• International Journal of Reliability and Applications
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• v.1 no.1
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• pp.89-104
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• 2000

Accelerated testing consists of a variety of test methods for shortening the life of products or hastening the degradation of their performance. This paper presents practical, modern statistical methods for evaluating the reliability of Nickel-Cadmium batteries at their design temperature of 2$0^{\circ}C$ by accelerated life test. Batteries have been life tested at three high temperature conditions, 50, 60, 7$0^{\circ}C$, respectively to yield failures quickly. The failures have been observed and judged by means of charge and discharge current integration. Analyses of life data from those conditions resulted in the Weibull distribution, which has been verified on the ground of the Kolmogorov-smirnov test and the pairwise t-test. Life data are modeled according to the Arrhenius life-temperature relationship. The mean life of tested batteries is assessed at about 590 cycles, and the activation energy of this chemical reaction is concluded to be 0.39eV as results. This study provides procedures for estimating the reliability of batteries in a short period, which has little been possible in domestic industries. The results can be applied in many fields such as proof testing, acceptance testing, and estimating assurance periods.

• Journal of Aerospace System Engineering
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• v.15 no.3
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• pp.105-113
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• 2021

This paper delineates the applied thermal environmental test profiles using test conditions and procedures based on MIL-STD-810 Method 501 (High Temperature Test Method) and Method 502 (Low Temperature Test Method). The test profiles have been optimized in order to comply with export customer's requirements and product reliability in high and low temperature environment for XKT-1 (KT-1 Export Version) aircraft. Additionally, the tests are suitable for large sized environmental chambers, which is one of the facilities of ADD (Agency for Defense Development) according to ETEMP (Environmental Test and Evaluation Master Plan). The results of these test profiles and test executions satisfy the customer requirements and product reliability. The present paper can be applied to the other export programs with more severe temperature conditions.

• Journal of Korean Society for Atmospheric Environment
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• v.21 no.2
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• pp.227-242
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• 2005

The aim of this study is to relieve the poor ventilation problem of the diesel locomotive engine load test building, located in an urban area. This paper evaluates the ventilation performances of the studied load test building based on the temperature measurement experiment and the computational fluid dynamics (CFD) during the engine load test. The temperature rise caused by the radiator blower of the building was turned out to be the main cause of disturbing the thermal conditions of the building. The indoor temperature distributions simulated by Fluent were validated with the temperature measurement results obtained from the studied building. The simulation results indicated that the comfort condition of this building was poor We suggested several remedial changes in the duct structure of this building for the improvement of the comfort conditions. In addition, a prototype drawing combining several improved design options was proposed. and then the simulation of the temperature distribution in the proposed prototype was performed. The result indicated that the indoor thermal condition of this proposed building was improved when compared with that of the current building.

• Transactions of the Korean Society of Automotive Engineers
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• v.4 no.1
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• pp.198-207
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• 1996

The effect of temperature, frequency and microstructure on fatigue crack propagation property of Ti-6A1-4V alloy has been investigated. The temperatures employed were room temperature, 20$0^{\circ}C$ and 40$0^{\circ}C$. The frequencies were 20Hz and 8 Hz. The microstructures tested were equiaxed and bimodal microstructures. Mechanical properties and fatigue crack growth rates were measured in different test conditions. From the experimental results, following conclusions were obtained. Bimodal microstructure showed superior fatigue crack growth resistance to equiaxed microstructure. Under all test conditions, fatigue crack growth rate increased with test temperature. Wine the frequency decreasing from 20Hz to 8Hz, fatigue crack growth rate increased.

