• Journal of the Korean Society for Industrial and Applied Mathematics
• /
• v.10 no.2
• /
• pp.41-47
• /
• 2006

The Renewal process and the Non-homogeneous Poisson process (NHPP) process are probably the most popular models for describing the failure pattern of repairable systems. But both these models are based on too restrictive assumptions on the effect of the repair action. For these reasons, several authors have recently proposed point process models which incorporate both renewal type behavior and time trend. One of these models is the Modulated Power Law Process (MPLP). The Modulated Power Law Process is a suitable model for describing the failure pattern of repairable systems when both renewal-type behavior and time trend are present. In this paper we propose Bayes estimation of the next failure time after the system has experienced some failures, that is, Mean Time Between Failure for the MPLP model. Numerical examples illustrate the estimation procedure.

• Journal of radiological science and technology
• /
• v.9 no.1
• /
• pp.131-135
• /
• 1986

The reciprocity law failure of the blue sensitive screen-film system was treasured, by authors. As a result, it has been found that reciprocity law failure is mote likely to occur at lower exposure, lower density and higher development temperature.

• Journal of the Korean Data and Information Science Society
• /
• v.18 no.2
• /
• pp.535-541
• /
• 2007

The Non-homogeneous Poisson process is probably the most popular model since it can model systems that are deteriorating or improving. The renewal process is a model that is often used to describe the random occurrence of events in time. But both these models are based on too restrictive assumptions on the effect of the repair action. The Modulated Power Law Process is a suitable model for describing the failure pattern of repairable systems when both renewal-type behavior and time trend are present. In this paper we propose maximum likelihood estimation of the next failure time after the system has experienced some failures, that is, Mean Time Between Failure for the MPLP model.

• Journal of Applied Reliability
• /
• v.9 no.2
• /
• pp.121-130
• /
• 2009

The power law process model the Rate of occurrence of failures(ROCOF) with monotonic trend during the operating time. However, the power law process is inappropriate when a non-monotonic trend in the failure data is observed. In this paper we deals with the reliability modeling of the failure process of large and complex repairable system whose rate of occurrence of failures shows the non-monotonic trend. We suggest a sectional model and a change-point test based on the Schwarz information criterion(SIC) to describe the non-monotonic trend. Maximum likelihood is also suggested to estimate parameters of sectional model. The suggested methods are applied to field data from an repairable system.

• Structural Engineering and Mechanics
• /
• v.11 no.4
• /
• pp.407-422
• /
• 2001

The linear constitutive relations and the failure criteria of composite materials made of thermoviscoelastic solids are presented. The post-failure material behavior is proposed and the dynamic finite element equations are formulated. However, a nonlinear term is kept in the energy equation because it represents the effect of the second law of thermodynamics. A general purpose nonlinear three-dimensional dynamic finite element program COMPASS is upgraded and employed in this work to investigate the interdependence among stress wave propagation, stress concentration, failure progression and temperature elevation in composite materials. The consequence of truthfully incorporating the second law of thermodynamics is clearly observed: it will always cause temperature rise if there exists a dynamic mechanical process.

• Geomechanics and Engineering
• /
• v.18 no.1
• /
• pp.97-109
• /
• 2019

Physical conditions play vital role on the mechanical properties of frozen soil, especially for the temperature and moisture content of frozen soil. Subsequently, they influence the subsidence and stress law of permafrost layer. Taking Jiangcang No. 1 Coal Mine as engineering background, combined with laboratory experiment, field measurements and empirical formula to obtain the mechanical parameters of frozen soil, the thick plate mechanical model of permafrost was established to evaluate the safety of permafrost roof. At the same time, $FLAC^{3D}$ was used to study the influence of temperature and moisture content on the deformation and stress law of frozen soil layer. The results show that the failure tensile stress of frozen soil is larger than the maximum tensile stress of permafrost roof occurring in the process of mining. It indicates that the permafrost roof cannot collapse under the conditions of moisture content in the range from 20% to 27% as well as temperature in the range from $-35^{\circ}C$ to $-15^{\circ}C$. Moreover, the maximum subsidence of the upper and lower boundary of the overlying permafrost layer decreases with the increase of moisture content in the range of 15% to 27% or the decrease of temperature in the range of $-35^{\circ}C$ to $-15^{\circ}C$ if the temperature or moisture content keeps consistent with $-25^{\circ}C$ or 20%, respectively.

