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چكيده انگليسي :

Study of subsurface stresses in spur gear by load sharing method Morteza Parsa Parsa morteza@me iut ac ir Date of Submission 09 17 2012 Department of Mechanical Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language FarsiSupervisor Saleh Akbarzadeh s akbarzadeh@cc iut ac ir Abstract Gears are used to transmit power between two parts of the same machine or between two devices often with a mechanicaladvantage that allows increasing or decreasing the rotational speed or torque from one shaft to another As is commonly the case in theanalysis of most tribological components the key parameters of interest in gears are the lubricant film thickness the dimensionlessfilm parameter and the coefficient of friction The first two parameters are important in terms of reliability and damage while thethird parameter is a measure of the efficiency of the gear set in terms of the required power In industrial applications the frictioncoefficient between the moving contacting surfaces is of vital importance in terms of power loss Another influential parameter inlubricated tribosystems is the roughness of the surfaces i e the micro geometrical irregularities of the surfaces Gears usually operateunder the mixed lubrication regime Hence it is always of interest to predict the portion of load carried by asperities as well as frictioncoefficient The aim of this research is to present a model that takes into consideration the surface properties gear geometry loadingcondition and velocity condition as the input and predicts the film thickness friction coefficient and the subsurface stresses along theline of action LoA When two bodies having curved surfaces are pressed together point or line contact changes to area contact andthe stresses developed in the two bodies are three dimensional Contact stress problems arise in the contact of a wheel and a rail inautomotive valve cams and tappets in mating gear teeth and in the action of rolling bearings In this model the contact of gear teeth at each point along the LoA is represented by the contact of two cylinders where the radii ofthese cylinders vary along the LoA The contact model for rough surfaces introduced by Greenwood and Williamson 1966 assumesthat the asperities deform elastically however in reality when the contact pressure exceeds the yield strength of the material elastic plastic deformation occurs The separation between the two rough surfaces is given by the film thickness which would exist betweentwo smooth surfaces under the same conditions of load speed and lubricant In this research The model of zhao et al of rough surfacesin contact has been combined with Moes central film thickness equation and load sharing concept of Johnson et al use to predictingthe film thickness friction coefficient load carried by film and load carried by asperity a long line of action Finally subsurfacestresses is obtained using the coefficient of friction and hertzian contact model Finally by use the FEM modeling for contact problemof pinion and gear then FEM results compared with the numerical solution The comparison between the present model and theresults from other published models shows an acceptable agreement A parametric study on the effect of the load speed and surfaceroughness on the coefficient of friction and asperities scaling factor is implemented The main advantages of the model are that themodel does not require solving the full EHL equations Also it generates reasonable results for rough surfaces The results are inacceptable agreement with other works This model can be used as a rapid prediction for the gear performance Keywords Spur gear Line of action Load sharing concept Friction coefficient and subsurface stresses

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