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In this letter, a switched six-port (SP) receiver is proposed for an accurate angle-of-arrival (AoA) finding system. The proposed switched six-port network consists of four antennas, two hybrid couplers, two dual-pole-dual-throw switches, and four power detectors. The proposed switched six-port receiver periodically selects two different antennas from four antennas, providing four different antenna spacings for a more accurate AoA detection. As a result, a smaller and more accurate AoA finding system has been achieved than a conventional dual six-port receiver that uses two different antenna spacings from four antennas. For validation, the proposed method was simulated, implemented, and measured. In the measurement, the averaged root-mean-square error of the estimated angle over the range of $-\text{90}^\circ$ to $\text{90}^\circ$ was $\text{3.16}^\circ$ with 20 sample numbers and a signal-to-noise ratio (SNR) of 15 dB.

The manufacturing process of large scaled Al 7050 alloy is difficult for the occurrence of solidification crack during casting. The aims of this study are the evaluations of microstructure and mechanical properties of extruded Al 7050 billet and ring forged one with large scale. Large scaled Al 7050 billet was casted by direct-chill casting process. The extruded and ring forged specimens were prepared from the casted ingot after residual stress relief and homogenization heat treatment, respectively. Microstructures, hardness and tensile test of the surface, middle and center part of each specimen were performed at room temperature. Sheared and elongated type grains were observed at the edge parts of surface and center area and its aspect ratios of grains were low and similar as 0.21 while that of middle area was closed to 0.92 value in ring forged Al 7050 alloy. The mechanical properties of extruded Al 7050 alloy were superior than those of ring forged one. The hardness values of surface and center part were slightly higher than that of middle part in ring forged Al 7050 alloy.

Caused corrosion by hydrogen on stainless steel using nondestructive technique is one of issues to be clarified in nuclear fusion industry. In this study, an ultrasonic wave was used to evaluate the degree of corrosion by hydrogen charging of stainless steel. The mechanical properties of hydrogen charged material including tensile strength and strain were discussed, and the change of surface of specimen according to the hydrogen charging quantities was observed. The relationship between fractography and ultrasonic wave characteristics on hydrogen charged material discussed. In addition, acoustic emission technique was applied to clarify the dynamic behavior such as dislocation, deformation and crack in material by loading. AE parameters of event, energy, amplitude and frequency were analyzed according to the degree of load, and optical AE parameter was derived to evaluate the degree of the damage of hydrogen charged stainless steel.

The aim of the present study is to identify the properties of intermediate phases formed on the bonding interface of hot pressed Cu/Al clad materials by transmission electron microscopy and nano-indentation analyses. Cu/Al clad materials were fabricated by hot pressing under 200 MPa at 250 °C for 1 h and then heat treated at 400 °C for 1 h. Nano-indentation measurement was conducted to evaluate the nanohardness and modulus of the intermediate phases formed between the Cu/Al interfaces. A 3-tier diffusion layer was observed at the Cu/Al interfaces. Knoop microhardness values at the bonding interface were 7 to 11 times that of the Cu and Al matrix metals. The intermediate phases formed at the bonding interface were Al4Cu9, AlCu, and Al2Cu. A mapping analysis confirmed that the Al and Cu particles moved via mutual diffusion toward the intermediate phases formed at the bonding interface. The nanohardness values of η2-AlCu and γ1-Al4Cu9 were 4 to 7 times that of the Cu and Al matrix metals. Nanohardness and Knoop microhardness measurement curves exhibited similar tendencies. The rigidity values of the respective intermediate phases can be arranged in descending order as follows: γ1-Al4Cu9 > η2-AlCu > θ-Al2Cu.

A stainless steel material is used as components for storing hydrogen gas and liquid hydrogen, or for transportation raw material and oil in storage container. Brittle fracture associated with hydrogen is observed for stainless steel and these phenomena of hydrogen embrittlement were very important for wide-ranging application of stainless steel. Many researchers have studied the hydrogen embrittlement from the mechanical and metallographic point of views. The aim of this study is to identify the material degradation by hydrogen embrittlement for 316L stainless steel using nondestructive evaluation. That is, the relationship between the mechanical properties of 316L stainless steel by hydrogen charging and nondestructive technique of acoustic emission technique and an ultrasonic wave is to be clarified. The relationship between fractography and ultrasonic wave characteristics on hydrogen charged material for 0hr and 24hr was discussed. SEM and optical microscope were used to inspect the fracture surface of hydrogen charged material. The fracture surface of the charged specimen became brittle, especially on the surface nearby. AE parameters of event, count, energy, amplitude and frequency were analyzed according to the degree of the damage of hydrogen charged stainless steel.

