• Corrosion Science and Technology
• /
• v.4 no.4
• /
• pp.147-154
• /
• 2005

The creep resistance of geogrids is one of the most significant long-term safety characteristics used as the reinforcement in slopes and embankments. The failure of geogrids is defined as creep strain greater than 10%. In this study, the accelerated creep tests were applied to polyester geogrids at various loading levels of 30, 50% of the yield strengths and temperatures using newly designed test equipment. Also, the new test equipment permitted the creep testing at or above glass transition temperature($T_g$) of 75, 80, $85^{\circ}C$. The time-dependent creep behaviors were observed at various temperatures and loading levels. And then the creep curves were shifted and superposed in the time axis by applying time-temperature supposition principles. The shifting factors(AFs) were obtained using WLF equation. In predicting the lifetimes of geogrids, the underlying distribution for failure times were determined based on identification of the failure mechanism. The results confirmed that the failure distribution of geogrids followed Weibull distribution with increasing failure rate and the lifetimes of geogrids were close to 100 years which was required service life in the field with 1.75 of reduction factor of safety. Using the newly designed equipment, the creep test of geogrids was found to be highly accelerated. Furthermore, the time-temperature superposition with the newly designed test equipment was shown to be effective in predicting the lifetimes of geogrids with shorter test times and can be applied to the other geosynthetics.

• Composites Research
• /
• v.26 no.2
• /
• pp.79-84
• /
• 2013

The prediction and analysis procedure of fatigue damage crack growth life for a stiffener bonded composite laminate panel including center hole and edge notch damage, was studied. It was performed on the basis of fatigue damage growth test results on a laminated skin panel specimens and the analysis results of stress intensity factor for the stiffener bonded composite panel. According to the comparison between experimental test and prediction results of fatigue damage growth life, it was concluded that the residual strength and damage tolerance assessment can be carried out along to the edge notch crack growth.

• Proceedings of the KIEE Conference
• /
• 2006.04b
• /
• pp.130-132
• /
• 2006

For the reliability assessment of solenoid actuator, firstly, we analyzed the cause of major failures and the effect of each failure modes through FMEA and FTA, and decided the main test items through 2-stage QFD. And then, as a measure of life of solenoid actuator, TypeII censored five data were collected from and operation test which was performed as the life test of solenoid actuator. In this paper, we present the reliability parameters of solenoid actuator like shape parameter, scale parameter, etc., which they are produced by MINITAB analysis and marking of Weibull probability paper using the measure of life, and also present the 6 kinds of detailed failure mode analysis.

• Journal of Applied Reliability
• /
• v.9 no.1
• /
• pp.37-45
• /
• 2009

Recently mechanical watt-hour meters are being replaced by electronic watt-hour meters. The replacement period of mechanical watt-hour meters is 7 years. This period is based on long term historical data. The replacement period of electronic watt-meters is also 7 years. This period is determined using the replacement period of mechanical watt-hour meters. However lifetime of mechanical watt-hour meters is different from the lifetime of electronic meters. In order to determine desirable replacement period of electronic watt-hour meters, accelerated life tests of major components in electronic watt-hour meters were performed. The test results showed that LCD was the component which had the shortest lifetime. In this paper, lifetime of electronic watt-hour meters manufactured by 3 company was estimated and life test standard for LCD was developed.

• Environmental Analysis Health and Toxicology
• /
• v.22 no.2 s.57
• /
• pp.171-175
• /
• 2007

Indigenous species means a species that is likely, due to historical presence, to occur at a specified site for some portion of its life span. Therefore, indigenous species can be useful as an indicator to assess environmental risk caused by hazardous chemicals in a specific site. So far a few toxicity studies using freshwater species which are indigenous to Korea have been carried out. In this study, a freshwater shrimp (Neocardina denticulata) indigenous to Korea was used for acute toxicity test of heavy metals. Neocardina denticulata were exposed to cadmium chloride $(CdCl_2)$, copper chloride $(CuCl_2)$ and zinc chloride $(ZnCl_2)$ using automatic flow-through system for 96 hours. The 96h LC50s were calculated as 0.043 $(0.042{\sim}0.045)mg\;CdCl_2/L,\;0.104(0.098{\sim}0.113)mg\; CuCl_2/L\;and\;2.021\;(1.633{\sim}2.594)mg\;ZnCl_2/L$. When compaired with some international standard species such as medaka(Oryzias latipes), Neocardina denticulata had high sensitivity. Therefore, this study suggested that Neocardina denticulata have possibilities for a sensitive test species to test heavy metal toxicity in aqua-system.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
• /
• 2009.05a
• /
• pp.21-23
• /
• 2009

