Md Simulation Of Dislocation Mobility During Cutting With Diamond Tip On Silicon

By means of Tersoff and Morse potentials, a three-dimensional molecular dynamics simulation is performed to study atomic force microscopy cutting on silicon monocrystal surface. The interatomic forces between the workpiece and the pin tool and the atoms of workpiece themselves are simulated. Two partial edge dislocations are introduced into workpiece Si, it is found that the motion of dislocations does not occur during the atomic force microscopy cutting processing. Simulation results show that the shear stress acting on dislocations is far below the yield strength of Si. (c) 2008 Elsevier Ltd. All rights reserved.

Molecular Dynamics Study Of Mechanical Behaviour Of Screw Dislocation During Cutting With Diamond Tip On Silicon

By means of Tersoff and Morse potentials, a three-dimensional molecular dynamics simulation is performed to study atomic force microscopy cutting on silicon monocrystal surface. The interatomic forces between the workpiece and the pin tool and the atoms of workpiece themselves are calculated. A screw dislocation is introduced into workpiece Si. It is found that motion of dislocations does not occur during the atomic force microscopy cutting processing. Simulation results show that the shear stress acting on dislocation is far below the yield strength of Si.

Damage analysis of tetragonal perovskite structure ceramics implicated by asymptotic field solutions and boundary conditions

Cracking of ceramics with tetragonal perovskite grain structure is known to appear at different sites and scale level. The multiscale character of damage depends on the combined effects of electromechanical coupling, prevailing physical parameters and boundary conditions. These detail features are exhibited by application of the energy density criterion with judicious use of the mode I asymptotic and full field solution in the range of r/a = 10(-4) to 10(-2) where r and a are, respectively, the distance to the crack tip and half crack length. Very close to the stationary crack tip, bifurcation is predicted resembling the dislocation emission behavior invoked in the molecular dynamics model. At the macroscopic scale, crack growth is predicted to occur straight ahead with two yield zones to the sides. A multiscale feature of crack tip damage is provided for the first time. Numerical values of the relative distances and bifurcation angles are reported for the PZT-4 ceramic subjected to different electric field to applied stress ratio and boundary conditions that consist of the specification of electric field/mechanical stress, electric displacement/mechanical strain, and mixed conditions. To be emphasized is that the multiscale character of damage in piezoceramics does not appear in general. It occurs only for specific combinations of the external and internal field parameters, elastic/piezoelectric/dielectric constants and specified boundary conditions. (C) 2002 Published by Elsevier Science Ltd.

Effects of entry conditions on cracked kerosene-fueled supersonic combustor performance

Supersonic combustion of thermally cracked kerosene was experimentally investigated in two model supersonic combustors with different entry cross-section areas. Effects of entry static pressure, entry Mach number, combustor entry geometry, and injection scheme on combustor performance were systematically investigated and discussed based on the measured static pressure distribution and specific thrust increment due to combustion. In addition, the methodology for characterizing flow rate and composition of cracked kerosene was detailed. Using a pulsed Schlieren system, the interaction of supercritical and cracked kerosene jet plumes with a Mach 2.5 crossflow was also visualized at different injection temperatures. The present experimental results suggest that the use of a higher combustor entry Mach number as well as a larger combustor duct height would suppress the boundary layer separation near the combustor entrance and avoid the problem of inlet un- start.