• 콘크리트학회논문집
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• 제16권3호
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• pp.397-406
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• 2004

최근 개발된 3차원 콘크리트 구성모델을 사용하여 구속을 받는 콘크리트와 철근콘크리트 기둥의 해석을 수행하였다. 편차응력과 체적응력 간의 상호작용이 포함되어있고, 비례 및 비례하지 않는 하중을 받는 경우에도 적용 가능한 아탄성 직교 콘크리트 구성모델을 변형률 제어 모델로 전산화하였다. 유한요소 전산화 과정에서 손상균열모델을 사용하였고, 균열은 주변형률 방향에 따라 회전 가능한 것으로 모델링하였다. 콘크리트 구성모델을 구속을 받는 콘크리트 공시체의 실험결과 그리고 캘리포니아 대학(샌디에고)에서 수행된 3개의 철근콘크리트 기둥의 실험결과와 비교하였다. 이를 통하여 비선형 콘크리트 구성모델에 근거한 유한요소해석 결과가 실험에서 관찰된 주요한 특징들을 잘 예측하고 있음을 보여주었다.

• 대한기계학회논문집A
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• 제38권7호
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• pp.727-734
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• 2014

본 논문은 유한요소 기반 다중스케일 연성파손모사 기법을 이용하여 결함이 존재하는 실배관의 파괴거동을 예측한다. 수정응력 파괴변형률 모델을 손상기준으로 선정하고 유한요소 손상해석을 통해 균열진전을 모사한다. 기준식의 결정에는 인장시험과 파괴인성시험 결과만이 요구되며 온도 $288^{\circ}C$ SA333 Gr. 6 탄소강에 적용하여 결과를 제시하였다. 요소크기-의존성 임계손상모델을 도입하여 손상해석의 수치해석적인 불안정성을 개선하였다. 본 연구에서 제안하는 가상시험법의 검증을 위해 미국 바텔 연구소에서 수행한 실배관 실험결과와 예측결과를 비교한다.

• 한국정밀공학회지
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• 제29권12호
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• pp.1296-1303
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• 2012

There is a certain limit to reproduce phenomena between the real vehicle and road, since the existing methods to verify durability of the wheel are mostly uni-axial tests. And the change of durability of the wheel can't be predicted since these tests don't consider the camber angle and lateral force as important factors. In this paper, the FE models of the wheel-tire and drum are created. Then, the vertical and lateral loads are applied to wheel-tire assembly and the camber angle is applied by inclining the wheel-tire assembly to the drum. Based on the analysis result, the crack position is predicted to be created in the body of the wheel. The variation of the stress according to the camber angle is verified and the maximum spot of the stress changes continually.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집A
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• pp.17-25
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• 2001

This paper briefly describes the new engineering method, called the enhanced reference stress method, to estimate J (or $C^*$) for non-linear fracture mechanics analysis of defective components, recently proposed by authors. The proposed method offers significant advantages over existing methods in terms of its accuracy, simplicity and robustness. Examples of application of the proposed method to typical piping integrity problems such as through-wall cracked pipes under combined loading, and surface cracked pipes under internal pressure and bending are given. Excellent agreements between the FE J and $C^*$ results and those of the proposed method provide sufficient confidence in the use of the proposed method. One notable point is that the proposed method can be used to estimate J (or $C^*$) along the crack front of surface cracks. Moreover simplicity of the proposed method makes it easy to extend to more complex problems. Thus the proposed method is attractive to assess the significance of defects under practical situations.

• Computers and Concrete
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• 제20권4호
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• pp.483-490
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• 2017

This paper studies on the behavior of reinforced concrete (RC) pipes used in basic sanitation in the conduction of storm water and sanitary sewer. Pipes with 800 mm and 1200 mm in diameter were analyzed. The 800 mm pipes were built with simple reinforcement and the 1200 mm pipes with double reinforcement. For the two diameters of pipes the presence or absence of the pocket was evaluated, and the denomination of each one is spigot and pocket pipe (SPP) and ogee joint pipe (OJP), respectively. The 3D numerical models reproduce the three-edge-bearing test that provides information about the strength and stiffness of the reinforced concrete pipes. The validation of the computational models was carried out comparing the vertical and horizontal displacements on the springline and crown/invert and it was also evaluated the reinforcement strains and the crack pattern. As a main conclusion, the numerical models represented satisfactorily the behavior of the pipes and can be used in future studies in parametric analysis.

