Brookfield DV3T Rheometer Manuel d'utilisateur télécharger pdf (Page 89)

Brookeld Engineering Labs., Inc. Page 89 Manual No. M13-2100

VII.4 The Casson Model

√hD

√τ =

√τ

(τ

=shearstress, τ

=yieldstress,h =plasticviscosity,and D =shearrate)

What does it tell you?

TheCassonmodelprovidesparameterssimilartothatoftheBinghammodel.However,unlike

theBinghammodel,itwasdevelopedformaterialsthatexhibitnon-Newtonianowafteryielding.

TheCassonmodelindicatestheproduct’syieldstress(τ

)whichistheamountofshearstress

requiredtoinitiateow,andtheproduct’splasticviscosity,

h,whichistheviscosityoftheproduct

after it yields.

Figure VII-4

When should you use it?

TheCassonmodelshouldbeusedwithnon-Newtonianmaterialsthathaveayieldstressandthat

do notexhibita“Newtonian-like”behavioroncetheybegintoow.Thismodelismostsuitable

foruidsthatexhibitPseudoplasticorshearthinning,owbehaviorafteryielding.

Theseuidshaveanon-linearowcurve.Thepointatwhichitcrossesthey-axisistheproduct’s

yieldstress(τ

).Toprotectthepointatwhichthecurvewillintersectwiththey-axis,theCasson

modellinearizesorstraightenstheplotbytakingthesquarerootofthedata.Toensureaccurate

extrapolationtoyieldstressitisbesttotakesomedataatlowshearrates.

1 2 ... 84 85 86 87 88 89 90 91 92 93 94 ... 124 125

Pas de commentaire

Brookfield DV3T Rheometer Manuel d'utilisateur Page 89