• Proceedings of the KAIS Fall Conference
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• 2006.05a
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• pp.223-226
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• 2006

The micro-gas sensor based on carbon nanotubes (CNTs) was fabricated and its gas sensing characteristics on nitrogen dioxide ($NO_2$) have been investigated. The sensor consists of a heater, an insulating layer, a pair of contact electrodes, and CNT-sensing film on a micromachined diaphragm. The heater plays a role in the temperature change to modify sensor operation. Gas sensor responses of CNT-film to $NO_2$ at room temperature are reported. The sensor exhibits a reversible response with a time constant of a few minutes at thermal treatment temperature of $130^{\circ}C$.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.2
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• pp.149-157
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• 2004

Implicit finite element analysis of the flat surface-straight edge hemming process is performed by using a commercial code ABAQUS/Standard. Methods of finite element modeling for springback simulation and contact pair definition are discussed. An optimal mesh system is chosen through the error analysis that is based on the smoothing of discontinuity in the state variables. This study has focused on the investigation of the influence of process parameters in flanging, pre-hemming and main hemming on final hem quality, which can be defined by turn-down, warp and roll-in. The parameters adopted in this parametric study are flange length, flange angle, flanging die corner radius, face angle and insertion angle of pre-hemming punch, and over-stroke of pre-hemming and main hemming punches.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.10a
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• pp.971-975
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• 2005

In this study, a car-door-controlled collision protection system using proximity sensor is proposed and its preliminary analysis and several preliminary experiments are conducted. The proposed system has three additional sub-components on the car-door that is, a pair of extra electro-magnetic actuator that are attached to the sliding bar of the open/close car-door four-bar mechanism, a proximity sensor that would be attached to the outside surface of the door which is likely to frequently contact to the object and a driving control circuit of the whole system. A proximity sensor is used to detect object close to the car-door, the driving control circuit provides actuating power command to the electro-magnets to generate braking force to stop the swing motion of the car-door. It is verified through kinematic analysis of the four-bar car-door open/close mechanism and through experiments that the magnitude of maximum electronic magnetic force could provide the braking force enough for this application. For this purpose, an electro-magnet driving circuit is implemented and tested. And also to increase the safety of the system a time delay circuit is implemented and tested.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.7
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• pp.677-684
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• 2010

Backlashes of gears provide gears for good lubrication and for removal of the interference between teeth by the wear and manufacturing errors. The backlash is the strong nonlinear factor to gears. This study deals with nonlinear modeling of helical gears with backlash. Excitation of helical gears comes from torque variation, the tooth surface error, and the periodical change of mesh stiffness. To study the effect of torque fluctuation, equation of motion for the single degree of freedom torsional model of helical gears with the periodical change of mesh stiffness and the backlash was derived. The Newmark beta method and the Newton-Raphson method were used to obtain the nonlinear behaviors of mesh forces of helical gears. All excitation frequencies initially caused the tooth separation and single-sided impacts of the gear pair and eventually led to the normal tooth contact. However, some special excitation frequencies caused the single-sided impacts in the entire time as well as the initial time. Damping increase reduced the duration of single-sided impacts, and the backlash increase caused those in the entire time domain.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.12
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• pp.1005-1011
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• 2016

The fundamental reason for gear noise is transmission error. Transmission error occurs because of STE (static transmission error) and DTE (dynamic transmission error), while a pair of gears is meshing. These errors are generated by the deflection of the teeth and the friction on the surface of the teeth. In addition, the vibration generated by transmission error leads to excited bearings. The bearings support the shafts, and the noise is radiated after exciting the gear casing. The analysis of the contact stress in helical gear tooth flanks indicates that it is due to impact loading, such as the sudden engagement and disengagement of a gear. Stress analysis is performed for different roll positions, in order to determine the most critical roll angle. Dynamic analysis is performed on this critical roll position, in order to evaluate variation in stresses and tooth contact force, with respect to time. In this study, transmission error analysis was implemented on a spur and helical gear with involute geometry and a modified geometry profile. In addition, in order to evaluate the intensity of impact due to sudden engagement and significant backlash, the impact factor was calculated using the finite element analysis results of static and dynamic maximum bending stresses.

