• Journal of Applied Reliability
• /
• v.10 no.1
• /
• pp.25-38
• /
• 2010

In this paper, an accelerated degradation test procedure for an electronic appliance compressor is proposed. We investigate the amount of wear of the compressor and consider several factors as accelerating factors. Finally we select the operating pressure as a main accelerating factor. The test condition of accelerated degradation test is determined. The modified accelerating test reduces the test time in design phase by using the suggested accelerating factor.

• Journal of Applied Reliability
• /
• v.9 no.1
• /
• pp.47-58
• /
• 2009

In this paper, an accelerated life test procedure for a vacuum cleaner motor is proposed. We investigate the failure mechanism of the motor and select some accelerating factors and determine the orifice size as a key accelerating factor. Three stress levels of orifice size are tested and the failure data with censored data are analyzed. The modified accelerating test will reduce the test time in design phase by using the accelerating factor.

• Proceedings of the KSME Conference
• /
• 2003.11a
• /
• pp.556-561
• /
• 2003

Flight bodies are subject to highly unstable and severe flow conditions during taking-off and landing periods. In this situation, the flight bodies essentially experience accelerating or decelerating flows, and the aerodynamic characteristics can be completely different from those of steady flows. In the present study, unsteady aerodynamic characteristics of an aerofoil accelerating at subsonic speeds are investigated using a computational method. Two-dimensional, unsteady, compressible Navier-Stokes simulations are conducted with a one-equation turbulence model, Spalart-Allmaras, and a fully implicit finite volume scheme. An acceleration factor is defined to specify the unsteady aerodynamics of the aerofoil. The results show that the acceleration of the subsonic aerofoil generally leads to a variation in aerodynamic characteristics and it is more significant at angles of attack.

• Archives of Plastic Surgery
• /
• v.33 no.1
• /
• pp.1-4
• /
• 2006

Cryopreserved fibroblast implants represent a major advancement for healing of chronic wounds. Bone marrow stromal cells, which include the mesenchymal stem cells, have a low immunity-assisted rejection and are capable of expanding profoundly in a culture media. Therefore, they have several advantages over fibroblasts in clinical use. The ultimate goal of this study was to compare the wound healing accelerating growth factor secretion of the bone marrow stromal cells with that of the fibroblasts and this pilot study particularly focuses on the growth factor secretion to accelerate wound healing. Bone marrow stromal cells and fibroblasts were isolated from the same patients and grown in culture. At 1, 3, and 5 days post-incubating, secretion of basic fibroblast growth factor(bFGF), vascular endothelial growth factor (VEGF), and transforming growth factor beta(TGF-${\beta}$) were compared. In TGF-${\beta}$ secretion fibroblasts showed 12~21% superior results than bone marrow stromal cells. In contrast, bFGF levels in the bone marrow stromal cells were 47~89% greater than that in fibroblasts. The VEGF levels of the bone marrow stromal cells was 7~12 fold greater than that of the fibroblasts. Our results suggest that the bone marrow stromal cells have great potential for wound healing accelerating growth factor secretion.

• Journal of Applied Reliability
• /
• v.18 no.3
• /
• pp.193-200
• /
• 2018

Purpose: In this study, the life of the motor is investigated by performing the accelerated life test with the brush wear of the industrial cleaner motor as the main failure mode. Methods: The accelerating stress factor of the accelerated life test is a voltage, which can increase the number of revolutions of the motor to accelerate the brush wear due to the friction between the brush and the commutator. Also, the accelerating stress level was determined after determining the maximum allowable level of the voltage through the preliminary test. Results: The motor failure time at each accelerating stress level was predicted by regression analysis with brush wear length as performance degradation data. The main failure mode, which is brush wear, of the motor was reproduced by this test. The shape parameter of the Weibull distribution was confirmed to be the same statistically at all accelerating stress levels by the likelihood ratio test. Conclusion: The life of the motor was investigated by performing the accelerated life test with the brush wear of the industrial cleaner motor as the main failure mode. Through the accelerating test method of the cleaner motor, various life expectancy and life expectancy of the acceleration factor are predicted.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2000.10a
• /
• pp.25-28
• /
• 2000

