• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.12 no.5
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• pp.338-345
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• 2002

The study presents a new testing and analysis method for brake judder on vehicle. For the identification of the excitation mechanism of a brake judder, it is necessary to measure the dynamic brake disc geometry during braking on vehicle. The non-contact sensor system was used to monitor the brake disc geometry. Brake torque variation (BTV) caused by disc thickness variation (DTV) is the primary excitation for brake judder. The mechanical effects generating BTV are linked not only to initial manufacturing tolerances but also to uneven wear. Therefore, the brake disc geometry should be strictly managed to initial condition. The aim of this study has been to measure the dynamic DTV and runout on vehicle and analyze the influence of test parameters on brake judder and compare the disc component with vehicle matching about the DTV Profile. As a result of this study, The amplitude of brake judder is proportional to vehicle speed and fluid pressure fluctuation on braking. The major sources of brake judder are directly related to disc thickness variation and side runout variation of corner assembly (disc, hub. bearing).

• Transactions of the Society of Information Storage Systems
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• v.3 no.1
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• pp.47-53
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• 2007

In this paper, a thermo-piezoelectric mechanism with integrated heaters and piezoelectric sensors has been studied for low power probe-based data storage. Silicon nitride cantilever integrated with silicon heater and piezoelectric sensor has been developed to improve the uniformity of cantilevers. Data bits of 40 nm in diameter were recorded on PMMA film. The sensitivity of the piezoelectric sensor was 0.615 fC/nm after poling the PZT layer. And, the $34\times34$ probe array integrated with CMOS circuits has been successfully developed by simple one-step bonding process. The process can simplify the process step and reduce tip wear using silicon nitride tip.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1998.06a
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• pp.507-513
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• 1998

In surface grinding, the conditions of the grinding wheel has much more significant effect on the machined workpiece as compared to other metal removal processes. The contact between the grinding wheel and the workpiece introduce heat and resistance, which restrict the self-dressing of the grits and result in burrs cracks on the workpiece. Therefore, before or during the grinding operation, it is necessary to self-dressing the grinding wheel for more accurate performance. In general, however, the choice of the dressing time has made by the operator's own decision or the condition of the workpiece. In this paper, a new method for finding the optimal dressing time of the grinding wheel is proposed. In order to develop a more sophisticated methodology, a non-contacting in-process optical measurement method using a laser beam has been introduced to find the glazing, loading, and spilling of the grinding wheel Simultaneously, a three-dimensional computer simulation of the grinding operation has been attempted based on the contact mechanism between the grinding wheel and the workpiece. The grains of the grinding wheel are simulated and the optimal dressing time is determined based on the amount of grain wear and work surface roughness.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.168-173
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• 2004

Fretting is a kind of surface degradation mechanism observed in mechanical components and structures. The fretting damage decrease in 50-70% of the plain fatigue strength. This may be observed in aircraft, automobile and nuclear power plant used in special environment and various loading conditions. In the present study, the characteristics of the fretting fatigue are investigated using the two aluminum alloy(Al2024-T3511 and Al7050-T7451). Through the experiment, it is found that the fretting fatigue strength of the Al7050-T7451 alloy decreased about 50% from the plain fatigue strength, while the fretting fatigue strength of the Al2024-T3511 alloy decreased about 45%. The tire track was widely observed in fracture surface area of oblique crack which was induced by contact pressure. These results can be the basic data to the structural integrity evaluation of aluminum alloy subjected to fretting damage.

• Elastomers and Composites
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• v.54 no.4
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• pp.299-307
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• 2019

Rubber friction properties include adhesion friction characteristics of the interface, hysteresis friction characteristics originating from repeated rubber deformations, and cohesion friction characteristics due to wear and tear. Cohesion friction is generally sufficiently small (< 3%) that it can be ignored, whereas adhesion friction has a relatively large contribution of 15%, but has not been investigated thoroughly. Therefore, through an adhesion friction study, the adhesion mechanism was examined and the relationship between friction characteristics and adhesion friction on dry surfaces was derived. The wet grip characteristics of tread rubber are fully described by the hysteresis characteristics of tires, but friction characteristics on dry roads are difficult to determine without adhesion factors. The results presented herein demonstrate that the combination of hysteresis and adhesion properties in the tread rubber sufficiently explained the characteristics of the dry grip. Based on the results of this study, technologies will be developed to determine the key factors governing adhesion friction characteristics and improve dry tire braking performance.

• Journal of the Korean Society of Mechanical Technology
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• v.13 no.2
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• pp.129-135
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• 2011

Dry CVT(Continuously variable transmission) consists of a driving pulley and a driven pulley joined by rubber V-belt. Each pulley consists of a fixed flange and a movable flange. The movable flange of the driving pulley has the centrifugal roller and a ramp plate in the flange. The movable flange moves toward a fixed flange under the actuation of a centrifugal roller, as the driving pulley speed increases. The main advantages of the Dry CVT with V-belt, which has been popular in Asia, are a simple mechanism, less maintenance and low cost. The important claim which have an influence on the performance of the Dry CVT is the wear of the centrifugal roller. In this study ball type is proposed instead of roller type of movable flange to resolve claim. Also experiments are carried out for new model to evaluate performances.

