical for helicopters. Therefore a deeper understanding of the degradation mechanisms is essential to accurately assess the time duration in which the helicopter gearbox can function under oil-out conditions and evaluate designs targeting the desired extension. Current methods for predicting the gearbox life and performance under the loss-of-lubrication situation are indeed largely experimental and experience-based and they provide only limited insights into the underlying physics of the evolving tribology of gears and bearings. One of the major technical barriers that currently limit the
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