• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.10a
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• pp.106-109
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• 2002

With the wide application of fiber-reinforced composite material in aero-structures and mechanical parts, the design of composite joint have become a very important research area because they are often the weakest areas in composite structures. In this paper, the failure area index method to predict the strength of the mechanically fastened composite joint which has the same stacking sequence was used and evaluated. By the used failure area index method, the strength of the mechanically fastened composite joint which has the specimen of different shape and stacking sequence could be predicted within 9.96%.

• Proceedings of the Korean Geotechical Society Conference
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• 1988.06c
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• pp.71-123
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• 1988

The aim of this paper is to examine the end bearing capacity of a pile in cohesionless soils. The ode of failure of soil due to pile installation is assumed from experimental observation of actual soil deformation. A new solution is proposed complying with the assumed mode of failure by employing the theory of cavity expansion. The effect of curvature of failure envelope is studied in relation to tile proposed solution. The influence of a curved failure envelope becomes larger with increasing degree of curvature and the level of confining stress. This effect in some cases or reduce the end bearing capacity by tore the 80 percent compared with that given by a straight failure envelope. For practical application of tile proposed solution, the method of determining the average volume change in the plastic zone is re-evaluated. The proposed solution is confirmed by comparing the theoretical values with experimental results obtained from model pile tests in a calibration chamber. The comparison shows that the proposed solution provides a reasonable prediction of end bearing capacity for both weak and strong grained soils.

• Proceedings of the KSME Conference
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• 2000.11a
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• pp.147-152
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• 2000

The ASF(Automatic Sheets Feeders) part of the printer has many bosses supporting gear-trains. Steel-pin bosses are substituted for plastic mold bosses because of advantages such as cost reduction, convenience of manufacturing and accuracy in dimension, but they have a weak point such as fatigue fracture due to low material strength, which causes a serious problem in the reliability of product. To prevent the fatigue fracture of bosses, we should exactly estimate the life to failure of the various shapes of bosses. We take the linear FEM analysis and the statistical method in this paper to figure out the life to failure of bosses. The maximum stress and life to failure of bosses can be easily estimated by this method. This paper specifies how to figure out the life to failure of bosses.

• International Journal of Precision Engineering and Manufacturing
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• v.8 no.3
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• pp.50-53
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• 2007

Improving the reliability or long-term dependability of a system requires a different approach from the previous emphasis on short-term concerns. The purpose of this paper is to present a reliability evaluation method for an oil cooler intended for high-precision machining centers. The oil cooler system in question is a cooling device that minimizes the deformation caused from the heat generated by driving devices. This system is used for machine tools and semiconductor equipment. We predicted the reliability of the system based on the failure rate database and conducted the reliability test using a test-bed to evaluate the life of the oil cooler. The results provided an indication of the reliability of the system in terms of the failure rate and the MTBF of the oil cooler system and its components, as well as a distribution of the failure mode. These results will help increase the reliability of oil cooler systems. The evaluation method can also be used to determine the reliability of other machinery products.

• Proceedings of the Korean Nuclear Society Conference
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• 1997.10a
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• pp.244-250
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• 1997

The mean time to failure (MTTF) expressing the mean value of the system life is a measure of system effectiveness. To estimate the remaining life of component and/or system, the dynamic mean time to failure concept is suggested. It is the time-dependent Property depending on the status of components. The Kalman filter is used to estimate the reliability of components using the on-line information (directly measured sensor output or device-specific diagnostics in the intelligent sensor) in form of the numerical value (state factor). This factor considers the persistency of the fault condition and confidence level in measurement. If there is a complex system with many components, each calculated reliability's or components are combined, which results in the dynamic MTTF or system. The illustrative examples are discussed. The results show that the dynamic MTTF can well express the component and system failure behaviour whether any kinds of failure are occurred or not.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.55 no.11
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• pp.476-484
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• 2006

