Won-Jo Park

A STUDY ON EVALUATION OF RESIDUAL STRESS BY MULTILAYER WELDING

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.

Wear Characteristics of SiC by Sintered Temperature and SiO2Contents

In this study, liquid phase sintered SiC (LPS-SiC) materials were made by hot pressing method. The particle size of nano-SiC powder was 30nm. Alumina (Al2O3), yttria (Y2O3) and silica (SiO2) were used for sintering additives. To investigate effects of SiO2, ratios of SiO2 contents were changed by five kinds. Materials have been sintered for 1 hour at 1760 C, 1780 C and 1800 C 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 flexural strength, 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 apply to load of 20N at 100RPM for 20min. Sintered density, flexural strength of fabricated LPS SiC increased with increasing the sintering temperature. And in case of LPS-SiC with low SiO2, sliding wear resistance has very excellent. Monolithic SiC 1800°C sintering temperatures and 3wt% have excellent wear resistance. †책임저자, 회원, 경상대학교 기계항공공학부 E-mail : wjpark@gnu.ac.kr TEL : (055)640-3183 FAX : (055)640-3188 경상대학교 기계항공공학부, 해양산업연구소 * 회원, 경상대학교 대학원 정밀기계공학과 ** 회원, 동의대학교 기계공학과 1. 서 론 우주항공 산업 및 에너지 산업이 급속히 발전 함에 따라 세라믹스와 실리사이드 계열의 금속간 화합물을 중심으로 1000°C를 넘는 온도에서 적용 할 수 있는 고기능성 극고온 구조 재료의 개발이 활발히 진행되고 있다. 세라믹스(ceramics)는 무기 재료를 주원료로 하는 산화물(oxide), 질화물 (nitride), 탄화물(carbide) 등과 같이 금속원소와 비 금속원소들이 이온결합(ionic Bonding) 및 공유결 합(covalent bonding)을 하고 있는 화합물을 의미 한다. 금속재료, 고분자재료 등에 비하여 강도, 경도, 내식성, 내열성 및 내마모성이 매우 크며, 이러한 우수한 특성으로 인하여 공업용 내열재료 에서 관심이 점점 높아지고 있는 물질이다. 구조 용 세라믹스의 경우 기계적 특성과 열적 특성이 우수하여 각종 엔진부품, 절삭공구, 브레이크류 라이닝(linning), 메카니컬 실(mechanical seal)등과 같은 산업부품에 사용되고 있으며, 이러한 세라 믹스로서 주로 탄화규소(SiC), 질화규소(Si3N4), 알 루미나(Al2O3) 및 지르코니아(ZrO2) 등이 사용되 고 있다. 이 중 특히 탄화규소는 질화규소에 비 해 상온에서의 강도와 인성은 낮지만, 1400 C 이 상의 초고온에서도 강도와 강성이 다른 구조용 세라믹스에 비해 우수하고, 내마모성, 내산화성,

A STUDY ON FRACTURE CHARACTERISTICS OF THE SM53C USED IN THE CAM SHAFT

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.

The preparation and electrochemical performances of Al-Si/C nanocomposite anode for lithium ion battery

The microstructure and electrochemical performance of Al-Si, Al-Si/C nanocomposite were investigated as the anode for lithium ion battery. The Al-Si nanoparticles were prepared by the arc-discharge method. The Al-Si/C nanoparticles were obtained by coated Al-Si nanoparticles with the precursor of glucose (C6H12O6) as the carbon source. It was indicated that the carbon coating on Al-Si nanoparticles can eliminate the negative effects on the electrochemical insertion/extractions of lithium ions, improve the initial capacity and cycle performances.

Manufacturing Process of Celmet Reinforced Aluminum Alloy Composite by Low‐Poressure Casting

A new process is proposed to fabricate an intermetallic compound, Al3Ni particles reinforced aluminum alloy matrix composite using the reaction between nickel celmet and molten aluminum. The intermetallic compound, Al3Ni particles reinforced aluminum alloy composite was manufactured with the low-pressure infiltration process method. Nickel celmet reacted with molten aluminum at 973K, and the intermetallic compound of Al3Ni was generated on the surface of the nickel celmet. The generated intermetallic compound, Al3Ni obtained the result which delamination from the surface of a nickel celmet and it distributes into the portion of aluminum matrix. The effects of processing variables, such as cooling rate and specific surface area of nickel celmet on the formation and dispersion behavior of Al3Ni were investigated

Fatigue Crack Growth Properties of Friction Stir Welded Dissimilar Aluminum Alloys

The presence of a crack can increase the local stress or strain, which can cause inelastic deformation and significantly reduce the life of a component or structure. Therefore, in this study, the fatigue crack growth (FCG) behaviors of friction stir welded Al 2024-T3 and Al 7075-T6 specimens were examined, with fatigue cracks growing parallel to the dynamically recrystallized zone at variable ΔK values and an R ratio of 0.3. In addition, the FCG values of the base metal Al 2024-T3 and Al 7075-T6 were tested under the same conditions and parameters as comparative groups. The results showed that compared with the base metal Al 2024 specimen, which had the best fatigue property, the welded specimen had only 88% of the fatigue cycles.

Study on Sliding Wear Characteristics and Processing of MoSi

Abstract In this study, a monolithic MoSi2 matrix reinforced with 20 vol% SiC particles, a SiC/MoSi2 composite matrix reinforced with 20 vol% ZrO2 particles, and a ZrO2/MoSi2 composite were fabricated using hot press sintering at 1350 for 1 h under a pressure of 30 MPa. The Vickers hardness and sliding wear resistance of the monolithic MoSi2, ZrO2/MoSi2, and SiC/MoSi2 composite were investigated at room temperature. A wear behavior test was carried out using a disk-type wear tester with a silicon nitride ball. The ZrO2/MoSi2 composite showed an aver-age Vickers hardness value and excellent wear resistance compared with the monolithic MoSi2 and SiC/MoSi2 composite at room temperature. Keywords: Friction coefficient, Monolithic MoSi2, Scanning Electron Microscopy, Sliding wear resistance 1. Introduction MoSi 2 , Mo 5 Si 3 , and other transition metal sili-cides have drawn considerable attention as struc-tural materials in oxidizing environments at ele-vated temperatures [1,2]. MoSi 2 is known to have excellent oxidation resistance, a high melting point (2020 ), moderate density, high thermal conductivity, and thermodynamic compatibility with other potential reinforcements [3,4]. MoSi

Study on Residual Stress Distribution in Thick Plate Welded Material Using Indentation Equipment

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.

THE EFFECT OF SHOT PEENING ON THE IMPROVEMENT OF FATIGUE STRENGTH AND FATIGUE CRACK CHARACTERISTICS OF THE ALUMINUM ALLOYS

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 STUDY OF EVALUATION TENSILE CHARACTERISTICS AND PLANE STRAIN FRACTURE TOUGHNESS IN INDUCTION SURFACE HARDENED OF THE SM53C STEEL

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.