• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.9
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• pp.1299-1304
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• 2010

We examined the working fracture behavior of a silicon-steel strip caused by deformation deviation by performing a pilot rolling test. The deformation deviation resulted in the edges (or center portion) of the strip being stretched and the other parts being compressed in the rolling direction; this was because of different degrees of deformation in these parts. We designed roll grooves shape to reflect the role of roll bending, which generates waviness in the strip in an actual cold rolling process, into the pilot rolling test. The material used in the rolling test was highsilicon steel (about 3%). The results of the test showed that the type of fracture in the strip specimen varied with the magnitude of the deformation deviation. The tensile stress produced at the strip edges because of the center waviness in the rolling direction was a crucial factor that resulted in edge cracking and a zigzag-shaped fracture at the center.

• Composites Research
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• v.16 no.3
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• pp.58-67
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• 2003

To perform the realtime strain and fracture monitoring of the smart composite structures, two optical fiber sensor systems are proposed. The two types of the coherent sources were used for fracture signal detection - EDFA with FBG and EDFA with Fabry-Perot filter. These sources were coupled to EFPI sensors imbedded in composite specimens. To understand the characteristics of matrix crack signals, at first, we performed tensile tests using surface attached PZT sensors by changing the thickness and width of the specimens. This paper describes the implementation of time-frequency analysis such as short time Fourier transform (STFT) and wavelet transform (WT) for the quantitative evaluation of fracture signals. The experimental result shows the distinctive signal features in frequency domain due to the different specimen shapes. And, from the test of tensile load monitoring using optical fiber sensor systems, measured strain agreed with the value of electric strain gage and the fracture detection system could detect the moment of damage with high sensitivity to recognize the onset of micro-crack fracture signal.

• Journal of the Korea Convergence Society
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• v.7 no.1
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• pp.177-182
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• 2016

In order that the track vehicle utilized on the purpose of heavy industry and military affair may endure the vehicle body with heavy weight, the link surrounding the mobile wheel is affected with the great force by the load transferred at the vehicle body. This happened force gives rise to a decline in the durability throughout the track. In this paper, the models with the shapes of track pads in common use are designed and the model at which the wear of track pad and the damage of link can be decreased effectively is contrived. Also, by applying this study result to the design of track vehicle, it can contribute to the safe design for damage prevention and durability improvement. It is possible to be grafted onto the convergence technique at the designed factor of pad shape and show the esthetic sense.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.12
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• pp.1186-1192
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• 2008

The reliability of gas turbine engine blades was studied. Yield strength, Young’s modulus, engine speed and gas temperature were considered as statistically independent random variables. The failure probability was calculated using five different methods. Advanced Mean Value Method was the most efficient without significant loss in accuracy. When random variables were assumed to have normal, lognormal and Weibull distributions with the same means and standard deviations, the CDF of limit state equation did not change significantly with the distribution functions of random variables. The normalized sensitivity of failure probability with respect to standard deviations of random variables was the largest with gas temperature. The effect of means and standard deviations of random variables was studied. The increase in the mean of gas temperature and the standard deviation of engine speed increased the failure probability the most significantly.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.1
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• pp.305-312
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• 2021

This study examines the damage to the submarine's escape trunk hatch spring through microstructure analysis. The cause of the escape trunk's damage during the submarine's construction and its improvement measures were reviewed. To determine the cause of breakage of the escape trunk spring, samples were taken from the damaged product and analyzed for chemical composition, hardness, and microstructure. In particular, the breakage part of the spring was analyzed in-depth by using a scanning electron microscope to determine the cause of corrosion destruction. Finally, a spring shape design method was proposed through the investigation of the cause of spring breakage. In addition, a newly improved spring was produced by applying a nylon coating with excellent corrosion resistance and abrasion resistance. Applying to an actual submarine trunk hatch revealed that the coating peeling phenomenon due to the contact between the springs is significantly improved when the hatch is opened or closed compared to the existing products.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.10a
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• pp.193-198
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• 2001

