Finite-temperature non-equilibrium quasi-continuum analysis of nanovoid growth in copper at low and high strain rates

Abstract

a b s t r a c tWe study dynamic nanovoid growth in copper single crystals under prescribed volumetric strain rates ranging from moderate ( _ ¼ 10 5 s À1 ) to high ( _ ¼ 10 10 s À1 ). We gain access to lower strain rates by accounting for thermal vibrations in an entropic sense within the framework of maximum-entropy non-equilibrium statistical mechanics. We additionally account for heat conduction by means of empirical atomic-level kinetic laws. The resulting mean trajectories of the atoms are smooth and can be integrated implicitly using large time steps, greatly in excess of those required by molecular dynamics. We also gain access to large computational cells by means of spatial coarse-graining using the quasicontinuum method. On this basis, we identify a transition, somewhere between 10 7 and 10 8 s À1 , between two regimes: a quasistatic regime characterized by nearly isothermal behavior and low dislocation velocities; and a dynamic regime characterized by nearly adiabatic conditions and high dislocation velocities. We also elucidate the precise mechanisms underlying dislocation emission from the nanovoids during cavitation. We additionally investigate the sensitivity of the results of the analysis to the choice of interatomic potential by comparing two EAM-type potentials.

Atomistic modeling and analysis of hydride phase transformation in palladium nanoparticles

“…In this work, we apply a novel computational method, referred to as Diffusive Molecular Dynamics (DMD), to investigate the detailed dynamics of hydride phase transformation in Pd nanoparticles, focusing on the two-way interaction between the motion of the phase boundary and the formation and evolution of misfit dislocations. DMD is a new paradigm for simulating long-term diffusive mass and heat transport while maintaining full atomic resolution [19,20,21,22,18,23,24,25,26,27,28]. The basic idea is to couple a calibrated empirical kinetic model for the evolution of lattice site occupancy with a non-equilibrium statistical thermodynamics model that supplies the requisite driving forces for kinetics.…”

On the role of initial void geometry in plastic deformation of metallic thin films: A molecular dynamics study

“…Traiviratana et al [16] found that the emission of dislocation loops is the primary mechanism of void growth in face-centered cubic (FCC) Cu when the specimen is subject to tensile uniaxial strains; Potirniche et al [17] revealed a pronounced effect of the specimen size on dislocation formation from voids and plastic flow in FCC Ni; Chang et al [18] showed that with an increasing temperature, the yield stress decreases while the void growth rate remains invariant; Bringa et al [19] studied the effect of the loading orientation in the void behavior in Cu, and their results exhibited a complex coupling of void growth, GB debonding, and partial dislocation emission into grains in nanocrystals; Seppälä et al [20] quantified the effect of stress triaxiality on the void growth in Cu; Deng et al [15] uncovered a strong configurational effect on the coalescence of voids in Cu under a shock loading. Using the quasicontinuum method, Marian et al [21] and Ponga et al [22] studied the nanovoid deformation in FCC Al under tension and simple shear, identifying a transitional strain rate between a quasistatic and a dynamic regime. The void growth in other types of lattice, including the body-centered cubic (BCC) [23] and hexagonal closepacked (HCP) systems [5], has also been probed.…”

Prismatic and helical dislocation loop generation from defects

“…The factor of 2x is employed as PDLs are formed in the positive and negative direction of each Burgers vector. Using these values for n neglects the formation of dislocation junctions and locks [32,33], which could render some sites for PDL generation inoperable. On the other hand, only a single cylindrical growth of the void in the directions of the dislocation's Burgers vector where n = 2.…”