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Sintered samples of Ti added TiO2 nanopowders were fabricated by combined application of magnetic pulsed compaction (MPC) and sintering. The effect of Ti nano powder on density, shrinkage and hardness of the samples were investigated as part of the study. The optimum processing conditions were found to be around 0.5 GPa MPC pressure and 1450°C sintering temperature, illustrating maximum density, hardness and minimum shrinkage. High pressure compaction using MPC was found to enhance density with increasing MPC pressure up to 0.9 GPa, and significantly reduce the total shrinkage (about 16% in this case) in the sintered bulks compared to other general processes (about 18%). While sintered samples blended with micro Ti showed presence of microstructural cracks, the samples with 1-2% nano Ti had less or no cracks on them. Overall, the inclusion of nano Ti indicated improvement in mechanical properties of TiO2 nanopowders sintered preforms as opposed to micro Ti-added TiO2.

The structural analyses of vacuum vessel have been performed to investigate the effect of shell thickness reduction on structural integrity. The finite element models of vacuum vessel considering original design and thickness reduction have been developed. The expected maximum thickness reduction possibly caused by forming and bending processes during fabrication was applied to the curved region of the analysis models. The linear elastic and nonlinear limit analyses have been performed. The structural integrity of main vessel including lower port stub extension has been verified in accordance with the requirements of RCC-MR. It is concluded that the inner and outer shells of main vessel still have enough strength margins under pressure and VDE (Vertical Displacement Event) load conditions in spite of thickness reduction. These results have been reviewed and approved by ITER Organization and ANB (Agreed Notified Body).

The ITER vacuum vessel support systems located in the lower level sustain loads in radial and vertical direction. The support system consists of various sub-components like a linkage system, a pot type bearing, a vertical rope, a toroidal constraint, and dampers. In order to examine performance of the mechanism of the system, a mock-up of the linkage system which is comparatively complicated has been manufactured. Various fabrication methods were studied through the mock-up fabrication, and also several tests have been done using the mock-up. Those include assembly study, stroke test, static load test and fatigue test. In the full stroke test, the functional mechanism of the support structure has been demonstrated. In the structural test, the strength of the all components is evaluated by measuring reaction and strain of each component. In order to investigate the effect of tolerances and the damage due to the tests, the performance tests were conducted before and after the static and fatigue tests. The backlash for each stage is found from measured displacement hysteresis. As results of those tests, the performance of the ITER vacuum vessel support structure as well as its structural integrity has been evaluated in this study.

To investigate the structural integrity of the ITER vacuum vessel (VV) and ports, the structural analyses of the regular equatorial and the lower remote handling (RH) ports have been performed. The advanced design of the equatorial regular port adopting a pure friction type flange has been recommended as a reference design by the ITER International Organization. The structural integrity of the equatorial port flange, sealing unit, and connecting duct has been reviewed by conducting nonlinear finite element analyses. The advanced design of the regular equatorial port flange with proper pretension is acceptable in the structural design point of view. From the local analyses for a connecting duct and a sealing unit, it has been found that the stresses are less than the allowable values. The structural analyses of the lower RH port have been also performed to verify the capability for supporting the VV. Since high local stress occurs at the gusset and supporting block, the case study for the lower port has been conducted to mitigate the stress concentration and to modify the component design. The strength of the lower RH port structures can be improved by the design modification of poloidal and toroidal gusset.

The poloidal field magnet system of the KSTAR consists of three pairs of coils using the cable-in-conduit conductors cooled by forced super-critical helium. The conductor of PF5 is Nb/sub 3/Sn superconductor with Incoloy 908 conduit, and that of PF6 and PF7 is NbTi superconductor with SS 316LN. The PF coils are self-supporting with regard to radial loads, and they are arranged symmetrically with respect to the equatorial plane. PF5 coil is connected to the TF coil structure at eight points by hinges, while PF6 and PF7 coils are connected at sixteen points by flexible plates to allow relative radial movements. In order to investigate the structural integrity, structural analysis has been conducted including buckling and fatigue analyses. The major design loads are dead weight, assembly loads, thermal load due to cool down, and electromagnetic loads under the critical load conditions. It is found that the PF magnet structures can safely withstand all operating conditions. In addition, AISI 316LN can be substituted for JJ1 as the material of the PF coil structures.

