• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.10
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• pp.747-752
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• 2019

By using the failure information and the cumulative test execution time obtained by performing the reliability growth test, it is possible to estimate the parameter of the reliability growth model, and the Mean Time Between Failure (MTBF) of the product can be predicted through the parameter estimation. However the failure information could be acquired periodically or the number of sample data of the obtained failure information could be small. Because there are various constraints such as the cost and time of test or the characteristics of the product. This may cause the error of the parameter estimation of the reliability growth model to increase. In this study, the Bayesian method is applied to estimating the parameters of the reliability growth model when the number of sample data for the fault information is small. Simulation results show that the estimation accuracy of Bayesian method is more accurate than that of Maximum Likelihood Estimation (MLE) respectively in estimation the parameters of the reliability growth model.

• Tunnel and Underground Space
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• v.32 no.3
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• pp.203-218
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• 2022

A hydro-mechanical study was performed to analyze the relationship between the magnitude of injection-induced seismicity and shut-in. In hydraulic analysis, the suspension of fluid injection makes the pore pressure gradient smaller while the pore pressure at the pressure front can reach the critical value for several hours after shut-in, which leads to the additional slip with wider area than during injection. The hydro-mechanical numerical analysis was performed to model the simplified fault system, and simulated the largest magnitude earthquake during shut-in stage. The effect of the abrupt suspension of fluid injection on the large magnitude earthquake was investigated in comparison with the continuous injection. In addition to the pore pressure distribution, it was found that the geometry of multiple faults and the stress redistribution are also important in evaluating the magnitude of the induced seismicity.

• Journal of the Semiconductor & Display Technology
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• v.22 no.4
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• pp.113-118
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• 2023

Maintenance of semiconductor equipment processes is crucial for the continuous growth of the semiconductor market. The process must always be upheld in optimal condition to ensure a smooth supply of numerous parts. Additionally, it is imperative to monitor the status of the robots that play a central role in the process. Just as many senses of organs judge a person's body condition, robots also have numerous sensors that play a role, and like human joints, they can detect the condition first in the joints, which are the driving parts of the robot. Therefore, a normal state test bed and an abnormal state test bed using an aging reducer were constructed by simulating the joint, which is the driving part of the robot. Various sensors such as vibration, torque, encoder, and temperature were attached to accurately diagnose the robot's failure, and the test bed was built with an integrated system to collect and control data simultaneously in real-time. After configuring the user screen and building a database based on the collected data, the characteristic values of normal and abnormal data were analyzed, and machine learning was performed using the KNN (K-Nearest Neighbors) machine learning algorithm. This approach yielded an impressive 94% accuracy in failure diagnosis, underscoring the reliability of both the test bed and the data it produced.

• Journal of Korean Tunnelling and Underground Space Association
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• v.25 no.2
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• pp.141-155
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• 2023

Monitoring technology based on electrical resistivity is widely used for non-destructive data collection and health analysis of underground structures and tunnels. Vulnerable sections such as fault zone generates many problems during construction of the tunnel. These problems cause displacement and stress changes of the ground. Therefore, it is necessary to predict the state of the fault zone section to ensure the mechanical stability of the underground structure. Monitoring the size of joints and the porosity of the fillings is essential for rocks. Previous studies have not considered the variety of fillings in rock joints. In this study, electrical resistivity tests were conducted according to the particle mixing state of the sandy fillings. When the size of fillings is decreased at the constant porosity, the electrical resistivity tends to increase. The results of this study are expected to be useful as basic electrical resistivity data for predicting the ground conditions and evaluation of the ground behavior that is containing sandy fillings in the rock joint for tunnels.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.16 no.2
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• pp.128-139
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• 2017

Railway is one of the public transportation systems along with shipping and aviation. With the recent introduction of high speed train, its proportion is increasing rapidly, which results in the higher risk of catastrophic failures. The wheel bearing to support the train is one of the important components requiring higher reliability and safety in this aspect. Recently, many studies have been made under the name of prognostics and health management (PHM), for the purpose of fault diagnosis and failure prognosis of the bearing under operation. Among them, the most important step is to extract a feature that represents the fault status properly and is useful for accurate remaining life prediction. However, the conventional features have shown some limitations that make them less useful since they fluctuate over time even after the signal de-noising or do not show a distinct pattern of degradation which lack the monotonic trend over the cycles. In this study, a new method for feature extraction is proposed based on the observation of relative frequency energy shifting over the cycles, which is then converted into the feature using the information entropy. In order to demonstrate the method, traditional and new features are generated and compared using the bearing data named FEMTO which was provided by the FEMTO-ST institute for IEEE 2012 PHM Data Challenge competition.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.3
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• pp.405-413
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• 1997

