Papers by Keyword: Multi-Scale Simulation

Abstract: Manufacturing of Silicon Carbide (SiC) based devices will soon require the accuracy and control typical of the advanced Si based nanoelectronics. As a consequence, the processes development will surely benefit of technology computer aided design (TCAD) tools dedicated to the current and future SiC process technologies. Plasma etching is one of the most critical and difficult process for optimization procedures in the micro/nanofabrication area, since the resultant 2D (e.g. in trenches) or 3D (e.g in holes) profiling is the consequence of the complex interactions between plasma and materials in the device structures. In this contribution we present a simulation tool dedicated to the etching simulation of SiC structures based on the sequential combination of a plasma scale global model and feature scale Kinetic Monte Carlo simulations. As an example of the approach validation procedure the simulations are compared with the characterization analysis of particular real process results.

Abstract: There have been many efforts to investigate and develop a numerical damage and failure models during metal forming process of lightweight alloys. Due to the difficulties experienced during experimental determination of the incurred damage during forming of lightweight alloys, many researchers have sought to predict the damage, failure and forming limit curves using numerical simulations. Conventional finite element analysis of metal forming processes for lightweight parts which have been subjected to a nonlinear strain history often breaks down due to numerical difficulties. Many scientific research works have attempted to use different mathematical methods to model the damage progression and failure of alloying material under large deformation. The damage initiation, progression and also failure of alloys are a result of accumulated damage under plastic deformation [1-3]. These models (single and multi-damage parameters) are generally based on energy and constitutive equations to simulate the fracture and failure processes in metal alloys. However, these methods have serious short comes in predicting the damage and failure in metal forming process with strain rate effects. In the present study, following the in-depth study of damage initiation and progression in lightweight alloys, a frame work has been setup to develop a numerical model for damage accumulation during forming process. Based on the existing damage theory, a mathematical extension for damage initiation and also damage accumulation under wide range of stress triaxiality (including near pure shear) has been developed. An experimental program has also been carried out using samples made from lightweight alloys. One of the main contributions of this paper is to show the advantages of using plasticity-based modified damage models to investigate the damage accumulation in cast aluminium alloys.

Abstract: Deformation and damage at the meso-scale level in representative volumes (RVE) of light ultrafine grained (UFG) alloys with distribution of grain size were simulated in wide loading conditions. The computational models of RVE were developed using the data of structure researches aluminum and magnesium UFG alloys on meso-, micro -, and nanoscale levels. The critical fracture stress on meso-scale level depends not only probabilistic of grain size distribution in RVE but relative volumes of coarse grains. Microcracks nucleation is associated with strain localization in UFG partial volumes in alloys with bimodal grain size distribution. Microcracks branch in the vicinity of coarse and ultrafine grains boundaries. It is revealed that the occurrence of bimodal grain size distributions causes the increasing of UFG alloys ductility, but decreasing of the tensile strength. The distribution the shear stress and the local particle velocity takes place at mesoscale level under dynamic loading of UFG alloys with bimodal grain size. The increasing of fine precipitations concentration not only causes the hardening but increasing of ductility of UFG alloys with bimodal grain size distribution.

Abstract: Transformation induced plasticity steels (TRIP steel) is a kind of low – alloying high strength steel with good combination of strength and plasticity. But the macro mechanical properties depend on the microstructure greatly. For simulation, macro finite element can’t consider the microstructure development fully and micro molecular dynamics can’t be used in macro engineering widely, so to investigate the material behavior of trip steel a multi-scale simulation framework which combined macro finite element simulation and micro molecular dynamics together was presented in this paper. The transformation technology between macro and micro simulation by internal variable was considered and macro displacement of integral point as boundary condition of micro molecular dynamics was discussed.

