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Plasticity in a Time-Dependent Study with Uniaxial Stress Strain Relation

Posted Jun 28, 2018, 2:29 p.m. EDT Structural & Acoustics, Structural Mechanics Version 5.3 1 Reply

Alec Yenawine
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Hello,

I am working on a model using NiTi, also referred to as Nitinol. I want to use the plasticity node to effectively represent the "twinning" or apparent speudoplasticity of the material.

I am trying to run a time dependent study in which a downward load is applied to the center of the plate and then released. I want to observe the resulting shape of the plate due to the force and any "plasticity" that has occured. However whenever my simulation reaches plasticity it does not converge.

I am using a uniaxial stress strain relation to define the material with perfectly plastic. However even after the initial yield stress I want the plasticity to follow the stress strain curve and not go perfectly plastic.

I feel like this should be a relatively simple problem but none of the COMSOL examples use a time-dependent study for any of their plasticity examples.

Any help would be appreciated

1 Reply Last Post Aug 8, 2018, 11:58 p.m. EDT
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Hello Alec Yenawine

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Narinder Singh
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Posted: 6 years ago Aug 8, 2018, 11:58 p.m. EDT

Hi,

I am having the exact same issue. Just trying to simulate a simple uniaxial tensile test that goes into plastic region. Using auxillary sweep with a stationary study works just fine, but as soon as I use a time-dependent study, none of the plasticity options seems to work properly. By properly I mean sometimes the study won't just converge up to the maximum strain, and almost all the time gives a stress-strain curve that oscillates weirdly around the expected trend value.

I am sure there is some tweak that needs to be applied to the solver somewhere to make it work. I have tried playing with time-steps, and some other solver settings, but no luck so far.

Would appreciate any help on this regard.

Thanks

Hi, I am having the exact same issue. Just trying to simulate a simple uniaxial tensile test that goes into plastic region. Using auxillary sweep with a stationary study works just fine, but as soon as I use a time-dependent study, none of the plasticity options seems to work properly. By properly I mean sometimes the study won't just converge up to the maximum strain, and almost all the time gives a stress-strain curve that oscillates weirdly around the expected trend value. I am sure there is some tweak that needs to be applied to the solver somewhere to make it work. I have tried playing with time-steps, and some other solver settings, but no luck so far. Would appreciate any help on this regard. Thanks

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