• Tribology and Lubricants
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• v.35 no.1
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• pp.71-76
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• 2019

The differential planetary gear reducer as a main component of the concrete mixer driving mechanism requires a strong torque to mix concrete compounds. As this component is currently dependent on imports, it is necessary to develop it by conducting a study on vibration analysis and the resonance problem. The noise and vibration of a concrete mixer reducer increase owing to the transmission error of planetary gears, and the damage of components occurs owing to the problems in design and production. In this study, the tooth-passing frequency is calculated to evaluate the noise and vibration of a mixer reducer, and a fast Fourier transform (FFT) analysis is conducted through a vibration test using an acceleration sensor. The vibration of the reducer is measured at three points of input and output of the shaft and planetary gear housing with fixed and variable revolutions per minute. The operating conditions of gears and bearings are evaluated by performing the FFT analysis, and the resonance problem is verified. The results show that No. 1 pinion and ring gears revolve disproportionately. The amplitude values appear high, and the wear of tooth faces occur in tooth-passing frequencies and harmonic components of No. 1 and No. 2 pinion-ring gears. Therefore, we conclude that design changes in the reducer and a correction of tooth profiles are required.

• Journal of Sensor Science and Technology
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• v.31 no.1
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• pp.57-63
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• 2022

This study describes a system that monitors the tool and cutting state of automatic beveling operation in real time. As a signal for cutting state monitoring, a motor current detected from the spindle drive system of the automatic beveling machine is used to monitor abnormal state. Because automatic beveling is processed using a face milling cutter, the cutting force mechanism is the same as the milling process. The predicted cutting torque is obtained using a cutting force model based on specific cutting resistance. Then, the predicted cutting torque is converted into the spindle motor current value, and cutting state stability is diagnosed by comparing it with the motor current value detected during beveling operation. The experimental results show that the spindle motor current can detect abnormal cutting state such as overload and tool wear during beveling operation, and can diagnose the cutting stability using the proposed equip-current line diagram.

• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.5
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• pp.407-415
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• 2008

The tubes in heat exchanger are typically made from copper alloy, stainless steel, carbon steel, titanium alloy material. type-439 ferritic stainless steel is ferromagnetic material, and furnish higher heat transfer rates than austenitic stainless steels and higher resistance to corrosion-induced flaws. Ferritic stainless steel can typically be found in low-pressure(LP) feedwater heaters and moisture separator reheaters(MSRs). LP feedwater heaters generally utilize thin wall type-439 stainless steel tubing, whereas MSRs typically employ a heavier wall tubing with integral fins. Service-induced damage can occur on the OD(outside diameter) surface of type-439 ferritic stainless steel tubing which is employed for MSRs tubing, and the most typical damage mechanism is vibration-induced tube-to-TSP(tube support plate) wear and fatigue cracking. The wear has been reported that occurs mainly on the OD surface. Accordingly, in this study, we have evaluated the flaw sizing capability of magnetic saturation eddy current technique using magnetic saturation probe and flawed specimen.

• Journal of the Korean Society of Clothing and Textiles
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• v.41 no.1
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• pp.84-97
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• 2017

Water vapor and thermal transmission properties of high emotional garments are important to evaluate wear comfort; in addition, the measuring methods of these properties are also critical for breathable and warm suit fabrics. In this study, the water vapor and thermal properties of composite yarn fabrics made of CoolMax, Tencel, and Bamboo fibers with filaments were measured and compared according to the measuring method. Water Vapor Transmittance (WVT) of the fabric woven by the sheath/core composite yarn in the warp direction was the highest due to the small staple fiber volume in the sheath/core yarn structure and high air voids in the sheath/core yarn fabrics. This property was also the highest in fabrics woven by bamboo staple yarns in the weft direction, and was the lowest on hi-multi filament fabrics. However, water vapor resistance ($R_{ef}$) of these fabrics by KSK ISO 11092 showed the opposite results to the water vapor transmittance method ($CaCl_2$ method); in addition, its correlation coefficient was low. The correlation coefficient between $R_{ef}$ and the drying rate was 0.719; therefore, the measurement mechanism of $R_{ef}$ is analogous to the drying property measurement. The thermal conductivity of the fabrics woven with compact staple yarn showed a high value; however, the hi-multi filament fabric showed low thermal conductivity. Therefore, fiber characteristics affect thermal properties more than yarn structure. The correlation between thermal property and moisture transport was also low. This study showed that: water vapor transmittance was active at the loose yarn structure, dry heat transport was vigorous at the compact yarn structure, and heat transport was affected more by fiber characteristics than yarn structure. In conclusion, sheath/core composite yarns were relevant to the high absorptive cool suit along with siro-fil and CoolMax/Bamboo staple yarns that were relevant to the heat diffusive cool suit.