• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.3
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• pp.17-24
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• 2019

Carbon Fiber Reinforced Polymers(CFRP) has widely utilized as a material for rehabilitation because of its light-weight, deformability and workability. Because CFRP is brittle material whereas steel is ductile, it is inappropriate to apply conventional design approach for steel reinforcement. For ductile material, the behavior of combined elements is on average of that of unit element due to the stress redistribution between elements after yielding. Therefore, the mean value of the stress of combined elements is equal to that of unit element and the standard variation is smaller. Therefore, although the design value can increase, it is used as constant value because it is conservative and practical approach. However, for brittle material, the behavior of combined elements is governed by the weaker element because no stress redistribution is expected. Therefore, both the mean value and standard variation of the stress of combined elements decreases. For this reason, the design value would decrease as the number of element increases although it is eventually converged. In this paper, in brittle material, it is verified that the combination of unit element with normal distribution results in combined element with weibull distribution, so the modifying equation of mechanical properties is proposed with respect to the area load applied.

• Proceedings of the Korean Nuclear Society Conference
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• 1998.05b
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• pp.124-129
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• 1998

고온고압 수화학 분위기를 모사한 조건에서 피로균열성장 거동에 관한 연구를 수행하였다. 고온고압분위기 모사를 위해 Load machaine, Autoclave, Water loop, 균열측정장치(Reversing DCPD) 그리고 전기화학변수 측정장치 등을 설치하였다. 우선 공기분위기 및 상온수화학 분위기에서의 시험을 통해 안정성을 확인하였으며, 안정한 조건에서 고온수화학분위기에서 실험을 수행하였다. 수화학 분위기에서 용존산소에 상관없이 취성파면이 관찰되었다. 용존산소의 양이 적을 경우(10ppb이하) 발견된 취성파면의 양은 연성파면에 비해 훨씬 적었으며, 용존산소가 높을 경우(8000ppb) 취성파면의 양이 많이 발견되었다. 산소포화된 고온수화학 분위기 피로시험결과는 피로균열성장이 주로 취성파면에 의해 이루어졌으며, 균열성장속도 또한 크게 증가하였다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.1 s.173
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• pp.250-258
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• 2000

The reinforcing effects of ductile short-fiber reinforced brittle matrix composites are studied by, measuring flexural strength, fracture toughness and impact energy as functions of fiber volume fraction and length. The parameters of fracture mechanics, K and J are applied to assess fracture toughness and bridging stress. It is found that fracture toughness is greatly, influenced by the bridging stress ill which fiber pull-out is occur. For the reinforcing effects as functions of fiber volume fraction($V_f$ = 1, 2, 3 %) and length(L = 3, 6. 10cm), the flexural strength is maximum at $V_f$ = 1% and both fracture toughness.

• Proceedings of the Korean Nuclear Society Conference
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• 1998.05b
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• pp.118-123
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• 1998

원자로 압력용기 재료로 사용되고 있는 ASTM SA508 및 SA533 계열의 재료는 결정구조가 체심입방격자(bcc)로서 시험온도별 최대흡수에너지(USE)에 대한 선도를 그리면 고온에서는 연성이 크고, 저온에서는 취성이 큰 전형적인 “S”자 형태의 Cv-천이온도곡선으로 나타난다. 그리고 조사전과 조사후의 연성-취성천이온도곡선을 흡수에너지값이 30ft-lb 또는 50ft-lb인 지점에석 비교해보면 재료의 조사취화(radiation embrittlement)현상으로 온도가 높은 쪽으로 이동됨을 알 수 있으며, 이러한 온도의 이동값은 원자로의 운전수명과 밀접한 관련이 있다. 따라서 조사전후의 흡수에 너지값에 따른 온도변화량를 정확하게 산출하기 위해서는 시편의 온도를 조절하는 장치 및 시편을 아주 짧은 시간내에 충격시험기의 앤빌까지 장전하는 장치 둥의 충격시험시스템 구축은 매우 중요하다. 이에 조사계시험시설(IMEF)에서는 원자로 압력용기 감시시험에 대한 충격시험시스템을 구축하였고, 이의 내용은 감시시험 수행에 기준이 되는 ASTM El85-82 및 과학기술처 고시 제 92-20호의 세부내용을 충분하게 만족시키는 것으로 확인되었으며, 이렇게 확인된 내용들은 현재 국내에서 수행되고 있는 감시시험에 적극적으로 활용되고 있다.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.5
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• pp.140-147
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• 2003