This study was carried out to observe and measure the microstructure, distance between dendrite arms, aspect ratio, and Knoop hardness change of extruded material formed by the hydro co-extrusion of Al3003/Al4004 clad material manufactured by the duo-casting method. The specimen of duo-casted Al3003/Al4004 clad materials was circle shaped, it was composed of Al3003 (outside) and Al4004 (inside) materials. The manufacturing conditions of the hydro co-extruded specimen were 423 K temperature and 6.5 ratio of extrusion. At the interface of the duo-casted Al3003/Al4004 clad material, a non-junction at the interface and non-metallic inclusions of Si- and Mn-based oxides were observed. Al3003 exhibits equiaxed crystals, Al4004 has a casted structure with dendrites before extrusion, showed slight deformation during extrusion, and then finally exhibited completely deformed structures after extrusion. In the cast material, the distance between dendrite arms increased, and the aspect ratio of dendrites tended to decrease from the surface to the center. However, in the case of the extruded material, neither Al3003 nor Al4004 changed significantly from the surface to the inside. As extrusion progressed, the Knoop hardness value at the interface of Al3003/Al4004 increased rapidly compared with those of Al3003 and Al4004 matrixes.

Embrittlement of material by hydrogen charging should be cleared for safety of storage vessel of hydrogen and components deal with hydrogen. A stainless steel is generally used as materials for hydrogen transportation and storage, and it has a big advantage of corrosion resistance due to nickel component in material. In this study, microscopic damage behavior of stainless steel according to the hydrogen charging time using nondestructive evaluation was studied. The surface of stainless steel became more brittle as the hydrogen charging time increased. The parameters of nondestructive evaluation were also changed with the embrittlement of stainless steel surface by hydrogen charging. Ultrasonic test, which is the most generalized nondestructive technique, was applied to evaluate the relationship between the ultrasonic wave and mechanical properties of stainless steel by hydrogen charging. The attenuation coefficient of ultrasonic wave was increased with hydrogen charging time because of surface embrittlement of stainless steel. In addition, acoustic emission test was also used to study the dynamic behavior of stainless steel experienced hydrogen charging. AE event at the hydrogen charged specimen was obviously decreased at the plastic zone of stress-strain curves, while the number of event for the specimen of hydrogen free was dramatically generated when compared with the specimens underwent hydrogen charging.

The effects of hydrogen charging on the mechanical properties of 304 stainless steels were investigated in conjunction with the detailed examinations of their fracture modes. The dependence of the absorbed impact energy and the surface hardness of the 304 stainless steels on the hydrogen charging time was characterized. The tensile properties of the 304 stainless steels by the variation of cross-head speed were also evaluated at the room temperature. The hydrogen charging was performed by an electrolysis method for all specimens of the 304 stainless steels. The mechanical properties of the 304 stainless steels exhibited the sensitivity of embrittlement due to a hydrogen charging. The correlation between mechanical properties and fracture surfaces was discussed.

This paper dealt with the interfacial bonding properties of Cu/Al clad materials by the variation of aging treatment times. Cu/Al clad materials were fabricated by a hot-pressing process. A subsequent heat treatment was also performed for the interfacial strengthening of Cu/Al clad materials. The characterization of Cu/Al clad materials was evaluated by means of OM, SEM, EDX and Knoop hardness test. Several diffusional layers were created at the interfacial region of Cu/Al clad materials, due to the chemical reaction of Cu and Al elements. The thicknesses of interfacial diffusion layers for Cu/Al clad materials increased with the increase of aging treatment time, accompanying the variation of intermetallic compounds. The hardness strengthening of diffusion layers by the increase of aging treatment time was also affected by the formation of η2 phase at the bonding interfacial region.

The objective of this study is to evaluate the elastic wave's characteristic on the crack in the weld of stainless steel materials using guided wave and acoustic emission, nondestructive tests. The stainless steel is expected as candidate of structural piping material under high temperature condition in nuclear fusion instrument, and a tungsten inert gas (TIG) weld technique was applied for making its jointing. The defect size of 20 mm was induced in the weld material. The guided wave, one of elastic waves, can propagate through very long pipe, and easily change to lots of modes by the defects in the structure. By analyzing the relationship between the mode conversion and the defects we can evaluate existing of the defects in weld material. In present study Nd-YAG laser was used to excite the guided wave by non-contact method, and AE technique was also used to clarify the mode conversion of guided wave by defect because lots of AE parameters of energy, count and amplitude can give more chances for analysis of mode conversion. The optimal AE parameters for the evaluation of the defects in weld zone using laser guided wave were derived.

During the use of API X70 steel as a pipeline structural material for the transportation of natural gas, hydrogen embrittlement can occur due to the hydrogen contained in natural gas. The aim of this study is to investigate the effects of the hydrogen content under high-pressure hydrogen gas conditions on the hydrogen embrittlement of air-cooled API X70 steel. The air-cooled API X70 steel was manufactured by hot rolling and was then air-cooled to room temperature. Tensile test specimens were held for 0 h, 1000 h, and 2000 h within a pressure vessel filled with 100% hydrogen gas at a gas pressure of 10 MPa, with the tensile tests then performed at room temperature. The microstructure of the API X70 steel consists of coarse polygonal ferrite, coarse pearlite, and fine acicular ferrite. The yield and tensile strength increased and elongation decreased considerably after a holding time of 2000 h compared to those of 0 h and 1000 h within the pressure vessel. The morphology of the fracture surface changed from ductile to brittle upon hydrogen gas charging. Secondary cracks were observed in both of the hydrogen-gas-charged specimens. No external cracks were formed on the surface of the tensile-tested specimen with a 0 h holding time; however, many external cracks were observed on the specimen surface subjected to hydrogen gas charging.

