• Journal of the Korean Society of Manufacturing Technology Engineers
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• 제26권4호
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• pp.425-429
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• 2017

During ultrasonic welding, plastic deformation, elastic hysteresis, and friction generate heat at the contact portions of the two materials to be welded, theoretically analyzing and experimentally measuring the temperature at the welded part are very important for identifying the heat affected zone. However, the welding temperature during ultrasonic welding wherein welding is performed in less than a second is a challenge. We investigated the effects of welding conditions such as welding time, welding pressure, and the ultrasonic vibration amplitude of horns on the temperature of welded surface of a Ni sheet of thickness 0.1 mm. We used a horn with a resonance frequency of 40 kHz and an ultrasonic welder. The temperature was measured using a intrared sensor, and its characteristics were investigated. Experimental results showed that increase in welding time and pressure and ultrasonic vibration amplitude of horns generally caused the increase in surface temperature of the weld.

• Transactions of the Korean Society of Automotive Engineers
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• 제6권1호
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• pp.151-162
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• 1998

During a straight driving and cornering maneuver by a vehicle various forces and moments are exerted on the tire's footprint. A cornering properties, handling and stability performances of vehicle can be predicted by these forces and moments values. Therefore, on this study, a lateral force and a aligning torque are predicted by these forces and moments values. Therefore, on this study, a lateral force and a aligning torque are predicted using a finite element method. Contact area of the tire between bead and wheel are fixed to simplify of a finite element model. Lateral force is exerted on the rigid surface as a real load with Coulum friction after inflate and load vertically. Then, rotate the tire's axle to simulate a free rolling untill taken the equilibrium of a aligning torque. Also, experimental observations are made to test a reliability of a FE analysis conducted in this study. The finite element analysis said that good agreement was obtained with experimental results of these cornering properties, giving confidence within about one percent. So it os recommended that a finite element analysis can be used as a good tool to predicted the tire cornering properties.

• Journal of the Korean Geophysical Society
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• 제7권1호
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• pp.31-40
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• 2004

When surveying the cultural heritages especially in the case of stone structures, preserving their original state is of primary importance. For the effective assessment of survey results of stone structure, the dynamic characteristics of that system should be considered. Dynamic characteristics of stone masonry structures depend on several factors such as coefficients of friction, contact conditions, and number of layers of bonding stones. These factors can be estimated by using the dynamic analysis results. This paper describes a method for natural frequency determination of traditional stone arch bridge subjected to compressive force. For this purpose, multi-layered granite brick models of for arch bridge were made and fundamental frequencies corresponding increasing axial forces were measured.

• Transactions of Materials Processing
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• 제14권9호통권81호
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• pp.772-778
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• 2005

This paper is concerned with the analysis of material flow characteristics of combined tube extrusion using pipe. The analysis in this paper concentrated on the evaluation of the design parameters for deformation patterns of tube forming, load characteristics, extruded length, and die pressure. The design factors such as punch nose radius, die corner radius, friction factor, and punch face angle are involved in the simulation. The combined tube extrusion is analyzed by using a commercial finite element code. This simulation makes use of pipe material and punch geometry on the basis of punch geometry recommended by International Cold Forging Group. Deformation patterns and its characteristics in combined forward and backward tube extrusion process were analyzed for forming loads with primary parameters, which are various punch nose radius relative to backward tube thickness. The results from the simulation show the flow modes of pipe workpiece and the die pressure at the contact surface between pipe workpiece and punch. The specific backward tube thickness and punch nose radius have an effect on extruded length in combined extrusion. The combined one step forward and backward extrusion is compared with the two step extrusion fer forming load and die pressure.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 한국소성가공학회 2004년도 춘계학술대회 논문집
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• pp.87-90
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• 2004

In this paper, net-shape forming of an automobile gear is investigated. Barrel, a component of automobile start motor, is adopted as a net-shape forming. In order to accomplish the goal of net-shape forming without cutting of tooth and cam after forming, forming ability is raised through billet treatment and die design. As a technique of billet treatment spheroidizing annealing of billet to get low hardness and molybdenum disulphide coating to get low contact friction between billet and die is carried out. One of critical points of die design, fillet radii variation of tooth of die is applied to get smooth surface of barrel after cold forging. As a measurement of tooth accuracy, distance between two pins and lead-tooth alignments are investigated. Cam profile accuracy is checked with a 3D measuring instrument. Results obtained from the tests revealed reasonable result with respect to design goal. By these results, the paper shows that reasonable results can be obtained by billet treatment and die design for net-shape forming.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 한국정밀공학회 2001년도 춘계학술대회 논문집
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• pp.699-702
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• 2001

