Modelling nanoindentation behaviour of thermoset
I am a Phd student at loughborough university and am working on modelling of nanoindentation behaviour of thermoset using MARC. Currently I am using creep in conjuction of plasticity (parabolic mohr columb) to simulate my load-unload plots. Regarding experimental results, I am having creep, tensile, compresion and DMTA test results at different strain rates and temperature.
Now I am struggling with defining a approximate material model to simulate my load-unload plot. Here are my questions.
1) Is the idea of coupling creep with plasticity, a better idea? relaxations during unloading seems to be difficult to model.
2) As there is significant amount of primary creep, steady state power law creep is not a better option. Is there any creep laws which can help to model rate primary creep in addition to secondary creep?
3) Will the hybrid model, be a better idea to model the rate dependent loading-unloading behaviour.
Thanks for your help.
A few comments:
Since you are likely interested mostly in small strains, I expect that there will be a few models that can capture the loading behavior.
The unloading behavior, in general, will be more difficult to capture, and will require the use of a more sophisticated model.
I am not sure I understand what you mean by "coupling creep with plasticity".
As I am sure you are aware, there are many different creep laws that have been develeped. Without knowing more about your material, it is difficult to say how accurate different creeps laws may be.
I think that a non-linear viscelastic (or viscoplastic) model might do well for your nanoindentation case. I would think that the Hybrid Model (HM) , or the Bergstrom-Boyce (BB) are good candidates.