• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.3
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• pp.603-609
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• 1990

Detection and non-propagating cracks of small fatigue crack for smooth and pre-cracked specimens were examined in a carbon steel. The fretting oxide induced crack closure triggered by the roughness induced crack closure has an important role in determing the length. The fatigue limit for the with no cracks or with a short pre-crack is lower at R=-1 than that at R=0. A non-propagating crack are quite different between points near the specimen's surface and those of deepest penetration.

• Journal of the KSME
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• v.32 no.1
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• pp.28-38
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• 1992

음향 방출법은 기존의 비파괴 시험보다 여러 가지 면에서 장점을 가지고 있고 또 그 응용범위는 매우 넓다. 그러나 아직 우리 나라에서는 그 사용 예가 많지 않다. 이 글에서는 음향 방출법에 대한 개요와 음향 방출법을 이용한 복합재료와 금속재료의 균열 거동 해석 예를 저자의 연구 결과를 중심으로 소개하고자 한다.

• Journal of the KSME
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• v.35 no.3
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• pp.242-251
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• 1995

균열(crack)을 갖는 부재의 강도를 평가할 때에 있어서 응력확대계수를 이용하는 데에 대한 합 리성은 현재까지 의심할 여지없는 사실로서 받아들여지고 있다. 그 근거는 소규모 항복의 조건이 만족되고 있을 때에는 균열의 치수가 틀리더라도 균열선단부근의 역학적 상태는 응력확대계수 만에 의해 지배된다는 사실에 있다. 한편, 노치(notch)를 갖는 부재의 강도를 평가할 때에 최대 응력만을 고려하는 것은 불충분하다. 예를 들면, 그것은 노치반경 .rho.가 10 mm 정도의 노치와 .rho.가 0에 상당하는 균열과는 최대응력 .sigma.$_{max}$를 같게 하더라도 역학적 상태의 가 혹함(severity)이 동일하게 되지 않는다는 사실로부터도 명백하다. 그렇다면, .rho.가 0과 10 mm의 중간값, 예를 들면 1 mm 혹은 0.1 mm일 때와 같은 역학적 상태의 가혹함이 생기기 위해서는 .sigma.$_{max}$가 얼마이면 될까\ulcorner 또는, 만약 .rho.가 틀릴 때, 동일한 현상(same phenomenon)이 생기지 않는다고 한다면 그것은 어떠한 물리적 배경에 근거한 것일까\ulcorner 이글에 서는 이러한 질문에 대한 해답과 함께 선형파괴역학과 선형노치역학이 생겨나게 된 간략한 역사적 배경과 선형노치역학의 개념에 대해 언급하기로 한다.

• Journal of Aerospace System Engineering
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• v.12 no.3
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• pp.38-44
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• 2018

Military aircraft may have fatigue cracks in structurally weak areas due to multiple factors such as the accumulation of flight time while perform various missions and unpredictable air conditions. As a fatigue crack progresses, there is a risk that the structure will be destroyed in extreme cases, which can have a significant impact on flight safety. In this study, a cracking phenomenon was observed during the periodic inspection the inner support of the fairing, which is installed to protect the connection between the wing and the body of the aircraft. Therefore, a study on a series of quality improvement processes for reformation was described. In order to identify the causes of cracks, pre-load generation occurrence during the wing assembly process was investigated and a fracture analysis was performed. Also, the design of the support structure was suggested in terms of preventing recurrence of cracks. The structural integrity was verified using a stress and fatigue life analysis.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.5
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• pp.473-478
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• 2009

The purpose of this study is to evaluate the behaviour of the plastic deformed zone at crack tip on the standard Charpy specimens which were taken from the multi-passed weld block of the pressure vessel steel. Notch was machined on the standard Charpy test specimens and pre-crack which was located around the fusion line was made under the repeat load. Four point bend and acoustic emission tests were carried out simultaneously. The size of plastic region at crack tip was calculated using stress intensity factor. Relationships between characteristics of acoustic emission and plastic zone size at crack tip were discussed through the cumulative AE energy. Regardless of the specimens, AE signals were absent within the elastic region almost and most of AE signals were produced at the plastic deformation region from yield point to the mid-point between yield and maximum load. More AE signals for the weldment were produced compared with the base-metal and PWHT specimen. Relations between plastic deformed zones at crack tip and cumulative AE energy for the weldment and PWHT specimen were different quietly from the base-metal. Besides, number of AE counts for the weldment was the larger than those of the base-metal and PWHT specimen.

