• Computers and Concrete
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• 제25권1호
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• pp.67-73
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• 2020

Traditionally used analytical approach to predict the fatigue failure of reinforced concrete (RC) structure is generally conservative and has certain limitations. The nonlinear finite element method (FEM) offers less expensive solution for fatigue analysis with sufficient accuracy. However, the conventional implicit dynamic analysis is very expensive for high level computation. Whereas, an explicit dynamic analysis approach offers a computationally operative modelling to predict true responses of a structural element under periodic loading and might be perfectly matched to accomplish long life fatigue computations. Hence, this study simulates the fatigue behaviour of RC beams with finite element (FE) assemblage presenting a simplified explicit dynamic numerical solution to show computer aided fatigue behaviour of RC beam. A commercial FEM package, ABAQUS has been chosen for this complex modelling. The concrete has been modelled as a 8-node solid element providing competent compression hardening and tension stiffening. The steel reinforcements are simulated as two-node truss elements comprising elasto-plastic stress-strain behaviour. All the possible nonlinearities are duly incorporated. Time domain analysis has been adopted through an automatic Newmark-β time incremental technique. The program consists of twelve RC beams to visualize the real behaviour during fatigue process and to obtain the reliability of the study. Both the numerical and experimental results indicate a redistribution of stresses along the time and damage accumulation of beam which severely affect the serviceability and ultimate capacity of RC beam. The output of the FEM analysis demonstrates good match with the experimental consequences which affirm the efficacy of the computer aided model. The controlled fatigue damage evolution at service fatigue load limits makes the FE model an efficient tool in predicting high cycle fatigue behaviour of RC structures.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2017년도 제48회 춘계학술대회논문집
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• pp.245-247
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• 2017

가스터빈 시동 시 터빈휠은 급격한 온도 변화와 원심하중을 받게 된다. 터빈휠 온도와 응력은 빠르게 증가하게 되며, 적용되는 시점과 정도가 서로 다를 수 있다. 온도 및 원심력 적용 속도 차이에 따른 수명 변화를 연구하기 위해서 열-기계피로 유한요소해석을 수행하였다. 시동 시 터빈휠 속도가 천천히 증가하고, 중단 시 천천히 감속하면 상대적으로 수명이 길어진다. 만약 속도 감소가 냉각속도보다 빠르면 오히려 수명이 증가한다.

• Steel and Composite Structures
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• 제36권1호
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• pp.75-86
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• 2020

The grid structures with welded hollow spherical joint (WHSJ) have gained increasing popularity for use in industrial buildings with suspended cranes, and usually welded with steel tube (ST). The fatigue performance of steel tube-welded hollow spherical joint (ST-WHSJ) is however not yet well characterized, and there is little research on fatigue life prediction methods of ST-WHSJ. In this study, based on previous fatigue tests, three series of specimen fatigue data with different design parameters and stress ratios were compared, and two fatigue failure modes were revealed: failure at the weld toe of the ST and the WHSJ respectively. Then, S-N curves of nominal stress were uniformed. Furthermore, a finite element model (FEM) was validated by static test, and was introduced to assess fatigue behavior with the hot spot stress method (HSSM) and the effective notch stress method (ENSM). Both methods could provide conservative predictions, and these two methods had similar results. However, ENSM, especially when using von Mises stress, had a better fit for the series with a non- positive stress ratio. After including the welding residual stress and mean stress, analyses with the local stress method (LSM) and the critical distance method (CDM, including point method and line method) were carried out. It could be seen that the point method of CDM led to more accurate predictions than LSM, and was recommended for series with positive stress ratios.

• Structural Engineering and Mechanics
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• 제61권3호
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• pp.389-396
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• 2017

Concrete pavements are subjected to traffic and environmental loadings. Repetitive type of such loading cause fatigue distress which leads to failure by forming cracks in pavement. Fatigue life of concrete pavement is calculated from the stress ratio (i.e. the ratio of applied flexural stress to the flexural strength of concrete). For the correct estimation of fatigue life, it is necessary to determine the maximum flexural tensile stress developed for practical loading conditions. Portland cement association PCA (1984) and Indian road congress IRC 58 (2015) has given charts and tables to determine maximum edge stresses for particular loading and subgrade conditions. It is difficult to determine maximum stresses for intermediate loading and subgrade conditions. The main purpose of this study is to simplify the analysis of rigid pavement without compromising the accuracy. Equations proposed for determination of maximum flexural tensile stress of pavement are verified by finite element analysis.

