Study On The Nanoindentation Based On Molecular Dynamics Simulation

Molecular dynamics simulations are carried out on the nanoindentation process of single crystal gold, and the results are illustrated in this thesis.The basic theory about molecular dynamics is introduced, and the selection of the potential function and algorithm are discussed. Based on these theories, the nanoindentation model of single crystal gold is built. The Morse potential function is utilized to simulate the inter-atom force, and the Leap-frog algorithm is employed to solve the equations of motion. The emphases are put on the research of the plastic deformation difference during the loading and unloading process and the variation of the force and potential energy with the tip-to-sample distance, and the contrast of the force of molecular dynamics simulations with that of the traditional theory.At small tip-to-sample distances, the adhesion force causes the tip and surface to jump-to-contact. The indentation process is divided into two ordinal phases: elastic deformation phase and ductile deformation phase. Inelastic deformation of the sample surface characterized by adhesion of gold atoms to the tip and formation of a connective neck of atoms forms as the tip separates from the sample. The hysteresis in the force versus tip-to-sample distance relationship is found upon approach and subsequent separation of the tip from the sample surface. When the tip approach the sample, the force of molecular dynamics simulations is smaller than that of rigid theory, and during the indentation process of the tip into the sample, the force of molecular dynamics simulations is far greater than that of Hertz theory.