• 한국생산제조학회지
• /
• 제22권1호
• /
• pp.173-177
• /
• 2013

The purpose of this paper is to investigate the influences on mechanical properties of two-stroke cycle motor pistons manufactured by casting, conventional forging and powder forging, through the comparison of characteristics, merits and disadvantages of each forming technology. For each forming technology, the optimal process parameters were determined through the experiments for several conditions, and microstructure, hardness, tensile strength and elongation of pistons are compared and analyzed. In conventional forging process, material temperature was $460^{\circ}C$ and the die temperature was $210^{\circ}C$ for the Al 4032. The optimal condition was found as solution treatment under $520^{\circ}C$ for 5 hours, quenching with $23^{\circ}C$ water, and aging under $190^{\circ}C$ for 5 hours. In powder forging process, the proper composition of material was determined and optimal sintering conditions were examined. From the experiment, 1.5% of Si contents on the total weight, $580^{\circ}C$ of sintering temperature, and 25 minutes of sintering time were determined as the optimal process condition. For the optimal condition, the pistons had 76.4~78.3 [HRB] of hardness, and 500 [MPa] of tensile strength after T6 heat treatment.

• 한국주조공학회지
• /
• 제29권1호
• /
• pp.45-51
• /
• 2009

Conventionally, Al-Sn bearing manufacturing involves casting the Al-Sn alloy and roll-bonding to a steel backing strip. This article will describe the microstructural control of Al-Sn metal bearing alloy following heat treatment. When the pure aluminum rod dipped in the melt of tin maintained below the melting point of aluminum, the melting of aluminum was accelerated with penetration of tin along the grain boundary of aluminum. The length of plate-shaped eutectic tin was decreased with heat treatment time. With even longer heat treatment time over 1 hour the length of eutectic tin didn't decrease any more, while resulting in coarsening of aluminum matrix. Exuded liquid of eutectic tin was formed at the surface of Al-Sn alloy after heat treatment even at below eutectic temperature.

• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 2008년도 춘계 학술발표회 초청강연 및 논문집
• /
• pp.385-392
• /
• 2008

Modern city have had a lot of high-rise building in high standards and multi-level performance. Using of city space reach better stages by using integration. These skyscraper have increased working load on ground. that building is efficiently designed for that soil capacity is well applied. With material side, big size pile, high strength concrete and high strength steel is used for that getting enough lobby space and resisting load increased of high-rise building. limit load test and load transmitted test can make soil capacity optimized. By the way, method of measuring pile capacity is more advanced and bigger. pile type applied by high rise building have underground excavation space, also reflect regional soil property and have some fact reviewed. A lot of high rise building recently is built as land mark in Seoul, Busan and Incheon. about method of measuring capacity of foundation pile, example of construction field is compared and reviewed.

• 콘크리트학회논문집
• /
• 제15권4호
• /
• pp.625-633
• /
• 2003

For the construction of open-topped steel box girder bridges, prefabricated concrete slab could offer several advantages over cast-in-situ deck including good quality control, fast construction, and elimination of the formwork for concrete slab casting. However, precast decks without reinforcements at transverse joints between precast slabs should be designed to prevent the initiation of cracking at the joints, because the performance of the joint is especially crucial for the integrity of a structural system. Several prestressing methods are available to introduce proper compression at the joints, such as internal tendons, external tendons and support lowering after shear connection. In this paper, experimental results from a continuous composite bridge model with precast decks are presented. Internal tendons and external tendons were used to prevent cracking at the joints. Judging from the tests, precast decks in negative moment regions have the whole contribution to the flexural stiffness of composite section under service loads if appropriate prestressing is introduced. The validity of the calculation of a cracking load fur serviceability was presented by comparing an observed cracking load and the calculated value. Flexural behavior of the continuous composite beam with external prestressing before and after cracking was discussed by using the deflection and strain data.

• Structural Engineering and Mechanics
• /
• 제50권6호
• /
• pp.817-834
• /
• 2014

An experimental program was designed in the current work to examine the structural behavior of ferrocement beams reinforced with composite materials under three point loadings up to failure. The experimental program comprised casting and testing of twelve ferrocement beams having the dimensions of 120 mm width, 200 mm depth and 1600 mm length. The twelve beams were different in the type of reinforcements; steel bars, traditional wire meshes (welded and expanded wire meshes) and composite materials (fiberglass wire meshes and polypropylene wire meshes). The flexural performances of the all tested beams in terms of strength, ductility, cracking behavior and energy absorption were investigated. Also all the tested beams were simulated using ANSYS program. The results of the experimental tests concluded that the beam with fiber glass meshes gives the lowest first crack load and ultimate load. The ferrocement beam reinforced with four layers of welded wire meshes has better structural behavior than those beams reinforced with other types of wire meshes. Also the beams reinforced with metal wire meshes give smaller cracks width in comparing with those reinforced with non-metal wire meshes. Also the Finite Element (FE) simulations gave good results comparing with the experimental results.