The Central Solenoid (CS) magnet system of the Korea Superconducting Tokamak Advanced Research (KSTAR) device consists of four pairs of superconducting coils compressed with the CS coil structure. The CS coil structure is operated as a preload structure to give an axial compression on the CS coils. The required axial compression is applied partly by using the pre-compression components in assembly stage and by the thermal contraction difference between the coil winding pack and the structure during cool down stage as well. In order to investigate the structural integrities and to increase the structural reliabilities of the KSTAR CS magnet, global and local structural analyses have been performed for various operation scenarios by developing three-dimensional finite element models. From the analysis results, it has been found that the CS magnet system can safely withstand the reference operation scenarios and the structural integrity of the CS magnet complies with requirements of the design criteria for KSTAR magnet system.

The central solenoid (CS) magnet system of the Korea Superconducting Tokamak Advanced Research (KSTAR) device consists of four pairs of segmented CS coils and a CS coil structure. The maximum repulsive force between CS coils is about 12 MN. The functions of the CS structure are to apply preload on the CS coils and to support the repulsive force between CS coils during operation. The designed axial compression of 15 MN at 4.5 K will be applied partly by assembling the preload structure at room temperature with preload of about 13.4 MN and partly by the thermal contraction difference between the CS coils and the structure during cool down. Additional preload will be given by minute adjustment of wedges. The structural analysis of the CS magnet system has been performed to verify the CS structure design reliability.

The toroidal field (TF) magnet system of Korea Superconducting Tokamak Advanced Research (KSTAR) device consists of 16 superconducting coils enclosed in steel cases. The TF cases are wedged along the inboard straight legs to sustain in-plane centering forces. The inter-coil structures contain adjustable shear keys and conical bolts to provide pre-loading in toroidal direction and to resist in-plane and out-of-plane forces, which are the most critical loads on the TF magnet system. For effective cooling of the TF case, a pad-type cooling channel has been designed to ensure structural and thermal stability. In order to investigate the structural integrity and to increase the structural reliability of the KSTAR magnet system, structural analyses have been conducted. From the analysis results, it has been found that the TF magnet structure can safely withstand the reference scenario operations.

An appropriate physical modeling and the corresponding numerical analysis system were developed to predict residual stresses and birefringence in injection molded parts such as a center-gated disk. The Leonov constitutive equation is adopted in order to predict flow-induced residual stresses and birefringence. Also the linear viscoelastic and photoviscoelastic constitutive equation taking into account density relaxation phenomena is employed to investigate the thermally induced residual stresses and birefringence. In the preliminary study, constrained quenching was investigated to consider only thermally induced residual stresses and birefringence. Residual stresses are tensile at the center, become compressive near the surface and then return to tensile again at the surface. Flow-induced birefringence has two peaks each of which originated from the filling and packing stages, respectively, and the thermally induced peak has a little flat shape over the whole thickness. Free volume theory was effective in predicting thermally induced residual stresses and birefringence.

Powder Injection Molding (PIM) filling process is one of the key processes towards a successful PIM. In this regard, the methods of slip characterization of powder-binder mixtures and a quasi-3-dimensional finite element simulation program based on Hele-Shaw approximation has been presented.In contrast to conventional injection molding of thermoplastics, there are many PIM parts that include thick regions. To simulate such thick PIM parts properly, a full 3-dimensional simulation program is needed. In this regard, we have been developing a full 3-dimensional finite element program for PIM filling process with the slip phenomena taken into account. For a computational efficiency, a pre-meshed finite element mesh was used with a scalar fill-factor to automatically update the computational domain during the filling.

