• Journal of Welding and Joining
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• v.15 no.6
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• pp.57-65
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• 1997

A study was undertaken to determine the influence of welding variables such as shielding and plasma gases, torch standoff, travel speed and heat input, etc. on the quality of plasma arc welds in Zircaloy-4 sheet, 2mm thick. Effect of shielding gases and their flow rates on the mechanical properties of Zircaloy-4 welds by plasma arc welding were determined in terms of tensile, bardness and bend tests. The microstructure and fracture surface of Zircaloy-4 welds were investigated by optical and scanning electron microscopies. In addition, the causes of porosity and undercut in plasma arc welds of Zircaloy-4 were also investigated. Zircaloy-4 weld bead width and depth by helium shielding gas showed a wider and deeper than those by argon. It was found that Zircaloy-4 welds with shielding gas of helium did dxhibit a little smoother and uniform weld beads than those with shielding gas of argon. It was also found that the optimum gas flow rates for Zircaloy-4 welding were 0.45l/min for plasma gas with Ar and 4.5 - 6 l/min for shielding gas with He. In addition, there was no big difference in the microstructure and fracture surface of the weld metals made by either Ar shielding gas or He shielding gas.

• Journal of Korean Society of Transportation
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• v.28 no.4
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• pp.177-186
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• 2010

The principal objective of this paper is to develop road design guidelines, especially for managed lane access spacing between the expressway on-ramp (or off-ramp) and managed lane access point. Managed lanes are typically located in the expressway median and are accessed by weaving across the mainlines. The high level of lane-changing activity present in weaving areas affects capacity significantly. One promising tool for the analysis of lane-changing activity is "gap acceptance theory." This paper estimates the capacity of weaving areas based on the estimated degree of traffic turbulence using gap acceptance theory. The degree of traffic turbulence is represented by a function of the probability that lane-changing vehicles can complete their maneuvers successfully in a given weaving distance. In developing road design guidelines based on the developed gap acceptance model, the minimum managed lane access spacing is determined where the capacity with respect to the managed lane access spacing becomes stable.