A viscoplastic finite element method for simulating powder sintering processes was presented. This method was formulated on the basis of the plasticity theory of a porous material to take the change in apparent volume during the sintering into consideration. To simulate non-uniform shrinkage in the sintering, the shrinkage strain-rate was included in the formulation. In addition, both microscopic and macroscopic shrinkages in the sintering were simulated by coupling the finite element method with the Monte Carlo method. The calculated results in sintering processes were shown.

View full abstract

Procedures for analyzing the internal stresses in powder compacts during sintering are reviewed. Sintering properties of powder compacts are taken into account in the macroscopic, component level analysis through a constitutive model, which is for compressible viscous bodies with the driving force of sintering, that is, the sintering stress. Although the fundamental nature of the sintering stress as well as the viscosity can be drawn by using microscopic model of sintering, the exact values for actual powder compacts should be measured by experiments. As an example, sinter-compression tests for metal/ceramic powder compacts are demonstrated in this review. The stress analysis of metal/ceramic graded powder compacts is also presented, and a method of suppressing surface cracks with modification on the sintering properties is described.

View full abstract

Discrete Element Method (DEM) is widely used to simulate behavior of powder material. It is well-known fact that interactions between particles affect this behavior. Especially, shape of the particle is the most important factor which governs these interactions. There have been reported some non-spherical models to simulate non-spherical powder particles. In the present paper, the author shows issues of these models and proposes a new model which can express arbitrary particle shapes. It is of great importance to develop a fast contact detection method for DEM simulation. A new method for the present particle model is developed and demonstrated in this paper.

View full abstract

Designs of materials relating to powders and their production process systems using powder simulation are described. The design of piezoelectric ceramics was performed using an estimation model for electromechanical properties (electromechanical coupling coefficient, piezoelectric constant, dielectric constant, elastic compliance) as an example of the material design. The design method allows the design of microstructure of piezoelectric ceramic with desirable electromechanical property. The development of functional materials as electro-ceramics by using the special characteristics of fine particles has become very active. The method gives useful information for the design of production process system of the ceramics. The control of flow behavior of fine particles based on the fully understanding on the flow mechanism of solid particles is important to produce the functional materials as electro-ceramics in industrial processes. Simulation methods for process handling and unit process operation for fine particles is described.

View full abstract

Three dimensional numerical simulation of sintering was performed to illustrate the interplay between shapes and forces in particle scale. The particle motion was driven by the force acting on a particle, i.e., a vector sum of sintering forces. This micro-mechanical principle was applicable not only to the densifying process but also the non-densifying process in sintering.

View full abstract

Recently, the inductor has become an important component in order to obtain high performance of the electric devices such as mobile telephone, and further improvement of the inductor performance is needed. Especially, the inductance under superimposed DC current is one of key properties for the application using inductor. However, it is difficult to satisfy such high performance only by an improvement of the magnetic material. Therefore it is required to establish the inductor shape design technique considering with the magnetic material properties in order to improve the inductor performance. In this paper, the shape optimization method of inductor using probabilistic optimize algorithm is discussed and the availability of this method is examined through the comparison between the calculation and the experiment. As a result, ∼60 % downsized shape can be derived from this optimization method maintaining the same performance of the original inductor.

View full abstract

The visualization technique we have developed is to coat the surfaces of structures with a paint that includes minute particles that emit light as a result of mechanical stimulation (elastico-luminescence, ESL). Thus, when the structures are subjected to force or vibration, the stress fields and danger levels of defects are made plainly visible at the same time as making the generation and location of defects, such as cracks that do not appear on the surfaces of structures, visible in real time due to luminecence intensity distribution on surfaces generated by stress. The positions and the danger levels of the cracks are detected simultaneously by using this technology, as invisible fatigue cracks and the undetectable stress concentrations of crack tips are made visual by coating metal plates with a paint that includes elastico-luminescent materials.

View full abstract

LaPO₄: Ce,Tb particles were prepared by precipitation from homogeneous solution using urea and hexamethylenetetramine (HMT). Effects of increasing molar concentration of cation and anion, adding hydroxylic carboxylic acid on the morphology and photoluminescence properties of LaPO₄: Ce, Tb phosphor were investigated. Prepared LaPO₄ was hydrate. The particles were needle-like shaped when using urea as a precipitant and rod shaped when using HMT. Both particle lengths were about 2 μm. Increasing molar concentration of H₃PO₄, the formed particles were smaller than that synthesized by the stoichiometric ratio and strongly agglomerated. Adding hydroxylic carboxylic acid as additives, the morphology of particles turned into various form such as spherical, cubic, rectangular and cross shape. However the morphology of LaPO₄: Ce, Tb phosphor was not homogeneous because of the morphology of TbPO₄ and CePO₄ which were bonding rod and cone. The prepared LaPO₄: Ce, Tb phosphor showed strong green emission by UV excitation. The luminescence intensity was stronger when using urea rather than HMT.

View full abstract

The combination of different inorganic structures enables the preparation of multifunctional hybrid materials. The control on the formation of low dimensional nano-objects with specific morphologies and sizes is also a determinant factor to define specific properties. In this aim, the influence of the basic medium on hydrothermally prepared titanate nanowires was studied. The presence of Na⁺ or K⁺ counter ions dramatically influenced the preparation of nanoparticles or nanowires of TiO₂ and titanate. In a second time, hybrid materials were prepared by the impregnation of the titanate nanowires by a solution of iron chloride followed by the addition of NaOH to induce the formation of iron oxide onto titanate nanowires by the co-precipitation method.

View full abstract

Polymer films containing silver nanoprisms and laser dye have been fabricated as amplifying random media where silver nanoprisms and laser dye act as scatterers and optical gain medium, respectively. Above a certain pump threshold, the sample containing silver nanoprisms gives rise to very sharp lasing peaks with linewidth much less than 1.0 nm, while the sample without silver nanoprisms only shows amplified spontaneous emission even when pumped at high energy, implying the important role of silver nanoprisms in the occurrence of laser oscillation. The number of laser modes increases with pump energy. The effect of scatterer density on the laser threshold has been examined, revealing that the scatterer density has to be controlled to optimize laser performance. Given that there are few reports on metal nanoparticles-based random lasers up to now, it is expected that this work will lead to extensive research toward laser devices with low threshold and high emission intensity.

View full abstract