• International Journal of Advanced Culture Technology
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• v.3 no.1
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• pp.46-51
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• 2015

The mechanical and electrical properties of aluminium alloy 6061 are reported in this present work. Aluminium alloys were homogenized at $550^{\circ}C$, for 5 hours and cooled in the furnace. The different thickness reductions of 60-90% on homogenized aluminium alloy plates were achieved by cryo-rolling. Later, the as rolled samples were aged by solution treatment at the temperatures of $520^{\circ}C$ for 1 hour, water quenched; subsequently aged at $160^{\circ}C$ for 8-24 hours and partial aged (not solution treatment) at $160^{\circ}C$ for 8- 24 hours. Mechanical and electrical properties of samples were investigated. The experimental result showed that the microhardness of cryo-rolled samples were increase with increasing the percentage of the thickness reduction. Moreover, the microhardness of cryo-rolled, aged by solution treatment samples were higher than those of the cryo-rolled and cryo-rolled, partial aged samples. The cryo-rolled alloys subjected to full aged at $160^{\circ}C$ for 24 hours exhibited the hardness of 125 HV and electrical conductivity values was 45.76 %IACS and the cryo-rolled alloys subjected to partial aged at $160^{\circ}C$ for 20 hours exhibited the hardness of 67 HV and electrical conductivity values was 49.67 %IACS.

• Proceedings of the KSR Conference
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• 2008.06a
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• pp.1653-1661
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• 2008

A trial run of locally-developed tilting train has been in process on Chungbuk line since the test vehicle was first produced. For the system stabilization, interface verification among the systems including track, structure, catenary and signaling system, not to mention the rolling stock, is very crucial. In the area of wayside structure, the stability of track structure and train run shall be evaluated through the review of impact by increased speed by developed train on track structure. The study thus was intended to evaluate the impact on track while a tilting train is running the conventional line(ballast track), which is vulnerable to accelerated train speed. The evaluation of tilting train test running the part of Honam line was conducted to identify the impact on existing track performance by tilting train. To identify the performance of each part of track components while tilting train and high speed train were running the existing line, wheel load, rail bending stress, vertical displacement of rail and sleeper were compared so as to evaluate the expected impact by tilting train for improving the train speed.

• Proceedings of the KSR Conference
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• 2009.05a
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• pp.529-538
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• 2009

A trial run of locally-developed tilting train has been in process on Chungbuk line since the test vehicle was first produced. For the system stabilization, interface verification among the systems including track, structure, catenary and signaling system, not to mention the rolling stock, is very crucial. Therefore, in this study, the dynamic rail force of the tilting (Hanvit 200), high-speed (KTX) and general (Mugunghwa) vehicle caused by driving in transition curve track was measured. And, it compared the tilting response with the other by using the measured wheel load data in transition curve track, and then evaluated probability the range of wheel load fluctuation for the variable dynamic vertical and lateral wheel load. As a result, a range of wheel load by occured a change of cant from the high-speed and general vehicle which had fixed bogie structure was distributed throughout small deviation (${\Delta}8{\sim}13kN$). Otherwise, in case of the tilting train which was consisted of the pendulum bogie structure was distributed wide range about large deviation (${\Delta}25{\sim}28kN$) by changed of cant.

• Korean Journal of Materials Research
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• v.19 no.8
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• pp.432-436
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• 2009

A Cu-Fe-P copper alloy was processed by accumulative roll-bonding (ARB) for ultra grain refinement and high strengthening. Two 1mm thick copper sheets, 30 mm wide and 300 mm long, were first degreased and wire-brushed for sound bonding. The sheets were then stacked on top of each other and roll-bonded by about 50% reduction rolling without lubrication at ambient temperature. The bonded sheet was then cut into two pieces of the same dimensions and the same procedure was repeated for the sheets up to eight cycles. Microstructural evolution of the copper alloy with the number of the ARB cycles was investigated by optical microscopy (OM), transmission electron microscopy(TEM), and electron back scatter diffraction(EBSD). The grain size decreased gradually with the number of ARB cycles, and was reduced to 290 nm after eight cycles. The boundaries above 60% of ultrafine grains formed exhibited high angle boundaries above 15 degrees. In addition, the average misorientation angle of ultrafine grains was 30 degrees.

• Korean Journal of Materials Research
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• v.27 no.1
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• pp.53-61
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• 2017

Magnesium alloys are of emerging interest in the automotive, aerospace and electronic industries due to their light weight, high specific strength, damping capacity, etc. However, practical applications are limited because magnesium alloys have poor formability at room temperature due to the lack of slip systems and the formation of basal texture, both of which characteristics are attributed to the hcp crystal structure. Fortunately, many magnesium alloys, even commercialized AZ or ZK series alloys, exhibit superplastic behavior and show very large tensile ductility, which means that these materials have potential application to superplastic forming (SPF) of magnesium alloy sheets. The SPF technique offers many advantages such as near net shaping, design flexibility, simple process and low die cost. Superplasticity occurs in materials having very small grain sizes of less than $10{\mu}m$ and these small grains in magnesium alloys can be achieved by thermomechanical treatment in conventional rolling or extrusion processes. Moreover, some coarse-grained magnesium alloys are reported to have superplasticity when grain refinement occurs through recrystallization during deformation in the initial stage. This report reviews the characteristics of superplastic magnesium alloys with high-strain rate and coarse grains. Finally, some examples of SPF application are suggested.

