• International Journal of Reliability and Applications
• /
• 제10권1호
• /
• pp.43-57
• /
• 2009

In this article, we study the reliability equivalence factor of a series system. The failure rates of the system components are functions of time t. we study two cases of non-constat failure rates (i) weibull distribution (ii) linear increasing failure rate distribution. There are two methods are used to improve the given system. Two types of reliability equivalence factors are discussed. Numerical examples are presented to interpret how one can utilize the obtained results.

• 산업기술연구
• /
• 제27권B호
• /
• pp.245-253
• /
• 2007

Failure rate serves as a pivotal role in reliability study. Of all, the constant failure rate is the most popularly used in field exercises. In reality, however, the electrical and electronic parts' life is represented by not only the constant failure rate but the decreasing and/or increasing failure rates. Explicit consideration and incorporation of them into the model development may yield more desirable results. In this study, we built a reliability model for failure rates varying over time intervals and derived well known measures such as probability density function, reliability function, mean life, moments, and mission time. We then evaluated mean life with consideration of the first-year multiplier and compared the results those with constant failure rate. The results given in the study may provide a reference applying for practical decision making.

• Clinical and Experimental Reproductive Medicine
• /
• 제29권2호
• /
• pp.77-82
• /
• 2002

Objective : This study is to evaluate the efficacy of intracytoplasmic sperm injection (ICSI) for previous fertilization failure with conventional in vitro fetrtilization (IVF), compared with ICSI for male factor. Method: The author analyzed the 3 years of clinical experience with ICSI retrospectively, between the conventional IVF failure group (IVF failure) and male factor group (male factor). Surgically retrieved epididymal or testicular spermatozoa for ICSI were excluded. The IVF failure group was 13 cycles of 6 patients and male factor group was 30 cycles of 15 patients. Results: The fertilization rates of the IVF failure group and male factor group were 63% and 66% respectively (p=0.635). The clinical pregnancy rates of the both group were 23.1% and 26.7% (p=0.804), and that of live birth rates were 15.4% and 13.3% (p=0.858). There were no significant difference between the two groups. Conclusion: The author concluded that ICSI can overcome previous fertilization failure, with the same fertilization and clinical pregnancy rates seen in patients with male factor.

• 대한산업공학회지
• /
• 제42권5호
• /
• pp.327-336
• /
• 2016

Prediction of customer failure rates plays an important role for establishing appropriate management policies and improving the profitability for industries. For these reasons, many LCD (Liquid crystal display) manufacturing industries have attempted to construct prediction models for customer failure rates. However, most traditional models are based on the parametric approaches requiring the assumption that the data follow a certain probability distribution. To address the limitation posed by the distributional assumption underpinning traditional models, we propose using parameter-free data mining models for predicting customer failure rates. In addition, we use various information associated with product attributes and field return for more comprehensive analysis. The effectiveness and applicability of the proposed method were demonstrated with a real dataset from one of the leading LCD companies in South Korea.

• Journal of Mechanical Science and Technology
• /
• 제15권7호
• /
• pp.1013-1021
• /
• 2001

A series of rabbit common extensor tendon specimens of the humeral epicondyle were subjected to tensile tests under two displacement rates (100mm/min and 10mm/min) and different elbow flexion positions 45°, 90°and 135°. Biomechanical properties of ultimate tensile strength, failure strain, energy absorption and stiffness of the bone-tendon specimen were determined. Statistically significant differences were found in ultimate tensile strength, failure strain, energy absorption and stiffness of bone-tendon specimens as a consequence of different elbow flexion angles and displacement rates. The results indicated that the bone-tendon specimens at the 45°elbow flexion had the lowest ultimate tensile strength; this flexion angle also had the highest failure strain and the lowest stiffness compared to other elbow flexion positions. In comparing the data from two displacement rates, bone-tendon specimens had lower ultimate tensile strength at all flexion angles when tested at the 10mm/min displacement rate. These results indicate that creep damage occurred during the slow displacement rate. The major failure mode of bone-tendon specimens during tensile testing changed from 100% of midsubstance failure at the 90°and 135°elbow flexion to 40% of bone-tendon origin failure at 45°. We conclude that failure mechanics of the bone-tendon unit of the lateral epicondyle are substantially affected by loading direction and displacement rate.

