• International Journal of Korean Welding Society
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• 제3권1호
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• pp.51-56
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• 2003

It is important to evaluate the fracture initiation behaviors of steel structure. It has been well known that the ductile cracking of steel would be accelerated by triaxial stress state. Recently, the characteristics of critical crack initiation of steels are quantitatively estimated using the two-parameters, that is, equivalent plastic strain and stress triaxiality, criterion. This study is paid to the fundamental clarification of the effect of notch radius, which can elevate plastic constraint due to heterogeneous plastic straining on critical condition to initiate ductile crack using two-parameters. Hense, the crack initiation testing were conducted under static loading using round bar specimens with circumferential notch. To evaluate the stress/strain state in the specimens was used thermal elastic-plastic FE-analysis. The result showed that equivalent plastic strain to initiate ductile crack expressed as a function of stress triaxiality obtained from the homogeneous specimens with circumferential notched under static loading. And it was evaluated that by using this two-parameters criterion, the critical crack initiation of homogeneous specimens under static loading.

• 한국압력기기공학회 논문집
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• 제18권2호
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• pp.54-60
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• 2022

ASME BPVC provides stress evaluation rules for Class 2 and 3 nuclear piping. However, such rules are difficult to be applied to reinforced wall-thinned pipes during service. To resolve this issue, a new method for stress evaluation of reinforced wall-thinned pipes is proposed in this work, based on the equivalent stiffness concept. By converting a reinforced wall-thinned pipe to an equivalent straight pipe having the same stiffness, stress evaluation can be proceeded using the current ASME BPVC rules. The proposed method is applied to pipes with 4 different normal pipe size and the effects of reinforcement and wall-thinning dimensions on evaluated stresses are discussed.

• 한국기계가공학회지
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• 제9권2호
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• pp.33-39
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• 2010

The thickness of original hinge model is changed for structural stability in this study. The front end with the largest deformation of 9.8813 mm or the rear middle part with the largest equivalent stress of 6082.6 MPa is respectively shown at door hinge. The lower part of joint pin head with the largest deformation of 0.17499 mm and the largest equivalent stress of 1540.2 MPa are shown. The advanced model with more thickness and stability is shown to have smaller displacement in half and smaller equivalent stress by 3 times by comparing with the original model.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2000년도 추계학술대회 논문집
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• pp.547-550
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• 2000

The steel pipe for fluid catalytic cracking(FCC) unit. petroleum refinery, is lined with refractory to protect the system from high-temperature of the internal flow. The property of the refractory has an effect upon the stress analysis of FCC unit. Because 1-D pipe element or 3-D shell element are usually used in commercial codes of stress analysis to evaluate the structural soundness, the equivalent elastic modulus considering steel and refractory should be applied. In the research, the theoretical method to obtain the value of the equivalent property is introduced and then the stress analysis is carried out with the part of FCC unit.

• 한국산학기술학회논문지
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• 제7권3호
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• pp.265-270
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• 2006

복합재로 된 판재에 대하여 동적 균열이 접합면을 따라서 진행되어 가면서 찢어져 나갈 때 그 계면 주위에서의 응력 상태 및 변형, 견인응력 등을 조사하였다. 최대의 등가응력 및 소성 변형율은 접촉이 바로 떨어지는 부분에서 그리고 판 끝부분의 휘어지는 부근에서 최대의 변형량이 되었다. 견인력은 0.015mm정도로 그 면이 떨어졌을 때 최대치 75 MPa로서 되었다가 서서히 낮아지면서 0.13mm이상 떨어졌을 때는 0으로 일정하게 되었다. 이러한 연구 자료로서 정확한 파괴강도 해석과 안전설계 및 새로운 고급재료의 개발에 필요한 자료를 제공할 수 있는 기초적인 연구를 수행함이 본 연구의 목적이다.

• 한국생산제조학회지
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• 제20권3호
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• pp.280-283
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• 2011

This study investigates the durability of car body and the safety of passenger inside car body in the case of the impact contact at passenger and car body. In case of front impact contact, maximum von Mises equivalent stress and principal stress become 3240.7MPa and 1634MPa respectively at the rear part of car body and the neck of dummy. And maximum total deformation occurred with 14.145mm at the hand of dummy. In case of side impact contact, maximum von Mises equivalent stress and principal stress become 7687.9MPa and 1690.7MPa respectively at the front part of car body and the lap of dummy. And maximum total deformation occurred with 16.414 mm at the foot of dummy. In case of rear impact contact, maximum von Mises equivalent stress and principal stress become 2366.6MPa and 1447MPa respectively at the front part of car body and the neck of dummy. And maximum total deformation occurred with 7.548mm at the rear part of car body. As the maximum von-Mises stress at side impact is shown with more than 700MPa as over two times at front or rear impact the danger of car body is increased. The great possibility of damage is shown at neck and hand of dummy with more than total displacement of 10mm.

