Z.Y. Qian¹, Z.D. Han¹, P. Ufimtsev¹, S.N. Atluri¹

CMES-Computer Modeling in Engineering & Sciences, Vol.6, No.2, pp. 133-144, 2004, DOI:10.3970/cmes.2004.006.133

Abstract The weak-form of Helmholtz differential equation, in conjunction with vector test-functions (which are gradients of the fundamental solutions to the Helmholtz differential equation in free space) is utilized as the basis in order to directly derive non-hyper-singular boundary integral equations for the velocity potential, as well as its gradients. Thereby, the presently proposed boundary integral equations, for the gradients of the acoustic velocity potential, involve only O(r⁻²) singularities at the surface of a 3-D body. Several basic identities governing the fundamental solution to the Helmholtz differential equation for velocity potential, are also derived for the further More >

L. G. Zhou¹, L. M. Hsiung², Hanchen Huang¹

CMES-Computer Modeling in Engineering & Sciences, Vol.6, No.3, pp. 245-252, 2004, DOI:10.3970/cmes.2004.006.245

Abstract Using molecular dynamics simulations, we study the deformation of polysynthetically twinned (PST) TiAl at room temperature. The simulation cell is pre-strained and thermodynamically relaxed to zero stress, so that no dislocations pre-exist in γ−α₂ interfaces. A uniaxial compression is then applied along one 1/6<112] direction. Our results show that interfacial dislocation pairs nucleate at the γ−α₂ interface under the compression. The glide and agglomeration of these dislocations lead to the nucleation of deformation twins from the interface. Based on our studies, twins may nucleate without pre-existing interfacial dislocations. Further we have monitored the propagation of the More >

R. Mathur¹, S. G. Advani², B. K. Fink³

CMES-Computer Modeling in Engineering & Sciences, Vol.4, No.5, pp. 587-602, 2003, DOI:10.3970/cmes.2003.004.587

Abstract Real number-coded hybrid genetic algorithms for optimal design of resin injection locations for the resin transfer molding process are evaluated in this paper. Resin transfer molding (RTM) is widely used to manufacture composite parts with material and geometric complexities, especially in automotive and aerospace sectors. The sub-optimal location of the resin injection locations (gates) can leads to the formation of resin starved regions and require long mold fill times, thus affecting the part quality and increasing manufacturing costs. There is a need for automated design algorithms and software that can determine the best gate and… More >

L. M. Hsiung, D. H. Lassila¹

CMES-Computer Modeling in Engineering & Sciences, Vol.3, No.2, pp. 185-191, 2002, DOI:10.3970/cmes.2002.003.185

Abstract Initial dislocation structures in as-annealed high-purity Mo single crystals, and deformation substructures of the crystals compressed at room temperature under different strain rates have been examined and studied in order to elucidate the physical mechanisms of dislocation multiplication and motion in the early stages of plastic deformation. The initial dislocation density was measured to be in a range of 10⁶ ~ 10⁷ cm⁻². More importantly numerous grown-in superjogs were observed along screw dislocation lines. After testing in compression, dislocation density (mainly screw dislocations) increased to 10⁷ ~ 10⁸ cm⁻². Besides, the formation of dislocation dipoles (debris) due to More >

R. Martinez¹, N. M. Ghoniem²

CMES-Computer Modeling in Engineering & Sciences, Vol.3, No.2, pp. 229-244, 2002, DOI:10.3970/cmes.2002.003.229

Abstract We focus here on the direct coupling of Dislocation Dynamics (DD) computer simulations with the Finite Element Method (FEM) to simulate plastic deformation of micro-scale structures, and investigate the influence of crystal surfaces on dislocation motion. A series of three-dimensional (3-d) DD simulations of BCC single crystals with a single shear loop in the (101)-[111] slip system are first presented. The purpose of these simulations is to explore the relationship between loop force distributions and the proximity of the loop to the crystal boundary. Traction boundary conditions on a single crystal model are satisfied through… More >

W. C. Liu, S. Q. Shi, C. H. Woo, Hanchen Huang¹

CMES-Computer Modeling in Engineering & Sciences, Vol.3, No.2, pp. 213-218, 2002, DOI:10.3970/cmes.2002.003.213

Abstract Using molecular dynamics method, we study the nucleation of dislocations and their subsequent propagation during the deposition of tungsten thin films under tension. Aiming to reveal the generic mechanisms of dislocation nucleation during the deposition of polycrystalline thin films, the case of tungsten on a substrate of the same material is considered. The substrate is under uniaxial tension along the [111] direction, with the thermodynamically favored (01^ˉˉ1) surface being horizontal. The simulation results indicate that the nucleation starts with a surface step, where a surface atom is pressed into the film along the [111^ˉˉ] More >

Karin Lin¹, D. C. Chrzan²

CMES-Computer Modeling in Engineering & Sciences, Vol.3, No.2, pp. 201-212, 2002, DOI:10.3970/cmes.2002.003.201

Abstract The 90° partial dislocation in Si is studied using a combination of Tersoff potentials and isotropic elasticity theory. Both periodic supercells and cylindrical cells are employed and the results compared. The dislocation core radius is extracted by fitting the results of atomic scale calculations to an expression for the elastic energy of the dislocation. The energy differences between two proposed reconstructions of the dislocation core are computed and found to depend systematically on the stress field imposed on the dislocation. It is suggested that hydrostatic stresses may introduce a core transformation. More >

E. Kuramoto, K. Ohsawa, T. Tsutsumi¹

CMES-Computer Modeling in Engineering & Sciences, Vol.3, No.2, pp. 193-200, 2002, DOI:10.3970/cmes.2002.003.193

Abstract In order to investigate the interaction of point defects with a dislocation, an interstitial cluster or a SFT (stacking fault tetrahedron), computer simulation has been carried out in model Fe and Ni crystals. The capture zone (the region where the interaction energy is larger than kT) was determined for various interactions. Calculated capture zone for T =500°C for SIAs (crowdion and dumbbell) around a straight edge dislocation is larger than that for a vacancy in both Fe and Ni. Capture zones for Ni are larger than those for Fe, suggesting that Ni (fcc) has a More >