As the huge energy transfer systems like as nuclear power plant and steam power plant are operated for a long time at a high temperature, mechanical properties are changed and ductile-brittle transition temperature is raised by degradation. So it is required to estimate degradation in order to assess the safety, remaining life and further operation parameters. The sub-sized specimen test method using surveillance specimen was developed for evaluating the integrity of metallic components. In this study, we would like to present the evaluation technique of the ductile-brittle transition temperature by the sub-sized specimen test. The four classes of the thermally aged 1Cr-1Mo-0.25V specimens were prepared using an artificially accelerated aging method. The tensile test and fracture toughness test were performed. The results of the fracture toughness tests using the sub-sized specimens were compared with the evaluation technique of the ductile-brittle transition temperature.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.579-584
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• 2001

As the huge energy transfer systems like as nuclear power plant and steam power plant are operated for a long time, mechanical properties are changed and ductile-brittle transition temperature is raised by degradation. So it is required to estimate degradation in order to assess the safety, remaining life, and further operation parameters. The sub-sized specimen test method using surveillance specimen was developed for evaluating the integrity of metallic components. In this study, we would like to present the evaluation technique of the ductile-brittle transition temperature by the sub-sired specimen test. The four classes of the thermally aged 1Cr-1Mo-0.25V specimens were prepared using an artificially accelerated aging method. The tensile test and fracture toughness test were performed. The results of the fracture toughness tests using the sub-sized specimens were compared with the evaluation technique of the ductile-brittle transition temperature.

• Magazine of the Korea Concrete Institute
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• v.10 no.3
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• pp.117-124
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• 1998

본 연구는 고성능 철근콘크리트 보의 연성능력에 관한 실험이다. 실험변수로는인장철근비( )와 하중재하형태(1점가력과 2점가력)가 있다. 콘크리트의 실린더 압축강도가 800-900㎏/㎠, 슬럼프 20∼25㎝ 및 슬럼프 플로우가 60∼70㎝인 고성능 철근콘크리트 보의 휨 실험 결과,고성능 콘크리트는 일반강도 콘크리트보다 취성적인 성질을 나타냈으며, 이러한 성질은 고성능 콘크리트의 연성능력을 감소시켰다. 고성능철근콘크리트의 경우 등가응력블록 변수는 MacGregor블록이나 New Zealand 규준을 사용하는 것이 바람직하다. 또한, 극한 곡률을 구할때는 cu= 0.0042값을 사용하는 것이 타당하다고 사료된다. 고성능 철근콘크리트 보의 경우, 현재 ACI 규준의 철근비에서 허용하는 2 및 4 이상의 연성지수 확보는 각각 '/ 0.30 범위에서 정적하중 상태의 경우 철근비가 - '=0.60 b이하에서 가능하고 휨 부재의 모멘트 재분배를 위한 경우는 철근비를 - '=0.33 b이하로 낮추어야 할 것으로 판단된다.

• Journal of Korean Tunnelling and Underground Space Association
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• v.18 no.5
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• pp.469-485
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• 2016

The failure of rock mass around deep tunnel, different from shallow tunnel largely affected by discontinuities, is dominated by magnitudes and directions of stresses, and the failures dominated by stresses can be divided into ductile and brittle features according to the conditions of stresses and the characteristics of rock mass. It is important to know the range and the depth of the V-shaped notch type failure resulted from the brittle failure, such as spalling, slabbing and rock burst, because they are the main factors for the design of excavation and support of deep tunnels. The main features of brittle failure are that it consists of cohesion loss and friction mobilization according to the stress condition, and is progressive. In this paper, a three-dimensional numerical model has been developed in order to simulate the brittle behavior of rock mass around deep tunnel by introducing the bi-linear failure envelope cut off, elastic-elastoplastic coupling and gradual spread of elastoplastic regions. By performing a series of numerical analyses, it is shown that the depths of failure estimated by this model coincide with an empirical relation from a case study.

• Proceedings of the KSME Conference
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• 2005.11a
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• pp.129.2-129.2
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• 2005

• Journal of the Korean Society for Precision Engineering
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• v.24 no.10
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• pp.13-18
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• 2007