The effects of hydro co-extrusion on the microstructure changes of aluminum hybrid duo-cast Al 3003/Al 4004 clad materials were studied. The specimen of duo-cast Al 3003/Al 4004 clad materials was in circle shape, and was composed of Al 3003(outside) and Al 4004(inside) materials. The specimen was extruded by the hydro co-extrusion equipment. The manufacturing conditions of the specimen were 423 K in temperature and 5 in extrusion ratio. The dimensions of the specimen were 80 mm in diameter of the Al 4004 material and 35 mm in thickness of the Al 3003 material before the hydro co-extrusion process, and 30 mm in diameter and about 5 mm in thickness after the extrusion process, respectively. The microstructure and the hardness for two specimens were investigated. The hardness value of cross section in the duo-cast Al 3003/Al 4004 clad materials before the extrusion process was increased in form of the parabola toward the center. However, after the extrusion process, it was almost constant in the portion of Al 4004 material. Lots of big voids above 1 mm in diameter in the specimen existed in the interfacing region of Al 3003 and Al 4004 materials before the extrusion process. These big voids disappeared after the process of hydro co-extrusion.

The objective of this research is to study the effect of various hydrogen charging quantities in austenitic stainless steel using nondestructive technique. The hydrogen charging equipment was designed to make charging the steel, and the specimens were charged for 2, 4, 10 and 24 hours in the equipment. An acoustic emission (AE) technique, nondestructive test, was used to evaluate the dynamic behavior of the hydrogen charged austenitic stainless steel specimen. The tensile load was applied the charged specimen with the attached AE sensor, and elastic waves caused plastic deformation and cracking in the specimen by external tensile loading were caught at the AE sensor and analyzed by the AE parameters such as count, energy, duration time, event and amplitude. In addition, ultrasonic wave was also used to evaluate the degree of hydrogen charging. The velocity and the attenuation ratio of the ultrasonic wave on the specimen with different hydrogen charging conditions were measured. The velocity was not changed but the attenuation ratio was linearly increased with the hydrogen charging time. The relationship between the results of nondestructive test including AE test and ultrasonic test and fractographic analysis by using SEM was discussed.

A TIG welded 316 stainless steel materials will have a large impact on the design and the maintenance of invessel components including pipes used in a nuclear power plant, and it is important to clear the dynamic behavior in the weld part of stainless steel. Therefore, nondestructive techniques of acoustic emission (AE) and ultrasonic wave were applied to investigate the damage behavior of welded stainless steel. The velocity and attenuation ratio of the ultrasonic wave at each zone were measured, and a 10 MHz sensor was used. We investigated the relationship between dynamic behavior and AE parameters analysis and derived the optimum parameters to evaluate the damage degree of the specimen. By measuring the velocity and the attenuation of an ultrasonic wave propagating each zone of the welded stainless steel, the relation of the ultrasonic wave and metal structure at the base metal, heat affected zone (HAZ) metal and weld metal is also discussed. The generating tendency of cumulated counts is similar to that of the load curve. The attenuation ratios from the ultrasonic test results were 0.2 dB/mm at the base zone, and 0.52 dB/mm and 0.61 dB/mm at the HAZ zone and weld zone, respectively.

This study improves the formability in fine-blanking the lock plate of car seat belts using a low carbon steel(SM35C) plate. The optimal die design for the forming process is proposed using rules for process planning based on theories and field experiences. The optimal design is analyzed using commercial finite element software in order to solve the fracture problems in the extrusion process. Through the improved layout based on the FEM results, the fracture of the extruded part and the roll over problem are solved. Furthermore, it is demonstrated through the shown from experiments that the extruded part does not break in the modified die.

The present work dealt with the high temperature thermal shock properties of 316 stainless steels, in conjunction with a detailed analysis of their microstructures. In particular, the effects of the thermal shock temperature difference and thermal shock cycle number on the properties of 316 stainless steels were investigated. A thermal shock test for 316 stainless steel was carried out at thermal shock temperature differences from 300℃ to 1000℃. The cyclic thermal shock test for the 316 stainless steel was performed at a thermal shock temperature difference of 700℃ up to 100 cycles. The characterization of 316 stainless steels was evaluated using an optical microscope and a three-point bending test. Both the microstructure and flexural strength of 316 stainless steels were affected by the high-temperature thermal shock. The flexural strength of 316 stainless steels gradually increased with an increase in the thermal shock temperature difference, accompanied by a growth in the grain size of the microstructure. However, a thermal shock temperature difference of 800℃ produced a decrease in the flexural strength of the 316 stainless steel because of damage to the material surface. The properties of 316 stainless steels greatly depended on the thermal shock cycle number. In other words, the flexural strength of 316 stainless steels decreased with an increase in the thermal shock cycle number, accompanied by a linear growth in the grain size of the microstructure. In particular, the 316 stainless steel had a flexural strength of about 500 MPa at 100 thermal-shock cycles, which corresponded to about 80% of the strength of the as-received materials.

