Microstructure to macro-scale using gradient plasticity with temperature and rate dependent length scale

Gradient plasticity theory formulates a constitutive framework on the continuum level that bridges the gap between the micromechanical plasticity and classical continuum plasticity by incorporating the material length scale. A micromechanical-based model of variable material intrinsic length scale is developed in the present work which allows for variations in temperature and strain rate and its dependence on the grain size and accumulated plastic strain. The material constants of the proposed model are calibrated using the size effect encounter in nanohardness experiments. In this regard, two different physically based models for Temperature and Rate Indentation Size Effects (TRISE) are also developed in this work for single and polycrystalline metals by considering different expressions of the geometrical necessary dislocation (GND) density. The results of indentation experiments performed on various single- and polycrystalline materials are then used here to implement the aforementioned framework in order to predict simultaneously the TRISE and variable length scale at different temperatures, strain rates and various grain sizes.