The increasing demand in industry to produce rectangular cans at the reduction by the rectangular backward extrusion process involves better understanding of this process. In 2-D die deflection and dimensional variation of the component during extrusion, punch retraction, component injection and cooling was conducted using a coupled thermal-mechanical approach for the forward extrusion of aluminum alloy and low-carbon steel in tools of steel. Backward extrusion FE simulation and experimental simulation by physical modeling using wax as a model material have been performed. These simulations gave good results concerning the prediction of th flow modes and the corresponding surface expansions of the material occuring at the contact surface between the can and the punch. There prediction are the limits of the can height, depending on the reduction, the punch geometry, the workpiece material and the friction factor, in order to avoid the risk of damage caused by sticking of the workpiece material to the punch face. The influence of these different parameter on the distribution of the surface expansion along the inner can wall and bottom is already determined. This paper deals with the influence of the geometry changes of the forming tool and the work material in the rectangular backward using the 3-D finite element method.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 한국소성가공학회 2006년도 춘계학술대회 논문집
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• pp.277-280
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• 2006

The hydroformability of aluminum alloy sheets at elevated temperatures have been investigated in this study. It is necessary to analyze the variations of the mechanical properties that depend on the forming temperature and the heat conduction during warm hydroforming. Therefore, in this study a coupled simulation of plastic deformation and temperature distribution in the warm hydroforming process is performed and compared with experimental data. The multi-purpose code DEFORM-2D can handle this type of calculations but it takes high computation time if contact heat transfer between die, tube and pressure medium occurs. Experiments were conducted by high temperature tribometer(pin-on-disk) allowing measuring the friction coefficients of the aluminum alloys at several temperatures and these results are applied to the coupled simulation by which the optimal process parameters such as internal pressure and preset temperature on hydroformability can be determined. The comparison of the FE analysis with the experimental results has shown that hydroformability given by bulge height, and temperature distribution of the tube specimen make a little difference with the FE results but the trend predicted by simulation agrees well with experiments.

• Transactions of Materials Processing
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• 제25권1호
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• pp.21-28
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• 2016

In the current study, reduction of springback is quantified and the reasons for the reduction are investigated. The testing involved a digital servo motion applied to a U-draw bending to produce a hat-type product from high strength steels such as DP780 and DP980. The change in springback is compared between the constant speed motion and three kinds of servocontrolled motions during forming experiments. In order to predict the springback for the servo-controlled tool motion, a finite element method was utilized for the springback analysis considering a kinematic hardening model for the steel. The comparison of springback between the analysis and the experiments shows that they have similar tendencies. Also, the analysis results indicate that the springback reduction is greatly influenced by a decrease in the friction coefficient, which originates from the contact and detach phenomena between the tooling and the blank during the up-and-down motion of the upper die following the servo-controlled motion.

• Transactions of Materials Processing
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• 제22권3호
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• pp.150-157
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• 2013

Fiber metal laminates (FMLs) are layered materials comprised of thin metal sheets and fiber reinforced plastic (FRP). This paper presents the numerical study of the formability enhancement of FMLs composed of an aluminum alloy and self-reinforced polypropylene (SRPP) composite. In this study, a numerical simulation based on finite element (FE) modeling is proposed to evaluate the formability of FMLs using ABAQUS/Explicit. The FE model, which included a single layer of solid and shell elements to model the blank, used discrete layers of the solid element with a contact model and shell elements with a friction based model for the aluminum alloy-composite interface conditions. This method allowed the description of each layer of FMLs and was able to simulate the interaction between the layers. It is noted through this research that the proposed numerical simulation described properly the formability enhancement of the FMLs and the simulation results showed good agreement with experimental results.

• Journal of The Korean Association For Science Education
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• 제8권1호
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• pp.57-72
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• 1988

It is very important for a teacher to know what his students know and what they do not; however, it seems not true for the most Korean secondary school science techers. This study tried to find students' misconception Newton's third law and the sources of the misconceptions. The researcher examined 609 students from middle schools, high schools, and college. In this study, students' understanding on Newton's third law were examined by school level, sex, stream (science and liberal arts), and departments. The following results were obtained by this study. 1. Students' understanding seemed to be improved continuously from middle school to university; however, their misconception (the most frequent incorrect selection of options of the test items) did not changed very much. 2. Students' answers were significantly affected by size of objects, existence of physical contact and the existence of life in the objects. 3. The answer were significantly affected by the source of attraction. 4. The answer to Newton's third law were affected by the magnitude of potential force which the target bodies have, state of motion, velocity, weight, friction and acceleration. This study could show the sources of the misconception on Newton's third law. The identified sources could be very useful for designing an instruction to teach Newton's third law in schools and universities.