• Proceedings of the Korea Concrete Institute Conference
• /
• 1999.04a
• /
• pp.135-140
• /
• 1999

The size effect of axial compressive strength of concrete in notched specimens was experimentally investigated. Based on the concept of the fracture mechanics and size effect law, theoretical studies for axial compressive failure of concrete were reviewed, and two failure modes of concrete specimen under compression were discussed. In this study, experiment of axial compressive failure, which is one of the two failure modes, was carried out by using double cantilever fracture specimens. By varying the slenderness of cantilevers and the eccentricity of applied loads with respect to the axis of each cantilever, the size effect of axial compressive strength of concrete was investigated, and predicted by Bazant's size effect law. The test results show that size effect appears conspicuously for all series of specimens. For the eccentricity of loads, the influence of tensile and compressive stress at the notch tip are significant and so that the size effect is varied. In other words, if the influence of tensile stress at the notch tip grows up, the size effect of concrete increases. And the fact that the fracture process zone must be sufficiently secured for more accurate experiment was affirmed.

• Journal of the Korea Concrete Institute
• /
• v.12 no.6
• /
• pp.99-108
• /
• 2000

The size effect on axial compressive strength in notched concrete specimens was experimentally investigated. Based on the concept of the fracture mechanics and size effect law, theoretical studies for axial compressive failure of concrete were reviewed, and two failure modes of concrete specimens under compression were discussed. In this study, experiments of axial compressive failure, which is one of the two failure modes, was carried out by using cylindrical specimens. Adequate notch length was taken from the experimental result of strength variation based on the notch length. And, by taking various sizes of specimens the size effect on axial compressive strength of concrete was investigated. Also, model equations were suggested by modified size effect law (MSEL). The test results show that size effect appears conspicuously for all series of specimens. Additionally, the effect of initial notch length on axial compressive strength was also apparent.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.21 no.2
• /
• pp.87-93
• /
• 2017

Many studies are conducted in several fields for fragility analysis of structures or elements which is a probabilistic seismic safety analysis in consideration with uncertainty of seismic loading. It is hard to directly conduct fragility analysis for an infrastructure with social importance due to its size. Therefore, a fragility analysis for an infrastructure mainly conducted in element level or conducted with scaled model built in accordance with similarity law. In this article, fragility analysis for prototype and scaled model of reinforced concrete column was conducted with numerical models which had been updated by the results of shaking table test and pseudo dynamic test. As a result, response stress from the numerical analysis result of prototype model was higher than that from scaled model due to different stiffness ratios between steel and concrete. However, the probability of failure for scaled model was higher than that for prototype model because failure criteria for scaled model was down due to similarity law. Also it was evaluated that probability of failure by using log normal standard deviation of response stresses by spectrum matched accelerograms was more reliable than probability of failure by using existing coefficient of variation normally used.

• Journal of the Korean Society of Safety
• /
• v.30 no.3
• /
• pp.13-19
• /
• 2015

Railway vehicle equipment goes back again to the state just before when failure by the repair. In repairable system, we are interested in the failure interval. As such, a statistical model of the point process, NHPP power law is often used for the reliability analysis of a repairable system. In order to derive a quantitative reliability value of repairable system, we analyze the failure data of the air brake system of the train line 7. The quantitative value is the failure intensity function that was modified, converted into a cost-rate function. Finally we studied the optimal number and optimal interval in which the costs to a minimum consumption point as cost-rate function. The minimum cost point was 194,613 (won/day) during the total life cycle of the braking system, then the optimal interval were 2,251days and the number of optimal preventive maintenance were 7 times. Additionally, we were compared to the cost of a currently fixed interval(4Y) and the optimum interval then the optimal interval is 3,853(won/day) consuming smaller. In addition, judging from the total life, "fixed interval" is smaller than 1,157 days as "optimal interval".