• 화약ㆍ발파
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• 제37권3호
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• pp.25-33
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• 2019

지하광산의 갱내 굴착 과정에서 폭약을 사용하여 발파하는 경우, 최외곽공의 폭력을 조절하여 외부 암반의 손상도 감소와 원활한 파단면을 형성하는 작업은 종업자의 안전 및 작업능률을 향상시키는 결과를 가져올 수 있다. 본 연구는 2차원의 동적파괴과정해석기법인 DFPA-2D 코드를 사용하여 단일 장약공에서 발파 시, 장약공의 직경과 디커플링 지수에 따라 생성되는 균열손상범위를 수치해석적으로 확인하였고 Sweden의 발파손상영역 경험식을 이용하여 암반손상범위를 예측하고 DFPA 해석결과와 비교하였다. 추가로 DFPA코드를 지하채광발파의 최외곽공 발파균열예측에 적용하여 파단면형성 및 발파손상발생 메커니즘에 대하여 검토하였다.

• Nuclear Engineering and Technology
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• 제53권3호
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• pp.974-987
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• 2021

This paper presents ductile fracture simulation of full-scale cracked pipe for nuclear piping materials using the cohesive zone model (CZM). The main objective of this study is to investigate the applicability of CZM to predict ductile fracture of cracked pipes with various crack shapes and under quasi-static/dynamic loadings. The transferability of the traction-separation (T-S) curve from a small-scale specimen to a full-scale pipe is demonstrated by simulating small- and full-scale tests. T-S curves are calibrated by comparing experimental data of compact tension specimens with finite element analysis results. The calibrated T-S curves are utilized to predict the fracture behavior of cracked pipes. Three types of full-scale pipe tests are considered: pipe with circumferential through-wall crack under quasistatic/dynamic loadings, and with 360° internal surface crack under quasi-static loading. Computational results using the calibrated T-S curves show a good agreement with experimental data, demonstrating the transferability of the T-S curves from small-scale specimen.

• Journal of Welding and Joining
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• 제26권3호
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• pp.51-60
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• 2008

This paper is to evaluate fracture characteristics of API 2W Gr.50 TMCP steel weldment typically applied for offshore structures, with the focus on the influence of heat input arising from flux cored arc welding. Based on the results and insights developed from this study, it is found that the toughness for both CTOD and impact exhibits a tendency to decrease as the weld heat input increases. The reheated zone of weldmetal exhibit lower hardness than solidified zone and microstructure that are liable to affect the toughness are acicular ferrite and martensite-austenite constituents (M-A). In particular, M-A is a more effective micro-phase for CTOD toughness than impact toughness.

• 한국정밀공학회지
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• 제19권5호
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• pp.43-50
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• 2002

Friction welding has many merits such as energy efficiency, simple processing, etc butt difficult to obtain good weld at the welded interface and heat affected zone. To date, the continuum mechanics and fracture mechanics are utilized to analyse stresses at the interface and propagation of cracks. In this study. STS304 and SM15C are selected because they can be differentiated distinctively from metallic point of view and crack can be observed easily. It is ovserved during friction welding that STS304, rotary part is hatter than SH15C, fixed part. The last fracture occurs around the center because the surface of fatigue fracture has smooth regions, due to the separation phenomenon in plastic flows layers and striation dimple pattern.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1999년도 봄 학술발표회 논문집
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• pp.42-49
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• 1999

Because the linear elastic tincture analysis has been proved to be insufficient in predicting the failure of cracked bodies, in recent years, a number of fracture concepts have been studied which remain applicable in the presence of large-scale plasticity near a crack tip. This work thereby presents a new finite element model, as accurate as possible, to analyze plane problems of ductile fracture under large-scale yielding conditions. Based on the incremental theory of plasticity, the p-version finite element analysis is employed to account for the values of J-integral, the most dominant fracture parameter, and the shape of plastic zone near a crack tip by using the J-integral method and equivalent domain integral method. The numerical results by the proposed model are compared with the theoretical solutions in literatures and the numerical solutions by the i,-version of F.E.M.

• 한국세라믹학회지
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• 제34권2호
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• pp.157-162
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• 1997

소결온도 및 열처리에 의하여 미세조직을 변화시킨 질화규소의 파괴강도특성 및 그 신뢰성 평가를 하였다. 결정립이 클수록 파괴인성치는 증가하였지만 굽힘강도는 저하하였다. 균열재의 파괴응력 $\sigma$c와 등가균열길이 ae와의 관계는 프로세스 존 크기 파기기준에 의한 계산 결과와 매우 잘 일치하였다. 그리고 굽힘파괴응력 $\sigma$F와 파괴인성치 KIC의 통계적 특성을 고려한 파괴평가고건을 제안하였다.

• 한국해양공학회지
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• 제7권2호
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• pp.91-102
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• 1993

The elastic-plastic fracture thoughness J sub(IC) of Nuclear Reactor Vessel Steel(SA 508-3) which has high toughness was discussed at temperatures RT, $-20^{\circ}C$, $200^{\circ}C$ and 1/2/CT specimen was used for this study. Especially the two methods recommended in ASTM and JSME were compared. It was difficult to find J sub(IC) by ASTM R-curve method with the specimen used for this research, while JSME R-curve method yielded good result. The stretched zone width menthod gave slightly larger J sub(IC) values than those by the R-curve method for SA 508-3 steel.

• Nuclear Engineering and Technology
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• 제44권1호
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• pp.79-88
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• 2012

Migration tests were performed with conservative tracers in a fractured zone that had a single fracture of about 2.5 m distance at the KURT. To interpret the migration of the tracers in the fractured rock, a solute transport model was developed. A two dimensional variable aperture channel model was adopted to describe the fractured path and hydrology, and a particle tracking method was used for solute transport. The simulation tried not only to develop a migration model of solutes for open flow environments but also to produce ideas for a better understanding of solute behaviours in indefinable fracture zones by comparing them to experimental results. The results of our simulations and experiments are described as elution and breakthrough curves, and are quantified by momentum analysis. The main retardation mechanism of nonsorbing tracers, including matrixdiffusion, was investigated.

• 산업기술연구
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• 제19권
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• pp.197-208
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• 1999

The process of localization of cracks and movement of the fracture process zone(FPZ) was studied using the acoustic-emission(AE) techniques. The rate of AE events and sources of AE activity were studied for mortar and rock specimens loaded in uniaxial compression. A series of transducers could be used to detect and AE activity. Based on the time differences between detection of the event at different transducers, source of AE activity could be detected. The rate of AE events increased sharply before peak load. The highest rate occurred just after peak load was attained. The effective crack length estimated from the modified linear-elastic fracture mechanics seemed consistent with the optical and AE measurements.

• Coupled systems mechanics
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• 제4권3호
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• pp.211-235
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• 2015

In this work we present a one-dimensional damage model capable of representing the dynamic fracture for elastodamage bar with combined hardening in fracture process zone - FPZ and softening with embedded strong discontinuities. This model is compared with another one we recently introduced (Do et al. 2015) and it shows a good agreement between two models. Namely, it is indicated that strain-softening leads to a sensitivity of results on the mesh discretization. Strain tends to localization in a single element which is the smallest possible area in the finite element simulations. The strain-softening element in the middle of the bar undergoes intense deformation. Strain increases with increasing mesh refinement. Strain in elements outside the strain-softening element gradually decreases to zero.