Abstract: The ideal strength of a nano-component, which is the maximum stress of the structure,
provides an insight into the mechanical behavior of minute material. We conducted tensile
simulations for cylindrical-shaped Cu nano-wires composed of an atomic chain as a core wrapped
around by shell(s) with the structure of (111) layers in an fcc crystal. The results are compared with
Cu atomic chain and sheet which are components of the nanowire. Young’s moduli and the ideal
strengths of the wires are less than a single atomic chain and a sheet. The mechanical strength of the
wire is weakened by the following three factors: (A) Change in electron arrangement caused by
combining core and shell; (B) Larger interatomic distance (inherent tensile strain) of the outer shell
introduced by the mismatch of atomic layers due to the curvature difference; (C) Mismatch between
shells due to curvature difference. Factor (A) reduces the bonding strength in the shell(s) that
occupy a greater part of the wire. 5-1 wire, which consists of a core and a shell, is weaker than the
single atomic chain and the single sheet due to (A) and (B). 10-5-1 wire, consisting of a core and
two shells, has less strength than 5-1 wire due to (C) in addition to (A) and (B).
Abstract: Nanoindentation is an interesting technique used to probe the local mechanical properties
of a material. Although this test has been widely used and developed over the world during the past
few years, it remains a lot of uncertainties regarding the interpretation of nanoindentation data. In
this study, we propose to simulate the nanoindentation test of FCC single crystals like Cu or Ni
using three numerical models. At the lowest scale, molecular dynamics simulations give details of
the nucleation of the first dislocations induced by the indentation. At an intermediate scale, discrete
dislocation dynamics simulations are performed to study the evolution of the dislocation
microstructure during the loading. Finally, at the upper scale, 3D finite element modelling using
crystal plasticity constitutive equations give a continuum description of the indentation induced
plasticity. It is shown how the different models are interconnected together.
Abstract: For the pressure-assisted master sintering surface (PMSS), the sintered density during hot
pressing is a unique function of the integral of a temperature function over time at a fixed pressure,
irrespective of the heating path. The present research was undertaken to develop the pressure-assisted
master sintering surface for silicon nitride known as potential material for high-temperature structural
applications due to its excellent mechanical and thermal properties. High-purity α-Si3N4 powder
(E-10 grade, Ube Industries) were mixed with 6.25% Y2O3 by alumina ball milling in ethanol for 3
hours. From the weight loss of ball mill after mixing, 1% Al2O3 was added. Consequently, SiN,
6.25% Y2O3 and 1% Al2O3 of powder mixture were prepared. After drying the resultant slurry at
100°C, the mixed powder were cold pressed at 300Mpa and made as disk of 25.4mm diameter and
2mm thickness. Then, densifications of silicon nitride were continuously recorded during heating at
two different ramping rates of 5°C/min and 10°C/min up to 1800°C at fixed pressures from 7 to 34
MPa. The pressure-assisted master sintering surface of silicon nitride was successfully constructed.
Using this surface, the final density can be predicted to about 1% accuracy for a fixed pressure and an
arbitrary temperature-time path.
Abstract: The integrated simulation model for microstructural design of Fe-C alloy using the
phase-field method and the homogenization method is proposed. First, the phase-field simulation is
performed to simulate the morphological change of the grain boundary ferrite to Widmanstätten
ferrite. Then, in order to clarify the effects of the morphology of the ferrite phase on the micro- and
macroscopic mechanical properties, the finite element analysis based on the homogenization method
is conducted with the representative volume element obtained from the phase-field simulation. This
numerical approach provides a powerful tool to investigate systematically the micro and macroscopic
mechanical behavior with the morphological change of the ferrite phase in the Fe-C alloy.
Abstract: The establishment of the coupled numerical model which enable to simulate the spherulite
formation and its mechanical behavior continuously is our final goal. In this paper, we have developed
Phase-field model for spherulte growth of polymer by generalizing the model proposed by Granasy et.
al.. The numerical simulations for single spherulite and multi-sperulites have been performed with
isotropic interface energy.