Cu/Al bar clad material was fabricated by a drawing process and a subsequent heat treatment. During these processes, intermetallic compounds have been formed at the interface of Cu/Al and have affected its bonding property. Microstructures of Cu/Al interfaces were observed by OM, SEM and EDX Analyser in order to investigate the bonding properties of the material. According to the microstructure a series of diffusion layers were observed at the interface and the thicknesses of diffusion layers have increased with aging time as a result of the diffusion bonding. The interfaces were composed of 3-ply diffusion layers and their compositions were changed with aging time at 400 °C. These compositional compounds were revealed to be η2, (θ+η2), (α+θ) intermetallic phases. It is evident from V-notch impact tests that the growth of the brittle diffusion layers with the increasing aging time directly influenced delamination distance between the Cu sleeve and the Al core. It is suggested that the proper holding time at 400 °C for aging as post heat treatment of a drawn Cu/Al bar clad material would be within 1 h.

This paper dealt with a liquid phase sintering process for the fabrication of carbon fiber reinforced SiC matrix composites (Cf/SiC), using a ultra-fine SiC particles and oxide additive materials. Especially, the thermal shock properties of Cf/SiC composites were investigated at the elevated temperatures. The characterization of monolithic SiC materials by the variation of starting SiC particle size was also examined. Monolithic SiC materials possessed an excellent density higher than about 3.0 mg/m3 and a good flexural strength of about 700 MPa, regardless of starting SiC particle size. Cf/SiC composites also represented a dense morphology in the intra-fiber bundle region, even if there were some amount of pores. However, the flexural strength of Cf/SiC composites greatly decreased at the thermal shock temperature of 400 °C.

The effect of He-injection on irradiation-induced segregation of aging treated Fe–12%Cr–15%Mn austenitic steels, which are candidate materials as the reduced radio-activation of structure material for nuclear and/or fusion reactors was investigated by using the 1250 kV high voltage electron microscope (HVEM) connected with an ion accelerator. The Fe–Mn–Cr steel has been irradiated at 573 K by three irradiation modes of single electron-beam irradiation, electron-beam irradiation after He-injection and electron/He+-ion dual-beam irradiation in a HVEM. Irradiation-induced segregation analyses were carried out by an energy dispersive X-ray analyzer (EDX) in a 200 kV FE-TEM with beam diameter of about 0.5 nm. Dislocation loops with strain contrast were formed during irradiation and the loop numbers density increased rapidly with irradiation dose for He-pre-injected specimens. Voids were not observed after irradiations with three irradiation modes up to 5.4 dpa at 573 K. Irradiation-induced segregations of Cr and Mn near grain boundary were observed in each irradiation condition, but the amounts of Mn segregation decreased in the cases of electron/He+-ion dual-beam irradiation compared with single electron-beam and electron-beam irradiation after He-injection conditions.

This paper dealt with the thermal shock properties of SiCf/SiC composites reinforced with two dimensional SiC fabrics. SiCf/SiC composites were fabricated by a liquid phase sintering process, using a commercial nano-size SiC powder and oxide additive materials. An Al2O3–Y2O3–SiO2 powder mixture was used as a sintering additive for the consolidation of SiC matrix region. In this composite system, Tyranno SA SiC fabrics were also utilized as a reinforcing material. The thermal shock test for SiCf/SiC composites was carried out at the elevated temperature. Both mechanical strength and microstructure of SiCf/SiC composites were investigated by means of optical microscopy, SEM and three point bending test. SiCf/SiC composites represented a dense morphology with a porosity of about 8.2% and a flexural strength of about 160 MPs. The characterization of SiCf/SiC composites was greatly affected by the history of cyclic thermal shock. Especially, SiCf/SiC composites represented a reduction of flexural strength at the thermal shock temperature difference higher than 800 °C.

