Today, ships and structures are becoming larger (large structures, vessels, FPSO, etc.). Thus, high-strength welding material is required. The advantages of welding over other joining methods, depending on the development of welding technology, include such things as ease of operation and the structures of simplification and the confidential excellence, etc. However, shrinkage and deformation also occur, because of the repeated heating and cooling. Welding residual stress has an adverse effect on stability, but, it was closely related fatigue strength and brittle fracture of structures. In this study, experimental and analysis were conducted, and AIS3000 used to measure residual stress, which were compare with ANSYS analysis results. Metal surface microstructure was observed at various weld spots, as well as HAZ, and base metal using the optical microscope, and component analysis and crystal plane were measured using an XRD and EPMA.

Recently, the production of shipbuilding and offshore plant industries, with a trend toward large structures, has led to an increased use of high strength ultra-thick plates. The use of ultra-thick plates increases the welding tasks, and the welding process generates distortion and residual stress in the weldment because of the rapid heating and cooling. Welding distortion and residual stress in the welded structure resulte in many troubles such as deformation and life deterioration. In particular, the welding residual stress has an important effect on welding deformation, fatigue, buckling strength, brittleness, etc. The purpose of this study was to evaluate the residual stress at a multi-pass weldment using an experimental method for EH36 high-tension steel. In this experimental method, AIS3000 was used to measure the residual stress of a welded part, HAZ, and base metal; EPMA and XRD were used to study the material properties.

Tadpole-shaped (Ni, Al)/AlN nanoparticles were synthe- sized via evaporating Ni-Al alloy in a mixed atmosphere of N2 and H2. As a counterpart, the spherical-shaped (Ni, Al)/Al2O3 nanoparticles were also prepared from the same target alloy while in a mixture of Ar and H2. The electromagnetic parameters of as-made nanoparti- cles/para-n composites were then investigated in the frequency range of 2{18GHz. Excellent microwave absorption can be obtained for the tadpole-shaped (Ni, Al)/AlN-para-n composite at high frequencies and in a thin layer, which is thought to be the result of the enhanced polarization in the anisotropic tadpole-shaped nanoparticles. With the increasing of the composite thickness, the frequency of efiective re∞ec- tion loss shifts towards lower frequencies due to an improved impedance match and absorption.

Recently, with the high performance and efficiency of machine, there have been required the multi-functions in various machine parts, such as the heat resistance, the abrasion resistance and the stress resistance as well as the strength. Fatigue crack growth tests were carried out to investigate the fatigue characteristics of high carbon steel (SM53C) experienced by high-frequency induction treatment. The influence of high-frequency induction treatment on fatigue limit was experimentally examined with the special focus on the variation of surface microstructure and the fatigue crack initiation and propagation through fractography. Also, the shape of hardening depth, hardened structure, hardness, and fatigue-fracture characteristics of SM53C composed by carbon steel are also investigated.

Cam shaft which is part of automobile engine is essential part when traveling and significant to fuel injection timing. And also, stiffness and efficiency are component of automobile sash which have a durability of the engine. High hardness and durability are necessary, because engine output is effect by cam shaft directly. So, High-Frequency Induction Hardening is very important. Therefore, in this study here are compared surface hardness characteristic and hardening depth of the SM53C used in the cam shaft. In order to estimate the shape of hardening depth, we investigated hardened structure, hardness, hardening and fracture characteristic of SM53C composed by carbon steel.

The abnormal wears such as unfair-wear and early-wear happen in the earn shaft surface of automobiles. These abnormal wears make efficiency of engines decrease and threaten safety of automobiles. The wear characteristics of the cam shaft is very important for the automobile safety. The cam shaft is surface-hardened by the high frequency induction. In this study, we investigated the wear characteristics of the hardened surface with a SM53C steel. The wear characteristics is examined according to the hardened depth and the amount of load.