Abstract: Convenient structure adjustment and thereby the achievement of suitable material and
technological properties is one of the very important areas of technological as well as material
research. In general, this issue includes a great number of parameters and variables. To find suitable
technological conditions, it is possible to use various kinds of modeling processes. One of them is
the utilization of thermomechanical simulators, which allow simulating the conditions of the real
processes to be simulated with sufficient accuracy. It is then possible to perform the optimization on
smaller specimens, while monitoring the real conditions with higher accuracy. This method was
used for the optimization of unconventional technological processes for selected alloying strategies
of low-alloyed multiphase steels. These strategies are designed to be applied to technologies, which
combine anisothermal forming and thermomechanical treatment of quasimassive components using
intensive plastic deformation. Incremental deformations allow a high amount of deformation to be
reached. It is also possible to obtain very fine grained structures by a suitable choice of temperature.
By a suitable choice of temperature it is also possible to obtain structures with very fine grain. At
the same time, the morphology of the structure and thus also its final mechanical properties can be
significantly influenced this way.
Abstract: The interactions of a dislocation with commonly observed irradiation induced defects such
as a stacking fault tetrahedron (SFT) and a void are studied using molecular dynamics (MD)
simulation methods. The simulation of an SFT interacting with a dislocation in face centered cubic
(FCC) copper (Cu) reveals that an SFT is a strong obstacle against a dislocation motion, with
dislocation detachment often involving an Orowan like mechanism. The resulting SFT generally
involves a shear step, although partial absorption is also observed in some specific interaction
geometries. Dislocation interaction with a void has been studied in body centered cubic (BCC)
molybdenum (Mo). The dislocation locally annihilates upon contact with the void and then
re-nucleates on the void surface as the dislocation glides past the void. The interaction results in the
simple shear of the void by one Burger’s vector. The obstacle strength of the void is measured using
conjugate gradient molecular statics (MS) method as a function of void size. A large increase in the
obstacle strength is observed for a void size greater than 3 nm in diameter.
Abstract: By using molecular dynamics simulation, misfit dislocation networks are made on
semi-coherent interfaces in a laminate structure of Ni and Ni3Al single crystals. The core structure of
the networks is discussed in detail, focusing on the different atomic configuration at the interfaces; e.g.
with or without Al atoms on the Ni3Al side. It is revealed that the networks can be a source of partial
dislocation loops under the external loading; however, the loops tend to form immobile wedge-like
stacking faults, analogous to the stacking fault tetrahedron (SFT), near the interface with Al atoms. On
the other hand, the loops propagate into both Ni and Ni3Al phases, from the network dislocations on
the interface without Al atoms.
Abstract: Strategy and function of a new developed FEM code COSMAP(COmputer Simulation of
MAterial Process) for surface hardening during of thermo-mechanical processing, including heat
treatment, carbonizing and nitriding, is briefly introduced in this paper. The simulation code is
developed based on the metallo-thermo-mechanical theory considering the coupled equations of
diffusion, heat conduction, inelastic stresses and kinetics of phase transformation. Some examples
of simulation and the experimental verification for carbonized quenching, carbonizednitrided-
quenching process of a cylinder and ring as well as a gear are illustrated, and comparison
of the simulated values of distortion, residual stresses and profile of induced phases with the
experimental data is made with some discussions.
Abstract: Using the first-principles calculation, the elastic constant C44 of Ag/Al multilayers with
different modulation periods from 0.43 nm to 2.27 nm has been evaluated in order to examine the
effect of atomic and electronic structures on it. With increasing modulation period, C44 decreases
and becomes close to that obtained by the conventional mixing rule, however, the difference of 8 %
still remains at the modulation period of 2.27 nm. As C44 correlates with the average interplanar
spacing, the decrease of C44 can be explained by the decrease of the charge density in the stacking
direction due to the increase of the average interplanar spacing. The difference in the electronic
structure is included in the effect of atomic structure.