The dynamic instability and natural frequency of an axially moving pipe conveying fluid are investigated. Thus, the effects of fluid velocity and moving speed on the stability of the system are studied. The governing equation of motion of the moving pipe conveying fluid is derived from the extended Hamilton's principle. The eigenvalues are insystem via the Galerkin vestigated for the pipe method under the simple support boundary. Numerical examples show the effects of the fluid veloc-ity and moving speed on the stability of system. Moreover, the lowest critical moving speeds for the simply supported ends have been presented. * 1. 서 론 내부에 유체를 가지는 파이프 구조물은 배관계 및 일반적인 기계장치에서 흔히 볼 수 있다. 파이프 내부에 흐르는 유체는 파이프 시스템의 동적특성 및 안정성에 큰 영향을 미치기 때문에 유체의 질량비와 유속에 의한 시스템의 안정성 해석에 관한 연구는 오랜 기간 많은 연구자들에 의하여 연구되어져 오고 있다 (1~3) . 또한, 축방향으로 움직이는 구조물은 기계 구동 벨트, 자기 테이프, 종이 등 여러 공학적, 산업적 분야에서 쉽게 접할 수 있다. 특히, 이송되는 보 구조물의 형태는 평판 톱의 블레이드나 밸브 액추에이터 등에서 그 예를 찾아 볼 수 있다. 이처럼 시스템의 불안정을 유발하는 주요 파라교신저자; 정회원, 동의대학교 기계공학과E-mail : isson92@deu.ac.krTel : (051)890-2239, Fax : (051)890-2232* 동의대학교 기계공학과** 한국폴리텍 VI대학 달성캠퍼스 자동차과 미터인 이송속도와 유속이 연성되어 전체 시스템의 안정성에 미치는 영향을 해석하는 것은 공학적으로 매우 중요한 문제라 할 수 있다. Wickert와 Mote

The dynamic behavior for the fabrication of carbon fiber reinforced SiC matrix composites( C f / SiC ) is investigated by the theory and experiment. The governing differential equation of a composite beam is derived via Hamilton's principle. The C f / SiC composites have been fabricated by a liquid phase sintering process, using the ultra-fine SiC particles and oxide additive materials. The SiC based materials are fabricated by using a commercial SiC powder with an average size of about 0.3µm. An Al 2 O 3- Y 2 O 3- SiO 2 powder mixture is used as a sintering additive. The compositional ratio ( Al 2 O 3/ Y 2 O 3) and its total amount ( Al 2 O 3+ Y 2 O 3) of additive materials are 1.5 and 10 wt%, respectively. Especially, the content of PVB is changed from 0 wt% to 10 wt%. The SiC based materials are sintered at the temperature of 1820°C under 30 MPa for 1 hr. In this study, the effect of content of PVB on the natural frequency and mode shape is obtained. Finally, the relationship between natural frequency and mechanical property of C f / SiC composites is discussed.

A shape memory alloy (SMA) as part of some products and system has been used to keep their shape at any specified temperature. By using this characteristic of the shape memory alloy it can be solved the problem of the residual stress by difference of coefficients of thermal expansion between reinforcement and matrix within composite. In this study, TiNi / Al 6061 shape memory alloy composite was fabricated through hot press method, and the optimal fabrication condition was created. The bonding effect of the matrix and the reinforcement within the SMA composite was strengthened by cold rolling. The SMA composite can be applied as the part of airplane and vessel, and used under tough condition of repetitive thermal shock cycles of high and low temperatures. Therefore, the thermal shock test was performed for the SMA composite, and mechanical properties were evaluated. The tensile strength of the SMA composite showed a slight decline with the thermal shock cycles. In addition, acoustic emission (AE) technique was used to quantify the microscopic damage behavior of cold rolled TiNi / Al 6061 shape memory alloy composite that underwent thermal shock cycles. The damage degree on the specimen that underwent thermal shock cycles was discussed. Actually AE parameters such as AE event, count and energy was analyzed, and these parameters was useful to evaluate the damage behavior and degree of the SMA composite. The waveform of the signal caused by debonding was pulse type, and showed the frequency range of 160 kHz, however, the signal by the fiber fracture showed the pulse type of high magnitude and frequency range of 220 kH.

The mechanical properties of SiCf/SiC composites have been investigated, based on detailed analyses of their microstructure. SiCf/SiC composites were prepared from fiber preforms by a slurry infiltration technique, in which a mixture with SiC, Al2O3, and Y2O3 particles was impregnated into the fabric structure. SiCf/SiC composites were consolidated by liquid phase sintering process, associated with the creation of secondary phases by the addition of Al2O3 and Y2O3 particles. The reinforcing material was a plain weave Tyranno SA SiC fabric with a carbon interfacial layer. The sintered density and the pore volume fraction of SiCf/SiC composites were about 3.0 Mg/m3 and about 10%, respectively. These SiCf/SiC composites had an average flexural strength of about 250 MPa at room temperature. They exhibited pseudo-ductile fracture behavior, due to the carbon interfacial layer. The introduction of the carbon interfacial layer greatly improved the fracture energy of SiCf/SiC composites.

This paper dealt with the microstructure and mechanical properties of SiC based composites reinforced with different reinforcing materials. The composites were fabricated using reinforcing materials of carbon nanotubes (CNT) and Tyranno Lox-M SiC chopped fibers. The volume fraction of carbon nanotubes was also varied in this composite system. An Al2O3–Y2O3 powder mixture was used as a sintering additive in the consolidation of the SiC matrix. The characterization of the composites was investigated by means of SEM and three point bending tests. These composites showed a dense morphology of the matrix region, by the creation of a secondary phase. The composites reinforced with SiC chopped fibers possessed a flexural strength of about 400 MPa at room temperature. The flexural strength of the carbon nanotubes composites had a tendency to decrease with increased volume fraction of the reinforcing material.