• Korean Journal of Applied Biomechanics
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• v.25 no.4
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• pp.465-474
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• 2015

Objective : A study and development of Korean Bobsleigh athletes's shoe which considers their physical condition has yet to be completed. So this study examines the effects of running shoes used by athletes based on plantar pressure and sprint time in order to provide raw data for the development of bobsleigh shoes suitable for Koreans. Method : The study selected seven bobsleigh athletes as subjects and selected three pairs of spiked running shoes from three companies, which will be referred to as Company N (Type A), Company A (Type B), and Company M (Type C). To analyze sprint time and plantar pressure for each shoe, the subject of the study were instructed to wear the selected shoes and to drag a sled at maximum sprint for 15 meters for 15 meters for in each condition that would be in real bobsleigh competitions. Results : The average sprint intervals for each athlete in each pair of shoes revealed Type C produce the fastest sprint in the order of Type C < Type A< Type B. Shoe Type C also had the largest contact area in order of Type C > Type B > Type A (p<.01). None of the three shoe types seem to yield a distinct advantage in terms of maximum average pressure or maximum pressure. Conclusion : In the future, functional analysis should be carried out by comparing the material properties, hardness, and toe spring of shoes based on the Type C shoe from Company M in order to develop bobsleigh shoes suitable for Koreans.

• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.6
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• pp.566-576
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• 2003

Carbon-fiber reinforced plastics (CFRP) composite laminates often possess strong in-plane elastic anisotropy attributable to the fiber orientation and layup sequence. The layup orientation thus greatly influences its properties in a composite laminate. It could result in the part being rejected or discarded if the layup orientation of a ply is misaligned. A nondestructive technique would be very beneficial, which could be used to test the part after curing and to require less time than the optical test. In this paper, ultrasonic scanners were set out for different measurement modalities for acquiring ultrasonic signals as a function of in-plane azimuthal angle. The motorized scanner was built first for making transmission measurements using a pair of normal-incidence shear wave transducers. Another scanner was then built fer the acousto-ultrasonic configuration using contact transducers. A ply-by-ply vector decomposition model has been developed, simplified, and implemented for composite laminates fabricated from unidirectional plies. We have compared the test results with model data. It is found that strong agreement are shown between tests and the model developed in characterizing cured layups of the laminates.

• Polymer(Korea)
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• v.34 no.2
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• pp.89-96
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• 2010

Adhesive binders with core-shell structure of organic/organic pair were prepared by emulsion polymerization of acrylic monomers, such as methyl methacrylate(MMA), ethyl acrylate(EA), n-butyl acrylate(BA), and styrene(St). Ammonium persulfate (APS) was used as an water soluble initiator in the presence of an anionic surfactant, sodium dodecyl benzene sulfonate (SDBS). Non-woven fabric and leather were impregnated with the adhesive binder. The surface of the impregnated fabric and leather were treated with plasma technique and then kinetics analysis and mechanical properties were measured. The conversions of the polymerization of core-shell binder (MMA/EA, MMA/BA) were greater than 90%. When the core-shell binder was prepared at equimolar conditions, the increasing effect of the core-shell binder on the state peel strength of the impregnated and plasma-treated non-woven/non-woven fabric has the order of MMA/St, EA/BA, BA/MMA, EA/St, and EA/MMA. When the core-shell binder was prepared at non-equimolar conditions, the increasing effect of the core-shell binder on the state peel strength of the non-woven fabric/leather has the order of MMA/BA, BA/EA, MMA/EA, St/MMA, and EA/St.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.3A
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• pp.310-318
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• 2007

The RFID system is a non-contact automatic identification system that identifies tags through a reading device by attaching small, inexpensive tags on goods. This system is expected to supplant barcodes, the contactless reading technique that is most widely used at present. The RFID system can be applied in a variety of areas. Among those, Ari Juels proposed an environment to prove that a pair of tags has been scanned simultaneously And he presented a yoking proof protocol for this. But the yoking-proof protocol is vulnerable to replay attack. Although modified yoking-proof protocols for alleviating this drawback have been proposed, they are not immune to replay attack, either. In this paper, we analyze problems of existing yoking-proof protocols and present a new protocol, which will make replay attack difficult, based on this analysis. We have also extend this protocol so that it can provide yoking proofs for n tags.

• Polymer(Korea)
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• v.34 no.1
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• pp.38-44
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• 2010

Core-shell particles of inorganic/organic pair were synthesized from $CaCO_3$ absorbed sodium dodecyl benzene sulfonate(SDBS) surfactant. Shell components were synthesized by sequential emulsion polymerization. Various monomers were used as shell components such as methyl methacrylate(MMA), ethyl acrylate(EA), butyl acrylate(BA), and styrene(St). Ammonium persulfate(APS) was used as an initiator and 2-ethylhexyl acylate(2-EHA) was used as a functional monomer, In the $CaCO_3$/organic core-shell particle polymerization, $CaCO_3$ absorbed surfactant SDBS of 0.5 wt% was prepared first and then core $CaCO_3$ was encapsulated by emulsion polymerization. 0.1 wt% of APS was added sequentially to minimize the formation of new monomer particle during shell polymerization. The structure of inorganic/organic core-shell particles were characterized by measuring the decomposition degree of $CaCO_3$ using HCl solution, thermogravimetric analyzer, scanning electron microscope, and transmission electron microscope.