• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.18 no.5
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• pp.449-454
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• 2009

This paper presents an experimental study on the failure characteristics of SnAgCu lead-free solder balls. To estimate the effect of Ag, three types of SnAgCu balls are first prepared by varying the weight percent of Ag(1.0, 3.0, 4.0 wt%) and then analyzed by reliability tests such as thermal shock, high speed ball shear, and drop tests. Thermal shock test reveals that the higher the weight percent of Ag is, the longer the fatigue lift becomes. To the contrary, high speed ball-shear test and drop test show that the shear strength and the fracture toughness of solder balls are inversely proportional to the weight percent of Ag, respectively, Reasons for these observations will be further investigated In the future work.

• 연구논문집
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• s.34
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• pp.29-38
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• 2004

The objective of this study is to investigate the pressure drop and heat transfer characteristics of the micro-fin tubes before and after the tube-expansion process. Test tubes are single-grooved micro-fin tubes made of copper with an outer diameter of 9.52 mm before the tube-expansion. The direct heating method is applied in order to make the refrigerant evaporated in the micro-fin tubes. The test ranges of the heat flux, mass flux, and the saturation pressure are 5 to 15kW/$m^2$, 100 to 200 kg/$m^2s$ and 540 to 790 kPa, respectively. The effects of the mass flux, heat flux, and the saturation pressure of the refrigerant on the pressure drop and the heat transfer are presented for the refrigerant R22. In the test conditions of this study, the heat transfer coefficient for the micro-fin tube after the tube-expansion is about 16.5% smaller than that before the tube-expansion because the fin height of micro-fin is reduced and the fin shape becomes flatter. The micro-fin tube after the tube-expansion has about 7.7% greater average pressure drop than that before the tube-expansion process.

• International Journal of Aeronautical and Space Sciences
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• v.11 no.4
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• pp.345-350
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• 2010

The repetitive vibrating action of an aerodynamic load causes an external fuel tank's horizontal fin to experience a shorter life cycle than its originally predicted one. Store separation analysis is needed to redesign the fin of an external fuel tank. In this research, free-drop tests were conducted using 15% scaled models in a subsonic wind tunnel in order to analyze the store separation characteristics of an external fuel tank. The store separation trajectory based on grid tests was also obtained to verify the results of the free-drop tests. The results acquired from the free-drop tests correlated well with the grid tests in regards to the trajectories and behavior of the stores separated from the aircraft. This agreement was especially noted in the early stages of the store separation.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.18 no.1
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• pp.43-49
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• 2005

The package used to transport radioactive materials, which is called by the shipping cask, must be safe under normal and hypothetical accident conditions. These requirements for the cask design must be verified through test or finite element analysis. Since the cost for FE analysis is less than the one for test, the verification by FE analysis is mainly used. But due to the complexity of mechanical behaviors, the results depend on how users apply the codes and can cause severe errors during analysis. In this paper, finite element analysis is carried out for the 9 meters free drop condition of the hypothetical accident conditions using LS-DYNA3D and ABAQUS/Explicit. We have investigated the analyzing technique lot the free drop impact test of the cask and investigated several vulnerable cases. The analyzed results were compared with each other. We have suggested a reliable and relatively simple analysis technique for the drop test of spent nuclear fuel casks.

• Journal of the Korean Data and Information Science Society
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• v.28 no.5
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• pp.1145-1152
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• 2017

Environmental tests are used to verify an equipment that can withstand the rigors of harsh environments. In general, military products have lots of experiences with extreme environment compared to commercial products. Therefore, the military products used in mountains require a tailoring process about temperature drop for the environmental test. The International Organization for Standardization publishes that the coefficient of temperature drop is $-6.5^{\circ}C/1000m$ from all around the world. However, there is no the criteria in the South Korea. In this paper, we calculate the coefficient of temperature drop. Also, an equation used as a tailoring process for a low temperature test of the products has been suggested.

