Bruce LaMattina

Atomic scale studies of spall behavior in nanocrystalline Cu

The micromechanisms related to ductile failure during dynamic loading of nanocrystalline Cu are investigated in a series of large-scale molecular dynamics simulations. Void nucleation, growth, and coalescence is studied for a nanocrystalline Cu system with an average grain size of 6 nm under conditions of impact of a shock piston with velocities of 250, 500, 750, and 1000 m/s and compared to that observed in single crystal copper. Higher impact velocities result in higher strain rates and higher values of spall strengths for the metal as well as nucleation of larger number of voids in smaller times. For the same impact velocity, the spall strength of the nanocrystalline metal, however, is lower than that for single crystal copper. The results obtained for void nucleation and growth in nanocrystalline Cu for various impact velocities and for single crystal copper [001] suggests two distinct stages of evolution of voids. The first stage (I) corresponds to the fast nucleation of voids followed by the second ...

An angular-dependent embedded atom method (A-EAM) interatomic potential to model thermodynamic and mechanical behavior of Al/Si composite materials

A new interatomic potential is developed for the Al/Si system in the formulation of the recently developed angular-dependent embedded atom method (A-EAM). The A-EAM is formulated by combining the embedded atom method potential for Al with the Stillinger–Weber potential for Si. The parameters of the Al/Si cross-interactions are fitted to reproduce the structural energetics of Al/Si bulk alloys determined based on the results of density functional theory calculations and the experimentally observed mixing behavior of the AlSi liquid alloy at high temperatures. The ability to investigate the thermodynamic properties of the Al/Si system is demonstrated by computing the binary phase diagram of the Al–Si system as predicted by the A-EAM potential and comparing with that obtained using experiments. The ability to study the mechanical behavior of the Al/Si composite systems is demonstrated by investigating the micromechanisms related to dynamic failure of the Al/Si nanocomposites using MD simulations.

ATOMISTIC STUDIES OF VOID‐GROWTH BASED YIELD CRITERIA IN SINGLE CRYSTAL CU AT HIGH STRAIN RATES

Dynamic fracture of ductile metals is attributed to the nucleation, growth, and coalescence of voids which eventually form the fracture surface. Large‐scale MD simulations are used to model void growth behavior in single crystal Cu at high strain rates. Yielding is studied for systems with various values of void fractions as well as combinations of loading conditions. The calculated yield surface of single crystal Cu for varying void fractions indicates the inability of traditional continuum models to predict void growth at high strain rates.