Learning Forum

[qmicheletti]

Hello everyone, I have a junction between two conductive material and with a current flow transmission. So, I would like to use Ansys and observe the resitivity variation with the torque one. You know how I can made that ? 
Thanks for your help !

[Sean Harvey]

Hello,

From a high level, one can consider modeling this at different levels.  The reduced resistivity to electrical current flow comes from a similar reason for thermal conduction in that the local asperities are put into better contact, increasing the contacting area at a small scale.  

One can imagine a model where a "rough" surface is modeled such that as the torque is increased the parts are clamped tighter and tighter and the contacting surface area increases.  The meshing to capture the scale of roughness will vary depending on what type of effects you wish to capture.  One can imagine a larger scale where parts deform and contact. Think of a bolt and washer and the washer is conical in shape.  As I torque, the washer compresses and contacts. One can also image at the surface roughness scale.   Ansys can capture at both scales, but for the surface roughness, you would be challenged to be able to model the large scale of your part and the small scale of the local roughness.  Not that you can't, it just becomes computationally unrealistic as you will have a very high mesh count, but it is not impossible.

So Ansys Mechanical has coupled field elements and contact that support electrical-thermal-structural degrees of freedom. You would need to set up the model with the coupled field static

But then you need an APDL command in the coupled field static branch of the tree to put in the current-based electrical boundary conditions, and also commands to modify the contacts (put commands under the contact) to include the electrical DOF and specify the electrical contact conductance (ECC)

I also want to point out that one can modify the ECC of the electrical contact to be pressure based.

7.2. Modeling Electric Contact (ansys.com)

So, one could theoretically make a micro-scale model determine what is the relationship between surface pressure and electrical conductance.  You have voltage or current between some blocks that are meshed to capture the roughness, push them together and then you measure the electrical performance.  Then you know the pressure versus conductance. You can take this tabular data and use it in a macro-scale model that does not model the local roughness, but it is accounting for it via a table.

Keep in mind that plasticity might also be necessary to capture the desired effects depending on the level of contact pressure you are considering.

I hope this helps give you a higher-level idea of what is possible.

Regards,
Sean