Abstract: Based on the principle of using atomistic force field, and the use of ultra-flexible multi-scale modeling techniques to predict the polycarbonate and polyimide polymer molecular structure and the elastic properties of the system. The model combines molecular modeling and nonlinear continuum mechanics basic principles, to simulate and predict the behavior of the material properties of the polymer molecular structure. For the polymer structure and properties, using a plurality of force field simulation to predict the contrast, and binding experiments measured polymer performance value, using static and dynamic molecular simulation technology for molecular mechanics energy minimization to solve.

Abstract: Quasicontinuum simulation of nanometric cutting was conducted on single crystal copper to investigate the effect of crystal orientation and cutting direction on nature of deformation of this material. The model reduces the degrees of freedom in simulations of nanometric cutting process without sacrificing important physics. The simulation results show the crystal orientation and cutting direction have a significant effect on the nature of deformation of nanometric cutting process. In addition, the variations of strain energy of workpiece atoms in different crystal set-ups are investigated.

Abstract: Multi-scale simulation of ordering process from electronic, atomistic scales to microstructural scale was carried out by hybridizing Phase Field Method (PFM) and Cluster Variation Method (CVM). The hybrid model was applied to disorder-L10 ordering process in Fe-Pd system. Furthermore, computation of relaxation constants in the PFM was attempted based on Path Probability Method (PPM) which is the time evolution version of the CVM, within a linearized analysis of order-order relaxation process.

Abstract: In contrast to microscale method (molecular dynamics) or macroscale method (FEM), multiscale modeling is a new, fast developing and challenging scientific field with contributions from many scientific disciplines in an effort to assure materials simulation across length/time scale. In this paper we propose MPM/MD handshaking method to establish multiscale modeling of thin film formation/nanocutting. First, the detailed handshaking method is presented for large scale simulation along with basic principles of the multiscale approach. Then, quantitative items: flatness, cutting force, adhesion between cluster and substrate, etc. are provided to avoid drawbacks of current qualitative manner. Finally, simulations are carried out to clarify the efficiency of system.

Abstract: Transport and surface interactions of proteins in nanopore membranes play a key role in many processes of biomedical importance. Although the use of porous materials provides a large surface-to-volume ratio, the efficiency of the operations is often determined by transport behavior, and this is complicated by the fact that transport paths (i.e., the pores) are frequently of molecular dimensions. Under these conditions, wall effects become significant, with the mobility of molecules being affected by hydrodynamic interactions between protein molecules and the wall. Modeling of transport in pores is normally carried out at the continuum level, making use of such parameters as hindrance coefficients; these in turn are typically estimated using continuum methods applied at the level of individual diffusing particles. In this work we coupled experimental evidences to manyscale molecular simulations for the analysis of hen egg-white lysozyme adsorption/diffusion through a microfabricated silicon membrane, having pores of nanometric size in only one dimension. Our joint efforts allowed us a) to elucidate the specific mechanisms of interaction between the biopolymer and the silicon surface, and b) to derive molecular energetic and structural parameters to be employed in the formulation of a mathematical model of diffusion, thus filling the gap between the nano- and the macroscale.

Abstract: Feature sizes of useful electronic devices are becoming smaller and reaching nanometer ranges. There is increasing demand to perform dynamic simulations of such nano-devices with realistic sizes. To date, various kinds of simulation methods have been used for materials and devices including the density-functional theory (DFT) and the molecular dynamics (MD) for atomistic mechanics and the finite element method for continuum mechanics. We review recent progresses in our multiscale, hybrid simulation schemes that combine those methods. The coarse-grained particles (CG) method originally proposed by Rudd and Broughton [Phys. Rev. B58 (1998), p. R5893] has features suitable to such hybridization. We improve the CG method so that it is applicable to realistic nanostructured materials with large deformations. A novel hybridization scheme that couples the DFT method with the MD method is presented, which is applicable to virtually any selection of the DFT region in a wide range of materials. Hybrid DFT-MD simulations of the H2O reaction with nanostructured Si and alumina systems under stresses are performed, to demonstrate significant effects of stress on the chemical reaction.