An EHL Film Thickness Calculator allows calculating central and minimum film thicknesses in a full film lubricated line (cylindrical) contact as a function of entrainment speed. The central and minimum film thicknesses are calculated using equations developed by Dowson et al [1,3] and Moes et al [2,4]. The equations used in the calculator are given below the calculator along with the definitions and references. The calculator allows choosing one of the two equations in the calculations. ## Central film thickness formulas

### Dowson et al formula 

Dowson and Toyoda developed a following equation for central film thickness calculations :

(1) where

(2) Definition of the dimensionless variables are given below.

Moes developed another central film thickness equation :

(3) where

(4) with

(5) ## Minimum film thickness formulas

### Dowson et al formulas

For the calculation of minimum film thickness in a cylindrical contact following Dowson , the following equations were used:

(6) With

(7) ### Moes et al formulas

According to Moes, the equations for calculation of the minimum film thickness are as follows:

(8) where

(9) with

(10) ## Definitions:

Poisson’s ratio dimensionless,
Young’s modulus of elasticity , [Pa],
Equivalent elastic constant , [Pa],
Base oil viscosity (dynamic) , [Pa ],
Pressure-viscosity coefficient , [ ],

Mean entraining velocity , [ ] in the equations by Dowson et al. For Moes et al equations, the sum velocity is used: , [ ]
Equivalent radii of curvature in X direction , [ ]
Normal applied load , [N]
Material parameter , , dimensionless
Speed parameter , , dimensionless
Load parameter , , dimensionless
Modified load parameter , , dimensionless
Viscosity parameter , ,  dimensionless

## References:

 Dowson, D.; Toyoda, S. A central film thickness formula for elastohydrodynamic line contacts. In Proceedings of the 5th Leeds-Lyon Symposium on Tribology, Leeds, UK, September 1978; pp. 60–65.

 H. Moes. Lubrication and beyond, University of Twente lecture notes, 2000.

 D. Dowson. Elastohydrodynamic and micro-elastohydrodynamic lubrication. WEAR, 190(2), December 1995.

 Moes, H. Optimum Similarity Analysis with applications to Elastohydrodynamic Lubrication. Wear 1992, 159, 57–66.

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