Simulating force on elastomers

[howiep]

Hi guys,


I'm designing a product that contains a silicone collapsing part moulded onto plastic suppourts, sort of like this collander, but it is asymmetrical (more of a dustpan shape)

[url]http://www.bettywilde.com/product.php?prid=215193&pn=Col lapsible-Colander[/url]


I am an intermediate-advanced Pro/E user, but haven't had much experience with Mechanica, or the other analysis tools. Would these tools give me the ability to find out things such as:
- Will thecollapsing partstay inside out, or pop back open on its own?
- How thick the material should be to make it collapse easily, and whether it will collapse evenly.


I suppose Iwould love it ifsomeone with experience could speculate about whether this sort ofcapability is possible, and if it would take tens of hours to learn and setup.


I have modelled some other elastomer products and eventually got them right by guesswork and prototyping, but this design ismore tricky, andlarger (therefore more expensive to prototype).


Thanks heaps,


Phil

 

[moriarty]

Cant help greatly - it will be difficult to model - large
displacement, rubber, bificating structure (popping in and
out) maybe there's a genius out there that can do that ....

digressing ... is this silicone bakeware stuff safe - we
used to make silicone rubber seals and they gave off toxic
white gas when they were temperature cured. We also have
used them on burners and they quote 250degC but if you run
them at this they go hard and break down gradually and coat
the burner internals with a white powder - not sure Id want
that in my food

 

[howiep]

Hi Moriarty,


Thanks for your advice. I suspected it was going to be too much of a mission, but it's good to have a second opinion to silence the "what if's" in my head as I try to magically predict how this silicone will behave.


Happy to answer yourquestion, our company does a lot of siliconekitchenware.The answer is that there are so many different grades of silicone, from cheap rubber substitutes, up to the stuff they use for medical implants. Good kitchenwarebrands usesilicone that is approved by FDA (US) and LFGB (Europe) standards. There are different standards for different uses. For examplesilicone used for a spoonhas to undergo a food contact test, where they boil it in oil, acid, water, etc and look for the migration of VOC's heavy metals, etc.European standards agenciesactually require samples from distributors to test themselves. Once we faileda test(by a tiny margin) and got in big trouble. So, I feel safe buying silicone cookware knowing what we have to go though to get it on the market.FYI US standards are less tough, if in still indoubt buy a brand that also sells in Europe.


As for the heat thing - A lot of cheap silicone grades are blended with rubber or plastic, and this reduces their heat/food safety properties. A good way to tell is to pinch or twist it. Ifyou see itgo whiteit's probably got filler in it.


Me thinks it's time to stop procrastinating and get back to this model.


Cheers,


Phil

 

[Atropos89]

You could try something like this. It's a video tutorial on living hinges and the warp feature by Leo Greene. Sure, it's in WF3, but the same idea applies.


Also, thanks for the info on the silicone kitchenware.

 

[wanqichao]

it's very hard to simulate this problem.


contact,super-elastic,large deform,....


you can try to analyse this problembased on some postulations.

 

[moriarty]

Thanks Phil for the reply - seems the quality of the
silicone supply line will be critical to the customers
health outcome.

With regards Mechanica analysis, I struggled modelling
the large displacement of a Belleville washer in WF4.
Mechanica did the large displacement OK but the calcs
didn't compare very well to other published results.

You might want to have a read of the following link about
Mechanica's new materials capabilities

http://communities.ptc.com/message/152791#152791

Seems there's a lack of documentation from PTC
Edited by: moriarty

 

[howiep]

Thanks for the info guys. Zach, that's something I hadn't seen before. I really need to learn more about mechanisms. The technique in the video looks interestinig, but I think it wouldn't be much more than a visual effect. For example the ridges on that bellows wouldn't ever strech flat like in real life because the warp tool doesn't factor in the length of the surface.


Moriarty the PTC doccument there looks mega complicated for a simple (and possibly innacurate) result.


As I said before, this one is in the waay too hard basket, but thanks heaps for the interesting info and advice. I will watch this space in the future.


Phil