Many particle-filled materials, such as powder/binder mixtures, are known to show slip phenomena at a solid wall. It is thus of great importance to characterize the slip phenomena for rheological data of particle-filled plastic materials and ultimately to introduce an appropriate slip modeling into the numerical simulations of the extrusion process. In order to simulate screw extrusion processes of such particle-filled materials, numerical analysis programs were developed via a finite element method and a finite difference method for quasi three-dimensional and two-dimensional flow models of extrusion processes, respectively, with the slip phenomena taken into account in terms of a slip velocity. The present paper presents detailed numerical methods to incorporate the slip velocity as a function of wall shear stress and discusses essential slip effects in the screw extrusion process using the slip-corrected and uncorrected viscosity data for both the two-dimensional flow and the quasi three-dimensional flow model. It was confirmed that the quasi three-dimensional result at the center line of the channel from the finite element analysis was in good agreement with the two-dimensional one from the finite difference analysis. Slip effects were found to be very significant on the overall flow behavior during the extrusion process from the numerical results based on viscosity data without the slip correction. These deviated from those based on the slip-corrected viscosity data, especially in analyzing the screw characteristics.

Our experimental data from a capillary rheometer clearly show that powder/binder mixtures for powder injection molding (PIM) experience so-called slip phenomena at the wall, like many particle-filled materials. It is thus of great importance to characterize quantitatively the slip, together with shear-thinning viscosity data of power/binder mixtures in view of proper numerical simulations of the PIM filling process. The slip at the wall could be quantified in terms of a slip velocity or in terms of a very thin slip layer. The present paper adopted the well-known Mooney's method for determining slip velocity, whereas the slip layer thickness was determined by a newly-proposed method. The slip velocity, or the slip layer thickness, thus determined were then introduced into the finite element analysis of the PIM filling process. This was found to have a significant effect on the overall flow behavior during the injection molding filling.

RESURF LDMOS transistors are utilized in high side driver applications and other applications that mandate electrical isolation between source and substrate by using isolated RESURF technology. However, the BCD process using conventional isolated RESURF LDMOS structures cannot provide high efficiency vertical NPN transistors due to the dependence of the RESURF LDMOS BV/sub dss/ (source to drain breakdown voltage) upon the epi thickness. In this paper, we propose a new isolated RESURF LDMOS. With the use of n-well near the drain region, we can avoid electric field concentration below the drain region. P-well dose, p-well length and extended drain dose should be optimized to reduce surface field of the proposed isolated RESURF LDMOS regardless of epi thickness.

A compensating ion-implantation method is introduced to make self-aligned extended-drain of 30 V lateral NMOS and PMOS transistors with the only one mask and to help the improvement of electrical SOA through the shift of the critical electric field position. In general, high voltage lateral MOS has been useful for high current and high voltage applications. In that case, we have to check up the critical electric field position and the current flow line occurring hot-carrier injection phenomenon because it results in unfavorable device destruction by secondary breakdown. In this paper, we shifted the critical electric field position from n+ drain edge to n+ drain bottom using self-aligned extended-drain formed by compensating ion-implantation. As a result, the occurrence of the secondary breakdown due to Kirk effect would be postponed.

Hierarchical Cu2ZnSnS4 nanostructures with various morphologies and sizes have been synthesised successfully using a simple solvothermal reaction. For the control of the size and morphology of Cu2ZnSnS4, polyvinylpyrrolidone was used as a structure-directing ligand. By changing the molecular weights and concentrations of the polyvinylpyrrolidone ligands, we prepared unique Cu2ZnSnS4 nanostructures ranging from discrete nanoparticle aggregates to nanoflower-like particles. Owing to the unique control of the nanostructures and their ecofriendly nature, the nanoflower-like Cu2ZnSnS4 materials are promising as excellent absorber materials for low-cost solar cells.

ZnO nanowire arrays were synthesised for dye-sensitised solar cell applications using the chemical bath deposition technique. To study the effect of the particle size in the seed layer on the growth and resultant photoconversion efficiency, we prepared various seeded FTO substrates by repeating the seed layer sol-gel coating process. It was found that changing the number of coating process merely increases the particle size of the ZnO seeds, and the increase in the seed particle size induces low growth rates. In addition, to enhance the nanowire growth rates, ammonia was added with polyethylenimine. Based on various characterisations such as XRD, SEM, and J-V curves, we discuss the effect of ammonia on the growth rates of ZnO nanowire, and suggest the optimum ammonia concentration for solar cell applications.