• Tunnel and Underground Space
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• v.24 no.1
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• pp.67-80
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• 2014

Long-term stability and delayed failure of granite were evaluated through the laboratory test based on Wilkins method and Brazilian disc test (BDT) which yields tensile strength, mode I fracture toughness and subcritical crack growth parameters. Then, the long-term strength of granite was estimated by using analytical models and long-term stability of compressed air-energy storage (CAES) pilot cavern pressurized up to 5 ~ 6 MPa was evaluated using numerical code, FRACOD with the determined subcritical crack growth parameters. The results of test and analyses showed that the subcritical crack growth index, n was determined as 29.39 and the inner pressure of 5 ~ 6 MPa had an insignificant effect on the long-term stability of pilot cavern. It was also found that the measurement and analysis of acoustic emission events can describe the accumulation of damage due to subcritical crack growth quantitatively. That is, AE monitoring can provide the current status of rock under loading if we make an identical installation condition in the field with that of the laboratory test.

• The Proceedings of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.3 no.4
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• pp.57-61
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• 1989

이 논문은 phenolic resin의 CTI에 대하여 기압을 파라메터로 고찰하였다.(IEC publication 112[습식법]). 1) 기압이 낮아짐에 따라 건조대의 형성 및 미소 불꽃방전을 발생하는 개시 적하수는 300[V] 이상에서 증가되고 있다. 2) 900[mb]에서 Tracking 파괴 적하수가 가장 높으며 기압이 낮아 질수록 CTI의 값은 증가하고 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.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.12 s.255
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• pp.1573-1580
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• 2006

In this study, fatigue tests were carried out under push-pull loading condition using spheroidal graphite cast iron in order to clarify the internal fatigue fracture mechanism in an extremely low cycle fatigue regime. It is found that a successive observation of internal fatigue damage it is found that the fracture processes go through three stages, that is, the generation, growth and coalescence of microvoids originated from debonding of graphite-matrix interface. It is also found that the crack which is initiated from the void propagates by coalescence of neighboring cracks and the fatigue crack growth rate can be expressed in form of the Manson-Coffin rule type. In this paper, quantitative analyses of fatigue properties for realization of simulation about fatigue life evaluation are also presented.

• 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.

• The Journal of Engineering Geology
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• v.9 no.3
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• pp.243-251
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• 1999

Granitic rock, by its nature, contains numerous micro-discontinuities including grain boundary, microcracks, microcavities and mineral cleavages. The brittle fracture of rock is a progressive procedure in which the failure occurs with prior microcracking. In this paper, initiation, propagation and interaction of microcracks are considered to be the dominant, controlling micromechanisms of macroscopic failure. The authors show a few patterns of microcrack initiation and propagation by using sequential photographs of water-saturated granite taken under triaxial compressive state. The failure process was observed directly and continuously by a newly developed triaxial compressive test system.

• Korean Journal of Materials Research
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• v.7 no.7
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• pp.623-631
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• 1997

본 연구에서는 주조 2상 스테인리스강의열시효에 대한 시효온도, 시효시간 및 Nb함유량의 영향을 관찰하기 위해 기계적 성질 및 조직을 조사하였으며 Nb을 함유한 주조 2상 스테인리스강의 파괴기구를 규명하기 위해 SEM에 의한 파단면 관찰과 WDS성분분석을 통해 파괴기구의 특성을 고찰하였다. 시효온도와 시효시간이 증가함에 따라 페라니트으 미소경도가 증가하였으며 항복강도의 경우 시효온도와 시효시간에는 영향을 받지 않았으나 Nb을 함유한 재료들이 Nb을 함유치 않은 재료들에 비해 다소 낮은 항복강도 값을 보였다. 충격흡수에너지 값은 시효시간 및 시효온도의 증가에 따라 시험된 모든 재료에서 저하되었는데 0.4% Nb을 함유하는 경우 Nb을 약간 함유하거나 함유치 않은 재료들에 비해 시효시간에 따라 급격한 감소 경향을 보였다. 파단면 관찰결과 페라이트 기지 또는 페라이트/오스테나이트 상경계에서 석출된 VbC를 비롯한 탄화물들이 취성저항성을 낮추는데 크게 기여했음을 알 수 있었다.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.20 no.3
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• pp.284-291
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• 2011

Numerical experiments on biological interfacial layer, DEJ by finite element software ABAQUS have been conducted to study its fracture behavior including crack bridging / arresting characteristics in the model. Crack growth simulation has been carried out by numerical tool, XFEM, devoted to study cracks and discontinuities. The fracture toughness of DEJ has been estimated before and after crack bridging. The implications of bridging in numerical study of fracture behavior of DEJ-like biological interface have been discussed. It has been observed that the results provided by the numerical studies without proper accommodation of bridging phenomenon can mislead. This study can be helpful for understanding the DEJ-like biological interface in terms of its fracture toughness, an important material characteristics. This property of the material is an important measure that has to be taken care during design and manufacturing processes.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.8
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• pp.2431-2435
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• 1996

In order to determine the effects of hydrostatic pressure on the mechanical behavior of graphite fiber reinforced composites, the modulus, fracture stress(maximum stress), and fracture strain of graphite/epoxy composites have been determined as a function of pressure. Composite specimens used in this study were 90-deg unidirectional and had a 60% fiber volume fraction. Compressive tests under five different pressure levels were conducted. The result showed the modulus measured from as initial slope of stress-strain curve increased bilinearly with pressure with a break at 200 MPa. It was also found that fracture stress and fracture strain increased in a linear fashion with pressure.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.9
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• pp.5743-5747
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• 2015

In this study, Fe-based bulk amorphous alloy powder manufactured using gas atomization fabrication was used for laser welding. the fracture behavior of welding layer were analyzed. Tensile test results show that the destruction occurred immediately after the elastic deformation, After plastic deformation of the substrate, the destruction occurred. The actual maximum tensile strength of the welding layer and the substrate are 959.9MPa and 220.4MPa. welding layer were each $485.5{\pm}21$ and $197.4{\pm}14$ to the substrate and the actual microhardness, The welding layer has very high hardness. The welding layer showed a very weak fine acicular structure. The base material was shown in the micro structure appear a coarse grain. SEM observations of the fracture after the tensile test. Fracture morphology of the base metal and the welding layer showed ductile fracture and brittle fracture, respectively.