• Computational Structural Engineering
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• v.7 no.3
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• pp.167-176
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• 1994

A local remeshing algorithm using Delaunay property is developed for the analysis on the phenomenon of quasi-static crack propagation, which is a typical problem of accompanying constantly varying geometry. The algorithm performs both remeshing and refinement. The use of M-integral is demonstrated to simulate crack propagation under mixed mode with the edge spalling problem.

• Journal of the Korean Society of Propulsion Engineers
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• v.16 no.6
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• pp.79-84
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• 2012

An experiment of rapid pressurization-induced crack propagation of solid propellant was conducted by using a windowed test chamber. A pre-cracked specimen of solid propellant is installed in the chamber, and highly compressed nitrogen gas in an accumulator pressurizes the chamber until the chamber pressure reaches set-up pressure to make the chamber depressurization. Pressure-time trace was obtained from the experimental result, and pressurization rate was defined from the trace. In this study, three pressurization rates (64.34, 73.86 and 85.44 MPa/s) are considered, and propagation lengths are measured. Also, a progression of the crack propagation recorded by a high-speed digital camera is presented.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.539-544
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• 2012

An experiment of rapid pressurization-induced crack propagation of solid propellant was conducted by using a windowed test chamber. A pre-cracked specimen of solid propellant is installed in the chamber, and highly compressed nitrogen gas in a accumulator pressurizes the chamber until the chamber pressure reaches set-up pressure to make the chamber depressurization. Pressure-time trace was obtained from the experimental result, and pressurization rate was defined from the trace. In this study, three pressurization rates (64.34, 73.86 and 85.44 MPa/s) are considered, and propagation lengths are measured. Also, a progression of the crack propagation recorded by a high-speed digital camera is presented.

• Magazine of the Korea Concrete Institute
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• v.14 no.6
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• pp.14-19
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• 2002

과연 콘크리트 구조물에 있어서 누수 균열은 문제가 되는 것일까？ 이에 대해 설계, 구조 시공, 재료(콘크리트), 방수, 품질 및 안전의 관련 전문가는 여러 가지 이견을 말하고 있다. 또한 콘크리트 구조물에 관계하는 발주자, 건축주, 사용자, 시공자의 입장도 상황에 따라 다르게 해석하고, 평가하고 있다. 예를 들면 일반적으로 발주자(건축주 등)는 시공자에게 누수 균열은 하자이므로 무조건 보수할 것을 요구하는 반면 사용자(언론 포함)가 문제를 제기할 때(공공공사의 경우) 발주자는 이에 대해 크게 문제되지 않는다고 답변하는 경우도 많다. 어떤 기술자는 콘크리트의 누수 균열은 피할 수 없는 사항이므로 근본적으로 해결할 수 없으므로 완벽한 시공 및 보수는 어렵고, 다만 전체적인 누수량이 어느 정도 이하가 되도록만 관리할 뿐이라고 말하고, 또한 지하 구조물의 누수 균열은 피할 수 없어, 누수를 시각적으로 가리기 위한 보호벽을 쌓아 관리하는 것이 당연하다고 말하는 기술자도 있다. 그럼에도 불구하고 일반 사용자들은 무조건 누수균열이 없어야 한다고 의견을 제시하고 있다. 특히 언론에 구조물 누수의 문제가 수시로 보도되어 관계자 및 관련 건설기술자들의 자존심이 크게 훼손되고, 이를 보수하기 위한 비용이 엄청나게 지출되고 있음을 볼 때 적당히 간과해서는 안될 문제임에는 틀림없다.(중략)

• Computational Structural Engineering
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• v.7 no.4
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• pp.119-126
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• 1994

One of the most serious promblems in the concrete structures is cracking failure due to the several complicated reasons. These cracks are not only serious structural problems, but also lower the durability and deteriorate the structural shape, which cause the reinforcement rust in the open air and sea water. An analytical study was undertaken to investigate the cracking problems in the one of concrete caissons using Finite Element Method. This caisson is modelled with plate elements and truss elements for the walls and lifting cables respectively and analyzed in the every construction stages, such as lifting, moving, sinking, filling, towing, setting, and proposed reasonable construction methods for the concrete caisson structures.