MAN-BAE LIM, SUN-CHUL HUH, WON-JO PARK Department of Mechanical and Precision Engineering, Gyeongsang Nat’l., Univ., Tongyoung, Gyeongnam, 650-160, Korea mblim@gnu.ac.kr Research Center for Aircraft parts Technology, Gyeongsang Nat’l., Univ., Jinju, Gyeongnam, 660-701, Korea schuh@gnu.ac.kr † Department of Mechanical and Aerospace Engineering, Gyeongsang Nat’l., Univ. Institute of Marine Industry, Tongyoung, Gyeongnam, 650-160, Korea wjpark@gnu.ac.kr

The earn shaft is very important for the safety of automobiles. The earn shaft needs a surface hardening process by high frequency induction to have both strength and toughness. It is required for safety of automobile to consider how the characteristics of tensile strength and toughness are changed according to the condition of surface hardness. In this study, we prepared surface hardened SM53C which is used as cam shaft materials. We examined the tensile strengths according to the depth of surface hardening and the effect of tempering. We also investigated the fracture toughnesses according to the depth of surface hardening(1mm, 2mm).

This experimental study investigates the fracture characteristics of the camshaft made with newly developed SM53C material. As part of the countermeasure, use the surface hardening heat treatment. Cam shaft which is a part of automobile engine is very essential when traveling and significant to fuel injection timing. Stiffness and efficiency are important for automobile sash which have a durability of the engine. High hardness and durability are necessary, because engine output is affected by cam shaft directly. So, high-frequency induction hardening is very important because of increasing the surface strength. The shape of hardening depth, hardened structure, hardness, and fracture characteristics of SM53C composed by carbon steel are also investigated.

This study is to investigate the effect of compressive residual stress on the fatigue crack growth characteristics. [1] Additionally we found the optimum shot peening condition. Shot peening was performed on velocity of 40 m/s, 50 m/s and 70 m/s. Compact tension specimen are A17075-T6 and A16061-T651. Fatigue crack growth rate ware expressed at crack tip as stress intensity factor range that is da/dN and Delta K. Frequency was 10 Hz and used sinusoidal. The result show that the fatigue characteristics was improved by shot peening. Also the optimum shot velocity condition was 50 m/s at A17075-T6 and 40 m/s at A16061-T651.

Metal fiber preform reinforced aluminum alloy composite as made by the infiltration of molten metal under low pressure casting process. The infiltration behavior of filling pattern and the velocity profile with low-pressure casting process was investigated. The thermocouple was inserted into the preform in order to observe the infiltration behavior. The infiltration of applied pressure time, 1, 2 and 5 s under constant pressure of 0.4 MPa was completely filled during 0.4 s. In these conditions, molten aluminum alloy has successfully infiltrated to FeCrSi metal fiber preform by low-pressure casting process. It was observed the porosity of composites for reliability of composites. The automobile piston was developed with FeCrSi reinforced aluminum alloy that is 0% porosity by the optimal applied pressure and applied pressure time.

Silicon carbide (SiC) materials have been extensively studied for high-temperature components in fusion blanket system and gas turbines, because they have excellent a hightemperature mechanical properties, high thermal conductivity and wear resistance. However, the brittle characteristics of SiC such as low strain-to fracture still impose a severe limitation on the practical application of SiC materials. Therefore, a study of the sliding wear characteristics and fabrication of SiC ceramic by sintering temperature and additives are need. As the result of abrasion, the friction coefficient of the monolithic SiC sintered at 1800°C was the lowest, and the friction coefficient of that sintered at 1760°C was the highest. The monolithic SiC manufactured at 1800°C showed the highest hardness and the lowest friction coefficient. The friction coefficient of the monolithic SiC sintered by the SiO2 contents of 2wt% was the lowest, and the friction coefficient that sintered by the SiO2 contents of 5wt% was the highest. 1800°C of sintering temperature and 2wt% of SiO2 contents ware shown high hardness, low friction coefficient and wear loss compare with other temperatures and SiO2 contents.

SiC materials have excellent high temperature strength, low coefficient of thermal expansion, good resistance to oxidation and good thermal and chemical stability etc. In this study, monolithic liquid phase sintered SiC (LPS-SiC) was made by hot pressing method with nano-SiC powder an average particle size is 30nm and less. Alumina (Al2O3), yttria (Y2O3) and silica (SiO2) particles were used for sintering additives. To investigate effects of SiO2, Al2O3/Y2O3 composition was fixed and then ratios of SiO2 were changed as seven kinds. Materials have been sintered for 1 hour at 1760, 1780 and 1800 under the pressure of 20MPa. The system of sintering additives which affects a property of sintering as well as the influence depending on compositions of sintering additives were investigated by measurement of density, mechanical properties such as Vickers hardness and sliding wear resistance were investigated to make sure of the optimum condition which is about matrix of SiCf/SiC composites. The abrasion test condition applies to load of 20N at 100rpm for 20min. Sintered density, abrasion property of fabricated LPS-SiC increased with increasing the sintering temperature. In case of LPS-SiC with low SiO2 content, has very excellent wear resistance.

