Key Engineering Materials Vols. 345-346

Abstract: Modified transverse and longitudinal tensile test techniques are proposed to evaluate the mechanical properties of nuclear fuel cladding materials under a hoop and axial loading condition in a hot cell. The ring specimen with a gage length of 3 mm and a width of 2 mm is designed to limit a deformation within the gage section and to maximize the uniformity of a strain distribution at the gage section. The loading grip is designed such that a constant curvature of a specimen is maintained during a deformation. The contact surface is lubricated with a graphite lubricant (Model P-37, Molykote Co.). A dogbone specimen with a gage length of 25 mm and a gage width of 2.5 mm has been designed for the longitudinal tensile test. The grip is designed such that any slippage at the gripping section does not occur during a test. Through the tensile test of an unirradiated Zircaloy-4 cladding tube and an SUS 316 steel seamless tube, it is found that the proposed techniques are appropriate for an estimation of the tensile properties of an irradiated nuclear fuel cladding in a hot cell.

Abstract: The effect of thermo-mechanical treatment (TMT) process on the strength and precipitation behavior of an 11%Cr-0.3Mo-1.6W steel during long term aging was investigated. The major precipitates in as-tempered specimen were identified as M23C6 (M=Fe,Cr) and MX (M=Ta,V;X=C,N). The M23C6 precipitate in TMT sample was more finely distributed due to the increased heterogeneous nucleation sites at dislocations. The tensile strength of TMT sample is higher than that of the conventional heat treatment (CHT) sample in as-tempered condition. However, Laves phase starts to precipitate additionally in the aged condition. The growth rate of Laves phase in TMT sample is much faster than that in CHT sample. Therefore, the difference in tensile strength between CHT and TMT sample decreases as the aging time increases.

Abstract: "Osseo" refers to bone and "integration" refers to how a prosthesis can be integrated with the bone in residual limbs both arms and legs. Osseointegration(OI) was originally defined as a direct structural and functional connection between ordered living bone and the surface of a loadcarrying implant. OI could be described as the modality for stable fixation of titanium implant to bone structure. The OI has become a realized phenomenon of importance in the dental and rehabilitation sciences since recently developed dentures and artificial limbs are directly attached to human skeleton by using osseointegrated implants. Previously, a study showed that bone strain generated potential (SGP) that is an electrical potential and considered to be generated by fluid flow in bone could be used as a parameter to examine the amount of OI on bone-implant interface. Since no study was performed to understand according to the point on behavior of SGP for the boneimplant composite. In this study, we used a multi-channel measurement system and investigated SGP according to the point. Four white New Zealand rabbits underwent pure titanium implant insertion surgery to tibia after amputation. After checking full OI at the end of the 5 weeks, experimental animals were euthanized and the amputated tibia-implants were harvested. Holes of 0.5mm in diameter were made on the tissue of the tibia and electrodes of 0.16mm in diameter were inserted to the holes. Then, the instrumented bone-implant composites were placed to a servo material testing machine to apply axial compressive displacement loadings. During the compression tests, SGPs were also measured. Magnitude of SGP was found to be significantly increased near bone and implant interface for the osseointegrated bone-implant composite.

Abstract: The reaction-sintered zirconia-alumina and zirconia-spinel ceramics having low firing shrinkage were prepared from ZrO2(Ca-PSZ)/Al and ZrO2(Baddellyite)/MgAl powder mixtures via the attrition milling and the effect of the characteristics of used raw powders was investigated. Flaky Al powders mixed with coarse Ca-PSZ powders was not effectively comminuted due to lower hardness of zirconia powders. So by using the alumina ball media or coarse Al2O3 powders rather than Al, the milling efficiency could be much more increased. When fused Ca-PSZ powder was reaction-sintered with Al at 1550
for 3 hours, the reaction-sintering and densification were somewhat difficult because the Ca-PSZ/Al powder mixture was not effectively comminuted. And the Ca ion in Ca-PSZ grains diffused into alumina grains during sintering so that the unstabilization of Ca-PSZ body was occurred which gave the cracks in the specimens. But when MgAl alloy powder was added to monoclinic zirconia, Mg and Al became to oxide at first and subsequently converted to spinel(MgAl2O4) during heating and finally unreacted MgO seemed to stabilize the zirconia. The oxides which formed at the oxidation process would have very fine grain size so that the reaction sintering was more effective to densification and homogeneous microstructure. The mechanical properties of reaction-sintered stabilized zirconia/spinel composite were better than only MgO stabilized zirconia. Sintering behavior in reaction and mechanical properties of sintered body were examined, with emphasis on the relations between spinel formation and mechanical properties.

