• Proceedings of the KSME Conference
• /
• 2001.06a
• /
• pp.561-566
• /
• 2001

A long bar impact test to alumina plates(AD 85 and AD 90) was carried out by using fabricated impact testing apparatus. The apparatus adopting a long bar of 2.1m in length made it possible to measure directly the applied impact force to the specimen during bar impact. The dimension of specimens was $33{\times}33mm$ and thickness was 3.4mm. Confinement of D2=18mm outer diameter and D1=10.5mm inner diameter was used to provide contact pressure to the specimen. Contact pressure of p=100 or 200MPa was applied to specimen before impact test. Damage caused in those cases were compared with the case of without contact pressure. The damage of specimen was different depending upon the pressure level of confinement. The existence of confinement had suppressed the development of radial cracks from the bottom of specimen and reduced the extent of damage as compared with cases without contact pressure(p=0MPa). Because the application of contact pressure to the specimen increased the apparent flexural stiffness of specimen during bar impact, it had produced the change of developed damage in the specimen; from the radial cracks to the local contact stress dominant damage. It would contribute to the improvement of the ballistic property in ceramic plates.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.26 no.4
• /
• pp.787-793
• /
• 2002

In this study, a bar impact test of low velocity was carried out to gain an insight into the damage mechanism and sequence induced in alumina plates(AD 85 and AD 90) under impact conditions. An experimental setup utilizing an instrumented long bar impact was devised, that can measure directly the impact force applied to the specimen and supply a compressive contact pressure to the specimen. During the bar impact testing, the influences of the contact pressure applied along the impact direction to the specimen on the fracture behavior were investigated. The measured impact force profiles explained well the damage behavior induced in alumina plates. The higher contact pressure to the specimen led to the less damage due to the suppression of radial cracks due to the increase in the apparent flexural stiffness of plate. It had produced the change of damage pattern developed in the specimen; from the radial cracks to the local contact stress dominant damage. It would contribute to the improvement of the ballistic property in ceramic plates. The observed results showed the following sequence in damage developed: The development of cone crack at impact region, the formation of radial cracks from the rear surface of plate depending on the plate thickness, the occurrence of crushing within the cone envelope and the fragmentation.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2018.05a
• /
• pp.247-248
• /
• 2018

In order to secure the variability of long-life housing, dry walls are used. The composite gypsum board panel is the most frequently used infill system for the wall, and it is an excellent construction method in terms of constructability and economic feasibility. However, there are also problems such as the destruction of Ondol pipes at the bottom floor and being unable to fix the light weight steel frame (M-bar) when a variable composite gypsum board panel is used. To solve such problems, a wall with a method of fixing only the top part without fixing the bottom floor is developed, but it is difficult to identify the durability of ceiling frame according to the tensile force of stud and the safety according to the Stiffness and impact resistance (soft body) of ceiling frame. Therefore, this study verified the effectiveness of infill system for the wall by conducting experiment on the stiffness and impact resistance of composite gypsum board panel according to the reinforcement of ceiling frame (wooden frame, double saw-toothed bracket, Cross M-bar). As a result, it was possible to secure the safety of wooden frame while the impact resistance and the Stiffness of double saw-toothed bracket and cross M-bar were not secured.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.25 no.4
• /
• pp.629-636
• /
• 2001

In order to investigate the possibility of impact punching in brittle materials, an experimental setup was developed. In the setup, a long bar as a punch was used to apply the impact load to the specimen plate and measure the applied impact force during the impact punching process. Impact punching tests with various shape of punches were performed in soda-lime glass and silicon wafer under a different level of contact pressure. The damage appearance after the impact punching was examined according to the applied contact pressure. The minimum contact pressure required for a complete punching in glass specimens without development of radial cracks around the punched hole was sought at each condition. The minimum contact pressure increased with increasing the thickness of specimens and decreasing the end radius of punches. The profile of impact forces was measured during the impact punching experiment, and it could explain well the behavior of the punching process in brittle material plates. The measured impact force increased with increasing the contact pressure applied to the plates.

• Journal of Korea Water Resources Association
• /
• v.52 no.spc2
• /
• pp.801-810
• /
• 2019

This study analyzes the impact on geomorphic changes downstream due to alternate bars developed weir upstream through laboratory experiments. The disturbance, such as a spur in the side wall, of the flow at the inlet of the channel triggers the development of alternate bar upstream at the beginning of the experiment, and gradually moved downstream with keeping their shapes over time. The bed in the downstream of weir in the mid of channel scoured due to the scarcity of sediment inflow because weir upstream traps it. Moreover, bar migration speed decreases as the bars approaches to the weir with time. However, as time increases, the alternate bars upstream migrate over the weir, and sediment in the eroded bed of the weir downstream are deposited. The phase of the bar upstream changes oppositely after passing through the weir. The phase of the bar downstream changes rapidly as the shape of alternate bar is clear upstream, which is affected by the strong disturbance. The phase of bar changes, and the bar migration speed decreases gradually with time, and finally stopped due to forcing effects on the bar by the disturbance. The faster the reaction of alternate bar with a long spur, the larger the bar height formed downstream and the shorter the bar length. This means that the larger the forcing effect of bar, the more it affects the bar migration. In addition, although the size of the alternate bar increases over time, the bar doesn't migrate downstream and a forced bar is generated.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.40 no.6
• /
• pp.573-579
• /
• 2016

Studies on the deformation behavior of materials subjected to impact loads have been carried out in various fields of engineering and industry. The deformation and fracture of members for these machines/structures are known to correspond to the intermediate strain-rate region. Therefore, for the structural design, it is necessary to consider the dynamic deformation behavior in these intermediate strain-rate ranges. However, there have been few reports with useful data about the deformation and fracture behavior at intermediate strain-rate ranges. Because the intermediate strain-rate region is located between quasi-static and high strain-rate regions, it is difficult to obtain the intermediate strain-rate using conventional reasonable test equipment. To solve this problem, in this study, the measurement reliability of the constructed drop-bar impact tensile test apparatus was established and the dynamic behavior at the intermediate strain-rate range of carbon steels was evaluated by utilizing the apparatus.

