Molecular dynamics simulations of void growth and coalescence in single crystal magnesium Tian Tang * , Sungho Kim, M.F. Horstemeyer Center for Advanced Vehicular Systems, Mississippi State University, 200 Research Boulevard, Starkville, MS 39759, USA Received 20 October 2009; received in revised form 17 March 2010; accepted 4 May 2010 Available online 9 June 2010 Abstract The growth and coalescence of voids in magnesium single crystals at the nanoscale have been investigated using molecular dynamics simulations and the embedded atom method. One void and two void specimens with identical initial void volume fractions were utilized to study the mechanism of void growth and coalescence. In order to study the influences of material length scale on void evolution in single crystals four specimen sizes with the same initial volume fraction of voids were considered. Investigations of the effects of temper- ature and strain rate were also performed. Uniaxial stress–strain curves were monitored during increasing employed strain. The simu- lation results show that the specimen size, loading strain rate and temperature had apparent influences on the twin or dislocation pattern, void evolution shape and uniaxial stress–strain responses, but negligible effects on the initial slopes of the uniaxial stress–strain curves. Furthermore, the nucleation stress of twin bands in orientation A – x[0 0 0 1]–y[1  21 0]–z[10  1 0] was much higher than that of plastic deformation in orientation B – x[1  21 0]–y[10  1 0]–z[0 0 0 1]. Published by Elsevier Ltd. on behalf of Acta Materialia Inc. Keywords: Molecular dynamics simulations; Void growth; Void coalescence; Magnesium single crystals; Embedded atom method 1. Introduction The nucleation, growth and coalescence of voids are the main causes of fracture of ductile materials such as the fcc metals aluminum and copper. Once voids have nucleated from non-metallic inclusions or at the interface between particles and the matrix subsequent damage proceeds by the void growth and coalescence. There have been numer- ous experimental studies [1–4] carried out on the macro- scale in order to obtain a qualitative and quantitative understanding of the mechanisms of growth and coales- cence of voids. However, it is very difficult to experimen- tally observe the evolution of the micromechanism of void growth and coalescence due to the tiny length scale of the problem. In the initial stage of void growth the scale of the voids may be in the range of nanometers. Therefore, only a few in situ observations of the micromechanism of the damage process have been made. For instance, Weck et al. [5] observed the features of void nucleation, growth and coalescence via in situ tensile tests coupled with X- ray tomography. In recent years computational continuum models have become to be very efficient and powerful tool to analyze the fundamental phenomena of void growth and coales- cence. There are a number of continuum models that have been proposed for the purpose of studying the influence of the geometry of the void, the material properties and the stress state. In general, unit cell models have been adopted by most researchers. One of the most widely known micro- mechanical models was proposed by Gurson [6], who derived a constitutive law for a plastic matrix containing spherical voids from an approximate plastic flow potential and used the volume fraction v f as the main state variable to characterize the damage process. Horstemeyer et al. [7] performed micromechanical finite element studies on the effects of temperature and void configuration on void growth and coalescence. They proposed a critical intervoid 1359-6454/$36.00 Published by Elsevier Ltd. on behalf of Acta Materialia Inc. doi:10.1016/j.actamat.2010.05.011 * Corresponding author. E-mail address: tian.tang@aggiemail.usu.edu (T. Tang). www.elsevier.com/locate/actamat Available online at www.sciencedirect.com Acta Materialia 58 (2010) 4742–4759