In this paper, the technology for accelerating degradation & life estimation on the traction motor was introduced with the stator form-winding sample coils of the 200 Class insulation system The accelerative degradation was performed in 10 cycles, which were composed of thermal stress, fast rising surge voltage, vibration, water immersion and overvoltage applying. After aging of 10 cycles, condition diagnosis test such as insulation resistance & polarization index, capacitance & dielectric loss and partial discharge properties were investigated in the temperature range of $20{\sim}160^{\circ}C$. Relationship between degradation conditions and diagnosis results were analyzed to find an dominative degradation factor at the end-life point

• Proceedings of the Korea Concrete Institute Conference
• /
• 2004.11a
• /
• pp.317-320
• /
• 2004

The setting time is very important factor affecting the quality of tunnel lining and reinforcement of sloped slope etc. Currently, however, the quality criteria of accelerating admixture to improve it is not established well. In this study, evaluation on setting time measuring methods of a cement accelerating admixture was performed. Six types of measuring methods were checked and a proper measuring method of the admixture were proposed as fellows: (1) the temperature of materials used shall be controlled exactly and (2) to evaluate the properties of it, an admixture usage of $5\%$ (ratio of cement weight) is recommended.

• Journal of the Korea Concrete Institute
• /
• v.17 no.6 s.90
• /
• pp.879-884
• /
• 2005

The setting time is a very important factor affecting the quality of tunnel lining and reinforcement of inclined slope etc. Currently, however, the quality criteria of accelerating admixture to improve it is not established well. In this study, evaluation on setting time measuring methods of cement mixed a accelerating admixture (AA) was performed using Gillmore and Vicat needle test methods. For both test methods, the setting time for addition at a time was better than post addition regardless of initial setting and final setting. For Gillmore needle test method, two types of measuring methods were selected and it is noted that setting time with cement type under the same accelerating admixture can be different. Accordingly, manufacturing company shall develop a less sensitive accelerating admixture to cement type. For Vicat needle test method, six types of measuring methods were used and a proper measuring method of the admixture were proposed as follows: (1) the temperature of materials used shall be controlled exactly and (2) to evaluate its properties, an admixture usage of $5\%$ (ratio of cement weight) is recommended.

• Journal of Welding and Joining
• /
• v.15 no.3
• /
• pp.79-87
• /
• 1997

This study was performed to evaluate basic characteristics of electron beam welding process for a 9% Ni steel plate. The principal welding process parameters, such as working distance, accelerating voltage, beam current and welding speed were investigated. The AB (Arata Beam) test method was also applied to characterize beam size and energy density of the electron beam welding process. The electron beam size was found to decrease with the increase of accelerating voltage and the decrease of working distance. So, in case of high voltage (150kV), spot size and energy density of electron beam were revealed to be 0.9mm and $6.5\times10^5W/\textrm{cm}^2$ respectively. The accelerating voltage among the welding parameters was found to be the most important factor governing the penetration depth. When the accelerating voltage of electron beam was low ($\leq$90kV), beam current and welding speed did not affect on the penetration depth significantly. However, in case of high voltage ($\geq$120kV), the depth of penetration increased very sensitively with the increase of beam current and the decrease of welding speed.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2004.03a
• /
• pp.347-352
• /
• 2004

The unsteady aerodynamic characteristics of an aerofoil gradually accelerating or decelerating at subsonic speeds are investigated through two-dimensional, unsteady, compressible Navier-Stokes simulations. An acceleration factor is defined to provide various acceleration or deceleration characters of the time-dependent flow over the aerofoil. The results show that an increase in the absolute value of the non-dimensional acceleration factor leads to a lesser change in the location and range of flow featues such as shockwave and boundary layer separation in a specific time range. Generally, the gradual speed-up and speed-down of the subsonic aerofoil results in different aerodynamic characteristics whose changes are more significant at angles of attack.