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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Transactions of the Korean Society of Mechanical Engineers A
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Journal DOI :
The Korean Society of Mechanical Engineers
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Volume & Issues
Volume 39, Issue 12 - Dec 2015
Volume 39, Issue 11 - Nov 2015
Volume 39, Issue 10 - Oct 2015
Volume 39, Issue 9 - Sep 2015
Volume 39, Issue 8 - Aug 2015
Volume 39, Issue 7 - Jul 2015
Volume 39, Issue 6 - Jun 2015
Volume 39, Issue 5 - May 2015
Volume 39, Issue 4 - Apr 2015
Volume 39, Issue 3 - Mar 2015
Volume 39, Issue 2 - Feb 2015
Volume 39, Issue 1 - Jan 2015
Selecting the target year
Determination Method of Ramberg-Osgood Constants for Leak Before Break Evaluation
Bae, Kyung Dong ; Ryu, Ho Wan ; Kim, Yun Jae ; Kim, Jin Weon ; Kim, Jong Sung ; Oh, Young Jin ;
Transactions of the Korean Society of Mechanical Engineers A, volume 39, issue 7, 2015, Pages 645~652
DOI : 10.3795/KSME-A.2015.39.7.645
In this study, a method for determining Ramberg-Osgood constants for leak-before-break evaluation was investigated. The Ramberg-Osgood constants were calculated for SA312, TP316, and SA-508 Gr.1a in an operating temperature of
. Incremental plasticity, using stress-strain data obtained from experiment, and deformation plasticity, using the Ramberg-Osgood constants, were considered in a finite element analysis. Using incremental plasticity and deformation plasticity, J-integrals and crack opening displacement values were calculated and compared. By comparing the results of incremental plasticity and deformation plasticity, a suitable method for determining Ramberg-Osgood constants for leak-before-break evaluation was confirmed.
Growth of Silicon-Germanium Quantum-dots Through Local Enhancement of Surface Diffusivity
Kim, Yun Young ;
Transactions of the Korean Society of Mechanical Engineers A, volume 39, issue 7, 2015, Pages 653~657
DOI : 10.3795/KSME-A.2015.39.7.653
A numerical investigation to simulate the selective growth of silicon-germanium quantum-dots via local surface diffusivity enhancement is presented. A nonlinear equation for the waviness evolution of film surface is derived to consider the effects of spatially-varying diffusivity, influenced by a surface temperature profile. Results show that the morphology of the initially planar film shapes into an undulated surface upon perturbation, and a steady-state solution describes a fully grown quantum-dot. The present study points toward a fabrication technique that can obtain selectivity for self-assembly.
Evaluation of Effect of Electric Energy Density on the Electroplasticity of 5052-H32 Aluminum Alloys
Yeom, Kyeong-Ho ; Hong, Sung-Tae ; Jeong, Yong-Ha ; Han, Kyung-Sik ; Han, Heung Nam ; Kim, Moon-Jo ;
Transactions of the Korean Society of Mechanical Engineers A, volume 39, issue 7, 2015, Pages 659~663
DOI : 10.3795/KSME-A.2015.39.7.659
In the present study, electroplastic tensile behaviors of aluminum 5052-H32 alloy specimens with different gage dimensions are investigated under a constant electric energy density (electric energy per unit volume). The experimental results show that equivalent electric energy densities induce nearly identical electroplastic behaviors even with different gage dimensions (length, width, or volume). Additionally, the experimental results demonstrate that the electroplastic behavior of the selected aluminum alloy is best described by the electric energy density, which is a function of current density and current duration, rather than individual current density or current duration. The results of the present study suggest that the electric energy density may replace current density and current duration as a design parameter in electrically assisted forming processes.
A Vibration-based Fault Diagnostics Technique for the Planetary Gearbox of Wind Turbines Considering Characteristics of Vibration Modulation
Ha, Jong M. ; Park, Jungho ; Oh, Hyunsoek ; Youn, Byeng D. ;
Transactions of the Korean Society of Mechanical Engineers A, volume 39, issue 7, 2015, Pages 665~671
DOI : 10.3795/KSME-A.2015.39.7.665
The performance of fault diagnostics for a planetary gearbox depends on vibration modulation characteristics, which can vary with manufacturing & assembly tolerance, and load condition. In this paper, a fault diagnostics technique that considers vibration modulation characteristics is proposed for the effective fault detection of planetary gearboxes in wind turbines. For identifying the vibration modulation characteristics in practice, re-sampled vibration signals are processed with narrow band-pass filters. Thereafter, the optimal position of the vibration extraction window is identified for effective detection of faulty signals under the varying vibration modulation characteristics. The proposed diagnostics technique makes it possible to perform robust diagnostics of the planetary gearbox with regard to the changeable vibration modulation effect. For demonstrating the proposed fault diagnostics technique, a 2-kW WT testbed is designed with two DC motors and gearboxes. A faulty gear with partial tooth breakage is machined and assembled into the gearbox.
