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Nonlinear structural material properties question

Hello all,

I've got a question about using nonlinear material properties for analyzing plastic parts for you gurus out there...

Summary of problem: I'm trying to analyze the impact of changing material on a certain plastic part. The current material is a PA6 nylon, the proposed one is a PA66 nylon, which is much tougher and better for the application. After some iterations, I've finalized the design geometry. I'm using multilinear stress-strain curves as input to an FEA. I've already done a linear analysis to determine where my problem areas are.

Now my question regarding stresses --- For IDENTICAL DESIGNS (and identical FE mesh), would a change in multilinear stress-strain curves result in different stresses? I know the stresses stay the same in a linear model, it's the deformations that will change. My loading is force (not displacement). Note that I'm assuming nonlinear elastic behavior, no hardening. I'm struggling with this, since intuitively, I think the stresses should be the same, and the strains/deformations will be affected by the nonlinear behavior.

Thanks in advance, S

Reply to
alef_null00
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As long as all material is in the initial slope of the stress-strain curve you have the linear situation, where the stress is independent of the material properties. Once you go over a slope change however there will be differences in your material properties between the parts where the stresses are over the slope change, and parts where they are not. Some parts of your structure will therefore become relatively less stiff than other parts. The stiffer parts will attract more of the load than in the situation with uniform material properties. The stress distribution will therefore be affected by the non-linear material.

Timo

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Reply to
Timo de Beer

Thanks Timo. I see what you mean. So that in mind, for the plastic material I'm analyzing --- the stress would be independent of the properties as long as I was in the first piecewise-linear portion of the curve correct? After that, even though the part wasn't yielding the local E would factor in? As you may know plastic curves are highly nonlinear with no noticeble "yield point." It's just a smooth curve till the end.

Thanks aga> As long as all material is in the initial slope of the stress-strain curve

displacement).

Reply to
alef_null00

Yes, that's a linear region.

Yep.

The modulus change will have a similar effect as yielding except less extreme.

Reply to
Jeff Finlayson

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