about ''maximum shear stress'' in material properties of Moldflow insight

[Anonymous]

Hello

there is a field in material details in Moldflow insight as '' maximum shear stress'' . i want to know the temperature of measuring this property. and if its possible, the way and standard of measuring it.

also as it varies with temperature variation, i want to know how can i calculate maximum shear stress for the same material in another temperature individually.

thank you in advance

[bernor_mf · Accepted solution]

Hi @Anonymous ,

The maximum shear stress in material data tab Recommended Processing refer to Shear Stress definition:
Stress caused by friction between the moving plastic and the mold wall and between the layers of plastic moving at different rates.

So it is about maximum shear stress in melt.
The shear stress varies with variations in the mold temperature, melt temperature, and injection time (flow rate).
Also wall thickness plays a role : increased wall thickness reduces shear stress

The maximum shear stress in the part should be below the material limit specified.

Typical result:
Shear stress at wall result

Hope this helps.
Regards,
Berndt

[Anonymous · Accepted solution]

Thank you dear berndt for your help

It was very useful

Best wishes

Alireza

[ikv]

Hi,

I would like to bring up that topic again, as we recently also had a discussion on it (or rather on the maximum shear rate value) and the given solution still leaves a few big questions open:

How is this value determined (which measurement method is used to obtain this value)? What does it concretely mean "degradation starts above this limit" --> how is degradation defined? A certain loss of molecular weight (how much)? A certain loss of mechanical properties? Which ones, how much? How are the shear conditions controlled experimentally to find out the limiting shear rate/stress?

Is there a standard procedure to follow in order to determine these two values for a material (max shear rate and shear stress) experimentally?

It would be great if someone had answers to these open questions.

Thanks in advance!

Best regards,

Thomas

[code-ps-main-account]

Hi,

This is an interesting topic, we had many of the same questions. Looking at flow simulations with a PC/ABS blend, 'our shear stress at wall' result is way too high according to the limit Moldflow sets. But we have no idea how that limit is determined.

I think due to stress relaxation, most of the stress during injection will disappear, so that will not be the main cause of the environmental stress cracking. Although the Moldflow help files tell us that it will be.

Does someone knows more on this?

Kind regards,

Nine Klaassen - Design Engineer at Code Product Solutions