• Tunnel and Underground Space
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• v.29 no.2
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• pp.124-134
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• 2019

Subcritical crack growth in rock material can occur under monotonic and cyclic loading. Subcritical crack growth plays an important role in evaluating the long-term stability of structures in rocks. This paper presents the results of studies conducted to determine subcritical crack growth parameters under monotonic and cyclic loading in rock-like material. The constant stress rate method was employed for monotonic loading. The subcritical crack growth parameter of n under cyclic loading was determined by the relation between the rate of crack growth per cycle and stress intensity factor range. The specimens contained pre-existing flaws with 45 and 60 degrees of inclination angle and flaws spacing and continuity were varied to arrange crack growth in shear or tensile manner. The results show that the parameter of n is almost constant regardless of the applied load conditions such as monotonic and cyclic or shear and tension.

• 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.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.4
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• pp.491-496
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• 2013

Finite element simulations of tensile tests were performed to determine the equivalent stress - equivalent plastic strain curves, critical equivalent stresses, and critical equivalent plastic strains. Then, the curves were used as inputs to finite element simulations of fracture toughness tests to determine the plane strain fracture toughness. The critical COD was taken as the COD when the equivalent plastic strain at the crack tip reached a critical value, and it was used as a crack growth criterion. The relationship between the critical COD and the critical equivalent plastic strain or the reduction of area was found. The relationship between the plane strain fracture toughness and the product of the critical equivalent stress and the critical equivalent plastic strain was also found.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2009.05a
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• pp.175-176
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• 2009

연성 기판을 기초로 하는 플렉서블 디스플레이 등의 연성 소자에 적용되는 TCO, 투습방지막의 기계적 특성을 시험하였다. 실제 사용 환경에서의 기계적 특성을 평가하기 위하여 굽힘시험과 인장시험을 적용하였다. PET 기판위에 PE-CVD 공정으로 성장된 실리콘 산화물 ($SiO_x$) 박막과 그 위에 스퍼터링 공정으로 성장된 투명 전도성 산화물 (TCO, Transparent Conducting Oxide) 박막의 시험 결과, 균열 생성 임계 변형량은 TCO 박막에 의해서 결정됨을 알 수 있었다. 따라서 향상된 기계적 특성을 얻기 위해서는 TCO 박막의 특성 제어가 필요하다.