• Journal of Biosystems Engineering
• /
• v.8 no.2
• /
• pp.18-25
• /
• 1983

The binders introduced in Korea were originally designed to be used for Japonica varieties which have realtively long stem and are highly resistant to shattering. In order to use it for Tongil varieties which are short and easy to be shattered, mechanical modifications are necessary to reduce a grain loss incurred during its operation. This study was intended to investigate the binding unit, one of the major factors affecting grain losses. The binding parts of three binders used in Korea were analyzed and the grain loss was experimentally assessed for these binders. The results obtained from this study are summarized as follows: 1. From the motion analysis of discharge mechanism, the trajectory of the discharge arm appeared to be either circular or skewed elliptic. The velocity of a circular path mechanism was constant and smaller than that of a skewed elliptic path mechanism. The discharge grain loss of the former was about twice less than that of the latter. 2. It was found that the grain loss incurred due to the collision of the paddy bundles and ground was considerably high for Tongil varieties. The auxiliary discharge bar gave a significant influence on the motion and posture of the bundles, and the degree of impact on ground. 3. The installation of an auxiliary bar, which guides the paddy bundles smoothly to ground in order to reduce impact when the bundles fall down on ground, appeared to be very effective since the grain losses could be decreased by about 1.6 percentage point. However, the guide bar should be installed after some mechanical modification to reduce the velocity of discharge arm has been made.

• Progress in Superconductivity and Cryogenics
• /
• v.10 no.1
• /
• pp.62-66
• /
• 2008

The characteristic of the superconducting magnetic energy storage(SMES) system is faster response, longer life time, more economical, and environment friendly than other uninterruptible power supply(UPS) using battery. So, the SMES system can be used to develop methods for improving power quality where a short interruption of power could lead to a long and costly shutdown. Recently, cryogen free SMES has developed using BSCCO(Bismuth Strontium Calcium Copper Oxide) wire. We fabricated and tested the conduction cooling system for the 600 kJ class HTS SMES. The experiment was accomplished for the simulation coils. The simulation coils were made of aluminium, it is equivalent to thermal mass of 600 kJ HTS SMES coil. The coil is cooled with two GM coolers through the copper conduction bar. In this paper, we report that the test results of cool-down and heat loads characteristics of the simulation coils. The developed conduction cooling system adapted to 600 kJ HTS SMES system and cope with the unexpected sudden heat impact, too.

• Annals of Hepato-Biliary-Pancreatic Surgery
• /
• v.27 no.3
• /
• pp.292-300
• /
• 2023

Backgrounds/Aims: Current literature presents limited data regarding outcomes following conversion at the time of minimally invasive pancreaticoduodenectomy (MI-PD). Methods: The National Cancer Database was queried for patients who underwent pancreaticoduodenectomy. Patients were stratified into three groups: MI-PD, converted to open pancreaticoduodenectomy (CO-PD), and open pancreaticoduodenectomy (O-PD). Multivariable modeling was applied to compare outcomes of MI-PD and CO-PD to those of O-PD. Results: Of 17,570 patients identified, 12.5%, 4.2%, and 83.4% underwent MI-PD, CO-PD, and O-PD, respectively. Robotic pancreaticoduodenectomy (R-PD) resulted in a higher lymph node yield (n = 23.2 ± 12.2) even when requiring conversion (n = 22.4 ± 13.2, p < 0.001). Margin positivity was higher in the CO-PD group (26.6%) than in the MI-PD group (21.3%) and the O-PD (22.6%) group (p = 0.017). Length of stay was shorter in the MI-PD group (laparoscopic pancreaticoduodenectomy 10.4 ± 8.6, R-PD 10.6 ± 8.8) and the robotic converted to open group (10.7 ± 6.4) than in the laparoscopic converted to open group (11.2 ± 9) and the O-PD group (11.5 ± 8.9) (p < 0.001). After adjusting for patient and tumor characteristics, both MI-PD (odds ratio = 1.40; p < 0.001) and CO-PD (odds ratio = 1.24; p = 0.020) were significantly associated with an increased likelihood of long-term survival. Conclusions: CO-PD does not negatively impact perioperative or oncologic outcomes.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2004.05a
• /
• pp.395-399
• /
• 2004

Four microalloyed steels containing B were investigated in terms of hardenability, mechanical properties and microstructure depending upon the cooling rates in order to develop the steel grade for the cold forged fasners. The alloy with the largest DI value among 4 alloys, which contains $0.12\%\;C,\;1.54\%\;Mn,\;0.65\%\;Cr,\;0.11\%V,\;0.040\%Ti\;and\;0.0033\%B$, showed the larest shift to the right hand side in the TTT diagram, implying the wide allowable cooling rate range subsequent to hot rolling in long bar processing, Mechanical tests indicated that yield strength are dependent upon the DI value in water quenched specimens but other properties showed almost the same values. In the same grade of steel, the increase in cooling rates causes the decrease in elongation but the increase in strength, reduction of area and Charpy impact values. Microstructural examination in steel grade with the larest DI values revealed martensitic structure In the water quenched state, a mixture of martensite and bainite in the oil quenched, and ferrite + pearlite in the air cooled and the forced air cooled but the latter showed finer microstructure.