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Adhesion strength characterization for different frame materials of handheld products
Ngoc San Ha,Thanh Duc Dao,구남서,곽재복,정순완 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.10
In this study, the adhesion strength for different frame materials of handheld products was investigated. To characterize the adhesive strength, a simple model of a cellphone that consists of a glass window attached to body frame using double-sided tape was designed and fabricated. The adhesion strength with different pull out speeds and aging times was measured using a conventional pull out testing method. To investigate the detailed delamination process of the adhesive layer, the digital image correlation technique was applied. Moreover, in recent years, the trend of using metal for a body frame of a cellphone has gradually increased due to the fashion of metal frames. Therefore, two materials for body frames were considered for testing in this study: aluminum was the representative metal and polycarbonate was the representative conventional material. The results showed that the strain at the interface between the adhesive layer and body frame is higher than that at the interface between adhesive layer and glass window for both cases of aluminum and polycarbonate frames. Moreover, the fracture energy in the aluminum body frame is higher than that in the polycarbonate body frame. In order to validate the experimental results, the cohesive elements in ABAQUS TM were used for the modeling bonding layer. The results showed a good agreement between simulation and experiment.
Thermal Strain Measurement of Austin Stainless Steel (SS304) during a Heating-cooling Process
Ha, Ngoc San,Le, Vinh Tung,Goo, Nam Seo,Kim, Jae Young The Korean Society for Aeronautical and Space Scie 2017 International Journal of Aeronautical and Space Sc Vol.18 No.2
In this study, measurement of thermophysical properties of materials at high temperatures was performed. This experiment employed a heater device to heat the material to a high temperature. The images of the specimen surface due to thermal load at various temperatures were recorded using charge-coupled device (CCD) cameras. Afterwards, the full-field thermal deformation of the specimen was determined using the digital image correlation (DIC) method. The capability and accuracy of the proposed technique are verified by two experiments: (1) thermal deformation and strain measurement of a stainless steel specimen that was heated to $590^{\circ}C$ and (2) thermal expansion and thermal contraction measurements of specimen in the process of heating and cooling. This research focused on two goals: first, obtaining the temperature dependence of the coefficient of thermal expansion, which can be used as data input for finite element simulation; and second, investigating the capability of the DIC method in measuring full-field thermal deformation and strain. The results of the measured coefficient of thermal expansion were close to the values available in the handbook. The measurement results were in good agreement with finite element method simulation results. The results reveal that DIC is an effective and accurate technique for measuring full-field high-temperature thermal strain in engineering fields such as aerospace engineering.
Thermal Strain Measurement of Austin Stainless Steel (SS304) during a Heating-cooling Process
Ngoc San Ha,Vinh Tung Le,Nam Seo Goo,Jae Young Kim 한국항공우주학회 2017 International Journal of Aeronautical and Space Sc Vol.18 No.2
In this study, measurement of thermophysical properties of materials at high temperatures was performed. This experiment employed a heater device to heat the material to a high temperature. The images of the specimen surface due to thermal load at various temperatures were recorded using charge-coupled device (CCD) cameras. Afterwards, the full-field thermal deformation of the specimen was determined using the digital image correlation (DIC) method. The capability and accuracy of the proposed technique are verified by two experiments: (1) thermal deformation and strain measurement of a stainless steel specimen that was heated to 590 ℃ and (2) thermal expansion and thermal contraction measurements of specimen in the process of heating and cooling. This research focused on two goals: first, obtaining the temperature dependence of the coefficient of thermal expansion, which can be used as data input for finite element simulation; and second, investigating the capability of the DIC method in measuring full-field thermal deformation and strain. The results of the measured coefficient of thermal expansion were close to the values available in the handbook. The measurement results were in good agreement with finite element method simulation results. The results reveal that DIC is an effective and accurate technique for measuring fullfield high-temperature thermal strain in engineering fields such as aerospace engineering.
Experimental Study on the Performance of a Bidirectional Hybrid Piezoelectric-Hydraulic Actuator
Jin, Xiao Long,Ha, Ngoc San,Li, Yong Zhe,Goo, Nam Seo,Woo, Jangmi,Ko, Han Seo,Kim, Tae Heun,Lee, Chang Seop The Korean Society for Aeronautical and Space Scie 2015 International Journal of Aeronautical and Space Sc Vol.16 No.4
The piezoelectric-hydraulic actuator is a hybrid device that consists of a hydraulic pump driven by a piezo-stack coupled to a conventional hydraulic cylinder. The actuator is of compact size, but can produce a moderate energy output. Such hybrid actuators are currently being researched and developed in many industrialized countries due to the requirement for high performance and compact flight systems. In a previous study, we designed and manufactured a unidirectional hybrid actuator. However, the blocking force was not as high as expected. Therefore, in this study, we redesigned the pump chamber and hydraulic cylinder and also improved the system by removing the air bubbles. Two different types of piezo-stacks were used. In order to achieve bidirectional capabilities in the actuator, commercial solenoid valves were used to control the direction of the output cylinder. Experimental testing of the actuator in unidirectional and bidirectional modes was performed to examine performance issues related to driving frequency, bias pressure, reed valve thickness, etc. The results showed that the maximum blocking force was measured as 970.2N when the frequency was 185Hz.