• Journal of Welding and Joining
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• v.35 no.2
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• pp.6-12
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• 2017

Ti-alloys have high specific strength and are widely used for the filed of space aeronautics plant. However, it is difficult to process Ti-Alloys due to its high yield strength and it cannot raise the machining speed because it has a possibility of catching fire while processing. In order to reduce the number of processes for the Ti-alloys, the researches related to Additive Manufacturing(AM) have been actively carried out at the moment. As for the initial stage of AM market related to Ti-alloys, it started to use the raw material of powder metal, and it is currently being developed based on welding. In this study, Interpass peening reduced the size of the primary ${\beta}$ grain in the z-axis direction, increased the nucleation site of ${\alpha}-colony$, and decreased the length and width of ${\alpha}$ laths as though interpass rolling. Interpass peening leads to an increase in yield/ultimate tensile strength without decrease elongation, resulting decrease in anisotropy of the material.

• Transactions of Materials Processing
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• v.9 no.1
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• pp.72-79
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• 2000

Dynamic recrystallization (DRX), which may occur during hot deformation, is important for the microsturctural evolution of 304 stainless steel. Especially, the current interest in modelling hot rolling demands quantitative relationships among the thermomechanical process variables, such as strain, temperature, strain rate, and etc. Thus, this paper individually presents the relationships for flow stress and volume fraction of DRX as a function of processing variables using torsion tests. The hot torsion tests of 304 stainless steel were performed at the temperature range of 900~110$0^{\circ}C$ and the strain rate range of 5x10-2~5s-1 to study the high temperature softening behavior. For the exact prediction of flow stress, the equation was divided into two regions, the work hardening (WH) and dynamic recovery (DRV) region and the DRX region. Especially, The flow stress of DRX region could be expressed by using the volume fraction of DRX (XDRX). Since XDRX was consisted of the critical strain($\varepsilon$c) for initiation of dynamic recrystallization (DRX) and the strain for maximum softening rate ($\varepsilon$*), that were related with the evolution of microstructure. The calculated results predicted the flow stress and the microstructure of the alloy at any deformation conditions well.

• International Journal of Automotive Technology
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• v.6 no.3
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• pp.259-268
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• 2005

In order to analyze the sheet drawability, the measurement of the plastic strain ratio was carried out for the 5182 aluminum alloy sheets in which were cold rolled without lubrication and subsequent recrystallization annealing. The average plastic strain ratio of the 5182 aluminum sheets was 1.50. It was considered that the higher plastic strain ratio was resulted from the ND//<111> component evolved during rolling and maintained during annealing. The AA5182/polypropylene/AA5182 (AA/PP/AA) sandwich sheets of the 5182 aluminum alloy skin sheet and the polypropylene core sheet with high formability have been developed for application for automotive body panels in future light weight vehicles with significant weight reduction. The AA/PP/AA sandwich sheets were fabricated by the adhesion of the core sheet and the upper and lower skin sheets. The AA/PP/AA sandwich sheet had high plastic strain ratio (1.58), however, the planar anisotropy of the sandwich sheet was little changed after fabrication. The optimum combination of directionality of the upper and lower skin sheets having high plastic strain ratio and low planar anisotropy was calculated theoretically and an advanced process for producing the sandwich sheets with high plastic strain ratio was proposed. The developed sandwich sheets have a high average plastic strain ratio of 1.55 and a low planar anisotropy of 0.17, which was improved more by 3.2 times than that of 5182 aluminum single sheet.

• Journal of Korean Society for Geospatial Information Science
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• v.9 no.2 s.18
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• pp.17-27
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• 2001

Buffering is one of the popular spatial analytical functions widely used in many proximity analyses. The buffeting inevitably entails a new polygon of specified edge that is simulated by rolling a ball around the buffering object. While buffering, the error on the buffering object propagates to the new buffered object. In this paper the error propagation behavior during the buffering operation is analyzed based on a pilot project for two different data models: polyline and spline curve. Thus, the error on the buffered objects are classified, mathematically defined, and measured. For measurements, the pilot project is designed and performed using a test site that is a lake boundary at Wisconsin, USA.

• Journal of the Korean Society for Railway
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• v.16 no.2
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• pp.79-84
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• 2013

The definition and classification of shunting, which involves the process of sorting rolling stock into complete train sets inside station yard, are not clearly specified in Korean domestic safety regulations for railway operations. As a result, collisions during shunting occur rather frequently compared with other types of accidents in railway operations. Therefore, new systematic safety principles are proposed in this paper to improve operation safety during shunting. The improvements in safety and efficiency derived from the newly proposed approach are analyzed and verified in field application.