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Mesoscale testing

Mesoscale testing

requires

accurate

motion

at

low

speeds Maximum velocity of 50 mm/s

Load range: 01 N (100 g) Insitu coefficient of friction monitoring (monitoring transitions)

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Small scale testing

Apparent contact

area

1

100

mm

2

More than 400 world wide test methods for small scale testing

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Large scale testing

Apparent contact

area

10

410

5

mm

2

Using large scale specimens aid towards reducing the effect of stress

concentrations near the sample edges

Sliding instabilities which are hidden in small scales show more frequently in

largescale

testing Large scale tests are closer to actual working conditions

Normal loading up to 6000 kN

Polymer samples150x150x20 mm 3

Counterface steel410x200x20 mm 3

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Meso scale to small scale correlation

pv value is contact pressure p x sliding velocity v, solid lubricant is PTFE

Meso scale tests are performed with flat on flat geometry at 1.15 N (0.0018 MPa),

3.30 N (0.0052 MPa), 5.16 N (0.0086 MPa) and 0.12, 0.5, 2.0, 8.0 m/s. Small scale tests are perfomed with cylinder on plate geometry at 50 N, 100 N, 150 N, 200 N and 0.3 m/s.

Scratch testing of polymer surfaces

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Scratch testing of polymer surfaces

Rigid tip on PMMA

pm

average contact pressure

pm

= Fn

/a

Y

Yield stress

a true contact area

R radius

of

tip

Indentation of polymers

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Indentation of polymers

In general, as load increases displacement increases due to both elastic and plastic

deformation of testing material When holding the load, viscoelastic (time dependent) effects are observed Elastic recovery is observed during unloading part

Berkovich tip3sided pyramid

a = 65.03 o

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Multidirectional vs unidirectional sliding

Friction induced molecular orientation in the unidirectional sliding of UHMWPE This is not the case during multidirectional sliding UHMWPE is used in artificial joint prosthetics

http://bmcortho.com/about/education.stryker_brochures.english.mis_hip.2.php

Polymer on polymer bearing sliding for MEMS

http://bmcortho.com/about/education.stryker_brochures.english.mis_hip.2.phphttp://bmcortho.com/about/education.stryker_brochures.english.mis_hip.2.phphttp://bmcortho.com/about/education.stryker_brochures.english.mis_hip.2.phphttp://bmcortho.com/about/education.stryker_brochures.english.mis_hip.2.phphttp://bmcortho.com/about/education.stryker_brochures.english.mis_hip.2.phphttp://bmcortho.com/about/education.stryker_brochures.english.mis_hip.2.php

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Polymer on polymer bearing sliding for MEMS

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PDMS frictionPolydimethylsiloxane

(PDMS) Elastomers

PDMS A has lower initial molecular weight than PBMS B Black lines are free and pendant chains emerging from the PDMS surface PDMS B Chains can be oriented and can reduce macroscopic friction coefficient

PDMS

A

Chains

are

short

and

are

sticking

to

AFM

tip,

increasing

the

friction

coefficient

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