Multiscale Friction Using a Nested Internal State Variable Model for Particulate Materials

Stone, T.W. (2008). Multiscale Friction Using a Nested Internal State Variable Model for Particulate Materials. Ph.D Dissertation. Department of Mechanical Engineering, Mississippi State University.

Abstract

In the current study we use a multiscale computational methodology to develop an internal state variable model that captures frictional effects during the compaction of particulate materials. Molecular dynamics simulations using EAM potentials were performed to model the contact behavior of spherical nickel nanoparticles. Simulation results for models consisting of various particle sizes and contact angles were compared to quantify the length scale effects of friction. The influence of friction on the microstructure was shown from the nucleation of dislocations near the interface region during sliding. By using an internal state variable theory to couple the microstructural changes due to friction observed at the nanoscale to a macroscopic rate-independent plasticity model, a multiscale friction model that captures the deformation behavior due to dislocations and interparticle friction was developed. The internal state variable friction equation is a function of the volume-per-surface-area parameter and can adequately represent all length scales of importance from the nanoscale to the microscale. The kinematics was modified by including a frictional component in the multiplicative decomposition of the deformation gradient in order to account for the frictional surface effects due to sliding, as well as frictional hardening/softening within the particles. The friction formulation was extended to the macroscale continuum model by determining the rate of change of the friction angle of the powder aggregate based on the evolution of the friction internal state variable. The constitutive model was coupled with the Bammann-Chiesa-Johnson (BCJ) rate-dependent plasticity model to capture the deformation behavior of the particles.