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.