• IE interfaces
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• v.23 no.2
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• pp.176-181
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• 2010

Warranty claim data analysis is a useful tool for the manufacturer because it contains many useful informations regarding reliability of the product in the real-world environments. Because of the nature of uncertainty and the incompleteness of data, some bias patterns are observed on warranty claim rate known as 'spikes'. Two types of spikes are considered. One is due to manufacturing-related failures. The other is caused by customer's behavior. This paper proposes a model by considering two types of spikes. Warranty claim data is analyzed with the proposed model. To represent spikes observed on the early warranty period, we classify failures into manufacturing-related failures and usage-related failures. Uniform distribution is assumed for the time delayed to diagnose and report by customers. By reducing maximum value of the delayed time by customers, the proposed model characterizes customer's rush in the vicinity of the warranty expiration limit. Experimental results by using the real warranty claim data show that the proposed model is better than the existing one in respect to MSE(Mean Squared Error). Moreover it is expected to estimate the failure rate more realistically with proposed model because it considers the delayed time to diagnose and report by customers.

• Journal of Applied Reliability
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• v.15 no.4
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• pp.256-261
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• 2015

The aim of this paper is to present some issues to be discussed in relation to failure rate of a system that has identical parallel units. It is assumed that Time-to-Failure of each unit has the same exponential distribution and all units are repairable with a periodic maintenance of time interval T. Effective failure rate is widely recommended for nonrepairable systems as the reciprocal of MTTF but it should not be applied for repairable systems if delayed maintenance is used. And equivalent failure rate of an imaginary system is taken into consideration, the reliability value of which is the same as that of the redundant system when time interval T is given. With a numerical example, failure rate, effective failure rate, and equivalent failure rate of the redundant system are analyzed comparatively.

• Journal of the Korean Society of Safety
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• v.33 no.3
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• pp.83-91
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• 2018

This paper suggests a weibull time delay model to evaluate failure risks in FMEA(failure modes and effects analysis). Assuming three types of loss functions for delayed time in failure cause detection, the risk of each failure cause is evaluated as its occurring frequency and expected loss. Since the closed form solution of the risk metric cannot be obtained, a statistical computer software R program is used for numerical calculation. When the occurrence and detection times have a common shape parameter, though, some simple results of mathematical derivation are also available. As an enormous quantity of field data becomes available under recent progress of data acquisition system, the proposed risk metric will provide a more practical and reasonable tool for evaluating the risks of failure causes in FMEA.

• Journal of Korea Society of Digital Industry and Information Management
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• v.8 no.4
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• pp.25-34
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• 2012

In this study, in the process of testing before the release of the software products designed, software testing manager in advance should be aware of the testing-information. Therefore, the effective learning effects perspective has been studied using the NHPP software. The finite failure nonhomogeneous Poisson process models presented and applied property of learning effect based on truncated time and delayed S-shaped software reliability. Software error detection techniques known in advance, but influencing factors for considering the errors found automatically and learning factors, by prior experience, to find precisely the error factor setting up the testing manager are presented comparing the problem. As a result, the learning factor is greater than autonomous errors-detected factor that is generally efficient model can be confirmed. This paper, a failure data analysis was performed, using time between failures, according to the small sample and large sample sizes. The parameter estimation was carried out using maximum likelihood estimation method. Model selection was performed using the mean square error and coefficient of determination, after the data efficiency from the data through trend analysis was performed.

• Journal of Chest Surgery
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• v.19 no.4
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• pp.744-749
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• 1986

Even in the hands of the expert endoscopists, an occasional instrumental perforation of the esophagus occurs. But instrumental perforation of the esophagus should not be difficult to diagnose if the possibility is borne in mind. Occasionally patient with esophageal perforations show little reaction at first, but usually they develop systemic manifestation if surgical management is delayed. Early surgical drainage of esophageal perforation is very important & effective therapeutic method. The delayed surgical treatment of esophageal perforation would have increased the morbidity & mortality by allowing mediastinitis & empyema thoracis. We have experienced 6 cases of delayed surgical management of instrumental perforation of esophagus from May 1974 to April 1986 in the department of thoracic and cardiovascular surgery, Yonsei University, college of the medicine. The ages ranged from 4 years to 57 years. The underlying esophageal diseases consisted of esophageal stricture in 3 cases, foreign bodies in the esophagus in 2 cases and esophageal ca. in one case. Most clinical manifestations on admission were high fever, chest discomfort, chest pain, dysphagia and subcutaneous emphysema. Most complications due to esophageal rupture were acute mediastinitis with or without empyema thoracis. Failure to diagnose promptly and failure to promptly institute adequate treatment undoubtedly were largely responsible for this patients death. All 6 patients had been taken delayed surgical drainage more than 24 hours following esophageal perforation. One patient had been in the open drainage state for long time and the another patient has been in the tracheostomy with postintubation vocal cord ulceration. The third patient died due to respiratory failure and sepsis due to fulminant mediastinitis & empyema thoracis. Even if the patients with esophageal perforation have been taken delayed surgical management, the patients should be survived with aggressive & effective surgical drainage with intensive post-operative care.