• 한국철도학회논문집
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• 제7권2호
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• pp.142-148
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• 2004

When material properties depend much on positions in a material or it is difficult to make test specimens from a material or component, an instrumented indentation test described in ISO 14577-1, 14577-2 or KS B 0950 can be used to measure material properties and damage. In this study, first of all, the principals of the instrumented indentation test, KS B 0950 are introduced and yield strengths, tensile strengths and work hardening exponents of base materials, heat affected zones and weld materials are measured. In addition, the influence of post-weld heat treatment on the material properties is investigated. Finally the fatigue lift of butt welded specimens are evaluated by the local strain approach. To calculate local strains and stresses, elasto-plastic finite element analysis is conducted using the measured properties.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.378-383
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• 2008

Bogie frame of the locomotive is an important structural member for the support of vehicle loading. A lot of study has been carried out for the prediction of the structural integrity of the bogie frame in experimental and theoretical domains. The objective of this paper is to estimate the structural integrity of the bogie frame. Strength analysis has been performed by finite element analysis. From these analysis, stress concentration areas were investigated. For evaluation of the loading conditions, dynamic stress were measured by using strain gage. It has been found that the stress and strain due to the applied loads were multi-axial condition according to the location of strain gage. The fatigue strength evaluations of the bogie frame are performed to investigate the effect of the multi-axial load through the employment of the critical plane approach.

• 한국정밀공학회지
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• 제25권4호
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• pp.86-92
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• 2008

This paper is to investigate the behavior of linear static structure stress, the fatigue and experimental shock fracture far engine base in the Auxiliary Power Unit to resolve its restricted electrical power problem. The shock fracture test was experimentally made under MIL standard criteria. The numerical results by finite element method had a good agreement with those from the shock test. The design data of predicting the fracture at the initial crack and the damage behavior of structure with shock and vibration load in the battle field can be obtained from shock test. In the functional shock test, the crack at the side parts of the engine base was found at peak acceleration of 40g.

• Nuclear Engineering and Technology
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• 제52권7호
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• pp.1481-1485
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• 2020

The creep behavior of Ni-Cr-W alloy at 950 ℃ has been investigated by a novel creep testing system which is capable of in-situ measurement of strain. Tubular specimens were pressurized with argon gas for effective stresses up to 32 MPa. Experimental results show that the thermal fatigue reduces the creep life of the tubular specimens and with the introduction of thermal cycling fatigue the primary stage disappears and the creep rate higher than the pure thermal creep (without thermal fatigue). Also the creep behavior of Ni-Cr-W alloy doesn't consist in the secondary stage. A new creep equation has been derived and implemented into finite element method. The results from the finite element analyses are in good agreement with the creep experiment.

• 한국자동차공학회논문집
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• 제13권4호
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• pp.39-48
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• 2005

Finite element analyses have been performed for the purpose of obtaining the robust and reliable design of engine cylinder block. Fatigue under high cycle operating loads is a primary concern and is evaluated by a probabilistic method. The robust and reliable design by a probabilistic method can provide satisfactory design conditions for the performance of the system under the influence of noise factors. Therefore, the design by this method will be desensitized to the uncontrollable noise factors. The simple methodology evaluates the distortion of main bore is proposed for the purpose of maintaining a well-controlled clearance between the crankshaft and main bores. The proposed methodology has proven a capability of predicting the distortion of the main bore under assembly, thermal, and firing loads. The calculated results are correlated well with the experimental ones.

• 한국구조물진단유지관리공학회 논문집
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• 제22권1호
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• pp.129-136
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• 2018

대형 용접 구조물에 대한 피로설계 수명의 예측은 일반적으로 Palmgren Miner과 등가손상도 방법 또는 선형누적손상도 방법을 사용한다. 또한 용접 구조물에서 피로 균열이 발생되면 잔존 수명은 S-N 곡선과 선형 파괴역학에 기초하여 예측되고 있다. 본 연구에서는 면외거셋 용접이음의 3차원 피로균열 진전거동과 피로수명을 예측하기 위하여 피로 시험을 실시하였다. 면외거셋 용접이음의 3차원 피로균열진전해석은 NX NASTRAN 및 FRANC3D를 이용하여 유한요소 해석을 실시하였다. 면외거셋 용접이음의 균열 형상비, 초기균열 크기 및 응력비에 미치는 영향을 검토하기 위하여 피로균열진전 해석을 실시하였다. 또한 초기균열크기, 균열 형상비와 응력비의 변화에 따른 3차원 피로균열진전 해석 결과와 피로시험결과를 비교하였다. 피로균열진전 해석결과, 피로균열 진전속도와 응력확대계수와의 관계에서 피로시험과 유사하게 나타남을 확인하였으며, 면외거셋 용접이음의 피로수명을 추정할 수 있음을 확인하였다.