생산현장 업무에서는 측정검사업무의 비중이 크다. 측정검사의 업무는 품질향상을 위한 활동이며 또한 고부가가치의 제품을 위해서도 중요하다. 고품질 고정밀도는 철저한 측정검사를 통하여 이루어진다. 제품의 치수를 정확히 측정하여 정밀도 있는 부품을 제작하고 불량부품이나 파손된 부품을 검사하여 제거함으로써 제품의 성은과 품질이 우수하게 인정된다. 이러한 측정검사작업의 정밀도향상, 생산성 향상을 위해서는 자동화가 필요하다. 측정검사의 자동화 (CAT : Computer Aided Testing)에는 영상처리를 이용하는 시각검사의 자동화가 중요한 분야이다. 영상처리를 이용한 시각검사의 대상은 결함검사, 두께검사, 형상칫수 검사, 물체의 위치, 방향, 종류의 파악 등이 있다.

• Proceedings of the Korean Society of Fisheries Technology Conference
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• 2003.10a
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• pp.23-26
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• 2003

정치망은 어군의 자연적인 이동 경로를 길그물로써 차단하여 어군을 운동장으로 유도한 후, 비탈그물을 통해 원통으로 들어가게 하여 어획하는 소극적 어구이다. 정치망이 수중에 형성하고 있는 공간의 규모와 형태는 해면에 떠있는 뜸의 형상 및 각 부분의 부설 깊이와 침강 수심을 조사하여 추정하고 있으나, 정치망이 설치된 해역의 조류 방향과 유속에 따라 수중 형상의 크기나 형태가 변형되어 어획량에 영향을 주는 요인이 될 뿐만 아니라 강한조류나 악천후에 의한 파손 등으로 조업 손실을 초래하기도 한다. (중략)

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.05a
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• pp.177-177
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• 2004

최근 높은 복잡한 형상의 고정밀도와 고성능을 갖는 제품들을 생산할 수 있게 하기 위하여 고속 가공기의 공구 셋팅 모니터링 시스템의 사용은 고속 가공기를 이용하여 생산하는 여러 제품 공정에 절대적으로 요구되고 있다. 가공물의 형상이 고정밀화 되어가고 있으며 이들의 가공 정밀도와 생산성을 향상시키고 공구들의 파손을 방지하고 공구의 셋팅 시간을 단축하는 것이 매우 중요하다.(중략)

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.6
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• pp.2037-2047
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• 1991

Strength is not simply a single given value but rather is a statistical one with certain distribution functions. This is because it is affected by many unknown factors such as size, shape, stress distribution, and combined stresses. In this study, a model of loss probability is proposed in view of the fact that one of the fundamental configuration of nature is hexagonal, for example, the shapes of lattice unit, grain, and so on. The model sues the concept of loss of certain element in place of Jayatilaka-Trustrum's length and angle of cracks. Using this model, the loss probability due to each loss of certain elements is obtained. Then, the maximum principal stress is calculated by the finite element method at the centroid of the elements under the tensile load for the 4,095 models of analysis. Finally, the failure probability of the brittle materials is obtained by multiplying the loss probability by the ratio of the maximum principal stress to theoretical tensile strength. Comparison of the result of the Jayatilaka-Trustrum's model and the proposed model shows that the failure probabilities by the two methods are in good agreement. Further, it is shown that the parametric relationship of semi-crack lengths for various degrees of birittleness can be determined. Therefore, the analysis of the failure probability suing the proposed model is shown to be promising as a new method for the study of the failure probability of birttle materials.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.31-35
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• 2004

The speed competition of optical disk drive has been accelerated with the fast advancement of its storage density and data transmission technology. The continuous increase of the spinning speed of CD meets the unexpected and catastrophic failure of disk during the operation. The effect of its thickness and outer radius of disk were investigated to reduce stresses and J-integral around the crack tip. The effect of its thickness was considered ahead of the crack tip. In the effect of outer radius of disk, linear elastic fracture mechanics was used to obtain the critical crack length, which indicates the onset length for unstable crack growth. This approach is so significant as to detect the growing crack by disk drive before the catastrophic failure, which will provide the standard size of its safety for high-speed disk drive.