Fragmentation dynamics in asperity collisions: A molecular dynamics simulation study

Abstract

We study asperity fragmentation where two slabs of materials, each with a thickness of ∼ 100 Å, are moving parallel to each other at an ∼ 200 Å separation and at a relative velocity ν varying from 1/100 to 1/10 the sound speed c0 of the material. On opposite surfaces of the slabs protrude two wedges of height and base equal to ∼ 133 Å and collide along an infinite line length transverse to the direction of motion. Brittle material and ductile material are modelled through the choice of interatomic potential functions which are Lennard-Jones and Embedded-Atom potential functions, respectively. Our interest is to learn about the fragmentation process due to asperity collision as a function of relative velocity and type of material. We find three distinct fragmentation regimes as a function of increasing impact velocity: 1) brittle fracture at a single apex resulting in material transfer to the other asperity and no accompanying transverse gap; 2) ductile fracture at both apexes resulting in a free fragment and resulting in a transverse gap; 3) midplane slip fracture with minimal material transfer and no transverse gap. The features for the LJ and EAM materials correlate well with the facts that the melting temperatures for the two materials at zero pressure are related by TmLJ ∼ 2.0TmEAM, and the vacancy formation energies are related by EvacLJ ∼ 3.0EvacEAM.