• Polymer(Korea)
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• v.25 no.2
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• pp.199-207
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• 2001

In the present study the cure behavior of diglycidyl ether of bisphenol-A(DGEBA) using an anhydride-based hardener in the presence of N,N-dimethyl benzyl amine (BDMA) or 1-cyanoethyl-2-ethyl-4-methyl imidazole (2E4MZ-CN) as an accelerator has been monitored and interpreted from the viewpoint of photophysical properties by means of fluorescence spectroscopy. To do this, 1,3-bis-(1-pyrene)propane (BPP) was well incorporated in the epoxy resin system by mechanical blending. The BPP probe, which is very sensitive to conformational change of the molecule influenced by the surrounding medium, successfully formed intramolecular excimer fluorescence. It is susceptible to the micro-viscosity or local viscosity and molecular mobility according to the epoxy cure. The cure behavior was explained with monomer fluorescence intensity ($I_{M}$ ), excimer fluorescence intensity ($I_{E}$ ) and $I_{M}$ /$I_{E}$ ratio as a function of cure time, cure temperature and accelerator. The present work agreed with the previous report on the cure behavior of an epoxy-anhydride system studied using DSC or torsion pendulum method. This study also suggests that the use of fluorescence technique may provide information on cure behavior of a thermosetting resin in a low temperature region, which has not been well interpreted by other analytical methods.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.11
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• pp.979-986
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• 2016

The tripod shafts of constant-velocity joint are used in both the trains KTX and KTX-sanchon. It is an important component that connects the motor reduction unit and the axle reduction unit in a power bogie. The tripod shaft not only transmits drive and brake torque in the rotational direction, but also slides in the axial direction. If the drive system is loaded with an excessive torque, the fuse part of the shaft will be fractured firstly to protect the other important components. In this study, a rig was developed for conducting torsion tests on the tripod shaft, which is a type of mechanical fuse. The tripod shafts were subjected to torsional fracture test and torsional fatigue test on the rig. The weak zone of the tripod shaft was identified, and its fatigue life was predicted using finite element analysis (FEA). After analyzing the FEA results, design solutions were proposed to improve the strength and fatigue life of the tripod shaft. Furthermore, the deterioration trend and time for failure of the tripod shaft were verified using the hysteresis loops which had been changed with the advancement of the torsional fatigue test.

• Composites Research
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• v.34 no.5
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• pp.317-322
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• 2021

When a complex load such as torsion, low-speed impact, or fatigue load is applied, the properties in the thickness direction are weakened through microcracks inside the material due to the nature of the laminated composite material, and delamination occurs. To prevent the interlaminar delamination, various three-dimensional reinforcement methods such as Z-pinning and stitching, and structural health monitoring techniques that detect the microcrack of structures in real time have been continuously studied. In this paper, the single-lap joints with I-fiber stitching process were manufactured by a co-curing method and their strengths and failure detection capability were evaluated. AE and electric resistance method were used for detection of crack and failure signal and electric circuit for signal analysis was manufactured, and failure signal was analyzed during the tensile test of a single-lap joint. From the experiment, the strength of the single lap joint reinforced by I-fiber stitching process was improved by about 44.6% compared to the co-cured single lap joint without reinforcement. In addition, as the single-lap joint reinforced by I-fiber stitching process can detect failure in both the electrical resistance method and the AE method, it has been proven to be an effective structure for failure monitoring as well as strength improvement.

• Steel and Composite Structures
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• v.35 no.5
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• pp.641-657
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• 2020

A unique lightweight string truss deployable bridge assembled by thin-walled fiber reinforced polymer (FRP) and metal profiles was designed for emergency applications. As a new structure, investigations into the static structural performance under the serviceability limit state are desired for examining the structural integrity of the developed bridge when subjected to unsymmetrical loadings characterized by combined torsion and bending. In this study, a full-scale experimental inspection was conducted on a fabricated bridge, and the combined flexural-torsional behavior was examined in terms of displacement and strains. The experimental structure showed favorable strength and rigidity performances to function as deployable bridge under unsymmetrical loading conditions and should be designed in accordance with the stiffness criterion, the same as that under symmetrical loads. In addition, a finite element model (FEM) with a simple modeling process, which considered the multi segments of the FRP members and realistic nodal stiffness of the complex unique hybrid nodal joints, was constructed and compared against experiments, demonstrating good agreement. A FEM-based numerical analysis was thereafter performed to explore the effect of the change in elastic modulus of different FRP elements on the static deformation of the bridge. The results confirmed that the change in elastic modulus of different types of FRP element members caused remarkable differences on the bending and torsional stiffness of the hybrid bridge. The global stiffness of such a unique bridge can be significantly enhanced by redesigning the critical lower string pull bars using designable FRP profiles with high elastic modulus.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.4
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• pp.275-283
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• 2013

In this paper, the structural optimum design method of composite rotor blade cross-section was investigated with the genetic algorithm. An auto-mesh generation program was developed for iterative calculations of optimum design, and stresses in the blade cross-section were analyzed by VABS (variational asymptotic beam sectional analysis) program. Minimum mass of rotor blade was defined as an object function, and stress failure index, center mass and blade minimum mass per unit length were chosen as constraints. Finally, design parameters such as the thickness and layup angles of a skin, and the thickness, position and width of a torsion box were determined through the structural optimum design method of composite rotor blade cross-section presented in this paper.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.131-136
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• 2004