The flexural strength of based composites reinforced with Nb sheets has been investigated, based on the detailed examination of their microstructure and fractured surface. Both sintered density and porosity of Nb/ composites were also examined. Nb/ composites were fabricated by different conditions such as temperature, applied pressure and its holding time, using a hot-press device. The volume fraction of Nb sheet in this composite system was fixed as 10%. The characterization of Nb/ composites were investigated by means of optical microscopy, scanning electron microscope and three point bending test. Nb/ composites represented a dense morphology at the interfacial region, accompanying the creation of two types of reaction layer by the chemical reaction of Nb and . Nb/ composites possessed an excellent density at the fabricating temperature of , corresponded to about 95% of theoretical density. The flexural strength of Nb/ romposites were greatly affected by the pressure holding time at the same fabricating temperature, owing to the large suppression of porosity in the microstructure. Especially, Nb/ composites represented a good flexural strength of about 310 MPa at the fabricating condition of , 30MPa and 60min, accompanying the pseudo-ductile fracture behavior by the deformation of Nb sheet and the interfacial delamination.

The thermal shock properties of SiC materials were investigated for high temperature applications. In particular, the effect of thermal shock temperature on the flexural strength of SiC materials was evaluated, in conjunction with a detailed analysis of their microstructures. The efficiency of a nondestructive technique using ultrasonic waves was also examined for the characterization of SiC materials suffering from a cyclic thermal shock history. SiC materials were fabricated by a liquid phase sintering process (LPS) associated with hot pressing, using a commercial submicron SiC powder. In the materials, a complex mixture of and powders was used as a sintering additive for the densification of the microstructure. Both the microstructure and mechanical properties of the sintered SiC materials were investigated using SEM, XRD, and a three point bending test. The SiC materials had a high density of about 3.12 Mg/m3 and an excellent flexural strength of about 700 MPa, accompanying the creation of a secondary phase in the microstructure. The SiC materials exhibited a rapid propagation of cracks with an increase in the thermal shock temperature. The flexural strength of the SiC materials was greatly decreased at thermal shock temperatures higher than , due to the creation of microcracks and their propagation. In addition, the SiC materials had a clear tendency for a variation in the attenuation coefficient in ultrasonic waves with an increase in thermal shock cycles.

To investigate the effect of aging treatment on irradiation-induced segregation of high Mn-Cr steel, specimens for electron-beam irradiation were prepared from the high Mn-Cr austenitic steel which was solution treated at 1 373 K for 1 h and aging treated at 573 K for 1 000 h, respectively. The electron-beam irradiation was performed at 573 K up to doses of 5.4 dpa in a 1 250 kV HVEM and irradiation-induced segregation analyses were carried out by an EDX in a 200 kV FE-TEM. The results show that void formation is not observed in both solution treated and aging treated ones. The amount of Cr segregation at the grain boundary decreases in the aged one; however, that of Mn is not changed in solution treated one.

The fabrication route of SiC materials by the complex compound of ultra-fine SiC particles and oxide additive materials has been investigated. Especially, the effect of additive composition ratio on the characterization of SiC materials has been examined. The characterization of C/SiC composites reinforced with plain woven carbon fabrics was also investigated. The fiber preform for C/SiC composites was prepared by the infiltration of complex mixture into the carbon fabric structure. SiC based composite materials were fabricated by a pressure assisted liquid phase sintering process. SiC materials possessed a good density higher than about 3.0 Mg/m 3 , accompanying the creation of secondary phase by the chemical reaction of additive materials. C/SiC composites also represented a dense morphology in the intra-fiber bundle region, even if this material had a sintered density lower than that of monolithic SiC materials. The flexural strength of SiC materials was greatly affected by the composition ratio of additive materials.

The characterization of liquid phase sintered(LPS) SiC based materials has been investigated with the analysis of microstructure and flexural strength. Especially, LPS - SiC materials were examined for the variation of test temperature and composition ratios ( Al 2 O 3,/ Y 2 O 3) of sintering additives. LPS - SiC based materials were fabricated by hot pressing(HP) associated with the liquid phase formation of sintering additives( Al 2 O 3, Y 2 O 3). LPS - SiCf / SiC composites were also fabricated with plane-woven(PW) Tyranno-SA fibers without an interfacial layer. LPS - SiC materials showed a dense morphology with the creation of the secondary phase like YAG. The composition ratio of sintering additives led to the variation of sintered density and flexural strength. The flexural strength of LPS - SiC materials was greatly decreased at the temperature higher than 1000°C. LPS - SiCf / SiC composites represented an average flexural strength of about 260 MPa, accompanying the catastrophic fracture behavior without any full-out phenomena.