Approximate Multi-Objective Optimization of a Quadcopter through Proportional-Integral-Derivative Control
Yoon, Jaehyun ; Lee, Jongsoo ;
Transactions of the Korean Society of Mechanical Engineers A, volume 39, issue 7, 2015, Pages 673~679
DOI : 10.3795/KSME-A.2015.39.7.673
In this study, the nondominated sorting genetic algorithm (NSGA-II) is used to obtain the optimized proportional-integral-derivative (PID) gain value that can quickly recover the motion of a quadcopter after a disturbance. Prior to PID control, the four-rotor quadcopter interval was defined using computational fluid dynamics (CFD). Through the definition of this model, the PID control algorithm was generated. To construct a response surface model, D-optimal programming was used for the generation of experimental points. For this purpose, a gain value that satisfies both the roll and altitude PID gain values is obtained. Using the NSGA-II, the gain value of shorten time of the quadcopter motion control can be optimized.
An Experimental Investigation of Dry Friction Noise for Several Metallic Materials
Baek, Jongsu ; Kang, Jaeyoung ;
Transactions of the Korean Society of Mechanical Engineers A, volume 39, issue 7, 2015, Pages 681~686
DOI : 10.3795/KSME-A.2015.39.7.681
The onset characteristics of friction-induced noise for a steel plate and 4 metallic pins (Cu, Ni, Al, Mg) were studied through the pin-on-disk machine and the reciprocating testing machine. The results showed that the negative slope of the friction curve was related to the onset time of friction noise. Particularly, Cu was found to be the best metallic material for preventing squeak noise in terms of the onset time and the negative friction slope.
An Experimental Study of In-Mold Coating of Automotive Armrests
Park, Jong Rak ; Lee, Ho Sang ;
Transactions of the Korean Society of Mechanical Engineers A, volume 39, issue 7, 2015, Pages 687~692
DOI : 10.3795/KSME-A.2015.39.7.687
A mold design for in-mold coating was developed to achieve simultaneous coating and injection molding of an automotive armrest. The developed mold includes one core and two cavities which are composed of a substrate cavity and a coating cavity. The core was attached to a movable plate and two cavities were mounted on a plate sliding in a stationary plate. In a two-step process, the part was first injection molded and subsequently, with the aid of a sliding table, was transferred to a second cavity. The materials used were PC/ABS for substrate and two-component polyurethane for coating. The experiments were conducted by changing the flow rate to investigate mixing characteristics. As the flow rate increased, the mixing improved. Additionally, the bubbles appeared over the substrate surface decreased with an increase of the weight of injected coating material.
Estimation of Fatigue Crack Growth Behavior of Cracked Specimen Under Mixed-mode Loads
Han, Jeong Woo ; Woo, Eun Taek ; Han, Seung Ho ;
Transactions of the Korean Society of Mechanical Engineers A, volume 39, issue 7, 2015, Pages 693~700
DOI : 10.3795/KSME-A.2015.39.7.693
To estimate the fatigue crack propagation behavior of compact tension shear (CTS) specimen under mixed-mode loads, crack path prediction theories and Tanaka's equation were applied. The stress intensity factor at a newly created crack tip was calculated using a finite element method via ANSYS, and the crack path and crack increment were then obtained from the crack path prediction theories, Tanaka's equation, and the Paris' equation, which were preprogrammed in Microsoft Excel. A new method called the finite element crack tip updating method (FECTUM) was developed. In this method, the finite element method and Microsoft Excel are used to calculate the stress intensity factors and the crack path, respectively, at the crack tip per each crack increment. The developed FECTUM was applied to simulate the fatigue crack propagation of a single-edge notched bending (SENB) specimen under eccentric three-point bending loads. The results showed that the number of cycles to failure of the specimen obtained experimentally and numerically were in good agreement within an error range of less than 3%.
Laser Welding Analysis for 3D Printed Thermoplastic and Poly-acetate Polymers
Choi, Hae Woon ; Yoon, Sung Chul ;
Transactions of the Korean Society of Mechanical Engineers A, volume 39, issue 7, 2015, Pages 701~706
DOI : 10.3795/KSME-A.2015.39.7.701
In this study, experimental and computer simulation results are compared and analyzed. Three-dimensional (3D) fabricated matrices from an MJM 3D printer were joined with poly-acetate thermoplastic polymers using a diode laser. A power range of 5-7 W was used to irradiate the boundary of two polymers. The heated polymers flowed into the matrices of the 3D fabricated structure, and reliable mechanical joining was achieved. Computer simulation showed the temperature distribution in the polymers, and flow direction was estimated based on the flux and temperature information. It was found that the more than the minimum energy threshold was required to effectively join the polymers and that two scans at low-speed were more effective than four scans at high speed.
