Gwi-Nam Kim

Mechanical properties of Cu matrix composite fabricated by extrusion process

Abstract Carbon nanotube (CNT) was applied in various fields for its superior electrical, mechanical and thermal characteristics. After composites were fabricated by extrusion process using ball-milled Cu–CNT powders, mechanical properties of Cu–CNT composites according to CNT fraction were reviewed. CNT (1%, 5% and 10%), Cu ( d =100 nm), zirconia balls (90 g) and ethanol (20 mL) were mixed and dispersed for 5 h at a speed of 500 r/min using a planetary ball mill. A billet ( d =50 mm, length=100 mm) was made with Cu, and the composite powders were filled up into billet using the uni-axial press. In the extrusion process, after the billet was heated at 880 °C for 1 h, specimens were produced in the shape of a round bar using the billet by applying a load of 200 t. The composite powders were measured for particle size by particle size distribution equipment. Then the specimen surface fabricated by extrusion was observed by SEM. Mechanical properties measured by the indentation equipment increased with increasing CNT content. The yield strength, tensile strength and hardness of the Cu–CNTs composites can be obviously improved.

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.

Experimental Study on Characteristics of Grinded Graphene Nanofluids with Surfactants

In earlier studies, much research has focused on increasing the efficiency of heat exchanger fields. Therefore, in this study, graphene nanofluid was fabricated for use as a heat transfer medium for a heat exchanger. Graphene has excellent electrical conductivity, mechanical properties, and heat transfer properties. It is expected that the heat transfer efficiency will be improved by fabricating the nanofluid. However, graphene is prone to sedimentation, because of its cohesion due to van der Waals binding force. In this experiment, a nanofluid was fabricated with enhanced dispersibility by surfactant and the ball-milling process. The zeta potential, absorbance, and thermal conductivity of the nanofluid were measured. As a result, when using the ratio of 2:1 (graphene:sodium dodecyl sulfate (SDS)), a higher thermal conductivity was obtained than in other conditions.

HYDRAULIC SYSTEM DESIGN AND STRUCTURAL ANALYSIS OF A BOP GANTRY CRANE

A blow-out preventer (BOP) gantry crane is an offshore plant that moves a BOP stack located on a drilling platform to a BOP trolley. However, such a plant has yet to be developed in Korea. Because BOP gantry cranes produced overseas are expensive, developing such cranes domestically is imperative. In this study, ANSYS was used to conduct a structural analysis on a BOP gantry crane model to simulate the roll and pitch motions of a drillship that were induced by waves and wind load as well as the weight of the crane. Moreover, Simulation X was used for implementing control-system and subsystem designs and to analyze a hydraulic system.

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.