The limited slip differential(LSD) is a device which enables the driving force to be transmitted from one slipping wheel to another wheel in such case that the car is stuck in clay or snow. When the unwanted slipping occurs on one wheel, the LSD temporarily restraints the differential motion to transmit the driving force in the other wheel. So far, many types of LSD were developed such as mechanical lock type, disk clutch type, viscous coupling type, torsion type and multiple clutch type. However these types of LSD is too complicated and expensive, so it is used only for 4WD outdoor vehicles, military vehicles, and a portion of deluxe car. So, many studies has been devoted to improve new types of LSD to cover those demerits of existing LSDs that the hydraulic LSD is developed as arepresentative result of that. The hydraulic LSD which uses the principle of gear pump is packed with viscous oil in tight container. When a slip occurs on one wheel, the hydraulic LSD generates torque caused by high oil pressure in the container. This study has been devoted to suggest an improved hydraulic LSD. In order to achieve it, we designed a new type of hydraulic LSD, produced it and did a rig test with it on real vehicle. From the rig test, it has been confirmed that the new type of hydraulic LSD can be directly applied to exiting vehicles without changing the design criteria

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.11
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• pp.762-769
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• 2017

The extensional stiffness in quasi-isotropic laminates is uniform in the radial direction, but the bending stiffness varies radially due to the stacking sequence. This paper addresses the directional dependency of the bending stiffness and its radial variation in three types of quasi-isotropic laminate reflectors consisting of unidirectional fiber composite materials (UDM) and randomly distributed composite materials (short fiber, RDM). The extensional stiffness and bending stiffness in optical reflectors using RDM are uniform, while the bending stiffness in those using UDM varies radially from 11% to 26%. Also, the stiffness sensitivity, such as the bend-twist or bend-torsion effect, due to the differences in the stiffness value in the composite, is large. These factors are problematic in the optical field requiring precision surfaces. Utilizing RDM might be one way to eliminate the presence of bending stiffness in composite mirror substrates.

• The Journal of the Korea Contents Association
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• v.11 no.10
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• pp.488-493
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• 2011

The Korean spine geometry and property data for researchers were made by KISTI and Catholic Institute for Applied Anatomy. We took whole spine CT, X-Ray, BMD scan for making high resolution cross-sectional spine images using more 20 donated cadavers(60 - 80 years). Then we constructed 3-dimensional volume model using serial CT images by Mimics software. The major morphometric parameters of vertebrae were measured. Mechanical motion and property data were obtained by the same cadavers using the DEXA for BMD and the spine simulator. The Korean spine geometry and property data could be used for research and development of medical device.

• Transactions of the Korean Society of Automotive Engineers
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• v.9 no.2
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• pp.107-115
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• 2001

It is required more precise analysis for practical load because of complexities and varieties of vehicle structure. To establish the numerical model, many researchers have been developed designing tools for linking F.E. Analysis results and experimental results. There studies have generally focused on each experimental method or analytical method separately. There are few studies based on both methods. This paper conceives new procedure for the determination of the load direction and magnitude applied on mechanical structures. New procedure is the combination of the analytical and empirical method with analyzed strain by F.E. Analysis under unit load and with measured principal stress by strain gages under driving load, respectively. In this paper, we theorize the procedure of practical load determination and make the validity and the practicality of the procedure with the application to T-shape jointed structure. F.E. Analysis is conducted to get the principal stress on arbitrary points in the F.E. model of T-shape joint under unit load. Then experiment is carried out to get the principal stress on the same points of F.E. model. To demonstrate the actual driving condition, the load conditions are bending and torsion. From these two data sets, the magnitude, the direction and the position of load can be obtained. Theory and practice do not always coincide; since there are some errors such as ill-poseness, measuring error and modeling error in experimental data, we examine the proper method of error minimization.

• Journal of Veterinary Clinics
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• v.37 no.4
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• pp.175-179
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• 2020

The objective of this study was to determine the effect of osteotomy angle and tibial proximal segment rotation angle on angular and torsional tibial deformities and to assess the trends of these deformities during the rotation of the tibial proximal segment in a center of rotation of angulation (CORA)-based leveling osteotomy (CBLO) by performing computer modeling of the tibia. Four tibias of toy breed dogs with no history of lameness were used in this study. Osteotomies were performed in the proximal tibias at angles of 0°, 10°, 20°, -10°, and -20°, perpendicular to either the proximodistal or craniocaudal tibial axes. The mechanical medial proximal tibial angle (mMPTA) and transcondylar (TC) and distal cranial tibial (CnT) axes were used to measure angular and torsional deformities, respectively. All tibias showed an increase in angular and rotational deformities with an increase in the tibial plateau rotation angle. The tibia with osteotomies performed in the proximodistal and craniocaudal directions showed the highest magnitude of torsional and angular deformities, respectively. The results of this study revealed a tendency of occurrence of angular and torsional deformities with osteotomy performed along the proximodistal and craniocaudal directions in the CBLO.