• 대한조선학회논문집
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• 제49권4호
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• pp.281-286
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• 2012

Single frame structures with notches were fractured by applying drop impact loadings at room temperature and low temperature. Johnson-Cook shear failure model has been employed to simulate the fractured single frame structures. Through several numerical analyses, material constants for Johnson-Cook shear failure model have been found producing the cracks resulted from experiments. Fracture strain-stress triaxiality curves at both room temperature and low temperature are presented based on the extracted material constants. It is expected that the fracture strain-stress triaxiality curves can offer objective fracture criteria for the assessment of structural fractures of polar class vessel structures fabricated from DH36 steels. The fracture experiments of single frame structures revealed that the structure on low temperature condition fractures at much lower strain than that on room temperature condition despite the same stress states at both temperatures. In conclusion, the material properties on low temperature condition are essential to estimate the fracture characteristics of steel structures operated in the Northern Sea Route.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2005년도 제24회 춘계학술대회논문집
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• pp.47-52
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• 2005

이 논문은 열폭발 실험에서의 열적, 화학적, 기계적 행동의 결과에 대한 3차원 모델 결과를 나타낸다. 폭발이 관찰되기 전까지 제한된 고 폭발물은 시간당 $1^{\circ}C$의 비율로 가열된다. 임의의 Lagrangian-Euler 코드를 사용하여 모델링된 가열, 점화 그리고, deflagration 단계는 구조적에서 동적인 hydro 시간단계까지 변하는 넓은 범위의 시간 영역에서 다루어 질수 있다. Johnson-Cook Failure Model (JCFM)에 실험적 고장분포를 더하여 폭발기기의 균열방향과 fragment의 크기를 예측할 수 있는 모델을 개발한다.

• 한국항공우주학회지
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• 제50권7호
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• pp.465-470
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• 2022

본 논문은 알루미늄 6061의 고속 충격 해석과 고속 충격 시험 결과를 비교 검증하여 금속 재료의 고속 충격에 의한 거동 특성을 연구하였다. 고속 충격 해석을 위해 만능재료시험기를 이용한 준정적 시험과 Hopkinson bar를 이용한 동적 시험을 통해 Huh-Kang 모델과 Johnson-Cook 파손 모델의 계수를 구했다. LS-DYNA 프로그램 해석을 이용하여 관통 속도와 형상을 결과로 예측했고 고속 충격 시험기를 이용한 시험 결과와 비교하였다. 이를 바탕으로 항공기 가스터빈 엔진 블레이드 컨테인먼트 평가 연구에 적용하고자 한다.

• 대한기계학회논문집A
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• 제40권2호
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• pp.167-173
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• 2016

본 논문은 유한요소해석을 이용한 고변형률 조건에서의 연성파손 해석기법을 제안한다. 고변형률 하중이 작용하는 구조물에 대한 파괴거동 예측을 위해 본 논문에서는 Johnson/Cook 모델을 고려한 수정응력 파괴변형률 모델을 사용하였다. 제시된 모델은 인장 실험 모사해석결과로부터 얻어지는 삼축응력 및 파괴변형률에 의해 파손이 정의된다. 다양한 실험속도의 인장 실험결과 및 정적 하중조건에서의 파괴인성 실험을 이용하여 수정응력 파괴변형률 모델의 변수를 결정하였다. 결정된 모델을 이용하여 동적하중조건에서 파괴인성시편에 대한 해석을 수행하였으며 해석결과와 실험결과를 비교하여 해석기법을 검증하였다.

• 국제강구조저널
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• 제18권5호
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• pp.1754-1760
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• 2018

The present article showcases a temperature dependent cohesive zone model (CZM)-based fi nite element simulation of drop weight tear test (DWTT), to analyse fracture behavior of pipeline steel (PS) at different temperatures. By co-relating the key CZM parameters with known mechanical properties of PS at varying temperature, a temperature dependent CZM for PS is proposed. A modified form of Johnson and Cook model has been used for the true stress-strain behavior of PS. The numerical model, using Abaqus/CAE 6.13, has been validated by comparing the predicted results with load-displacement curves obtained from test data. During steady-state crack propagation, toughness parameters (such as CTOA and CTOD) were found to remain fairly constant at a given temperature. These toughness parameters, however, show an exponential increase with increase in temperature. The present paper offers a plausible approach to numerically analyze fracture behavior of PS at varying temperature using a temperature dependent CZM.

