Rheology Information - No shear stress at shear rates > 0

[Dean_B]

I am a mechanical engineer working for a company who will be undertaking slurry pipeline design.

We have basic rheology information on the slurry however i am unsure why the shear stress does not increase until a particular shear rate. Has anyone struck this before?

Research on the internet has come up short, typically the fluids start increasing from zero or of course if they have a yield stress they start higher on the y axis.

I have attached typical non-newtonian curves:

And the supplied rheology information:

Any help is appreciated.


Cheers
Dean

 

[Compositepro]

It is probably due to a zeroing error in the instrument. One Pascal is a very low stress.

 

[rotw]

Highly dilatant fluid which would require highly sensitive instrumentation to make meaningful measures at low shear rates?

 

[SuperSalad]

rotw probably has the right idea. If you were measuring at mPA or smaller units, you might be seeing a more "normal" curve for a dilatant fluid. The fact that the curves follow a fairly regular path with regard to concentration after the instrument starts reading would imply to me that the material's properties can be predicted with the correct level of precision.

Andrew H.

http://www.mototribology.com

 

[chicopee]

What are the components of the slurry? If it is a form of "plastisol" is it possible that some curing is taking place as the shear rate is increasing due to a temperature increase of the slurry.

 

[chicopee]

See my attachment regarding the graphs relating to rheology. I suspect that your slurry behaves pretty much like a pseudoplastic formulation according to my attachment which I got when I worked for a major international chemical company back in the early 70's.

 

[Dean_B]

Thanks for the comments,

I have since been in touch with the company who produced the results. They have stated that the instruments used were not precise enough for the fluid and that rather than no data they put in zeros.

This would suggest a dilantant type fluid.

 

[rotw]

So they do have a threshold whereby any shear stress value that is lower than the threshold is set to zero by the program handling the acquisition?