Tribology Lab• Objectives: Characterize elastohydrodynamic (EHD) lubrication using an optical

technique. The study involves:– Measurement of the lubricating film thickness as a function of:

• rolling velocity• normal load

– Comparison of the measured film thickness with a theoretical film thickness (from the Hamrock & Dawson equation)

• Experimental Setup:

ME 4053

Nd

Glass plate (connected to motor)Steel ball

LightSource

MonitorCamera

LoadingMechanism

Light Source:

Contact Area

FiberopticCable

Camera

aperture

condenser

Semi-reflectiveSurface

Experimental Setup (cont’d)

rc

Nd

top view: side view:

W(load)

Fringe pattern

Camera

LightBeam

h

oilfilm

glassdisc u

Nd: rpm; u: rolling velocity; h: film thickness

Rolling velocity:60

2 dcNru

Measured oil film thickness: )(2

N

nh , where:

: wavelength of light in air (600nm) N: fringe order

n: refractive index of oil (1.5) : phase shift constant (0.1)

fringes)(dark 0.5,1.5,

)fringesbright(,3,2,1

exp

Experimental Procedure: obtain the following table for W=16N & W=30N

Fringe N Nd (rpm) Nd (rpm) u (m/s) h (nm) ht (nm)fringe order trial 1 trial2 velocity experimental theoretical

Dark 0.5 2 2 80Bright 1 180Dark 1.5 280Bright 2 380Dark 2.5 480Bright 3 580Dark 3.5 680Bright 4 780

measured computed from Nd, N computed fromHD equation

Theoretical Thickness, ht: The Hamrock & Dawson Equation

])()()(9.1[ 53.0*067.0*67.0* GWURht

R: ball radius W*: dimensionless load parameterU*: dimensionless speed parameter G*: dimensionless material parameter

t

Results Presentation:

*Practical note on load adjustment:

Load = 2 x (spring value - tare value)

Ex: to get W=16N, set spring value to 11.2N16 = 2 x (11.2 - 3.2)

(tare = 3.2N)

Theoretical/Experimental Comparison:

10-2

10-1

100

10-8

10-7

10-6

Rolling velocity (m/sec)

Film

th

ick

nes

s,

h (

m)

Comparison of theoretical and experimental film thickness

Theoretical data, W=16N Experimental data, W=16NTheoretical data, W=30N Experimental data, W=30N

Reporting Requirements

• Notebook entry only• Must have objective, setup, procedure, per usual.

Be sure to have plot of results similar in format to what is shown on previous slide

• Provide conclusions. Be sure to address how well experimental results match theoretical and explain relationship between normal load, rolling velocity, and film thickness