• Journal of Chest Surgery
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• v.28 no.11
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• pp.977-982
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• 1995

Early repair of complex congenital heart malformation may lead to life-threatening respiratory and hemodynamic embarrassment on sternal closure. We performed delayed sternal closure in nine neonates to avoid a fatal outcome in these situations. Primary elective open sternum was used in 8 [66.7% and primary sternal closure in 4 [33.3% of the 12 patients studied. one patient with primary sternal closure underwent delayed sternal reopening in the intensive care unit. Of the 9 patients with open sternum, 2 patients died of low cardiac output and acute renal failure respectively before delayed sternal closure. 7 patients could undergo delayed sternal closures 3 days after initial operation. The mean age at open cardiac procedure was 14.3 days [range 3 to 30 and mean preoperative weight was 3.4kg [range 2.8 to 4.1 . The aortic cross-clamping time was longer in the group with open sternum than the group with closed sternum [p=0.042 . There was no morbidity and mortality related to delayed sternal closure. Given the low morbidity and potential benifits, this technique should be used in neonates after open heart procedures when postoperative mediastinal compression produces frank low cardiac output or respiratoy compromise during a trial of sternal closure.

• Journal of Welding and Joining
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• v.5 no.2
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• pp.53-59
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• 1987

The effect of applied stress, current density and heat-treatment after welding on the time to fracture, fracture behavior was investigated by the method of constant load tensile testing under catholic charging with hydrogen in E.B. welded 250,300 Grade 18% Ni Maraging steel sheet. The main results obtained are as follows: 1. All specimen showed the characteristic delayed failure and the time to fracture showed decreasing tendency with the increase in current density and applied stress. 2. Hydrogen embitterment susceptibility of notched specimen after solution-treatment and aging after welding was more increased than that of aged smooth specimen and as welded specimen. 3. Fracture surface showed a typical intergranular fracture on the border, a dimple pattern in the center of specimen and some quasi-cleavage fracture between the intergranular and the dimple.

• Journal of Korean Society for Quality Management
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• v.44 no.2
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• pp.373-388
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• 2016

Purpose: This paper suggests a hierarchical time delay model to evaluate failure risks in FMEA(failure modes and effects analysis). In place of the conventional RPN(risk priority number), a more reasonable and objective risk metric is proposed under hierarchical failure cause structure considering time delay between a failure mode and its causes. Methods: The structure of failure modes and their corresponding causes are analyzed together with the time gaps between occurrences of causes and failures. Assuming the severity of a failure depends on the length of the delayed time for corrective action, a severity model is developed. Using the expected severity, a risk priority metric is defined. Results: For linear and quadratic types of severity, nice forms of expected severity are derived and a meaningful metric for risk evaluation is defined. Conclusion: The suggested REM(risk evaluation metric) provides a more reasonable and objective risk measure than the conventional RPN for FMEA.

• Proceedings of the KSME Conference
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• 2001.11a
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• pp.155-160
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• 2001

This paper describes a probabilistic fracture mechanics (PFM) analysis based on Monte Carlo (MC) simulation. In the analysis of CANDU pressure tube, it is necessary to perform the PFM analyses based on statistical consideration of flaw generation time. A depth and an aspect ratio of initial semi-elliptical surface crack, a fracture toughness value, delayed hydride cracking (DHC) velocity, and flaw generation time are assumed to be probabilistic variables. In all the analyses, degradation of fracture toughness due to neutron irradiation is considered. Also, the failure criteria considered are plastic collapse, unstable fracture and crack penetration. For the crack growth by DHC, the failure probability was evaluated in due consideration of flaw generation time.

• Journal of Digital Convergence
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• v.13 no.12
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• pp.143-149
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• 2015

This study aims to analyze the predict capability of some of the popular software NHPP reliability models(Goel-Okumo model, delayed S-shaped reliability model and Rayleigh distribution model). The predict capability analysis will be on two key factors, one pertaining to the degree of fitment on available failure data and the other for its prediction capability. Estimation of parameters for each model was used maximum likelihood estimation using first 80% of the failure data. Comparison of predict capability of models selected by validating against the last 20% of the available failure data. Through this study, findings can be used as priori information for the administrator to analyze the failure of software.