• 한국주조공학회지
• /
• 제35권1호
• /
• pp.1-7
• /
• 2015

In this study, we investigated the effect of carbon on mechanical properties with different austempering conditions of high carbon(0.7~1.3wt.%C)-2.0wt.%Si steels. The specimens were austenitized at 850, 925 and $1020^{\circ}C$, and austempered at 260, 320 and $380^{\circ}C$ for the various period of time from 3 min to 300 min. After heat treatment, the evolution of stage I and stage II was identified with optical microscope, XRD and hardness test. When the austempering temperature was $260^{\circ}C$, the microstructure consisted of the lower ausferrite while the upper ausferrite micro-structure was formed at $380^{\circ}C$. As the austempering temperature increases from 260 to $380^{\circ}C$, the tensile strength decreases and elongation increases. In addition, when carbon content increases, tensile strength and elongation decrease.

• 한국해양공학회지
• /
• 제15권1호
• /
• pp.98-103
• /
• 2001

This paper is conducted to compare the seismic design standard of a bridge column such as the Korean Bridge Design Standard(KBDS), EC 8, NZS 3101 and ATC 32. The KBDS adopted the seismic design requirements in 1992. The earthquake magnitude in Korea is compared with those in the west coast of the USA. It may be said that the current seismic design requirements of the KBDS provides design results, that are too conservative especially for transverse reinforcement details and amounts in reinforced concrete columns. This fact usually creates construction problems in concrete casting, due to congestion of transverse reinforcement. Furthermore, the effective stiffness; $I_{eff}$ depends on both the axial load P/$A_gF_{ck}$ and the longitudinal reinforcement ratio $A_{st}/A_g, so it is the conservative to use the effective stiffness I$_{eff}$ than the gross section stiffness Ig. Seismic design for the transverse reinforcement content of the concrete column was analyzed and considered to have an extreme-fiber compression strain, response modification factor, axial load and effective stiffness etc.c.

• 대한금속재료학회지
• /
• 제48권8호
• /
• pp.749-756
• /
• 2010

Low carbon steels were oxidized isothermally at 1050 and $1180^{\circ}C$ for 4 hr in air in order to determine the effect of alloying elements Si, S, Cu, Sn, and Ni on oxidation. For oxidation resistance of low carbon steels, the beneficial elements were Si, Cu, and Ni, whereas the harmful elements were S and Sn. The most active alloying element, Si, was scattered inside the oxide scale, at the scale-alloy interface, and as an internal oxide precipitate. The relatively noble elements such as Cu and Ni tended to weakly segregate at the scale-alloy interface. Sulfur and Sn were weakly, uniformly distributed inside the oxide scale. Excessively thick, non-adherent scales containing interconnected pores formed at $1180^{\circ}C$.

• Steel and Composite Structures
• /
• 제21권6호
• /
• pp.1327-1345
• /
• 2016

$Al_2O_3$/SiC particulate reinforced (Metal Matrix Composites) MMCs which were produced by using stir casting process, bending strength and hardening behaviour were obtained using an analysis of variance (ANOVA) technique that uses full factorial design. Factor variables and their ranges were: particle size $2-60{\mu}m$; the stirring speed 450 rpm, 500 rpm and the stirring temperature $620^{\circ}C$, $650^{\circ}C$. An empirical equation was derived from test results to describe the relationship between the test parameters. This model for the tensile strength of the hybrid composite materials with $R^2$ adj = 80% for the bending strength $R^2$ adj = 89% were generated from the data. The regression coefficients of this model quantify the tensile strength and bending strengths of the effects of each of the factors. The interactions of all three factors do not present significant percentage contributions on the tensile strength and bending strengths of hybrid composite materials. Analysis of the residuals versus was predicted the tensile strength and bending strengths show a normalized distribution and thereby confirms the suitability of this model. Particle size was found to have the strongest influence on the tensile strength and bending strength.

• Tribology and Lubricants
• /
• 제35권1호
• /
• pp.24-29
• /
• 2019

In this work we investigated the friction and wear characteristics of a magnesium alloy, which has been receiving much attention as a light metal in industrial applications such as automobiles and aerospace. Magnesium is one of the lightest structural material that has high specific strength, lightweight, low density and good formability. However, current issue of using magnesium alloy is that magnesium has weakness against temperature. As the temperature increases, magnesium undergoes poor creep resistance and ease of softening, and therefore, its mechanical strength decreases sharply. To solve this issue, a new type of magnesium alloy that retains high strength at high temperature has been proposed. The tribological behavior of this alloy was investigated using a tribotester with reciprocating motion and heating plate. A stainless steel ball was used as a counter surface. Results showed that extrusion process has similar wear behavior to the commonly used casting process but retains good mechanical strength and durability. The presence of an alloying element enhanced the wear properties especially in high temperature. This study is expected to be utilized as fundamental data for the replacement of high density materials currently used in mechanical industries to a much lighter and durable heat-resistant materials.