• Magazine of korean Tunnelling and Underground Space Association
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• v.3 no.2
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• pp.91-107
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• 2001

• Composites Research
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• v.26 no.3
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• pp.201-206
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• 2013

The electrical resistance measurement was investigated as a damage monitoring method. In this study, 0.5 wt% Carbon nanotube reinforced polypropylene (CNT/PP) composites were evaluated under compressive fatigue loading. The shape of specimens was $20^{\circ}$ curved round type. Compression strength and electrical resistance were measured at different sections of specimen during compression. The microcracks of CNT/PP composites were detected based on the changing ratio of electrical resistance. Micro-damage during compressive fatigue test could be detected by electrical resistance measurements. The reason is that the contact points of CNTs in composites decreased under fatigue loading. During compressive fatigue test, larger change of electrical resistance was detected at the microcrack sections. It was proved that microcracks could be detected by electrical resistance measurement under compression test, whereas the real delamination parts were consistent with the predicted results by electrical resistance measurement.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2011.04a
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• pp.123-126
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• 2011

본 논문에서는 점탄성 매트릭스와 탄성 강화입자로 구성된 복합재료의 크리프 거동예측을 미세역학 기반의 시뮬레이션을 통하여 수행하였다. 에폭시 고분자로 이루어진 복합재료의 경우 재료 특성상 탄성적 거동뿐 아니라 점성적 거동도 함께 발생하게 된다. 이렇듯 점탄성 거동을 보이는 재료의 경우 탄성만을 고려한 해석방법으로는 한계가 있으며 점성적인 특성 또한 고려되어야 한다. 점탄성 복합재료의 해석을 위해서 손상을 고려한 미세역학 기반의 해석 (Ju and Chen, 1994) 과 Mesquita and Coda (2002)의 근사식을 사용하였다. 이를 통해 구한 재료 물성은 복합재료의 크리프 거동예측을 위한 Kelvin-Voight (KV) 모델과 Standard Linear Solid (SLS) 모델에 적용되었다. 최종적으로 본 연구에서 제안한 손상을 고려한 점탄성 모델의 예측과 시험결과를 비교 수행하여 결과의 타당성을 검증하였다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.12 no.2
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• pp.149-159
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• 1999

본 연구에서는 고유진동수를 사용하여 균열의 위치와 크기를 발견하는 비파괴 균열발견모델을 유도하고 Euler-Bernoulli 보를 대상으로 이 모델의 적합성을 검증하였다. 먼저, 균열위치예측모델과 균열크기예측모델로 이루어진 균열발견체계를 제시하였는데, 균열위치예측모델은 모드민감도와 고유진동수 사이의 선형적인 관계로부터 간접적으로 유도되었으며 균열크기예측모델은 균열발생에 의한 변형에너지의 손실을 진동특성치의 변화와 비교하는 동적 파괴역학적 방법으로부터 유도되었다. 다음으로, 기존에 발표된 양단-자유보에 대한 진동모드 실험결과를 사용하여 균열위치와 균열크기를 예측하고 평가하므로 균열발견모델의 적합성과 적용성을 실험적으로 검토하였다. 대부분의 손상시나리오에서 균열위치와 균열크기 예측치는 실제값과 근사하게 일치하였다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.1A
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• pp.115-123
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• 2008

The performance prediction of fiber-reinforced composites has attracted engineer's attention in many fields, and the various theoretical and numerical methods have been proposed to predict the behavior of the fiber-reinforced composites. An evolutionary damage model for progressive interfacial debonding between circular fibers and the matrix is newly incorporated into the micromechanics-based elastoplastic model proposed by Ju and Zhang (2001) in this framework. Using the proposed model, a series of numerical simulations are conducted to illustrate the elastoplastic behavior and evolutionary damage of the framework. Furthermore, the influence of the evolutionary interfacial debonding on the behavior of the composites is investigated by comparing it with the result of a stationary damage model.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.4
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• pp.425-433
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• 2001

A correlation between fatigue damage and acousto-ultrasonic (AU) parameters has been obtained from signals acquired during fatigue loading of the single-lap joints of a carbon-fiber reinforced plastic (CFRP) laminates and A16061 plate. The correlation showed an analogy to those representing the stiffness reduction $(E/E_0)$ of polymer matrix composites by the accumulation of fatigue damage. This has been attributed to the transmission characteristics of acoustic wave energy through bonded joints with delamination-type defects and their influence on the change of spectral content of AU signals. Another correlation between fatigue cycles and the spectral magnitude of acoustic emission (AE) signals has also been found during the final stage of fatigue loading. Both AU and AE can be applied almost in real-time to monitor the evolution of damage during fatigue loading.

• 한국방재학회:학술대회논문집
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• 2010.02a
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• pp.79.1-79.1
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• 2010

본 연구에서는 케이슨식 방파제 구조물에 대하여 기초마운드의 잠재적인 손상 모니터링에 관한 연구를 수행하였다. 이를 위해 첫째, 케이슨식 방파제 기초마운드의 이상 상태 여부를 판단하기 위하여 진동응답 분석기법을 선정하였다. 둘째, 선정된 기법에 의한 손상 예측 가능성의 검증을 위하여 케이슨식 방파제의 구조모형을 제작하였다. 셋째, 모형케이슨에 대한 유한요소 모델 생생하여 기초마운드의 손상에 따른 진동응답을 분석하였다. 마지막으로, 모형케이슨에 대한 진동실험을 통하여 기초마운드의 손상 예측을 수행하였다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.44 no.1
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• pp.19-32
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• 2024

An investigation into the detailed safety diagnosis report indicates that domestic highway bridges mainly suffer from defects, deterioration, and damage due to physical forces. In particular, deterioration is an inevitable damage that occurs due to various environmental and external factors over time. In particular, bridge deck is very vulnerable to cracks, which occur along with various types of damages such as rebar corrosion and surface delamination. Thus, this study evaluates a correlation between heterogeneous damage and deterioration environment and then identifies the main causes of such heterogeneous damage. After all, a bridge heterogeneous damage prediction model was developed using random forests to determine the top five factors contributing to the occurrence of the heterogeneous damage. The results of the study would serve as a basic data for estimating bridge maintenance and budget.

• 지반과기술
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• v.8 no.2
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• pp.56-60
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• 2011

• Journal of Chest Surgery
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• v.34 no.12
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• pp.937-943
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• 2001

Background: The aims of this study are to determine the predicting factors related with cardiovascular injuries in sternal fractures and to suggest the indication of emergency echocardiography. Material and Method: A retrospective review of the Ewha Womans University Mok-Dong Hospital trauma registry revealed 40 patients, that visited the hospital with a sternal fracture a over 5-year period. We analyzed 4 factors as predicting factors; 1) presence of restraint, 2) presence of associated injuries, 3) presence of a past medical history involving cardiovascular system, and 4) Revised Trauma Score(RTS). We, also, assessed the utility of conventional study methods involving cardiovascular injuries, such as ECG, chest X-ray, and enzyme level. Based on the methods, we inferred an indication for emergency echocardiography in sternal fractures. Result: Statistically significant predicting factors were the presence of a past medical history involving cardiovascular system and abnormal RTS on admission. Usage of emergency echocardiography depended upon the predicting factors and the results from conventional evaluations. We can now suggest the indications of emergency echocardiography in sternal fractures as 1) if more than two studies reveal abnormality without any significant predicting factors, and 2) if more than one study reveals abnormality with any significant predicting factors. Conclusion: The past medical history involving cardiovascular system and initial vital signs imply the presence of cardiovascular injuries in sternal fractures. And if needed, emergency echocardiography should be performed.