Victor Brizmer

A Laser Surface Textured Parallel Thrust Bearing

The potential use of a new technology of laser surface texturing (LST) in parallel thrust bearings is theoretically investigated. The surface texture has the form of micro-dimples with pre-selected diameter, depth, and area density. It can be applied to only a portion of the bearing area (partial LST) or the full bearing area (full LST). Optimum parameters of the dimples, and best LST mode, are found in order to obtain maximum load carrying capacity for a thrust bearing having parallel mating surfaces. A comparison is made with optimum linear and stepped sliders showing that parallel LST sliders can provide similar load carrying capacity. Scheduled for Presentation at the 58th Annual Meeting in New York City April 28–May 1, 2003

Experimental Investigation of Laser Surface Textured Parallel Thrust Bearings

Performance enhancements by laser surface texturing (LST) of parallel-thrust bearings is experimentally investigated. Test results are compared with a theoretical model and good correlation is found over the relevant operating conditions. A comparison of the performance of unidirectional and bi-directional partial-LST bearings with that of a baseline, untextured bearing is presented showing the benefits of LST in terms of increased clearance and reduced friction.

Friction and contact between rough surfaces based on elastic-plastic sphere and rigid flat interaction

The review of a very broad research program carried out at Technion on different aspects of the fundamental contact and friction problem is presented. Sliding inception is treated as a material failure mechanism. This is different from the conventional local Coulomb friction law approach that is based on a certain arbitrary friction coefficient or some modified forms that assume power law dependency between the normal and tangential stresses at the contact interface. The reviewed models show strong effect of the external normal load and nominal contact area on the static friction coefficient contrary to the classical laws of friction. Contact of rough surfaces plays an important roll in friction modeling. Surface roughness can be modeled by multitude asperities having spherical summits of uniform curvature but a statistical height distribution. A single asperity interaction can be modeled by the contact between an elastic-plastic sphere and a rigid flat. Hence, the results obtained for the contact of a sphere and flat can be extended to the case of rough surfaces contact and friction. Since the static friction is considered as a yield mechanism the problem of the elasticity terminus of a spherical contact is also discussed concerning perfectly slip and full stick contact conditions, and failure inception of ductile and brittle materials. The multiple load-unload contact cycles are also considered.

A Model for Junction Growth of a Spherical Contact

The evolution of the contact area (junction growth) of an elastic-plastic preloaded spherical contact subjected to an additional tangential loading is investigated theoretically. The normal preloading leads to the formation of a junction that can support additional tangential load. A gradual increase of this tangential load, while the normal preload remains constant, can incept plasticity of the contact zone in case the initial normal preload was elastic or enhance an existing one, thus lowering the tangential stiffness of the junction. Finally, the tangential stiffness approaches zero which corresponds to sliding inception (i.e. loss of stability). The evolution of the contact area during the tangential loading prior to sliding inception reveals an essential junction growth which depends on the magnitude of the normal preload. The mechanism causing this junction growth seems to be new points of the sphere surface, which originally lay outside of the initial contact area that are coming into contact with the rigid flat during the tangential loading. A theoretical relation is developed for the dependence of junction growth on the normal preload, which correlates well with some limited experiments.Copyright

Elastic-Plastic Spherical Contact Under Combined Normal and Tangential Loading

The behavior of an elastic-plastic contact of a deformable sphere and a rigid flat under combined normal and tangential loading with full stick contact condition is investigated theoretically. This allows static friction modeling under highly adhesive conditions. Combined loading begins with a normal preload that produces an initial contact area and causes elastic or elastic-plastic deformations in the contact zone. The full stick contact condition leads to a junction between the contacting bodies which can bear tangential loading. On the second stage of the loading process, the tangential load is being applied gradually, while the normal load remains constant. The maximum tangential load that can be supported by the junction prior to sliding inception is determined as the static friction. The effect of normal load on this static friction is investigated. The evolution of the contact area during the tangential loading revealed an essential “junction growth” mainly just before sliding inception.Copyright

THE EFFECT OF CONTACT CONDITIONS ON REPEATED LOADING OF AN ELASTIC-PLASTIC SPHERICAL CONTACT

The influence of both full stick and perfect slip contact conditions on the unloading and multiple loading of a deformable sphere by a rigid flat is investigated using the finite element method for various values of the Poisson’s ratio and the modulus of elasticity over the yield strength ratio. The residual deformations and stress field within the sphere tip, as well as changes in the size of the contact area following multiple loading cycles are analyzed.Copyright

Failure Inception of a Spherical Contact Under Slip and Stick Conditions for Various Material Properties

Failure inception of a deformable sphere loaded by a contacting rigid flat is analyzed separately for perfect slip and for full stick conditions and various material properties of the sphere. Ductile yielding and brittle failure inception of the sphere is identified by the critical interference and associated normal loading as well as the location of the first yield or failure occurrence. The analysis is based on the analytical Hertz solution for frictionless slip condition and on a numerical solution for stick condition. Failure inception is determined by using either the von Mises criterion of plastic yield or the maximum tensile stress criterion of brittle failure.Copyright