The paper is to evaluate for reliability of LED Modules for Lighting by ALTs(Accelerated Life Tests). The recently, some of KS were established by law of LED Modules for Lighting(KS C 7651, KS C 7652 and KS C 7653), but reliability assessment methods of LED Modules for Lighting were not established. Therefore, the paper aided companies to test methods for accelerated life testing by themselves.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
• /
• 2009.05a
• /
• pp.208-210
• /
• 2009

The paper is to evaluate for reliability of LED Channel Modules by ALTs(Accelerated Life Tests). The recently, some of KS were established by law of LED Lamps for Lighting(KS C 7651, KS C 7652 and KS C 7653), but reliability assessment methods of LED Channel Modules were not established. Therefore, the paper aided companies to test methods for accelerated life testing by themselves.

• Journal of Oriental Neuropsychiatry
• /
• v.7 no.1
• /
• pp.15-37
• /
• 1996

This thesis investigates 220 female students ranging from 19 to 26 years old attending universities in the Wonju area to determine the correlations between mental health and the density of serum iron . According to their serum iron levels, they were divided into three groups and analyzed with the GARS Scale Assessment and the THI Test Assessment. The results are as follows;1. On the comprehensive GARS Scale tests, for all groups, task, occupation and levels of university-related frustration(1) marked the highest scores.2. On the comparative assessment of each group's GARS Scale scores, Group A showed higher stress perception in terms of personal relationship(2,3) than any orther groups. 3. On the comprehensive THI test scores coverring all groups, Multiple subjective symptoms(I) marked the highest scores. 4. On the comparative assessment of each group's THI test scores, Group A showed higher Multiple subjective symptoms(I) and Irregularities of life(G) than any orther groups.5. Comparing and analyzing the GARS Scale Assessment and the THI Test, we found that Group A showed high stress perception, which may cause psychosomatic diseases such as 'yu zheng(鬱證;melancholia). With those results, we can see that the contant of serum iron is correlated to stress perception and the condition of mental health. In the future studies using the GARS Scale and the THI Test, it will be necessary to examine more subject groups in terms of multi-aspects and to investigate the standard group in more detail.

• Polymer(Korea)
• /
• v.32 no.5
• /
• pp.440-445
• /
• 2008

The failure mechanism and failure morphology of linear low density polyethylene (LLDPE) tubing under hydrostatic pressure were investigated. Microscopic observations using video microscope and scanning electron microscope indicate that the failure mode is a brittle fracture including cracks propagated from inner wall to outer wall. In addition, oxidation induction time and Fourier transform infrared spectroscopy results show the presence of exothermic peak and the increase in carbonyl index on the surface of fractured LLDPE tubing, due to thermal-degradation. An accelerated life test methodology and testing system for LLDPE tubing are developed using the relationship between stresses and life characteristics by means of thermal acceleration. Statistical approaches using the Arrhenius model and Weibull distribution are implemented to estimate the long-term life time of LLDPE tubing under hydrostatic pressure. Consequently, the long-term life time of LLDPE tubing at the operating temperature of $25^{\circ}C$ could be predicted and also be analyzed.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.37 no.9
• /
• pp.1169-1174
• /
• 2013

Most products are indeed governed by multiple failure modes. However, there are few cases in which reliability analysis applies to only one failure mode at a time. Furthermore, reliability data do not include information about failure modes, or the reliability analysis is performed using a representative failure mode. The Weibull shape parameter for failure modes is more important than one for products in the reliability qualification test. This paper presents reliability analysis methods for a mechanical component with multiple failure modes. These methods include the competing failure modes (CFM) method and the mixed Weibull method. Pneumatic cylinder test data with three failure modes are presented to estimate the shape parameter for each separate failure mode. In addition, reliability measures (B10 life, characteristic life) of the pneumatic cylinder considering three failure modes were compared with those assuming a single failure mode.