• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.3
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• pp.39-46
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• 2020

Carbonation is a deterioration which degrades structural and material performance by permitting CO₂ and corrosion of embedded steel. Service life evaluation through deterministic method is conventional, however the researches with probabilistic approach on service life considering loading and cold joint effect on carbonation have been performed very limitedly. In this study, probabilistic service life evaluation was carried out through MCS (Monte Carlo Simulation) which adopted random variables such as cover depth, CO₂ diffusion coefficient, exterior CO₂ concentration, and internal carbonatable materials. Probabilistic service life was derived by changing mean value and COV (Coefficient of variation) from 100 % to 300 % and 0.1 ~ 0.2, respectively. From the analysis, maximum reduction ratio (47.7%) and minimum reduction ratio (11.4%) of service life were obtained in cover depth and diffusion coefficient, respectively. In the loading conditions of 30~60% for compressive and tensile stress, GGBFS concrete was effective to reduce cold joint effect on carbonation. In the tensile condition, service life decreased linearly regardless of material types. Additionally service life rapidly decreased due to micro crack propagation in the all cases when 60% loading was considered in compressive condition.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.3
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• pp.259-265
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• 2016

Recently, life prediction models for Pb-based and Pb-free solders used in chip resistor assemblies under thermal cycling have been introduced. The models suggest that the field lifetimes of Pb-free solders would be better than those of Pb-based solders when used for chip resistors under thermal cycling conditions, while the lifetime of the chip assemblies under accelerated test conditions show a reverse relationship. In this study, the prediction models were verified by applying the model to another research case. Finite element models were built, thermal cycling conditions were applied, and the energy densities were calculated. Finally, life prediction analysis was conducted for the cases where Pb-based and Pb-free solders were used. The prediction results were then compared with the test data of the case. It was verified that the predictions of the developed life cycle models are on the practical scale.

• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.4
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• pp.315-321
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• 2003

The integrity of the turbine rotors can be assessed by measuring the material properties at service temperature. In order to evaluate the remanent life of turbine rotor steel nondestructively, a measurement system of reversible magnetic permeability using an alternating perturbing magnetic field was constructed. We present a new non-destructive method to evaluate the remanent life of 1Cr-1Mo-0.25V steel using the value of reversible magnetic permeability. This method is based on the existence of reversible magnetic permeability in the differential magnetization around the coercive field strength. We measured the first harmonics voltage induced in a coil using a lock-in amplifier tuned to an exciting frequency. The Results of reversible magnetic Permeability and Wickers hardness on the aged samples show that the peak interval of reversible magnetic permeability (PIRMP) and Vickers hardness decreases as aging time increases. A softening curve is obtained from the correlation between Vickers hardness and the PIRMP. This curve can be used as a non-destructive method to evaluate the remanent life of turbine rotor steel.

• Journal of Korean Society of Steel Construction
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• v.22 no.3
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• pp.209-218
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• 2010

The fatigue phenomenon, which is induced by stress accumulation due to the repeated loading of vehicles in the long term, is one of the main factors of the span of life of a steel bridge. In this paper, the effects of traffic properties on the fatigue life of ordinary short- and medium-span steel plate girder bridges that are exposed to relatively large dynamic effects are investigated. From the analysis, it was known that the fatigue life of the bridge becomes shorter with increasing traffic volume and number of large vehicles, and is affected by the weights of the vehicles. Based on the analysis results, a new parameter that can represent the traffic property that affects the fatigue life of the subject bridge is suggested, and the validity of the parameter is confirmed.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.05a
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• pp.385-390
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• 2009

The gas turbine engine structures usually are placed on high thermal mechanical stress condition. For general low cycle fatigue evaluation, simple fatigue criterion based on critical plane approach is developed. LCF life of turbine wheel is evaluated with this criterion and process contrived together.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.11A
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• pp.995-1003
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• 2005

Since the sensor network nodes have a small size and limited battery power, there have been many studies for reducing their energy consumption. Each sensor node can show different energy usage according to the frequency of event sensing and data transmission, and thus they have different lifetime. So, some nodes may run out of energy that causes disconnection of paths and reduction of network lifetime. In this paper, we propose a new energy-efficient routing algorithm for sensor networks that selects a least energy-consuming path among the paths formed by node with highest remaining energy and provides long network lifetime and somewhat uniform energy consumption by nodes. Simulation results show that our algorithm extends the network lifetime and enhances the network reliability by maintaining relatively uniform remaining energy distribution among sensor nodes.

