Showing papers by "Fabrizio Cleri published in 1997"
TL;DR: In this article, the atomic-level displacement and stress fields on the activated slip plane before and after a crack tip dislocation are extracted from a molecular dynamics simulation, and the role of surface steps in dislocation nucleation and crack-tip blunting is demonstrated.
Abstract: By isolating the process of dislocation emission from a crack tip under an applied tensile stress, we extract from a molecular dynamics simulation the atomic-level displacement and stress fields on the activated slip plane before and after the nucleation event. The stress-displacement relations so obtained provide a direct link with recent continuum descriptions of brittle versus ductile behavior in crack propagation. Crack-tip shielding by the emitted dislocations is demonstrated, as is the role of surface steps in dislocation nucleation and crack-tip blunting. {copyright} {ital 1997} {ital The American Physical Society}
109 citations
TL;DR: In this paper, a fully atomistic technique for fracture simulations is applied to the study of dislocation emission from a crack tip in an elastically anisotropic f.c. crystal.
23 citations
TL;DR: In this article, the Peierls-Nabarrock continuum mechanics model of dislocation nucleation was used to interpret the experimental results of fracture response in symmetric-tilt grain boundaries in Cu.
Abstract: We use the Peierls-Nabarro continuum mechanics model of dislocation nucleation, modified according to the results of atomistic simulations, to interpret the experimental results of fracture response in symmetric-tilt grain boundaries in Cu. We then directly perform Molecular Dynamics simulations of fracture propagation and dislocation emission from a microcrack placed in the interface plane of the symmetric-tilt (221)(221) grain boundary in fee Cu. Direction-dependent fracture response is observed in agreement with experiments, namely the microcrack advancing by brittle fracture along the [114 ] direction and being blunted by dislocation emission along the opposite [1 1 4] direction. Moreover, we are able to quantify important differences with respect to the continuum model due to the shielding of the stress field at the crack-tip and to the presence of the excess stress at the interface.
2 citations
TL;DR: In this paper, tight-binding molecular dynamics simulations of typical high-energy grain boundaries in silicon have been used to show that the atomic structure of the interface in thermodynamic equilibrium is similar to that of bulk amorphous silicon and contains coordination defects.
Abstract: Tight-binding molecular dynamics simulations of typical high-energy grain boundaries in silicon show that the atomic structure of the interface in thermodynamic equilibrium is similar to that of bulk amorphous silicon and contains coordination defects. The corresponding electronic structure is also amorphous-like, displaying extra states in the forbidden gap mainly localized around the coordination defects, where large changes in the bond-hybridization character are observed. It is proposed that such coordination defects in disordered high-energy grain boundaries are responsible for the experimentally observed gap states in polycrystalline Si.
1 citations
TL;DR: The porting of a O( N 3 ) TBMD code on different MIMD computers, with either distributed or shared memory, by using appropriate software tools is described, and the new perspective of using specialized platforms to deal with large-scale T BMD simulation is discussed.
Abstract: Atomistic modelling of Materials Science problems often requires the simulation of systems with an irreducibly-large unit cell, such as amorphous materials, fullerites, or systems containing extended defects, such as dislocations, cracks or grain boundaries. Large-scale simulations with the Tight-Binding approach must face the computational obstacle represented by the O( N 3 )-scaling of the diagonalization of the Hamiltonian matrix. This bottleneck can be overcome by parallel computing techniques and/or the introduction of faster, O( N )-scaling algorithms. We report the activities performed in the frame of a collaboration among several research groups on the porting of TBMD codes on parallel computers. In particular, we describe the porting of a O( N 3 ) TBMD code on different MIMD computers, with either distributed or shared memory, by using appropriate software tools. Furthermore, preliminary results obtained in the porting of an O( N ) TBMD code on an experimental, hybrid MIMD-SIMD computer architecture are reported. The new perspective of using specialized platforms to deal with large-scale TBMD simulation is discussed.