Analytical and experimental determination of rate and temperature-dependent length scales using nanoindentation experiments

This work addresses the temperature and rate indentation size effects (TRISE) encountered in nanoindentation experiments and the corresponding material intrinsic length scales at different strain rates. The same value for the material length scale cannot be used for different rate, temperature, and accumulated plastic-strain conditions. A variable length scale is introduced in this work and used on two different face-centered cubic (FCC) metals. Indentation experiments are performed on copper and aluminum polycrystalline samples for different strain rates. To check the validity of the assumed concept for local hardening in nanoindentation, additional experiments are conducted on single-crystal materials. The existing theories describing the indentation size effects and length scales are reviewed, and a physically based model that depends on strain rate, accumulated plastic strain, and temperature that were scaled with hardness experiments results is proposed for length scales. Furthermore, numerical simulations are performed by using the ABAQUS software and a physically based viscoplasticity constitutive model.