nano scale structure contact

[jingansong]

Hi everyone,

Is abaqus available for simulation of nano scale structure contact? I did run micro scale structure contact successfully, but when I created the geometry at 10^-3 scale level of the previous one, and kept the units system the same (so it is supposed to be nano scale), I saw a warning message that the mass of xxx is less than xxx, and the simulation couldn't run because of excessively distortion at the very beginning. Can some one talk about this? Thank you!

 

[IceBreakerSours]

Excessive distortion is *not always* the reason for divergence. Have you checked the .dat/.msg files and the Job Diagnostics menu for clues?

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[jingansong]

Hi IceBreakerSours,

The warning message that the mass of xxx is less than xxx, is the one I haven't seen before. I checked the units, it should be correct because I used it in the micro scale simulation.

 

[IceBreakerSours]

First of all, and I am sure you'd agree Abaqus doesn't care whether your geometry is in microns or miles. Next, in any geometry, you could chose any set of units but for FEA one should chose units that will not cause round-off errors (which, can cause zero pivots if you are familiar with Gaussian elimination). So, for example, it is better to have units in which the stiffness is 2134.. MPa or 2.134.. GPa instead of 2.134..e9 Pa.

Coming to your model, you need to tell us more about the problem. What element types are you using? What type of analysis and solver are you using? Boundary/loading conditions? Constraints?

Are you new to this forum? If so, please read these FAQ:

http://www.eng-tips.com/faqs.cfm?fid=376

http://www.eng-tips.com/faqs.cfm?fid=1083

 

[jingansong]

IceBreakerSours,

I'm doing a simulation that a sphere is sliding on a plate while penetrating to it. The plate is moving on the sliding direction, and the sphere is moving on the penetration direction, so I specified these two perpendicular velocities on them, respectively. The units for the model are nm, nN, kg/nm^3, GPa, s. The step is a dynamic explicit with adiabatic heat effect. And the contact is general contact. In the material property, I included the density, elastic (isotropic), plastic (Johnson-Cook hardening), Johnson-Cook damage, inelastic heat fraction, specific heat. And the element type is C3D8R. Adaptive mesh is applied on the plate, and distortion control is used on the sphere. The warning message is that "the ratio of deformation speed to wave speed is 130.43 at increment 45780". The error message is excessive distortion. It happened at the very beginning of the simulation. Do you have any idea what the reason is for this? Thank you very much!