Recently, the steel parts used at the aerospace and automobile industries are required to be used high stress more than ever before in need of the weight down. Therefore, used material steel have to be a high stress, which is an indispensable condition in this field. At the consideration of parts design, high hardness of the lightweight parts has an benefit of saving fuel and material. In this study, the surface conditions are measured to know the influence on fatigue properties by shot peening. In this study, the optimum shot peening condition is investigated. Fatigue test was accomplished to investigate the effects of compressive residual stress by shot peening on fatigue characteristics. Test results show the fatigue characteristics were increased by optimum peening condition. But the fatigue characteristics were decreased by under peening or over peening condition.

Optimal welding condition in resistance spot welding of 7075-T6 aluminum alloy sheets with the thickness of 0.4mm was investigated by the tensile-shear strength tests and Taguchi method in experimental design with changing various welding conditions respectively. The tensile-shear tests were carried out at cross-head speeds of 0.1mm/min in accordance with the KS B0851. Design methods were systematically performed using an L-27(39) orthogonal array table. In the experimental design, three control factors of resistance spot welding conditions were electrode force, welding current and welding time. Electrode force conditions were 882N, 1323N and 1764N, and welding current were 13.5kA, 14kA and 14.5kA, and welding time were 3cycle, 4cycle and 5cycle.

Since the ceramic has excellent qualities in light weight, abrasion resistance and heat resistance etc, compared with the metal, it has been actively examined in order to apply for the structures such as gas turbine and turbo charger etc, which require high strength and heat resistance. But it is not desirable to be used for the structural material since the ceramic is fragile, so the join with the metal with abundant toughnees has been studied. However, during the cooling process, the joint residual stress develops on the ceramic/metal joint by the difference in thermal expansion coefficient between two materials and it affects the bending strength significantly. Also, in order to use the joint material as the structural material, the study about the fatigue of thermal cycle of actual use statement is necessary. Therefore, to ensure security and improvement of the bending strength of joint material, the state of residual stress distribution to the high temperature-thermal cycle, and studied the effects of thermal cycle and state of residual stress distribution on the strength of joint material as well.

This is a study of fatigue strength of weld deposits with transverse cracks in plate up to 50 mm thick. It is concerned with the fatigue properties of welds already with transverse cracks. A previous study of transverse crack occurrence, location and microstructure in accordance with welding conditions was published in the Welding Journal (Lee et al., 1998). A fatigue crack develops as a result of stress concentration and extends with each load cycle until fatigue occurs, or until the cyclic loads are transferred to redundant members. The fatigue performance of a member is more dependent on the localized state of stress than the static strength of the base metal or the weld metal. Fatigue specimens were machined to have transverse cracks located on the surface and inside the specimen. Evaluation of fatigue strength depending on location of transverse cracks was then performed. When transverse cracks were propagated in a quarter- or half-circle shape, the specimen broke at low cycle in the presence of a surface crack. However, when the crack was inside the specimen, it propagated in a circular or elliptical shape and the specimen showed high fatigue strength, enough to reach the fatigue limit within tolerance of design stresses.

Molybdenum disilicide ( MoSi 2) is considered to be a promising high temperature material for turbojet and hypersonic engines in aerospace and various industrial applications, because of a high melting point (2030°C), adequate density (6.3g/cm3) and an excellent oxidation resistance. Some researches on MoSi 2 have been carried out but the wear behavior of this material is seldom studied. This paper focused on the effect of sintering temperature of MoSi 2 on the wear behavior. MoSi 2 powder was evaluated from the variation of fabricating conditions such as preparation temperature 1250°C, 1350°C and 1500°C. Wear tests were performed with a sliding speed of 5.21mm/sec and a normal load of 8kgf. Each test was run over a period of 6 hours. The wear behavior is evaluated with respect to the hardness of materials. Hardness test was carried out with a Micro-Vickers hardness tester. As a result of the tests, the friction coefficient was decreased with the increasing sintering temperature of MoSi 2 but the friction coefficient did not vary much for all specimens at temperatures. Hardness values decreased with a decrease in sintering temperature because the indentation under a lower temperature probably contained more defects.