Fe Modeling Of Nano-Indentation

Good question, and I will start by saying that I don't have an answer on this one--the available analytical approaches are quite good for addressing basic materials characterisation in purely viscoelastic materials (a list of references is contained in discussion elsewhere on this iMechanica site as well as on my own website).

For routine materials characterisation, it is critical to have relatively simple approaches for data analysis, especially in nanoindentation where combinatorial approaches and automated instruments can be used for analysis of large numbers of samples or individual indentation tests. To meet this criterion of "simpleness" an analytical approach with easy, closed-form solutions is a necessity. The routine adaptation of Berkovich indentation arrived with the Oliver-Pharr approach to data analysis, and similar analytical techniques are already available for viscoelastic contact. Thus, there may be specific cases in which a FE approach is useful, but for the most part analytical approaches are a really good first approach to the problem, both in bulk and thin film materials with time-dependent mechanical responses.

That said, there are cases in which the analytical approaches might leave something to be desired, and in which the use of an FE model might be quite useful. One possibility is in multiphase composites or polymer blends, in which the indenter might contact two phases with different viscoelastic responses. Further, I believe there is substantial work to be done in sharp contact (Berkovich, cube-corner, etc.) where the interactions between viscoelastic and plastic deformations are complicated. Although we have done some work on viscous-elastic-plastic contact in sharp nanoindentation using approximate analytical approaches, this work was preliminary in nature and could be usefully probed more fully with FE analysis, especially given the fact that the time-dependent behavior in sharp indentation is unlikely within the linearly viscoelastic regime.

wahmad

Would you please tell me if there is any FE analysis of the indantaion on a nanocomposite polymer?

regards

Ahmad

Hallo..

Is there any FE model that can be used to analyse the effect of residual stress in material assessed by micro-indentation?

I make a reseach by artificially introduce residual stress in the bending bar of Al-alloy. Then I try to collect the material parameters by using micro-indentation.

My result shows that the compressive residual stress vs tensile residual stress is not exactly opposing each other compared to free stress condition. The decreasing of indentation depth caused by compressive residual stress compared to free-stress condition is lower compared to the increasing of indentation depth caused by tensile residual stress within the same amount of residual stress.

This is not the case if you have residual stress assessed with tensile test, because mostly the graph will be opposing each other compare to free stress condition.

Any one can help me to explain this phenomenon?

Thank you.