Discussion Forum

This problem is more difficult than it seems. What do you use as the heat source?

I think the heat source will be the plastic/elastic deformation from impact. There will probably be no friction because everything is aligned and there is no sliding.

Hi

then what do we know of heat exchage in metals when deforming plastically ?

By the way I have a similar problem right now on my attempts to see heating of small shape memory materials wires under large deformations from vibrations, with metal phase change and ambient air/water exchanges, ... tricky, I'm still searching for references on the thermal apsects, any ideas ... out there ?

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Good luck
Ivar

What if there is no plastic deformation, only elastic?

Ivar, I am not sure if this will help, but this paper looks promising for you:

Thermal stabilization of Shape Memory Alloy wires
Kloucek, Petr; Reynolds, Daniel R.; Seidman, Thomas I. Source: Proceedings of SPIE - The International Society for Optical Engineering, v 5049, p 24-34, 2003
Abstract: We show that fast, localized heating and cooling of a Shape Memory material can provide a very effective means of damping vibrational energy. We model the thermally induced pseudo-elastic behavior of a NiTi Shape Memory wire using a variant of the Landau-Devonshire potential. We assume that the wire consists of martensitic NiTi single crystals. Dynamically, we model the material response using conservation of momentum and a nonlinear heat equation. We use a frame invariant version of the Fourier heat flux which incorporates dependence on the atomic lattice through the strain. In the settings used in this paper, the computational experiments confirm that circa 80% of the vibrational energy can be eliminated at the moment of the onset of the thermally induced phase transition.

Hi

Thanks I will definitively take a closer look.
I'm currently reading the excellent and all new book of O. Kastner "First Principles Modelling of Shape Memeory Alloys", MD simulations, Springer 2012 (ISBN:978-3-642-28618-6) but I do not see how I can fool COMSOL to do MD, anyhow my WS is not "big" enough, but finding some way to model it closer "on average" would help me

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Have fun Comsoling
Ivar

Hi

The heat lost from plasticity is relatively straightforward to model compared to elastic heat dissipation. All materials have some level of material damping (which causes energy loss), especially at high frequencies, and impact involves very high frequency transients. The problem is getting the high frequency damping characteristics. You can model that elastic loss as a viscoelastic material in COMSOL.

Regarding the plastic heat dissipation I would add it as a volumetric heat source = Factor x Sigma_ij x plastic strain rate_ij. “Factor” is a constant that gives the fraction of plastic deformation that gets converted to heat (typically a high value close to 1.0).

Nagi Elabbasi
Veryst Engineering

Hi Ivar,

I found another reference by the same authors Ryan provided (Kloucek et al.) publically available through LLNL. It’s called “Computational Modeling of Vibration Damping in SMA Wires”. It looks really good in my opinion. When it comes to the constitutive modeling of SMAs I really like the papers by Auricchio and the book by Lagoudas titled “Shape Memory Alloys: Modeling and Engineering Applications”.

Hi Nagi

I'll definitively take a closer look. Some month's ago, there were a few others also looking for SMA modelling exampls/articles, hope they are still listening ;)

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Having fun Comsoling ...
Ivar

Yes, of course, here we are :P.

I am working hard on trying to get the this model (SMA model that Seelecke already implemented in COMSOL),

Let's see if all together can get it!

www.comsol.com/papers/5181/download/Seelecke_pres.pdf

www.comsol.com/papers/5181/

I have problems with the PDE equations, it says that I have a singular matrix. Do you have any idea about where the problem could be?

Failed to find consistent initial values.
Singular matrix.

There are 30 void equations (empty rows in matrix) for the variable mod1.u1.
at coordinates: (0.0333333), (0.0666667), (0.1), (0.133333), (0.166667), ...
and similarly for the degrees of freedom (empty columns in matrix).
Last time step is not converged.


Thanks!!

Yes, of course, here we are :P.

I am working hard on trying to get the this model (SMA model that Seelecke already implemented in COMSOL),

Let's see if all together can get it!

www.comsol.com/papers/5181/download/Seelecke_pres.pdf

www.comsol.com/papers/5181/

I have problems with the PDE equations, it says that I have a singular matrix. Do you have any idea about where the problem could be?

Failed to find consistent initial values.
Singular matrix.

There are 30 void equations (empty rows in matrix) for the variable mod1.u1.
at coordinates: (0.0333333), (0.0666667), (0.1), (0.133333), (0.166667), ...
and similarly for the degrees of freedom (empty columns in matrix).
Last time step is not converged.


Thanks!!