The nondestructive properties of liquid phase-sintered silicon carbide (LPS-SiC) materials were investigated by an ultrasonic method, in conjunction with the examination of their mechanical properties and microstructures. The damage behaviors of LPS-SiC materials by the cyclic thermal shock were also examined. LPS-SiC materials were fabricated at the temperature of 1820 °C, using the additives of Al 2 O 3 , and Y 2 O 3 particles. The compositional ratios of additive materials (Al 2 O 3 /Y 2 O 3 ) for LPS-SiC materials were changed from 0.4 to 1.5 with the total amount maintained at 10 wt%. The LPS-SiC materials represented a good density of about 3.2 Mg/m 3 and an average flexural strength of about 810 MPa at an additive composition ratio of 1.5. The properties of LPS-SiC materials such as density and flexural strength were more strongly correlated with the attenuation coefficient than with the velocity of ultrasonic wave. The attenuation coefficient of LPS-SiC materials also increased with the increase of thermal shock cycles, reflecting the increased microcrack density.

This paper dealt with the microstructure and the flexural strength of monolithic SiC and SiC f /SiC composite materials. Especially, the mechanical property of SiC based materials were investigated at the elevated temperatures of 1000 and 1200 °C in the argon atmosphere. The microstructural variation of SiC based materials by the thermal exposure at the bending test temperature was also analyzed. SiC based materials were fabricated by a liquid phase sintering process (LPS), using an additive materials of Al 2 O 3 and Y 2 O 3 . A two-dimensional weave of Tyranno SA fibers were utilized as a reinforcing material for SiC f /SiC composite. SiC based materials was sintered at the temperature of 1820 °C for the creation of secondary phases. LPS-SiC materials represented a good density of about 3.1 Mg/m 3 and an average flexural strength of about 750 MPa at the room temperature. The sintering density of LPS-SiC f /SiC was also similar to that of LPS-SiC materials. However, the flexural strength of LPS-SiC based materials greatly decreased with the increase of test temperature.

Primary water stress corrosion crack (PWSCC) in the piping used at the nuclear power plant has been one of the major issues for the safety of plant. The major objective in this paper is to clarify the corrosion degree and damage by the PWSCC using nondestructive technique. The instrument of the tube typed reactor with the internal conditions of the temperature of 473K under pressure of 10 MPa was designed for corrosion of the material. The tensile specimens of the same material with the reactor were corroded in the reactor for evaluation of mechanical properties according to the corrosion. The corrosion of the specimen was maintained over one year, and an acoustic emission technique was applied to inspect the corrosion damage of the specimen periodically. A tensile test was performed for the corroded specimen, and then the elastic waves caused the deformation of the corroded specimen were analyzed. With the increase of the corrosion time the elastic waves generated in the specimen due to the tensile load showed a little difference, and these differences of the waves work as a cause of the change of acoustic emission (AE) parameters. The number of AE events at the beginning of the load increased with the corrosion time. AE parameters of amplitude and energy decreased as the corrosion times increased, while the level of duration time and count were increased with the corrosion periods. The velocity and attenuation of the elastic wave were also analyzed for the specimen, and these factors showed a close relation with the corrosion times. In addition, SEM and XRD analysis were performed to evaluate the damage behavior of the carbon steel due to corrosion.

A study on corrosion evaluation by using ultrasonic waves and acoustic emission technique is presented. The experimental equipment was established to improve the corrosion process of carbon steel pipe. The carbon steel pipe was under 473K temperatures and 10Mpa pressure conditions, and ultrasonic wave and acoustic emission techniques were used to inspect the degree of corrosion after a certain period of time. Ultrasonic bulk waves are limited by the poor time resolution when used in the measurement of corrosion depth in thin wall structures because the corroded surfaces cause unclear echo signal edges. Therefore, in this study, the ultrasonic guided waves were generated on the pipe because the thickness of pipe was thin. Various wave modes were subsequently generated on the pipe to evaluate the implications of corrosion thinning on group velocity, transmission and reflection amplitudes. The amplitudes of the transmitted and the reflected waves are influenced by couplent material. In order to reduce the effect of coupling acoustic emission sensor was used. Acoustic emission technique has lots of parameters to evaluate the corrosion besides amplitude parameter. Among parameters energy, count, and frequency were useful parameters to measure the degree of corrosion inside the carbon steel pipe under 473K temperatures.

The nuclear power plant has lots of pipes that the fluid of high temperature and high pressure flows. Among the pipe materials used at secondary circuit of the power plant the carbon steels are sensitive to corrosion due to their material properties. In this study, both ultrasonic test and acoustic emission test were used to study the corrosion effect for the carbon steel pipe nondestructively. The carbon steel specimens were in the pipe under 473K temperatures and 10MPa pressure conditions for corrosion processing. According to the degree of corrosion the strength of the specimen was evaluated, and the thickness of the corrosion specimens was also measured by using the ultrasonic wave. The experimental results showed that the attenuation factor was also increased as a depth of corrosion increased. The measured depth of the real corrosion by ultrasonic test shows the good agreement with that by an optical microscope. In order to understand the corrosion effect for the failure mechanism of carbon steel, a failure test on the specimen with various corrosion conditions was performed. An acoustic emission technique was also used to evaluate the degree of damage of corrosion specimen in real time. Acoustic emission technique is proved a useful method for on-line monitoring the microscopic failure mechanism and the damage location for the structures.