• Smart Structures and Systems
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• 제20권6호
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• pp.669-682
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• 2017

The normalised version of bispectrum, the so-called bicoherence, has often proved a reliable method of damage detection on engineering applications. Indeed, higher-order spectral analysis (HOSA) has the advantage of being able to detect non-linearity in the structural dynamic response while being insensitive to ambient vibrations. Skewness in the response may be easily spotted and related to damage conditions, as the majority of common faults and cracks shows bilinear effects. The present study tries to extend the application of HOSA to damage localisation, resorting to a neural network based classification algorithm. In order to validate the approach, a non-linear finite element model of a 4-meters-long cantilever beam has been built. This model could be seen as a first generic concept of more complex structural systems, such as aircraft wings, wind turbine blades, etc. The main aim of the study is to train a Neural Network (NN) able to classify different damage locations, when fed with bispectra. These are computed using the dynamic response of the FE nonlinear model to random noise excitation.

• 한국산업융합학회 논문집
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• 제25권6_2호
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• pp.1047-1053
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• 2022

The leaf spring for a truck absorbs shocks or vibrations from the road surface while driving with the elastic force of the material and prevents the shock from being transmitted to the vehicle body. It is subjected to cyclic stress, and fatigue fracture occurs frequently. This study analyzes fractured leaf spring from a 25 ton truck that has been operating for about a year. In the fractured portion, which is the origin of crack, inclusions were observed, and fatigue failure was caused by cyclic stress. In the stress calculation and FE analysis, the stress at the center of the leaf spring was obtained to be 54~65% of the yield strength of the base material and damaged material. It is most important to prevent the mixing of impurities in the steel manufacturing for leaf springs. The large stress portion of the leaf spring needs to introduce compressive residual stress by peening etc.

• 대한기계학회논문집A
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• 제40권8호
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• pp.693-701
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• 2016

본 논문에서는 파괴역학적 방법으로 노치 결함을 평가해 보았다. 인장 하중과 굽힘하중이 작용하는 중앙 균열, 모서리 균열 평판 구조물을 바탕으로 노치 크기를 달리하며 한계하중 및 에너지해방률을 유한요소 해석의 J-적분으로 도출하였다. 노치의 반경이 커짐에 따라 한계하중은 큰 변화가 없었으며, 에너지해방률는 커지는 양상을 보였다. 노치 반경에 따른 재료 파괴인성($J_{IC}$)측정을 위해 실험을 대신한 유한요소 연성파손 모사기법을 사용하였다. 그 결과 노치 크기 증가에 따른 에너지해방률 증가량 대비 파괴인성($J_{IC}$) 증가량이 더욱 큰 양상을 보였다. 이런 결과를 통해 노치 반경이 커질수록 균열 진전에 대한 저항성이 커진다는 사실을 알 수 있었다.

• Computers and Concrete
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• 제24권6호
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• pp.527-539
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• 2019

In this paper, the fracture characteristics of concrete specimens with different notch depths under three-point flexural loads are studied by finite element and fracture mechanics methods. Firstly, the concrete beams (the size is 700×100×150 mm) with different notch depths (a=30 mm, 45 mm, 60 mm and 75 mm respectively) are tested to study the influence of notch depths on the mechanical properties of concrete. Subsequently, the concrete beams with notch depth of 60 mm are loaded at different loading rates to study the influence of loading rates on the fracture characteristics, and digital image correlation (DIC) is used to monitor the strain nephogram at different loading rates. The test results show that the flexural characteristics of the beams are influenced by notch depths, and the bearing capacity and ductility of the concrete decrease with the increase of notch depths. Moreover, the peak load of concrete beam gradually increases with the increase of loading rate. Then, the fracture energy of the beams is accurately calculated by tail-modeling method and the bilinear softening constitutive model of fracture behavior is determined by using the modified fracture energy. Finally, the bilinear softening constitutive function is embedded into the finite element (FE) model for numerical simulation. Through the comparison of the test results and finite element analysis, the bilinear softening model determined by the tail-modeling method can be used to predict the fracture behavior of concrete beams under different notch depths and loading rates.

• 한국정밀공학회지
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• 제32권2호
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• pp.167-172
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• 2015

In order to prevent crack in thick weld zones, the preheating process such as induction and gas torch heating needs to be applied. Among them induction heating is the most effective heat source because it has rare thermal effect and very rapid heating characteristics. In this paper, when the induction heating method is used to improve arc welding, the temperature distribution and magnetic field density of the welding zones are analyzed by simultaneously solving heat transfer and electromagnetic field equation. In particular, cone and flat type coils are designed and induction heating effects of each type are compared to identify heating characteristics on a V-groove weld joint. As a result, a cone shape coil is more efficient in the preheating process. When induction heating and arc welding system is designed for thick plate with V-groove weld joint, the results in this paper could be applied.