• 한국경영과학회지
• /
• 제18권1호
• /
• pp.71-78
• /
• 1993

A Baysian approach is proposed is estimating the mission failure rates by criticalities. A mission failure which occurs according to a Poisson process with unknown rate is assumed to be classified as one of the criticality levels with an unknown probability. We employ the Gamma prior for the mission failure rate and the Dirichlet prior for the criticality probabilities. Posterior distributions of the mission rates by criticalities and predictive distributions of the time to failure are derived.

• Structural Engineering and Mechanics
• /
• 제30권2호
• /
• pp.177-190
• /
• 2008

Material failure behavior is generally dependent on loading rate. Especially in brittle and quasi-brittle materials, rate dependent material behavior can be significant. Empirical formulations are often used to predict the rate dependency, but such methods depend on extensive experimental works and are limited by practical constraints of physical testing. Numerical simulation can be an effective means for extracting knowledge about rate dependent behavior and for complementing the results obtained by testing. In this paper, the failure behavior of a brittle material under different loading rates is simulated by molecular dynamics analysis. A notched specimen is modeled by sub-million particles with a normalization scheme. Lennard-Jones potential is used to describe the interparticle force. Numerical simulations are performed with six different loading rates in a direct tensile test, where the loading velocity is normalized to the ratio of the pseudo-sonic speed. As a consequence, dynamic features are achieved from the numerical experiments. Remarkable failure characteristics, such as crack surface interaction/crack arrest, branching, and void nucleation, vary in case of the six loading cases. These characteristics are interpreted by the energy concept approach. This study provides insight into the change in dynamic failure mechanism under different loading rates.

• International Journal of Reliability and Applications
• /
• 제10권2호
• /
• pp.101-107
• /
• 2009

In the accelerated tests, the importance of correct failure analysis must be strongly emphasized. Understanding the failure mechanisms is requisite for designing and conducting successful accelerated life test. Under this presumption, a rational method must be identified to relate the results of accelerated tests quantitatively to the reliability or failure rates in use conditions, using a scientific acceleration transform. Most widely used models for relating the results of accelerated tests quantitatively to the reliability or failure rates in use conditions are an accelerated failure time model and a proportional hazards model. The purpose of this research is to compare the usability of the accelerated failure time model and proportional hazards model in the accelerated life tests.

• 전기학회논문지P
• /
• 제59권2호
• /
• pp.154-157
• /
• 2010

In this paper, the Time-varying Failure Rates(TFR) of power distribution system components are extracted from the recorded failure data of KEPCO(Korea Electric Power Corporation) and the reliability of power distribution system is evaluated using Mean Failure Rate(MFR) and TFR. The TFR is approximated to bathtub curve using the exponential and Weibull distribution function. In addition, Kaplan-Meier estimation is applied to TFR extraction because of incomplete failure data of KEPCO. Also the reliability of the real power distribution system of Korea is evaluated using the MFR and TFR extracted from real failure data, respectively and the results of each case are compared with each other. As a result, it is proved that the reliability evaluation using the TFR is more realistic than MFR. In addition, it is presented that the application method at power distribution system maintenance and repair using the result of TFR.

• 전기학회논문지P
• /
• 제66권1호
• /
• pp.33-37
• /
• 2017

This paper describes the modeling of the failure rate estimation technique for applying the asset management technique to electric power facilities. There are many modeling techniques to estimate the failure rate. In this paper, the characteristics of the normal distribution, exponential distribution, weibull distribution, and piecewise linear functions are discussed. When evaluating reliability, the evaluation may be less meaningful if the sample data is insufficient. Therefore, Weibull distribution and piecewise linear function are adopted as the most suitable functions for estimating the failure rate of power facilities and the resulting failure rate function is derived.