A Theoretical Study on Ratcheting Fatigue Behavior of Copper Nanowire Using Classical Molecular Dynamics Simulation

Abstract

Accumulation of plastic strain during asymmetric fatigue cycling of materials is known as ratcheting. Damage accumulation by means of ratcheting deformation is detrimental to materials as it reduces low cycle fatigue life, which is conventionally estimated by the Coffin – Manson relationship. It is known that damage of materials is related to the physical details of local discontinuities present at various length scales starting from nano to mega meters. Its assessment is commonly directed to acquire knowledge about these discontinuities by using molecular dynamics simulation performed at nanoscale. The aim of this investigation is to theoretically study the ratcheting fatigue behavior of copper nanowires at various temperatures using molecular dynamic simulation with Embedded Atom Method Finnis–Sinclair potential. In this regard, firstly, the tensile behavior of the nanowires have been estimated at various temperatures. It has been found that tensile strength decreases with increase in temperature, as expected. The ratcheting fatigue behavior has been investigated under different asymmetric cyclic loading conditions: (i) with varying stress ratios (R = –0.2, –0.4 and –0.6) at room temperature and (ii) at a fixed stress ratio (R = –0.2) with varying temperatures (100 K, 300 K, 500 K and 700 K). It has been observed from the results that accumulation of ratcheting strain increases with increase in stress ratio and temperature. The increase in strain accumulation in the nanowires is correlated with increased plastic damage that increases with increase in stress ratio. In addition, increased softening of the nanowires with temperature results in increased strain accumulation. The simulation results on accumulation of ratcheting strain are in good agreement with the reported experimental data on pure copper.