Abstract: In this research, the optimal grinding condition has been obtained by design of experiment(DOE) for the development of aspheric lens for the 3 Mega Pixel, 2.5x optical zoom camera-phone module. Also, the WC mold was processed by the method of ultra precision grinding under this optimal grinding condition. The influence of DLC coating on form accuracy (PV) and surface roughness(Ra) of the mold was evaluated through measurements after DCL coating using ion plating on the ground mold. Also, aspheric glass lens was molded by before and after the use of the mold of DLC coating, respectively. The optical characteristics of each sample, which were molded by the different mold, were compared with each other.

Abstract: The safety valve has been designed to protect high pressure vessels. A fracture plate made of a circular thin plate is located within the safety valve. The circular thin plate has an outlet for fluid release and to help decrease the pressure. As such, fracture of the circular thin plate can occur at the appointed pressure. In this study, design variables of the safety valve were used to control fracture pressure so that it was easy to apply in the development of a new model of a safety valve. Design variables were fluid diameter of the safety valve, thickness of the fracture plate, filet radius of the clamping bolt, fracture pressure, and clamped torque of the clamping bolt. Design variables were selected, since the fracture experiment indicated that these variables might play a critical role in the fracture of the circular thin plate. Fracture pressure was calculated by the finite element analysis method and analyzed to affect the design variables on the fracture pressure. Using regression analysis, main design variables such as the fluid diameter, the thickness and the fillet were selected and the relationships of the variables were expressed by a regression equation. Furthermore, finite element analysis method and the regression equation were verified comparing with the experiment result.

Abstract: The thin films of indium tin oxide (ITO) are used for a variety of electronic devices such as solar cells, touch panels, liquid crystal displays (LCDs). However, these electronic devices are not strong enough against heavy impact since their ITO thin films are deposited on glass substrates. Therefore, ITO thin films were prepared by the inclination opposite target type DC magnetron sputtering equipment onto the Polyethylene Terephthalate (PET) substrate at room temperature using oxidized ITO with In2O3 and SnO2 in a weight ratio of 9:1. In this study, the transmittance, resistivity and electromagnetic wave shielding effectiveness of the ITO thin films prepared at various sputtering time (20~80min namely film thickness; 130~500nm) are measured. The results show that transmittance of the ITO thin films could show about 70% in the range of a visible ray by the variation of film thickness. It also can be seen that a minimum exists in the resistivity of ITO thin films for the variation of film thickness. Electromagnetic wave shielding effectiveness was increased as film thickness increased.

Abstract: Laser peening without protective coating (LPwC) has been applied to metallic materials using low energy pulses of a Q-switched and frequency-doubled Nd:YAG laser. Compressive residual stresses of several hundred megapascals were imparted on the surface of the materials. Redistribution of the residual stress in the top surface due to thermal loading was evaluated non-destructively by synchrotron radiation of SPring-8. Accelerating stress corrosion cracking (SCC) tests showed that LPwC prohibited SCC of sensitized materials. LPwC largely prolonged the fatigue lives of titanium alloys, aluminum alloys and austenitic stainless steels.

Abstract: Material selection became one of the important activities for engineers in design and manufacturing processes. A selected material at the beginning of design stage affects functionality of the designed part as well as manufacturability and cost of the final product. Unfortunately there are not many accessible material databases that can be properly used for design. In this research, a web-based material database was constructed. In order to assist designers to compare different materials, two-dimensional and three-dimensional graphs for comparison of material properties were provided via the web browser. Using these graphical tools, multi-dimensional comparison was available in more intuitive manner. In addition, this web site is open to the public, and one may add new material properties to the database in order to compare the data with existing materials. To provide the database in a commercial CAD (Computer Aided Design) environment, API (Application Programming Interface) modules were developed using Web services. The web-based material database can be accessible from http://fab.snu.ac.kr/matdb.

Abstract: The codeposition behavior of submicron sized diamond with nickel from nickel electrolytes has been investigated. Electroplating of diamond dispersed nickel composites was carried out on a rotating disk electrode (RDE). The effects of current type and current density on the electrodeposited Ni-diamond composite coating were investigated. The effects of pH and surfactants on the composite coating were also investigated. The hardness of coating was measured with varying electroplating conditions. As diamond was incorporated into the coating, the hardness of coating as well as the wear resistance was improved. The surface morphologies of the Ni-diamond composite coatings were observed using FESEM.