Paper for the Special Session on Nanostructured Materials at the 45 th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference and Exhibit Stress Distribution During Deformation of Polycrystalline Aluminum by Molecular-Dynamics and Finite-Element Modeling

In this paper, a multiscale modelling strategy is used to study the effect of grain-boundary sliding on stress localization in a polycrystalline microstructure with an uneven distribution of grain size. The development of the molecular dynamics (MD) analysis used to interrogate idealized grain microstructures with various types of grain boundaries and the multiscale modelling strategies for modelling large systems of grains is discussed. Both molecular-dynamics and finiteelement (FE) simulations for idealized polycrystalline models of identical geometry are presented with the purpose of demonstrating the effectiveness of the adapted finite-element method using cohesive zone models to reproduce grain-boundary sliding and its effect on the stress distribution in a polycrystalline metal. The yield properties of the grain-boundary interface, used in the FE simulations, are extracted from a MD simulation on a bicrystal. The models allow for the study of the load transfer between adjacent grains of very different size through grain-boundary sliding during deformation. A large-scale FE simulation of 100 grains of a typical microstructure is then presented to reveal that the stress distribution due to grain-boundary sliding during uniform tensile strain can lead to stress localization of two to three times the background stress, thus suggesting a significant effect on the failure properties of the metal.

[1]  W. G. Wolfer,et al.  Elastic Properties of Grain Boundaries in Copper , 1989 .

[2]  K. Jacobsen,et al.  Softening of nanocrystalline metals at very small grain sizes , 1998, Nature.

[3]  Michael Ortiz,et al.  Mixed Atomistic and Continuum Models of Deformation in Solids , 1996 .

[4]  Huajian Gao,et al.  Crack nucleation and growth as strain localization in a virtual-bond continuum , 1998 .

[5]  K. Merkle.  High resolution electron microscopy of interfaces in fcc materials , 1990 .

[6]  Shigeto R. Nishitani,et al.  Grain boundary energies of Al simulated by environment-dependent embedded atom method , 2001 .

[7]  E. Iesulauro.  DECOHESION OF GRAIN BOUNDARIES IN THREE-DIMENSIONAL STATISTICAL REPRESENTATIONS OF ALUMINUM POLYCRYSTALS , 2006 .

[8]  Simon R. Phillpot,et al.  Length-scale effects in the nucleation of extended dislocations in nanocrystalline Al by molecular-dynamics simulation , 2001 .

[9]  M. Parrinello,et al.  Polymorphic transitions in single crystals: A new molecular dynamics method , 1981 .

[10]  Sidney Yip,et al.  Ideal Pure Shear Strength of Aluminum and Copper , 2002, Science.

[11]  Terence G. Langdon,et al.  Identifiying creep mechanisms at low stresses , 2000 .

[12]  S. Phillpot,et al.  Deformation twinning in nanocrystalline Al by molecular-dynamics simulation , 2002 .

[13]  S. Nosé.  A unified formulation of the constant temperature molecular dynamics methods , 1984 .

[14]  D. He,et al.  Deformation twins in nanocrystalline Al , 2003 .

[15]  J. Hutchinson,et al.  The relation between crack growth resistance and fracture process parameters in elastic-plastic solids , 1992 .

[16]  K. Merkle.  Atomic structure of grain boundaries , 1994 .

[17]  Simon R. Phillpot,et al.  Dislocation processes in the deformation of nanocrystalline aluminium by molecular-dynamics simulation , 2002, Nature materials.

[18]  Michael J. Mehl,et al.  Interatomic potentials for monoatomic metals from experimental data and ab initio calculations , 1999 .

[19]  D. Wolf,et al.  Structure-energy correlation for grain boundaries in F.C.C. metals—III. Symmetrical tilt boundaries , 1990 .

[20]  S. G. Srinivasan,et al.  Deformation mechanism in nanocrystalline Al: Partial dislocation slip , 2003 .

[21]  D. Wolf,et al.  Tailored elastic behavior of multilayers through controlled interface structure , 1994 .

[22]  D. Medlin,et al.  A dislocation-based description of grain boundary dissociation: application to a 90° 〈110〉 tilt boundary in gold , 2001 .

[23]  Joseph O'Rourke,et al.  Computational Geometry in C. , 1995 .

[24]  Jens Lothe John Price Hirth,et al.  Theory of Dislocations , 1968 .

[25]  D. Seidman,et al.  〈110〉 symmetric tilt grain-boundary structures in fcc metals with low stacking-fault energies , 1996 .

[26]  Tadahiko Watanabe,et al.  Geometrical study on the inhomogeneous deformation of polycrystals due to grain-boundary sliding , 1996 .

[27]  Xuemei Cheng,et al.  Deformation Twinning in Nanocrystalline Aluminum , 2003, Science.

[28]  M. O'Keefe,et al.  Atomic structure of a Σ99 grain boundary in aluminium: A comparison between atomic-resolution observation and pair-potential and embedded-atom simulations , 1990 .

[29]  D. Wolf,et al.  Dislocation–dislocation and dislocation–twin reactions in nanocrystalline Al by molecular dynamics simulation , 2003 .