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Yield simulation?

Yield simulation?

Yield simulation?

(OP)
Hi everyone, I only have the basics with FEA so I'm hoping this isn't a dumb question. I'm working with Strand7 and have a simple structure modeled (roughly an ovoid coming out of a flat surface) that will be deformed from a load pulling it to the side. It's a basic setup so far, using isotropic material properties and non-linear analysis. I was wondering later about how much force would be needed to cause a break in the structure, and found in the literature that the material used has a fracture toughness of 4.12±0.4MPam^1/2
(http://jeb.biologists.org/content/jexbio/215/9/150...).
However, I've only done simple stresses / deformations / etc before and never had to deal with any fracturing. Can someone explain how I would go about doing this in Strand7? I'm not sure if this involves entering a stress/strain table into the model or if there's a way to calculate from the results I already have if the stress is "too much" in any location.
Thank you for any help!

RE: Yield simulation?

what material? is it ductile?

RE: Yield simulation?

(OP)
It's sclerotized insect cuticle, which isn't really ductile.

RE: Yield simulation?

The link says it's a similar ductility to wood, so that's pretty ductile compared with many materials.

I'd suggest:
- do your own trials with a simple elasto-plastic model
- review the literature and see what other people are doing
- review the Strand7 web-notes for relevant material
- when you have a clearer idea of the basic approach, speak to the Strand7 suppliers and get their recommendations about how to best handle it in that program.

Note that there are quite a few optional settings for the non-linear analysis solver, and the defaults are not necessarily the best, especially if you are going to have large plastic strains.

Doug Jenkins
Interactive Design Services
http://newtonexcelbach.wordpress.com/

RE: Yield simulation?

It may be possible to work the formula No. 4 for Kc backwards and compute
the Fb or breaking forces of different test done in that reference. You
could then apply that force in your model to their geometry and compute the
stresses in the beam/tube. Q you can get from literature like Murakami's
books on stress intensity factors, or maybe for pipes in bending you can get
the formulas for Q from a standard like British Standard 7910.

Kc however requires that some flaw/crack be present.
Seems that in the wet state a minimum crack length is necessary for initiating
fracture at that point. One could maybe use that to compute "yield" stress.
For these types of materials yield is not really something like the 0.2% offset
value for ductile materials. Usually the stress-strain curve is more or less
and elastic line, maybe a bit non-linear at the top, and fracture.

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