Experimental Study of the Redistribution of Welding Distortion According to the Partial Removal of Welded Structure
Kim, Yong Rae ; Wang, Chao ; Kim, Jae Woong ;
Transactions of the Korean Society of Mechanical Engineers A, volume 39, issue 7, 2015, Pages 707~712
DOI : 10.3795/KSME-A.2015.39.7.707
During the welding process, welding distortion is caused by the non-uniformity of the temperature distribution in the weldment. Welding distortion is redistributed because the residual stress and rigidity change according to the removal of the welded structure. In shipbuilding in particular, this phenomenon may be observed during the cutting process of lugs that are attached to blocks for transfer. The redistribution of welding distortion also causes problems, such as damage to the cutting tool. The aim of this study is to experimentally analyze the redistribution of welding distortion because of the partial removal of the welded structure. In the experiments conducted in this study, fillet welding and cutting were performed, and longitudinal bending and angular distortion in the welded structures were then investigated and analyzed.
Fatigue Damage Analysis of a Low-Pressure Turbine Blade
Youn, Hee Chul ; Woo, Chang Ki ; Hwang, Jai Kon ;
Transactions of the Korean Society of Mechanical Engineers A, volume 39, issue 7, 2015, Pages 713~720
DOI : 10.3795/KSME-A.2015.39.7.713
The sizes of the final blades of a low-pressure (LP) steam turbine have been getting larger for the development of high-capacity power plants. They are also larger than the other blades in the same system. As a result, fatigue damage is caused by a large centrifugal force and a low natural frequency of the blade. Recently, many failure cases have been reported due to repeated turbine startups and their prolonged use. In this study, the causes and mechanism of failure of a LP turbine blade were analyzed by using a finite element method to calculate the centrifugal force, the natural frequency of a stress-stiffening effect, and the harmonic response. It was observed that the expected fatigue damage position matched the real crack position at the airfoil's leading edge, and an equivalence fatigue limit approached a notch fatigue limit.
A Door Frame for Wind Turbine Towers Using Open-Die Forging and Ring-Rolling Method
Kwon, Yong Chul ; Kang, Jong Hun ; Kim, Sang Sik ;
Transactions of the Korean Society of Mechanical Engineers A, volume 39, issue 7, 2015, Pages 721~727
DOI : 10.3795/KSME-A.2015.39.7.721
The mechanical components for wind turbines are mainly manufactured using open-die forging. This research introduces an advanced forging method to produce the door frame of the tubular wind turbine tower. The advantages of this new forging method are an increase in the raw material utilization ratio and a reduction in energy cost. In the conventional method, the door frame is hot forged with a hydraulic press and amounts of material are machined out because of the shape difference between the forged and final machine products. The proposed forging method is composed of hot forging and ring rolling processes to increase the material utilization ratio. The effectiveness of this new forging method is deeply related to the ring rolled blank dimension before the final forging. To get the optimal ring rolled blank, forged shape prediction using the finite element analysis method was applied. The forged dimensions produced by the new forging method were verified through the first article production.
Effects of Specimen Size and Side-groove on the Results of J-R Fracture Toughness Test for LBB Evaluation
Kim, Jin Weon ; Choi, Myung Rak ; Oh, Young Jin ; Park, Heung Bae ; Kim, Kyung Su ;
Transactions of the Korean Society of Mechanical Engineers A, volume 39, issue 7, 2015, Pages 729~736
DOI : 10.3795/KSME-A.2015.39.7.729
In this study, the effects of specimen size and side-groove on the results of the J-R test for leak-before-break (LBB) evaluation were investigated. A series of J-R tests were conducted at both RT and
, using three different sizes of compact tension (CT) specimens machined from SA508 Gr.1a piping material: 12.7 mm-thick 1T-CT, 25.4 mm-thick 1T-CT, and 25.4 mm-thick 2T-CT with and without side-groove. The results showed that side-grooving reduced the J-R curve for all specimens and the effect of side-grooving was more significant at
than at RT. As the thickness of the specimens decreased and the width of the specimens increased, the J-R curve slightly decreased at RT but it increased at
. However, the variation in the J-R curve of SA508 Gr.1a with the thickness and width of CT specimen was insignificant.