• The Korean Journal of Applied Statistics
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• v.34 no.5
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• pp.735-744
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• 2021

Maintaining the lifetime of a product is one of the objectives of quality control. In real processes, most samples are constructed with censored data because, in many situations, we cannot measure the lifetime of all samples due to time or cost problems. In this paper, we propose two cumulative sum (CUSUM) control charting procedures to monitor the mean of type I right-censored lognormal lifetime data. One of them is based on the likelihood ratio, and the other is based on the binomial distribution. Through simulations, we evaluate the performance of the two proposed procedures by comparing the average run length (ARL). The overall performance of the likelihood ratio CUSUM chart is better, especially this chart performs better when the censoring rate is low and the shape parameter value is small. Conversely, the binomial CUSUM chart is shown to perform better when the censoring rate is high, the shape parameter value is large, and the change in the mean is small.

• Journal of the Korean Recycled Construction Resources Institute
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• v.9 no.3
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• pp.236-245
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• 2021

It is very important for structure designer to understand the service life variation since a wide range of service life is evaluated with changing exposure conditions and design parameters. Recently, for zero-carbon, waste plastic has been used for fuel for clinker production and this yields increase in chloride content in cement. This study is for evaluation of changing service life in the concrete with increasing initial chloride content due to usage of plastic-SRF(Solid Refuse Fuel) considering various exposure conditions and design parameters. For this, 4 levels of initial chloride content were assumed, and the service life was assessed using LIFE 365 program considering various environmental conditions including 3 levels of surface chloride content. As for analysis parameters, critical/initial chloride content, blast furnace slag powder replacement ratio, W/B(Water to Binder) ratio, cover depth, and unit mass for binder are adopted. Service life decreases with increasing initial chloride content and a significant reduction of service life is not evaluated permitting up to 1,000ppm of initial chloride content. With increasing slag replacement ratio, a longer service life can be secured since blast furnace slag powder has the effect of reducing the diffusion of external chloride ions and fixing the free chloride. It is thought that increasing initial chloride content up to European standard is helpful for enhancing sustainability and reducing carbon emission. Though the reduction in service life due to an increase in the initial chloride content is not significant in slag-concrete with low surface chloride content, careful consideration for mixing design should be paid for the exposure environment with high surface chloride content.

• Korean journal of applied entomology
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• v.15 no.4 s.29
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• pp.179-184
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• 1976

Laboratory experiments were conducted to clarity the early-spline host·selectivity by the small brown planthopper(SBPH), Laodelphax striatellus Fallen, and green rice Leafhopper(GLH), Nephotettix cincticeps Uhle., on the bailey (the variety Suweon #18) and water foxtail (Alopeculus aequadis Sosbol). The host selectivity was evaluated on the bases of feeding and ovipositional perferences of the insects on the plants and their biological effects on the plants. The nymphs of SBPH much more preferred barley for feeding than water forxtail, while the nymphs of GLH relatively prefered water foxtail. There was no significant difference in ovipositional preference by SBPH among the test plants, and ovipositional preference by GLH Ivas significantly lower on barley and water foxtail than on rice. Nymphal growth an4 adult emergence of SBPH were significantly faster and higher on barley than on water foxtail. No adult emergence of GLH was observed on barley, and adult emergence was still quite lower even on water foxtail. The adult of SBPH fed on barley showed longer longevity aad higher fecundity than that of SBPH from water foxtail and rice. The adult GLH fed ell water foxtail shorted relatively shorter longevity and to)ver fecundity than that of GLH on rice. In conculsion, barley seems to be more adequate for spring host of SBPH than water foxtail, but barley may not be quite adequate for spring host of GLH. At presont moment, GLH seems rather to primarily select the water foxtail than barley as a spring host, even if the water foxtail is not so adequate for development of GLH.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.7 no.1
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• pp.83-92
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• 1987

Fatigue fracture of reinforced concrete structures are characterized by considerably larger strains and microcracking as compared to fracture of R.C. structures under static loading. The strain of stirrup is increased suddenly by the occuring of inclined crack and the average strain ${\epsilon}_{\omega}$ of all stirrups in a structure at maximum load increase approximately in proportion to log N. The structures critical in longitudinal reinforcement seemed to have an endurance limit of 60~70 percent of static ultimate strengths for 1,000,000 cycles. In this test, the average fatigue strength at 1,000,000 cycles for all structures tested was approximately 65 percent of the static ultimate strength.