• Journal of Energy Engineering
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• v.15 no.3 s.47
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• pp.146-153
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• 2006

A performance test of the stainless steel based sintered metal filter was conducted on the low and intermediate level radioactive waste (LILW) vitrification process. The applicability of the metal filter was based on the test results as well. The baseline pressure drop of the metal filter was evaluated similar to the ceramic filter. During the test, when the flow rate of off-gas was $110Nm^{3}/h$, the total baseline pressure drop was shown as $92mmH_{2}O$. The total pressure drop was attributed to the filter media and the residual dust layer and the value of each was $25mmH_{2}O\;and\;67mmH_{2}O$ respectively. The SEM-EDS spectrum and micrograph of the metal filter specimen showed, no corrosion and no physical damage both at the skin membrane and at the support layer. And most of the baseline pressure drop was caused by the deposition of dust on the surface of the membrane. In conclusion, even though the filter exposure time was short at the test, the performance of the stainless steel based metal filter was acceptable for the treatment of LILW vitrification process.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.12
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• pp.1037-1044
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• 2014

In this study, we designed a drop test system considering lunar surface environment and tested landing gear of experimental lunar lander. The lunar lander would be landed at soil place for soft landing. When the lunar lander touches down, the acceleration of the lander is largely affected by mechanical characteristics of the lunar soil. Accordingly, a drop test using lunar soil is needed to verify the performance of the lunar landing gear. Because the lunar soil is not available generally, we developed a lunar simulant KAUMLS(Korea Aerospace University Mechanical Luna Simulant) based on mechanical properties of the lunar soil of NASA's LUNA PROJECT. In addition, drop tests on steel plate and dry sand are performed to evaluate impact characteristics by the surface environment.

• The Journal of Korean Physical Therapy
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• v.31 no.4
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• pp.222-227
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• 2019

Purpose: This study examined the influence of longitudinal arch on the strength and muscle activity of the abductor hallucis in the standing position in subjects with and without navicular drop signs. Methods: A sample of 34 subjects with and without navicular drop signs between 22 and 28 years of age were enrolled in this study. The strength and muscle activity of the abductor hallucis was measured using a tensiometer. The Smart KEMA System and electromyography device was used on the subjects with and without navicular drop signs. Two groups were classified using the navicular drop test to identify the longitudinal arch of the foot. The strength of the abductor hallucis was evaluated in standing, both with and without an external arch support condition. The two-way mixed ANOVA was used. The level of statistical significance was set to ${\alpha}=0.05$. Results: The strength and muscle activity of the abductor hallucis in standing was significantly higher with external arch support than that without the external arch support in the group with navicular drop signs. There was no significant difference in the abductor hallucis strength and muscle activity with and without external arch support in the subjects without navicular drop signs. Conclusions: The strength and muscle activity of the abductor hallucis in standing can be influenced by the external arch support in the group with navicular drop signs. The strength measurement of the abductor hallucis in standing should be separately performed in conditions with and without longitudinal arch of foot.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.12 s.177
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• pp.117-123
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• 2005

This paper deals with the finite element model of the monitor fur the simulation of directional free drop tests such as the backward and vertex free drop as well as the associated free-drop experiment. The model was made for an unconditional stable solution fur the explicit integration algorithm. It was found through the comparison between simulation and experimental results that the general behaviors at the time of impact were observed to well correlate with each other in terms of acceleration, displacement, contact force and stress of monitor components.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.3
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• pp.231-239
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• 2002

Experiments on the single phase cooling heat transfer and pressure drop with microfin tubes were performed using water as a test fluid. Experimental data were obtained in the range of Reynolds number 3000 ~40000 and Prandtl number 4-6. The data of microfin tubes presented the characteristics of rough surface tube in pressure drop and heat transfer Experimental data were compared with the heat transfer and friction factor correlations of smooth tubes. Heat transfer enhancements of microfin tubes were lower than pressure drop penalty factors. The helix angle is more significant parameter in both of the pressure drop and heat transfer than the relative roughness. The correlations of Nusselt number and friction factor were suggested for the tested microfin tubes. Maximum deviations between correlations and experimental data were within $\pm15$% for Nusselt number and $\pm10$% for friction factor.