Papers by Keyword: Monte-Carlo Simulation

Abstract: The effect of cutting-edge truncation on the grinding mechanism of quartz glass as a hard and brittle material was investigated. From computer-aided grinding simulations and experiments on surface plunge grinding it was found that cutting-edge truncation decreases the ground-surface roughness and the maximum grain depth of cut; however, the maximum grain depth of cut approaches a constant value depending on the grinding wheel specifications. The alternative means of making the maximum grain depth of cut much smaller than this constant value is to increase the speed ratio. Cutting-edge truncation should be terminated at the optimum truncation depth to avoid the high grinding forces resulting from the flattening of cutting edges.

Abstract: The phase stability of silicon nitride is examined using a series of first principles phonon calculations. -phase shows slightly higher free energy than  in the temperature range from 0 to 2000K. The difference between  and is only 0.02 eV/Si3N4 or 2 kJ/mol at 300 K. The result is consistent with the experimental report by high-temperature oxide-melt-drop solution-calorimetry. Similar calculations are made for ZrO2, Ga2O3, BN and some perovskites. Using cluster expansion technique combined with a large set of first principles calculations, the cation disordering of II-III spinel oxides and the phase diagram of diamond vs. c-BN are theoretically investigated. Theoretical results on the atomic structures of  and  sialons are also shown.

Abstract: In this paper, we present the Monte-Carlo simulation that we developed and used to design and to interpret the data of a new kind of lifetime spectrometer especially constructed for the determination of the ortho-positronium (o-Ps) re-emission yield from thin mesoporous silica films. The main issue was to have the detection efficiency independent of the o-Ps re-emission energy. This was done in order to avoid a bias of the results related to the positron implantation energy. Furthermore, the simulation is used to calculate the detection efficiencies for annihilation events yielding 2 and 3 gamma photons allowing a precise evaluation of the absolute yield of o-Ps produced in the samples. Calculations were performed using the GEANT4 package. New classes were written to describe the different decay types related to the Ps formation in matter. Moreover, the propagation and interaction of the o-Ps reemitted in a vacuum cavity were also included in the simulation.

Abstract: We demonstrate a Dual-Pearson approach to model ion-implanted Al concentration profiles in 4H-SiC for high-precision design of high-voltage power devices. Based on the Monte Carlo simulated data for 35-400 keV implantation, we determine the nine Dual-Pearson parameters and confirm precise reproduction of profiles of 1015-1021 cm-3 Al with sufficient smoothness. This leads to a direct incorporation of implanted Al profiles into a device simulator. The influence of dose and energy on channeling is also discussed from the view point of implantation-induced disorder in 4H-SiC.

Abstract: The mechanism of layer growth as well as defect formation in the SiC crystal is fundamentally important to derive its appropriate performance. The purpose of the present study is to investigate competitive adsorption properties of growth species on the various 4H-SiC polytype surfaces. Adsorption structure and binding energy of growth species in the experimentally condition on various SiC surfaces were investigated by density functional theory. For the SiC(000-1) and SiC(0001) surfaces, the adsorption energy by DFT follows the orders C > H > Si > SiC2 > Si2C > C2H2. Furthermore, based on the DFT results, amount of adsorption of each species in the experimental pressure condition were evaluated by grand canonical Monte Carlo method. H and Si are main adsorbed species on SiC(0001) and SiC(000-1) surfaces, respectively. The ratio of amount of adsorption of Si to H was depending on the surface structure that might explain different growth rate of the surfaces.

Abstract: In order to understand the mechanism of the bending motion of the electroactive polymer actuators from the molecular interaction, we performed Monte Carlo simulations in two length scales; the micrometer scale and the nanometer scale. In the micrometer scale picture, the bending motion of an actuator can be viewed as the inhomogeneous expansion/contraction of the three layer system. We theoretically formulated the deformation of the actuator in terms of the elastic constants and the stress exerted due to the applied voltage. For the nanometer scale, noting that the electrodes of the EAP actuators have porous structures, we modeled the anode and the cathode by the porous electrodes where the ions are confined in the space with the dimension comparable to the ion size. We found that significant osmotic stress arises in the porous electrodes when voltage is applied. The results of such multi-scale analyses are combined with the experimental results to obtain the insights into the molecular mechanism of the actuators and to give the guideline for the molecular design of the actuators.

Abstract: In order to evaluate fatigue reliability of single structure under random load, based on rainflow counting range of stress-time history, fatigue strength reliability of structure is obtained by means of stress-strength interference theory and Dirlik’s probability density function of rainflow counting range, as well as by assuming that fatigue limit accords with normal distribution. Also by using Miner’s damage cumulative theory, assuming that fatigue life accords with lognormal distribution, and taking into account dispersion of damage cumulative criterion value, given finite life reliability of structure is obtained by means of Monte-Carlo simulation method. The results show that although maximum range in stress-time history is greater than fatigue limit, when a majority of cycle range in stress-time history is less than fatigue limit, structure has high reliability of fatigue strength. The results of given finite life reliability indicate that although structure has high reliability fatigue strength under single stress-time history, fatigue reliability of structure experiencing many cycles will gradually decrease.

Abstract: Simple and easy uncertainty estimation method is proposed. Provided that specification or simple experimental result is available, possible variance and covariance in error are estimated and Monte-Carlo simulation reflecting constraint caused by the covariance can be performed. Comparison between uncertainties obtained by the proposed method and that by actual measurements on real CMM shows good agreement within 1 m µ over-estimation.

Abstract: A method of Monte Carlo combined with welding experiments was adopted to study the grain size and microstructure in welding heat affected zone of the ferrite stainless steel. Firstly, the kinetic equation of grain growth was established with the experimental data . Then , a simulation procedure based on the kinetic equation was worked out. Agreement between Monte Carlo simulation result and the real experiment results was obtained.

Abstract: We present Monte Carlo simulations of the first stages of the coherent precipitation of Cu in α-Fe during thermal ageing and under irradiation. The simulations are based on a diffusion model by vacancy and self-interstitial jumps, the parameters of which are fitted on ab initio calculations. The simulations of precipitation kinetics during thermal ageing are compared with experimental ones. They reveal that precipitates containing up to several tens of atoms can be much more mobile than individual copper atoms, due to the trapping of vacancies in Cu. Monte Carlo simulations are also used to analyze the coupling between fluxes of point defects and Cu which occurs under irradiation and the possible resulting radiation induced segregation phenomena.