• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1999.10a
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• pp.13-13
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• 1999

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2009.04a
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• pp.259-262
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• 2009

지진이나 충돌 등과 같은 동적 하중은 하중 속도에 따라 재료의 파괴 거동이 변하기 때문에 하중 속도는 하중의 위치나 크기와 더불어 재료의 파괴 거동을 결정짓는 중요한 요소 중 하나이다. 특히 콘크리트와 같은 취성재료의 경우 재료의 속도 의존적 거동에 의해 가해진 하중으로부터 발생된 균열의 형상이나 진행 형태가 변하므로 전체 구조물의 거동에도 큰 영향을 끼친다. 따라서 취성재료를 이용한 속도 의존적 파괴 거동에 관한 연구는 그 중요성에 의해 다양한 방법으로 진행되어져 왔으나, 해석을 통한 빠른 하중에서의 파괴 거동 해석은 대부분 무시되어왔다. 하지만 최근 폭발과 같은 매우 빠른 하중에서의 재료의 파괴 거동 대한 관심이 증대되고 있고, 그에 관한 연구의 필요성도 점차 커지고 있다. 따라서 본 연구에서는 irregular lattice model의 하나인 rigid-body-spring networks(RBSN)를 이용하여 취성 재료의 파괴 거동해석에 적합한 수치 해석 모델을 개발하였다. 동적 해석을 위해 각 요소에 질량을 부여하고, 각 요소의 거동은 시간 적분에 의하여 계산된다. 이를 이용하여 빠른 하중에서의 취성 재료의 파괴 거동 특성을 분석하고 기존 실험과의 비교를 통해 수치 해석 모델의 타당성을 입증하였다.

• Tunnel and Underground Space
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• v.10 no.2
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• pp.227-236
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• 2000

The fracture toughness can be measured by the two testing methods using chevron-notched specimen according to the ISRM Working Group of Commission of Testing Methods. They are chevron bend (CB) test and short rod (SR) test. In this study, the suggested methods (Level I tests) were conducted on the CB and SR specimens of Chuncheon granite. In addition. the J-integral analysis was combined with an acoustic emission technique to determine the fracture toughness. The results from two telling methods were analyzed in terms of the anisotropy and the acoustic emission characteristics.

• Journal of the Korea Concrete Institute
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• v.14 no.1
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• pp.58-66
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• 2002

The objective of this study is to examine the fracture characteristics of concrete at early ages such as critical stress intensity factor, critical crack-tip opening displacement, fracture energy, and bilinear softening curve based on the concepts of the effective-elastic crack model and the cohesive crack model. A wedge splitting test for Mode I was performed on cubic wedge specimens with a notch at the edge. By taking various strengths and ages, load-crack mouth opening displacement curves were obtained, and the results were analyzed by linear elastic fracture mechanics and the finite element method. The results from the test and analysis showed that critical stress intensity factor and fracture energy increased, and critical crack-tip opening displacement decreased with concrete ages from 1 day to 28 days. By numerical analysis four parameters of bilinear softening curve from 1 day to 28 days were obtained. The obtained fracture parameters and bilinear softening curves at early ages may be used as a fracture criterion and an input data for finite element analysis of concrete at early ages.

• Tunnel and Underground Space
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• v.27 no.3
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• pp.121-131
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• 2017

We studied the time-dependent behaviors of rock and concrete materials by conducting the static and dynamic long-term strength tests. In particular, acoustic emission(AE) signals generated while the tests were analyzed and used for the long-term stability evaluation. In the static subcritical crack growth test, the long-term behavior and AE characteristics of Mode I and Mode II were investigated. In the dynamic long-term strength test, the fatigue limit and characteristics of generation of AE were analyzed through cyclic four points bending test. The graph of the cumulative AE hits versus time showed a shape similar to that of the creep curve with the first, second and third stages. The possibility for evaluating the static and dynamic long-term stability of rock and concrete is presented from the log - log relationship between the slope of the secondary stage of cumulative AE hits curve and the delayed failure time.