In the present paper, it is attempted to reconfirm the "Intelligent" material properties using both the sintered TiNi/Al(1100) matrix composite made by powder metallurgy method and the squeeze-casted TiNi/Al6061 specimens. A metal matrix composite is, its fault has been considered to deteriorate a strength of composite by heating residual stress of the matrix. Therefore, it is necessary to remove a tensile residual stress, to produce the strength of a composite better. On the contrary, if compressive residual stress happens in matrix of composite in place of tensile residual stress, it will make the strength of composite better. So that, this paper introduce the development of a high strength of composite, by using compressive residual stress well, on the study. By using these specimens, shape memory strengthening effects in tensile strength and fatigue crack propagation above inverse transformation temperature of TiNi fiber were investigated. We occurs the prestrain and volume fraction for to discuss the effects of a composite strength. Moreover, by SEM observation, the effect of the residual stress at the interface between Al matrix and TiNi fiber and some brittle precipitation layers such as inter metallic compounds on fracture mechanisms was discussed metallurgically.urgically.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.8
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• pp.239-245
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• 2018

The importance of reliability in the development of weapons systems and reliability tests has been emphasized recently. Therefore, this study evaluated a reliability test design method of a bladder type accumulator and proposed a process for reliability test design. To design the reliability test of the accumulator, the main failure modes and failure mechanisms were investigated, and the main stress factors were analyzed to select the appropriate acceleration model. A steady - state reliability test was designed according to the number of samples, and the reliability level and accelerated life test time were calculated according to the acceleration factor computed using the selected acceleration model.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.15 no.2
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• pp.45-50
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• 2005

During oxidation process, several type of defects are formed on the surface of the silicon crystal which was damaged mechanically before oxidation. As the size of abrasive particle increases multiple dislocation loops are produced favorably over oxidation-induced stacking faults, which are dominantly produced when ground with finer abrasive particle. These defects are not related with the crystal growth process like Czochralski or directional solidification. During directional solidification process, twins and stacking faults are the two major defects observed in the bulk of the silicon crystal. On the other hand, slip dislocations produced by the thermal stress are not observed. Thus, not only in single crystalline silicon crystal but also in multi-crystalline silicon, extrinsic gettering process with programmed production of surface defects might be highly applicable to silicon wafers for purification.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.6
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• pp.797-804
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• 2013

In this study, the authors develop a methodology for a diagnostic system with a vibration parameter that is influenced by environmental factors. The data tends to have a varying average over time. Often, these features are found in statistical data retrieved from a production line. If we utilize existing statistical techniques for these features, we could derive an incorrect diagnostic conclusion based on the different average values. To overcome the limitations of previous methods, the authors apply a function analyzed through regression analysis to predict the mean value and corresponding upper and lower limits at each stage. This technique also provides corresponding statistical parameters in varying dynamic means. To validate the proposed methods, we retrieve data from the engine assembly line of H Motors and verify the results.

• Magazine of the Korean Society of Agricultural Engineers
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• v.38 no.6
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• pp.83-95
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• 1996

The normal cement concrete is widely used material to build the construction recently, but it has a fault to increase the dead load on account of its unit weight is large compared with strength. So, main purpose of this study was to establish the physical and mechanical properties of lightweight concrete using expanded polystyrene bead on fine aggregate and natural gravel, expanded clay and pumice stone on coarse aggregate. The test rusults of this study are summarized as follows; 1. The water-cement ratio of concrete using pumice stone was larger than that of the concrete using natural gravel and expanded clay. 2. The unit weights of concrete using pumice stone and expanded caly were shown less than 1,000g/$m^3$. 3. The compressive strengths of all types were shown less than 60kg/$cm^2$, tensile and bending strengths were shown less than l3kg/$cm^2$ and 3lkg/$cm^2$$^2$, respectively. 4. The pulse velocity of concrete was shown similar with using natural gravel and pumice stone, and shown the lowest using pumice stone. 5. The dynamic modulus of elasticity of concrete was shown considerably smaller, and shown the lowest using pumice stone. 6. The static modulus of elasticity of concrete using expanded clay and pumice stone were shown considerably smaller, and shown 22% ~29% as compared with the dynamic modulus of elasticity. 7. The stress-strain curves of concrete were shown similar, generally. And the curves were repeated at short intervals increase and decreased irregularly.