This study dealt with the corrosion resistance for the carbon steels under a pressurized water atmosphere at the elevated temperature. The nondestructive test was also used to evaluate the damage degree of corrosion test specimen. The corrosion test for carbon steels was carried out at the temperature of 200 °C under a water pressure of 10 MPa. The corrosion time for carbon steel was changed up to 20 weeks. The strength of carbon steel by the degree of corrosion was investigated by a tensile test. The carbon steel showed an average tensile strength of about 500 MPa after the corrosion period of 20 weeks, accompanying the weight loss of about 2.5 %. The attenuation coefficient of ultrasonic wave can be utilized as useful parameters to inspect the corrosion damages of carbon steels.

The long-term corrosion strength properties for the carbon steels under pressurized water atmosphere have been investigated, in the conjunction with the detailed analysis of their microstructures. The corrosion test for carbon steels was carried out at the temperature of 200°C under a water pressure of 10 MPa. The corrosion test samples were maintained up to 50 weeks in the tube shaped reactor. The mechanical strength and the microstucture of carbon steels suffered from the long term corrosion test were evaluated by SEM, XRD and tensile test. The weight loss of carbon steel by the corrosion test was also examined. The tensile strength of carbon steels decreased with the increase of corrosion time under a pressurized water atmosphere, accompanying the creation of severe corrosion damages like stress corrosion crack.

Copper/aluminum/stainless steel (Cu/Al/STS) clad materials were made by rolling and heat treatment process. These specimens were evaluated the formability and bonding strength of Cu/Al/STS clad materials. Thin disc specimens for TEM observation were prepared from the interfaces of Cu/Al and Al/STS by using the Focused Ion Beam (FIB) utility. Brittle oxide film formed on copper surface during heat treatment at 673K~773K. Diffusion bonding was observed at the interface of Cu/Al. Reacted region was formed in the interface of Al/STS with width about 10nm, while in the case of Cu/Al was formed about 1,600nm width. It was also observed nanosized crevice in reacted region of Al/STS interfaces.

In this study, elastic waves of ultrasonic and acoustic emission were used to evaluate the propagation characteristic of the wave in pipe, and study on mode conversion of the elastic wave due to the cracks in the pipe was also performed. An acoustic emission (AE) sensor was used to receive the propagated ultrasonic wave. AE technique has a merit that it can identify the received ultrasonic wave by the analysis of the AE parameters such as count, energy, frequency, duration time and amplitude. For transmitting and receiving of the wave, a wedge for universal angle was manufactured. The optimum angles for transmitting of ultrasonic wave and signal receiving at the attached AE sensor on the pipe were determined. Theoretical dispersion curve was compared with the results of the time-frequency analysis based on the wavelet transformation. The received modes showed a good agreement with theoretical one. The used ultrasonic sensor was 1MHz, and AE sensor was broadband (100kHz – 1200kHz). The artificial cracks were induced in the pipe to measure the propagation characteristics of the elastic wave for the cracks. AE parameters for the received signals were also varied with the crack types in the pipe. AE parameters of amplitude and duration time were more effective factors than the analysis of mode conversion for evaluation of the cracks in the pipe.

SiC/SiC composites and monolithic SiC materials have been fabricated by the melt infiltration process, through the creation of crystallized SiC phase by the chemical reaction of C and Si. The reinforcing material used in this system was a braided Hi-Nicalon SiC fiber with double interphases of BN and SiC. The microstructures and the mechanical properties of RS-SiC based materials were investigated through means of SEM, TEM, EDS and three point bending test. The matrix morphology of RS-SiS/SiC composites was greatly composed of the SiC phases that the chemical composition of Si and C is different. The TEM analysis showed that the crystallized SiC phases were finely distributed in the matrix region of RS-SiC/SiC composites. RS-SiC/SiC composites also represented a good flexural strength and a high density, accompanying a pseudo failure behavior.

This paper dealt with the fabricating process of liquid phase sintered (LPS) SiC ceramics containing the oxide additives of Al2O3 and Y2O3, in conjunction with the evaluation of their mechanical properties. LPS-SiC ceramics was sintered at the temperature of 1820 oC under an applied pressure of 20 MPa and a pressure holding time of 2 hour. A commercial SiC powder with an average size of about 0.3 μm was used as a starting powder. LPS-SiC ceramics with additive composition ratios of 1.5 and 2.3 (Al2O3/Y2O3) represented an excellent density of about 3.2 Mg/m3. LPS-SiC ceramics had a flexural strength of about 800 MPa and a fracture toughness of about 8.0 MPa⋅m0.5 at an additive composition ratio (Al2O3/Y2O3) of 1.5.