• Tunnel and Underground Space
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• v.23 no.3
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• pp.219-227
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• 2013

Although Mohr-Coulomb failure criterion has limitations in that it is a linear criterion and the effect of the intermediate principal stress on failure is ignored, this criterion has been widely accepted in rock mechanics design. In order to overcome these shortcomings, the Hoek-Brown failure criterion was introduced and recently a number of 3-D failure criteria incorporating the effect of the intermediate principal stress on failure have been proposed. However, in many rock mechanics designs, the possible failure of rock mass is still evaluated based on Mohr-Coulomb criterion and most of practitioners are accustomed to understanding the strength of rock mass in terms of the internal friction angle and cohesion. Therefore, if the equivalent Mohr-Coulomb strength parameters of the advanced failure criteria are calculated, it is possible to take advantage of the advanced failure criteria in the framework of the Mohr-Coulomb criterion. In this study, a method expressing the tangential Mohr-Coulomb strength parameters in terms of the stress invariant is proposed and it is applied to the generalized Hoek-Brown criterion and the HB-WW criterion. In addition, a new approach describing the geometric meaning of the ${\sigma}_2$-dependency of failure criteria in 3-D principal stress space is proposed. Implementation examples of the proposed method show that the influence of the intermediate principal stress on the tangential friction angle and cohesion of the HB-WW criterion is considerable, which is not the case for the 2-D failure criterion.

• Journal of Adhesion and Interface
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• v.14 no.3
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• pp.121-127
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• 2013

In this work, the thermoplastic polyurethane (TPU) was melt-blended with EPDM, NBR and BR to form TPU/Rubber blend films, their composition and friction-induced surface fracture relationship was investigated. TPU/EPDM and TPU/BR blends exhibited the improved friction-induced surface fracture, especially the effect of BR was excellent. With addition of more than 10 wt% BR, TPU/BR blends exhibited the improved friction-induced surface fracture. The increase of the soft segment with increasing BR content, which was confirmed by scanning electron microscopy (SEM) analysis enabled us to estimate the improved friction-induced surface fracture.

• Journal of the Earthquake Engineering Society of Korea
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• v.14 no.5
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• pp.23-31
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• 2010

In this study, a shaking table test was performed for the evaluation of the failure capacity of an anchor foundation system in the case of an aged condition. For the shaking table test, three kinds of specimens were manufactured as follows: 1) a non-damaged anchor; 2) a specimen with cracks running through the anchor; and 3) a specimen with cracks along the expected corn-shape fracture away from the anchor. A dynamic characteristic was determined through a measurement of the frequency response function (FRF), and the seismic capacity was evaluated by using a shaking table test. Failure capacities were calculated using an acceleration response and it was compared with the anchor design code.

• Proceedings of the KIEE Conference
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• 2015.07a
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• pp.453-454
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• 2015

낙뢰에 대한 전력계통의 적절한 보호를 위해서 피뢰기/아킹혼의 적절한 보호작동 설계가 필요하다. 피뢰기/아킹혼은 낙뢰에 의해 이상전압 발생시 섬락 동작을 통하여 계통을 보호하므로, 절연파괴 특성에 대한 상세한 연구가 필요하다. 본 논문에서는 피뢰기/아킹혼의 섬락동작에 직접적인 영향을 주는 절연갭의 미세조정에 따른 절연파괴 특성에 대한 연구를 실험적으로 수행하였다. 실험 결과, 갭간격이 증가할수록 절연파괴전압은 증가하고, 그 증가폭은 지수적으로 감소하는 전형적은 방전 특성을 확인하였으며, 그 상세한 변화 값을 측정하였다. 또한 표준 갭간격에서의 섬락특성과 섬락전압 분포도를 구하여 절연협조 상태를 분석하였다.

• Journal of Welding and Joining
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• v.25 no.4
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• pp.9-14
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• 2007

선박의 고강도화 및 극후물화가 진행됨에 따라 선체 구조물의 파괴 특성에 대한 관심이 높아지고 있으며, 최근 균열정지의 관점에서 취성균열 정지특성에 대한 연구가 활발히 이루어지고 있다. 기존의 연구결과에 따르면 65mmt 이상의 극후물 용접부에 대해서 취성균열 정지특성의 저하가 발생할 가능이 있다고 보고되고 있으며, 취성균열 정지특성이 우수한 강재의 개발 이외에 용접부 보강재의 부착, 보수 용접 실시 등 개선 방안을 마련하기 위한 다양한 연구가 진행되고 있다. 그러나 극후물 용접부 취성균열 전파기구에 관한 규명은 현재 전무한 실정이며, 강재 두께의 영향 이외에 용접 입열량 용접부 잔류응력 등의 효과가 복합적으로 검토되어야 한다. 아울러 극후물 용접부 균열정지 파괴인성의 평가, 대형파괴시험을 대체할 소형시험법의 개발 및 검증 등에 관한 연구가 요구된다.