Discussion Forum

Hi Marjan

is it the "shear bands" you are looking for ?
then I'm not sure you will really find then, because for me they develop from material defaults around grain boundaries or something along that line. And mostly our material data does not contain any "defects"

Buckling for me remains linked to a "dynamic effect" and often show mode shape ratios of the starting deformation region

But what is sure is that the shear bands develop along regions of high shear gradients, and that probably dynamic (acoustic or phonon?) help to see them grow, once initiated

But I'm not a material specialist (at most a systems engineer), would like to hear the comments of true material socialists here :)

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Good luck
Ivar

Hi Ivar,

Thanks for your reply. I learned sth new but I was on a wrong way. The main challenge is :

I have noticed that if I use linear elastic model for my soft support (E=60 MPa) with Poisson ratio = 0.4, when I indent 350 nm with a spherical indenter which is 2 micrometer radius and rigid (strain reaches 30 percent under the indenter) , the Poisson ratio effectively changes from o.4 to 0.2. How did I figured it out?

If I use Hertz model to fit simulation results, they only match perfectly when I plug in Poisson ratio of 0.2 rather than o.4. I have seen some papers that say freezing happens and the Poisson ratio changes. It has made me confused for what to use to fit simulation data. I want to fit them with Poisson ratio = 0.2 but I need a good argument. Unfortunately I have to stick to Hertz model.

I do not know it is better to say that the material property changes and the linear elastic material property fails a kind of or a hardening starts as the mesh elements are distorted and the comsol software cannot keep the Poisson ration effectively constant. I have sub nanometer mesh and I need them.

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Marjan

Hi

I would assume that 30% strain is not to be considered as the "linear regime" so you need other physics here, but again I'm no material specialist, so I would need to dig into my book again, and currently I do not have any free time, I'm stuck on my own heavy TS simulations and this still for a couple of days ;)

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Good luck
Ivar

Hi Ivar,

If no one answered me, then I will return back to you :). I know it is not elastic and I see that comsol is showing hardening. But I am doing simulation in an experimental group that want to stick to Hertz model. what I see is a kind of geometrical hardening by mesh distortion.

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Marjan

Hi

do not forget "support" they have specialists

And there are more people on the Forum but perhaps many too lazy (or lets say too occupied) to give a hand here

But I'll certainly appreciate to learn more on the non lin material aspects and how to choose what physics for the many strange materials I start to see.

Eg. Somebody has asked me about simulating multiphysics of biological organs, that's going to be an interesting one mixing structural, HT, fluids, ACDC, and or RF ... I wonder where I can get those complex material properties from ;)
Time will tell ...

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Good luck
Ivar

Hi Ivar,

Thanks. I will send an email to support at the end of next week. I also have seen the nonlinear materials and I hate them. Chemists and biologist have from beginning of their studies accepted that the real world is very different from the theories that they have. Though it was very difficult for me as a physics with structured brain to work with them.

Good luck. RF module is very different from the rest. But we already have liquid- solid mechanics module together as a multiphysics interface in version 4.3. That might be a good start.

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Marjan