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Unformatted text preview: Journal of Tribology Technical Note This section contains shorter technical papers. These shorter papers will be subjected to the same review process as that for full papers. Evaluation of a Model for the Evolution of Wear in a Scotch-Yoke Mechanism W. Gregory Sawyer, Kelvin I. Diaz, Matthew A. Hamilton, and Brian Micklos Department of Mechanical Engineering, University of Florida, Gainesville, FL 32611 A nearly ideal two-dimensional scotch yoke mechanism was con- structed to test a model of wear depth as a function cycle number. Model variables include the reciprocating mass, a two dimen- sional wear-rate, crank radius, and angular velocity. The model originally developed by T. A. Blanchet (1997), was nondimension- alized and simplified under conditions of large numbers of cycles, to predict the importance of including coupling based solely on a ratio of maximum allowable wear depth to the crank radius. Ex- periments show a linear progression of wear over two distinct regions, suggesting a sudden transition in wear modes just after 1.5 million cycles. The need for cycle or time dependent wear rates in analysis, which is a potentially far more significant source of error, is clearly illustrated by the experiment and discussed. @ DOI: 10.1115/1.1537271 # Introduction The ability to predict the useful life of a dynamic mechanism is of great importance to many designers and engineers. To accu- rately predict how a mechanism will perform over an extended number of cycles requires knowledge of how the components are changing during operation. A number of researchers have used numerical techniques to model wear in simulations of various contact problems and simple mechanisms @ 112 # . Additionally, there are two closed form solutions known to the authors @ 13,14 # . Generally, there is good agreement between the trends predicted by these numerical techniques, and the results gathered experi- mentally. The closed form expressions for the evolution in the components geometry and kinematics as a result of wear @ 13,14 # are untested. Blanchet @ 13 # published a two dimensional model for the simple harmonic oscillator known as the Scotch Yoke ~ a sche- matic is shown in Fig. 1 ! . This mechanism is composed of a disk with a rigidly attached pin that slides within a vertical slot con- nected to a mass that slides within a frictionless guide. The mechanism produces a purely sinusoidal motion when the faces of the vertical slot are both straight and parallel. Equations ~ 1 ! ~ 3 ! are the contact force F n ( u ), the wear depth D n ( u ), and the posi- tion of the slider X n ( u ) respectively. These equations are in terms of the number of crank revolutions n , the radius of the crank R ~ mm ! , the mass m ~ kg ! , the thickness of the slider b ~ mm ! , the angular coordinate u , the angular velocity u ~ 1/s ! , and a two- dimensional wear-rate k ~ mm 2 /N ! , which is a wear depth per line load. The model is developed for a specific harmonic oscillatorload....
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This note was uploaded on 08/22/2011 for the course EGM 4313 taught by Professor Mei during the Spring '08 term at University of Florida.
- Spring '08