young modul prediction 1

[trentar]

hallo, does anybody has expiences with theoretical predictions of young modulus? Can you calculate (assume its value) for plastic materials by any theoretical approch?
thanks in advance
r.

 

[TVP]

Is this for a commercially produced alloy, e.g. steel, aluminum, titanium, etc.? If so, then there is no need to calculate or make a prediction. Just use the accepted values listed in handbooks, etc. FYI, the elastic modulus is primarily determined by chemical bonding, and by crystallographic orientation. This means that carbon and alloy steels have the same elastic modulus, and heat treatment doesn't effect it, for example.

 

[cloa]

I think he means polymers. The theoretical calculations for young's modulus for alloys is not that close to real materials. It would be considerably worse for plastics- most of which don't have simple young's modulus due to lack of a crystalline structure and they are so sensitive to temperature and other conditions.

 

[trentar]

So, than youngs module for plastic (polymer) is not constant?!

Let say for very high temperatures and high loads how do you estimate than plate deflection? Which youngs module do you use? Only temperature dependence for young module is not wnough additionally one term must arive othervise you wil get unnormal deflection that is deflection above possble!

can you suggest more?

thank you
r

 

[SnTMan]

Testing

 

[patprimmer]

Plastics creep under load. This means that you can't get a true youngs modulus as it is also time dependent.

Testing under your real world conditions then using a pretty big fudge factor is the only safe way. That is why plastic automotive inlet manifolds have metal inserts at the bolt holes so as to take the continuous compressive load from the bolts and so prevents them coming loose and falling out.

Manifolds are typically made from heavily glass filled nylon 6.6 which has very good creep resistance for a plastic, but is still left wanting in this regard.

Simple test.

Take a test plaque, mark of an accurately measured distance along its axis

Clamp on end to a fixture with space under it.

Firmly attach a load to the other end so it stretches along the axis.

Qiuckly measure the distance between the lines.

Leave it a week, then a month and remeasure both loaded and with the load removed. That experiment tells the story.

Some raw materials manufacturers publish isocronis (isochronis?) stress strain curves, but they are probably reluctant to pass them on to the general public.

Regards
Pat
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[Pud]

As above - YM is very much strain-rate related for polymers and never quoted.

It's isochronous Pat - (well it is where I live, anyway).

Here's a top Google hit... DSM info

See attached file.



www.tynevalleyplastics.co.uk

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[Guest102023]

Test it (tricky) or google it (simple).

 

[patprimmer]

Testing it is actually about as simple as any mechanical properties test can be.

Harry you are right. I was to slack to get out my old ICI data.

I guess they spell it the same in Gordie land as they do in Welyn Garden City, but you northerners probably say it a bit different though.

Regards
Pat
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[Maui]

Young's modulus for some non-metals (including ABS plastics and carbon fiber reinforced plastics) are listed here in addition to those of metals and alloys:

http://www.engineeringtoolbox.com/young-modulus-d_417.html

For an understanding of how to actually calculate a theoretical value for Young's modulus for metals see faq330-1441


Maui

http://www.EngineeringMetallurgy.com

 

[patprimmer]

For plastics it will be an "apparent" or short term value due to the creep factor. While it may be published, it should be used with great caution.

Regards
Pat
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