• Journal of the Korean Society for Precision Engineering
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• v.12 no.7
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• pp.178-188
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• 1995

A study on the temperature distribution of tungsten carbide alloy steel(WC-Co) in surface grinding was conducted to improve the surface finish and to find optimum grinding conditions which would lead to efficient grinding operation by theoretical finite element method analysis and experimental test of workpiece under various conditions. Based on the comparixion of test results and FEM analysis data, it is concluded that the FEM computer simulation of heat transfer is useful in predicting the temperature distribution of test material that the increase of temperature is more infuleneced by the grinding depth than the grinding speed. And that the grinding energy flux of dey grinding is 4 to 6 time greater than wet grinding regardless of grinding speed and finally that the heat transfer does not take place in depth deeper than 3mm from the grinding surface.

• Aerospace Engineering and Technology
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• v.9 no.1
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• pp.35-41
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• 2010

The temperature of the flight objects in high speed increases due to the aerodynamic heating. MINIVER and CFD approach are used to predict the aerodynamic heating conditions of KSLV-I. MINIVER is based on the empirical method. And the CFD approach predicts the aerodynamic heating conditions after the analysis of the surface temperature and the surface heat flux directly. In this study, the aerodynamic heating conditions using CFD approach are considered. The PLF temperature for these aerodynamic heating conditions is compared with the flight test data of KSLV-I.

• Journal of Applied Reliability
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• v.18 no.2
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• pp.95-103
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• 2018

Purpose: Environment test aim to validate the guarantee of required capability of materiel against various environment conditions which exposed during materiel life-cycle. In this paper, environment test design procedure and tailoring guideline for Korean peninsula and periphery climate are proposed. Methods: To design tailoring guideline, climate data which are regarding Korean peninsula and periphery regions provided from Korea Meteorological Administration (KMA) and National Climatic Data Center (NCDC) are used. Conclusion: For effective environment test, it is important that environment test have to design in considering environment conditions during materiel life-cycle. It is concluded that the high temperature test level can be softer than the test criteria in MIL-HDBK-310, however, the low temperature test level will be expected to be $2{\sim}6^{\circ}C$ harsher than MIL-HDBK-310.

• Journal of Ocean Engineering and Technology
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• v.22 no.1
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• pp.75-82
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• 2008

A vibration-based damage-monitoring scheme is proposed that would generate an alarm showing the occurrence and location of damage under temperature-induced uncertainty conditions. Experiments on a model plate-girder bridge are described, for which a set of modal parameters was measured under uncertain temperature conditions. A damage-alarming model is formulated to statistically identify the occurrence of damage by recognizing the patterns of damage-driven changes in the natural frequencies of the test structure and by distinguishing temperature-induced off-limits. A damage index method based on the concept of modal strain energy is implemented in the test structure to predict the location of damage. In order to adjust for the temperature-induced changes in the natural frequencies that are used for damage detection, a set of empirical frequency correction formulas is analyzed from the relationship between the temperature and frequency ratio.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.171-172
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• 2006

The effect of the preparation factors, such as the feeding mode and rate of raw materials, the reaction temperature and the surfactant on the size distribution of molybdenum trioxide particle were investigated by orthogonal test. The optimum conditions for the preparation of $MoO_3$ precursors are as following; opposite feeding fast, reaction temperature of $60^{\circ}C$ and adding dispersant.

• Journal of the Korean Society for Heat Treatment
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• v.29 no.6
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• pp.284-291
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• 2016

High temperature alloy steel such as Ni-Cr-Mo-V material has excellent properties of high strength and high heating resistance. It has been used for several military weapon components such as gun barrel of a warship, turbine rotor and turbine disk for nuclear power plant. Being curious about this material required excellent wear resistance and durability in extreme environmental conditions. A dry wear test at the ambient air and Ar gas conditions in the room temperature were performed in this study. What's more a lubricant wear test at different temperature was conducted. In addition that DLC was coated on Ni-Cr-Mo-V alloy steel substrate with a thickness of $3{\mu}m$, a property of it was compare with lubricant conditions. All the coefficient of friction and wear volume, comparing with DLC coated specimens. The test parameters were selected as follows: 10 N for normal load; 80 rpm for sliding wear speed; and 300 m for the sliding wear distance.