Showing papers by "Itzhak Green published in 2006"

The Behavior of Thrust Washer Bearings Considering Mixed Lubrication and Asperity Contact

Abstract: The behavior and life of a tilted flat thrust washer bearing is modeled by a comprehensive numerical code. The goal is to investigate the conditions that distress thrust washer bearings through numerical techniques. The thrust washer bearing supports non-axisymmetric loads within the planetary gear sets of automatic transmissions and consists of flat-faced washers placed between an idle helical gear and its contacting face. Because of non-axisymmetric loading, the gears and washers tilt in relation to the carrier, forming a converging gap that may produce hydrodynamic lift. Various coupled numerical schemes model sliding friction, boundary lubrication, asperity contact, thermo-viscous effects, and full film lubrication. The model provides predictions of frictional torque, bearing temperature, hydrodynamic lift, and other indicators of bearing performance. The results show that the bearing operates in the regimes of boundary lubrication, mixed lubrication, and full-film lubrication, and that the bearing ca...

Experimental Investigation of Thermal and Hydrodynamic Effects on Radially Grooved Thrust Washer Bearings

Abstract: In this study, an experimental investigation on the effects of grooves on thrust washer bearings is investigated. Eight equally sized grooves are machined about 100 μ m deep into one side of a flat-faced steel washer. This thrust washer bearing is located between a helical gear and its carrier and is tested on a test rig capable of measuring frictional torque and the temperature of the bearing at different speeds. It is found that the grooved washers had lower bearing temperatures and failed at significantly higher loads than the control washer with no grooves. For a test procedure with varying operating conditions, the coefficient of friction is also significantly lower for the grooved washers. However, the grooved washers had about the same coefficient of friction as the control washers at each step when the speeds are very high. The results from various tests suggest that the increased amount of lubricant passing through the grooved surface of the washer removes heat from the washer bearing by convecti...

A Finite Element Study of the Deformations, Forces, Stress Formations, and Energy Losses in Sliding Cylindrical Contacts

Abstract: This work presents the results of a Finite Element Analysis (FEA) used to simulate two-dimensional (2D) frictionless sliding between two interfering elasto-plastic cylinders. The materials for the cylinders are both modeled as elastic-perfectly plastic and follow the von Mises yield criterion. The FEA results in trends in the deformation, reaction forces, stresses, and net energy loss as a function of sliding distance. All these results are found to be related to the magnitude of vertical interference. In addition, equations representing the pattern followed by the residual deformation for each of these interference cases are shown. Contour plots of the von Mises stresses are also presented to show the formation and distribution of stresses with increasing plastic deformation as sliding progresses. This work shows that for the plastic loading cases the ratio of the vertical force to the horizontal reaction force is not zero at the point where the cylinders are perfectly aligned about the vertical axis. This work also presents empirical equations that relate the net energy loss due to sliding under an elasto-plastic deformation as a function of the sliding distance. In addition, a “load ratio” of the horizontal reaction force to the vertical one is defined. Although this is analogous to the common definition of the coefficient of friction between sliding surfaces, it just contains the effect of energy loss in plasticity. The values of the contact half-width are obtained for different vertical interferences as sliding progresses.Copyright © 2006 by ASME

Predicting the coefficient of restitution of impacting elastic-perfectly plastic spheres

Abstract: The current work presents a different meth- odology for modeling the impact between elasto- plastic spheres. Recent finite element results modeling the static deformation of an elasto-plastic sphere are used in conjunction with equations for the variation of kinetic energy to obtain predictions for the coeffi- cient of restitution. A model is also needed to predict the residual deformation of the sphere during rebound, or unloading, of which several are available and com- pared in this work. The model predicts that a signifi- cant amount of energy will be dissipated in the form of plastic deformation such that as the speed at initial im- pact increases, the coefficient of restitution decreases. This work also derives a new equation for the initial critical speed which causes initial plastic deformation in the sphere that is different than that shown in pre- viously derived equations and is strongly dependant on Poisson's Ratio. For impacts occurring above this speed, the coefficient of restitution will be less than a value of one. This work also compares the predictions between several models that make significantly differ-