• 대한기계학회논문집A
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• 제37권4호
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• pp.491-496
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• 2013

인장시험을 유한요소 시뮬레이션하여 등가응력-등가소성변형률 곡선, 임계 등가응력과 임계 등가소성변형률을 결정하였다. 그리고, 이 곡선을 입력하여 파괴시험을 유한요소 시뮬레이션하여 평면변형률 파괴인성치를 결정하여 보려고 하였다. 균열선단절점에서 등가소성변형률이 임계 등가소성변형률에 도달할 때 균열개구변위를 임계 균열개구변위로 취하여 균열성장조건으로 사용되었다. 임계 등가소성변형률이나 단면감소율과 파괴시험 임계 균열개구변위와 관련성을 찾아보고, 임계 등가응력과 임계 등가소성변형률을 동시에 적용하여 파괴시험 파괴인성치와의 관련성도 찾아보았다.

• 한국방재학회 논문집
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• 제8권2호
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• pp.39-43
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• 2008

Determination of strain associated with shear modulus and damping ratio during torsional test is complicated. This is due to nonuniform stress-strain variation occurring linearly with radius in a soil specimen in torsion. A conventional equivalent radius approach proposed by Chen and Stokoe appears to be adequate for evaluating strain associated with shear modulus at low to intermediate strain levels. This approach is less accurate for damping measurement, particularly at high strain. Modified equivalent radius approach was used to account for the nonuniform stress-strain effect more precisely. The modified equivalent radius approach was applied for hyperbolic, modified hyperbolic, and Ramberg-Osgood models. The results illustrate the usefulness of the modified equivalent radius approach and suggest that using a single value of equivalent radius ratio to calculate strains is not appropriate.

• 한국정밀공학회지
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• 제31권6호
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• pp.551-557
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• 2014

Ideally, it is preferable to obtain the fracture characteristics of a piping from the fracture toughness of real pipes. However, a fracture toughness test on real pipes not only incurs much expense, but is very difficult to perform. Therefore fracture toughness tests have been carried out with standard specimens instead of real pipes. But, the estimates of fracture toughness obtained from standard specimens are more conservative than those of real pipes owing to the difference in the constraint effect between real pipes and standard specimens. Therefore, we have been studied with equivalent stress gradient specimen (ESG) which is designed to behave equally compared to real pipe about stress gradient on crack tip. In this study, we will evaluate fracture characteristics of equivalent stress gradient specimen by using analytical methods and compare with those of real pipe. And finally investigate suitability of equivalent stress gradient specimen.

• Structural Engineering and Mechanics
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• 제35권5호
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• pp.571-592
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• 2010

An energy-based fatigue life prediction framework was previously developed by the authors for prediction of axial, bending and shear fatigue life at various stress ratios. The framework for the prediction of fatigue life via energy analysis was based on a new constitutive law, which states the following: the amount of energy required to fracture a material is constant. In the first part of this study, energy expressions that construct the constitutive law are equated in the form of total strain energy and the distortion energy dissipated in a fatigue cycle. The resulting equation is further evaluated to acquire the equivalent stress per cycle using energy based methodologies. The equivalent stress expressions are developed both for biaxial and multiaxial fatigue loads and are used to predict the number of cycles to failure based on previously developed prediction criterion. The equivalent stress expressions developed in this study are further used in a new finite element procedure to predict the fatigue life for two and three dimensional structures. In the second part of this study, a new Quadrilateral fatigue finite element is developed through integration of constitutive law into minimum potential energy formulation. This new QUAD-4 element is capable of simulating biaxial fatigue problems. The final output of this finite element analysis both using equivalent stress approach and using the new QUAD-4 fatigue element, is in the form of number of cycles to failure for each element on a scale in ascending or descending order. Therefore, the new finite element framework can provide the number of cycles to failure at each location in gas turbine engine structural components. In order to obtain experimental data for comparison, an Al6061-T6 plate is tested using a previously developed vibration based testing framework. The finite element analysis is performed for Al6061-T6 aluminum and the results are compared with experimental results.