The failure prediction and preventive maintenance for the equipment of nuclear power plant area using reliability-centered maintenance have been grown. On the other hand, the maintenance for power distribution system consists of time-based maintenance mainly. In this paper, the new maintenance algorithms for power distribution system are developed considering reliability indices. First of all, Time-varying failure rates are extracted from data accumulated at KEPCO using exponential distribution function and weibull distribution function. Next, based on the extracted failure rate, reliability for real power distribution system is evaluated for applying the effective maintenance algorithm which is the analytic method deciding the maintenance point of time and searching the feeder affecting the specific customer. Also the algorithm deciding the maintenance priority order are presented based on sensitivity analysis and equipment investment plan are analyzed through the presented algorithm at real power distribution system.

• Structural Engineering and Mechanics
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• v.20 no.1
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• pp.123-141
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• 2005

Design details pertaining to the connection between some recently developed fiber reinforced polymer (FRP) composite deck systems and the supporting girders require openings through cells of the deck. This significantly changes the stress distribution in these components. As a result, the conventional assumptions that deck designs are controlled by their stiffness, and not strength, needs a closer examination. This paper proposes an analytical method to investigate the stress states and failure mechanisms using a type of "global-local" modeling perspective, incorporating classical lamination theory and first ply failure criterion with use of appropriate stress concentration factors around the cutouts. The use of a "smeared-stress" approach is presented as a potential means of simplifying certain FRP specific complexities, while still enabling prediction of overall failure.

• Journal of Information Processing Systems
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• v.12 no.1
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• pp.109-128
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• 2016

This paper presents a new combined forecasting method that is guided by the soft set theory (CFBSS) to predict business failures with different sample sizes. The proposed method combines both qualitative analysis and quantitative analysis to improve forecasting performance. We considered an expert system (ES), logistic regression (LR), and support vector machine (SVM) as forecasting components whose weights are determined by the receiver operating characteristic (ROC) curve. The proposed procedure was applied to real data sets from Chinese listed firms. For performance comparison, single ES, LR, and SVM methods, the combined forecasting method based on equal weights (CFBEWs), the combined forecasting method based on neural networks (CFBNNs), and the combined forecasting method based on rough sets and the D-S theory (CFBRSDS) were also included in the empirical experiment. CFBSS obtains the highest forecasting accuracy and the second-best forecasting stability. The empirical results demonstrate the superior forecasting performance of our method in terms of accuracy and stability.

• The Transactions of the Korean Institute of Power Electronics
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• v.21 no.4
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• pp.328-334
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• 2016

This paper examines the reliability of a VSC-HVDC valve based on a modular multilevel converter (MMC) HVDC system. The main objective of this paper is to determine the redundancy of the MMC valve. Several prediction methods are introduced, but the binomial failure method is selected to be used. To determine the availability and reliability prediction of MMC valve, which comprises a DC/DC converter, a gate driver, a capacitor, and an IGBT, the failure data of the MMC module are used as the tracking data according to the experimental result. This method uses a simplified equation to find the valve redundancy by transforming the binomial function to De Moivre's formula. This method is the first to be used to find the valve margin.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.3
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• pp.600-611
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• 1994

The purpose of this research is to propose a model for the prediction of residual strength. For this purpose, two-paremeter model based on Caprino's is developed and formulated by the ratio of indentation due to impact and normalized residual strength. The damage zone is considered only as an indentation. Impact tests are carried out on laminated composites by steel balls. Test material is carbon/epoxy laminate. The specimens are composed of $[{\pm}45^{\circ}/0^{\circ}/90^{\circ}]_2$ and $[\pm}45^{\circ}]_4$ stacking sequence and have $0.75^T{\times}0.26^W{\times}100^L(mm) dimension. A proposed model shows a good correlation with the experimental results And failure mechanism due to high impact velocity is discussed on CFRP laminates to examine the initiation and development of damage by fractography and ultrasonic image ststem. The effect of the unidirectional ply position on the residual strength is considered here.