• Journal of Welding and Joining
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• v.15 no.4
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• pp.99-108
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• 1997

Analytical model for the temperature distribution and the cooling rate of weld in dual beam laser welding is presented for investigating the possibility of controling the cooling rate. The model is based on the solutions to the problem of heat flow due to the distributed and line heat sources for preheating and welding respectively in plates with finite thickness. The effects of beam power, beam distribution parameter, interbeam distance, and welding speed on the resulting temperature distribution and cooling rate are presented. The cooling rates of dual beam laser weld at the weld centerline under the investigated conditions are reduced to as one third of those of welds which were produced by single beam laser. And it appeared that the cooling rate of dual beam laser weld is strongly dependent on the process parameters of preheating laser beam power and welding speed.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2012.10a
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• pp.623-624
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• 2012

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.61-64
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• 2004

This study presents results from an experimental work for two normal prestressed concrete beams and three dual prestressed concrete beams. The dual prestressed concrete beams made with normal concrete in compression zone and high performance steel fiber reinforced concrete in partial depth of tension zone. Through cyclic loading test under low frequency, structural behavior and resistance to dynamic loading for dual prestressed concrete beams are investigated. Considerable increase of crack and yield load capacity of Dual prestressed concrete beam is shown compared with normal prestressed concrete beam. In addition, re-loading and un-loading rigidity of dual prestressed concrete beam under cyclic loading are increased comparing with normal prestressed concrete beam.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.37-40
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• 2005

Reinforced dual concrete beam (RDC beam) is the reformed system that improves the overall structural properties of beam by partially applying high performance steel fiber reinforced concrete (HPSFRC) in the lower tension part of conventional reinforced concrete beam (RC beam). Fatigue test was done to prove the structural superiority of RDC beam. As a result of fatigue test, the deflection of RDC beam was decreased obviously and the slope of number of cycle-deflection relation curve of RDC beam was increased gently in comparison with RC beam.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.400-403
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• 2002

This paper presents a shearographic technique for measuring in-plane strains. During the measurement, the test object is illuminated alternately with two laser beams, symmetrically with respect to the viewing direction. Employing a phase shift technique, the phase distributions due to object deformation for each beam are obtained separately. The difference of the two phase distributions depicts the derivative of in-plane surface displacements. The technique is equivalent to a system of many strain gages.

• Proceedings of the Materials Research Society of Korea Conference
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• 1998.11a
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• pp.44-44
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• 1998

• Nuclear Engineering and Technology
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• v.56 no.8
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• pp.3129-3138
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• 2024

The in-situ TEM irradiation experiments of zirconium alloy were conducted at 573 K, 673 K, and 773 K utilizing a 400 keV Kr + single beam and a 400 keV Kr+ and 30 keV He + dual beam. The results show that a large number of dislocation loops have been characterized in the matrix of the zirconium alloy under irradiation. With increasing the irradiation damage dose, some dislocation loops have reacted with one another to form a larger dislocation loop, which has finally formed dislocation lines or other defect structures. In zirconium alloys irradiated with Kr + single beam and Kr+ and He + dual-beam radiation, the proportion of <a> type dislocation loops with different Burgers vectors is essentially the same at low damage doses, but the proportion of interstitial type dislocation loops with the same Burgers vectors is obviously different. The amorphization of the second phase and the dissolution of the small-sized second phase were also pointed out. With the increase in temperature, the density of the dislocation loop in zirconium alloy gradually decreases, and the size of dislocation loop first increases and then decreases. Kr+ and He + dual beam irradiation increases the size of dislocation loops but decreases their density as compared with Kr + single beam irradiation.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.2
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• pp.1-7
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• 2021

A computer simulation was performed to study the effectiveness of temperature on the type of laser heat source in the context of the heterogeneous welding of aluminum and copper materials. Three different types of heat sources were used in the computer simulation: 1) Single Beam Straight Scan, 2) Single Beam Wobble Scan, and 3) Dual Beam Straight Scan. Among these sources, dual beam straight scan was found to be the most effective from the viewpoint of heat source control. Because the difference between the melting temperatures of copper and aluminum is approximately 400℃, a clear separation of heating temperature was required, and the dual beam straight scan provided superior controllability in this regard. When using the dual beam, the temperature of the 90:10 split was considerably easier to control than that of the 50:50 split. The optimal offset was calculated to be 4 mm off to the copper side, where the melting temperature and thermal conductivity were higher. In this manner, computer simulation was effectively used for determining the optimal laser beam hear source control without performing an actual laser welding experiment.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.11
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• pp.1161-1169
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• 2003

In this paper, ADE(Axially Displaced Ellipse) Gregorian dual reflector antennas, which are the special form of Gregorian dual reflector antennas, were analyzed. In the procedure of antenna analysis, the aperture field distribution was obtained by using the geometrical optics and their far-field radiation characteristics were analyzed by using the aperture field method. The analysis results such as antenna efficiency, HPBW(Half Power Beam Width), FNBW(First Null Beam Width), and FSL(First Sidelobe Level) were presented as functions of edge taper and size of main reflector and subreflector. From the results in this paper, we could confirm that ADE reflector antennas have the different radiation characteristics from the classical dual reflector antennas.

• Smart Structures and Systems
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• v.11 no.2
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• pp.217-240
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• 2013

In this paper, practical methods to utilize PZT's dual piezoelectric effects (i.e., dynamic strain and electro-mechanical (E/M) impedance responses) for damage detection in beam-type structures are presented. In order to achieve the objective, the following approaches are implemented. Firstly, PZT material's dual piezoelectric characteristics on dynamic strain and E/M impedance are investigated. Secondly, global vibration-based and local impedance-based methods to detect the occurrence and the location of damage are presented. Finally, the vibration-based and impedance-based damage detection methods using the dual piezoelectric responses are evaluated from experiments on a lab-scaled beam for several damage scenarios. Damage detection results from using PZT sensor are compared with those obtained from using accelerometer and electric strain gauge.