Computational study of nanoindentation in aluminium and its alloys

Abstract

Nanoindentation is a useful technique to measure mechanical properties of material such as elastic modulus, hardness, etc. It is possible to measure the local properties of homogeneous or heterogeneous material using nanoindentation. In this thesis, nanoindentation simulations are performed for Aluminium (Al) and its major alloys (Al − M g and Al − Cu) adopting molecular dynamics and finite element approach. In molecular dynamics approach, effects of indentation depth, indenter size and indentation velocity for single crystal Al with <001>, <110> and <111> indentation direction have been investigated using the EAM (Embedded Atomic Method) potential. Effects of grain size for polycrystalline Al have also been investigated. Later, M g and Cu are added at different percentage (1 to 10%) with the different crystallographic orientation of pure Al to create its alloy and nanoindentation simulations are performed on them. From all the atomistic simulations, load-displacement curves are obtained, and hardness and elastic modulus of materials are calculated from those curves. The plastic behaviors of materials, which are mainly governed by the dislocation formation and propagation, are studied thoroughly to understand incipient dislocation mechanism during loading and unloading processes of indentation. The surface imprints on the materials after the unloading process are also investigated as it provides useful information of the material behavior for the experimental study. In this study, a novel technique is also introduced to achieve atomistic level results from the finite element simulation of nanoindentation. For this purpose, the molecular dynamics tensile test data for Al and its alloys are used as input properties for finite element analysis which reduces the simulation timescale significantly compared to molecular dynamics approach without compromising the accuracy of results. Finally, results from the finite element simulation are compared with the molecular dynamics results which show good agreement.