Ab initio atomistic simulation of the strength of defective aluminum and tests of empirical force models.

Abstract

The effects of atomic-scale voids on the strength and mechanical behavior of aluminum at zero temperature are investigated using the total-energy pseudopotential method. A series of calculations are performed in which the defective system is extended by a small increment and then is relaxed to its ground state configuration. The total energy and stress are determined at each level of strain. The ``tensile test'' of the defective system is compared with the results of an experiment on a perfect system. These simulations employ a quantum mechanical scheme and show the processes of deformation around the defects including the initiation of dislocations and slip. They can also be used as a database on which to test models based on simpler atomistic potentials. We use them in that way to test a Sutton-Chen model tuned to our quantum mechanically simulated system, and a pairwise model by way of contrast to metallic bonding. The Sutton-Chen model shows significant void expansion at about 60% of the failure strain, an effect which is not seen in the ab initio calculations. The ab initio calculations suggest how empirical models such as the Sutton-Chen scheme can probably be improved to reflect better the nature of metallic bonding.