Investigating Damage Evolution at the Nanoscale: Molecular Dynamics Simulations of Nanovoid Growth in Single-Crystal Alu
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ICTING failure in ductile materials requires understanding the complex process of damage evolution, whereby voids nucleate, grow, and coalesce.[1–23] This type of failure mechanism is intrinsically a multiscale process that spans from the nanoscale to the macroscale. The void growth mechanism has been studied extensively at the microscale and the macroscale.[1,2,11–13,24–31] In recent years, physically motivated damage evolution laws have been used to try to reveal the nature of the ductile failure process in materials. These laws are supported by numerous experiments that have measured void growth and coalescence as a M.A. BHATIA, Graduate Research Assistant, and K.N. SOLANKI, Assistant Professor, are with the School for Engineering of Matter, Transport, and Energy (SEMTE), Arizona State University, Tempe, AZ 85287. Contact e-mail: [email protected] A. MOITRA, Postdoctoral Fellow, is with the Department of Chemical Engineering, The Pennsylvania State University, University Park, PA 16802. M.A. TSCHOPP, Assistant Research Professor, is with the Center for Advanced Vehicular Systems, Mississippi State University, Mississippi State, MS 39762. Manuscript submitted March 21, 2011. Article published online February 10, 2012 METALLURGICAL AND MATERIALS TRANSACTIONS A
function of the applied stress.[1,2] However, these experiments are often difficult to conduct, and in many cases, the characterization techniques for measuring void volume fraction (vvf) are destructive. There different continuum models are proposed to model void growth in two and three dimensions.[3–5,32] Continuum models are based on the physical understanding that in the course of plastic deformation, microvoids nucleate and grow until a localized plastic necking or fracture of the intervoid matrix occurs, which causes the coalescence of neighboring voids. One of these models was proposed by Gurson[3] and was extended phenomenologically by Needleman and Tvergaard[4] (the so-called GTN model). Other micromechanical damage models based on continuum damage mechanics and thermodynamics have also been proposed, such as one by Rousselier.[33] Previous on isolated void growth work conducted by Rice and Tracey,[11] McClintock,[20] and Edelson and Baldwin[24] shows its dependence on both stress triaxiality and volume fraction. Moreover, Fleck et al.[12] proved numerically that lower stress triaxiality causes the Gurson model to overestimate softening caused by void nucleation. Additionally, Needleman[13] developed a continuum-based cohesive zone interface model for VOLUME 44A, FEBRUARY 2013—617
nucleation (debonding) and void growth for a weaker matrix material. Similarly, Pardoen and Hutchinson[16] developed a void cell model for void growth and coalescence. However, these continuum damage models often cannot account for the nature of dislocation behavior associated with void growth caused by the intrinsic length and time scales associated with dislocation nucleation, propagation, and its interactions. Void nucleation, growth, and coalescence is a multiscale d
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