• Nuclear Engineering and Technology
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• 제48권5호
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• pp.1252-1263
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• 2016

This paper presents a numerical method to simulate ductile tearing in cracked components under high strain rates using finite element damage analysis. The strain rate dependence on tensile properties and multiaxial fracture strain is characterized by the model developed by Johnson and Cook. The damage model is then defined based on the ductility exhaustion concept using the strain rate dependent multiaxial fracture strain concept. The proposed model is applied to simulate previously published three cracked pipe bending test results under two different test speed conditions. Simulated results show overall good agreement with experimental results.

• International Journal of Naval Architecture and Ocean Engineering
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• 제10권1호
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• pp.103-118
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• 2018

When collision accident between ships or between ship and offshore platform occurs, a common phenomenon that occurs in structures is the plastic deformation accompanied by a large strain such as fracture. In this study, for the rational design against accidental limit state, the plastic material constants of steel plate which is heated by line heating and steel plate formed by cold bending procedure have been defined through the numerical simulation for the high speed tension test. The usefulness of the material constants included in Cowper-Symonds model and Johnson-Cook model and the assumption that strain rate can be neglected when strain rate is less than the intermediate speed are verified through free drop test as well as comparing with numerical results in several references. This paper ends with describing the future study.

• Nuclear Engineering and Technology
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• 제54권7호
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• pp.2386-2394
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• 2022

In this paper, smooth and notched bar tensile tests of austenitic stainless steel 304 are performed, covering four different multi-axial stress states and six different strain rate conditions, to investigate the effect of the stress triaxiality and strain rate on fracture strain. Test data show that the measured true fracture strain tends to decrease with increasing stress triaxiality and strain rate. The test data are then quantified using the Johnson-Cook (J-C) fracture strain model incorporating combined effects of the stress triaxiality and strain rate. The determined J-C model can predict true fracture strain overall conservatively with the difference less than 20%. The conservatism in the strain-based acceptance criteria in ASME B&PV Code, Section III, Appendix FF is also discussed.

• Computers and Concrete
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• 제9권1호
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• pp.21-33
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• 2012

This paper presents the numerical simulation of the rigid 12.6 mm diameter kinetic energy ogive-nosed projectile impact on plain and fiber reinforced concrete (FRC) targets with compressive strengths from 45 to 235 MPa, using a three-dimensional finite element code LS-DYNA. A combined dynamic constitutive model, describing the compressive and tensile damage of concrete, is implemented. A modified Johnson_Holmquist_Cook (MJHC) constitutive relationship and damage model are incorporated to simulate the concrete behavior under compression. A tensile damage model is added to the MJHC model to analyze the dynamic fracture behavior of concrete in tension, due to blast loading. As a consequence, the impact damage in targets made of plain and fiber reinforced concrete with same matrix material under same impact velocities (650 m/s) are obtained. Moreover, the damage distribution of concrete after penetration is procured to compare with the experimental results. Numerical simulations provide a reasonable prediction on concrete damage in both compression and tension.

• 한국해양공학회지
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• 제33권3호
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• pp.259-271
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• 2019

It is important to obtain reasonable predictions of the extent of the damage during maritime accidents such as ship collisions and groundings. Many fracture models based on different mechanical backgrounds have been proposed and can be used to estimate the extent of damage involving ductile fracture. The goal of this study was to compare the damage extents provided by some selected fracture models. Instead of performing a new series of material constant calibration tests, the fracture test results for the ship building steel EH36 obtained by Park et al. (2019) were used which included specimens with different geometries such as central hole, pure shear, and notched tensile specimens. The test results were compared with seven ductile fracture surfaces: Johnson-Cook, Cockcroft-Latham-Oh, Bai-Wierzbicki, Modified Mohr-Coulomb, Lou-Huh, Maximum shear stress, and Hosford-Coulomb. The linear damage accumulation law was applied to consider the effect of the loading path on each fracture surface. The Swift-Voce combined constitutive model was used to accurately define the flow stress in a large strain region. The reliability of these simulations was verified by the good agreement between the axial tension force elongation relations captured from the tests and simulations without fracture assignment. The material constants corresponding to each fracture surface were calibrated using an optimization technique with the minimized object function of the residual sum of errors between the simulated and predicted stress triaxiality and load angle parameter values to fracture initiation. The reliabilities of the calibrated material constants of B-W, MMC, L-H, and HC were the best, whereas there was a high residual sum of errors in the case of the MMS, C-L-O, and J-C models. The most accurate fracture predictions for the fracture specimens were made by the B-W, MMC, L-H, and HC models.