• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 추계학술대회 논문집
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• pp.198-201
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• 2005

Monobloc technology Provides a homogeneous material along the complete tubular shaft without any discontinuity between the interconnecting tube and the stems as is found when the tubes and stems have been Joined by welding. Cold tube drawing is a technique that can be applied for manufacturing of those monobloc tubular shafts with several advantages such as high productivity and cost reduction. The present study is concerned with the investigation about the process parameters related with tool configuration. In order to obtain successfully formed SIS(Steering Input Shaft) without any defects, advanced design of mandrel is presented and analyzed by the FEM and ductile fracture criterion in this paper.

• 상하수도학회지
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• 제29권6호
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• pp.659-666
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• 2015

In this study, Hazen-Williams C value of pipes in wide waterworks system was estimated and statistically analyzed. Hazen-Williams C value of water pipe was predicted after 20 years of service period. From the results, it was found that C value of water pipe for treated water maintained higher value of 110 after 20 years of installation. Furthermore, it was found that velocity coefficients of steel pipe for less than and more than 20 years of installation were 117.7 and 109.3, respectively. C value of ductile iron pipe for less than and more than 20 years of installation were 118.1 and 114.2, respectively. In this study, it was also found that small value of C is used in the design of water pipe system. Therefore, excessively bigger size of pipe can be determined in the design of water pipe system. From the results of present study, optimum value of C can be used to avoid the oversized design of water pipe system.

• Nuclear Engineering and Technology
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• 제52권8호
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• pp.1732-1741
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• 2020

The structural integrity of welded joints in the reactor pressure vessel (RPV) is directly related to the safety of nuclear power plants. The RPV is made from SA508-III steel in a pressurized water reactor. In this study, we investigated the effects of temperature on the tensile and fracture toughness properties of Chinese SA508-III welded joint in different sampling areas in order to provide reference data for structural integrity assessments of RPVs. The specimens used in tensile and fracture toughness tests were fabricated from the base metal (BM), weld metal (WM), and the heat-affected zone (HAZ) in the welded joint. The representative testing temperatures included the ambient temperature (20 ℃), upper shelf temperature (100 ℃), and service temperature (320 ℃). The results showed that temperature greatly affected the fracture toughness (JIC) values for the SA508-III welded joint. The JIC values for BM and HAZ both decreased remarkably from 20 ℃ to 320 ℃. The fracture morphologies showed that the BM and HAZ in the welded joint exhibited fully ductile fracture at 20 ℃, whereas partial cleavage fracture was mixed in ductile fracture mode at 100 ℃ and 320 ℃. The WM exhibited the ductile and cleavage fracture mixed mode at various temperatures, and the JIC values showed slight changes.

• Steel and Composite Structures
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• 제27권6호
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• pp.727-745
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• 2018

The design criteria and the corresponding performance levels characterize the response of extended stiffened end-plate beam-to-column joints. In order to guarantee a ductile behavior, hierarchy criteria should be adopted to enforce the plastic deformations in the ductile components of the joint. However, the effectiveness of thesecriteria can be impaired if the actual resistance of the end-plate material largely differs from the design value due to the potential activation of brittle failure modes of the bolt rows (e.g., occurrence of failure mode 3 in the place of mode 1 per bolt row). Also the number and the position of bolt rows directly affect the joint response. The presence of a bolt row in the center of the connection does not improve the strength of the joint under both gravity, wind and seismic loading, but it can modify the damage pattern of ductile connections, reducing the gap opening between the end-plate and the column face. On the other hand, the presence of a central bolt row can influence the capacity of the joint to resist the catenary actions developing under a column loss scenario, thus improving the joint robustness. Aiming at investigating the influence of these features on both the cyclic behavior and the response under column loss, a wide range of finite element analyses (FEAs) were performed and the main results are described and discussed in this paper.

• 한국전산구조공학회논문집
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• 제30권2호
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• pp.185-189
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• 2017

일반교량 내진설계의 목적은 지진발생 직후에 긴급차량의 통과를 허용하도록 하는 '붕괴방지설계'의 수행이다. 도로교설계기준은 연성구조를 구성하여 '붕괴방지설계'를 수행하는 규정을 제시하고 있으며 이 과정에서 연결부분과 하부구조에 적용하는 응답수정계수가 핵심적인 역할을 한다. 하부구조 응답수정계수의 경우 도로교설계기준은 연성과 여용력을 고려한 계수인 반면 AASHTO LRFD 교량설계기준은 교량의 중요도를 핵심, 중요 및 일반으로 구분한 인위적인 인자를 추가로 반영한 계수를 제시하고 있다. 이 연구에서는 강재받침과 철근콘크리트 교각기둥으로 구성된 일반교량을 선정하고 도로교설계기준의 설계조건과 함께 하부구조 응답수정계수를 차등 적용하는 경우의 설계결과를 비교, 검토하였으며 이로부터 하부구조 응답수정계수의 차등 적용 시 설계기준에 요구되는 보완사항을 제시하였다.

• 대한토목학회논문집
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• 제26권1A호
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• pp.173-181
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• 2006

지진격리교량은 내진설계가 도입된 이후 실무에서 많이 설계, 시공되고 있으나 현재 실무에서 제시하고 있는 설계결과는 불필요하게 높은 기능수행수준과 취성파괴메커니즘으로 내진설계개념에 부합하는 설계라 할 수 없다. 이는 기존의 설계관행인 하부구조의 과다한 강성과 내진설계방식의 인식부족에 기인한 것이다. 이 연구에서는 기존의 설계관행에 의해 설계된 지진격리교량을 선정하고, 동일한 교량에 격리받침 대신 강재받침을 사용한 강재받침교량을 설정하여 비교내진설계를 수행하였으며, 이로부터 내진설계에서 요구되는 성능수준을 확보하기 위한 각 교량의 내진설계절차를 제시하였다. 강재받침교량에 비해 지진격리교량은 시산법과 반복해석을 적용해야 하는 복잡한 설계절차가 요구되는 반면 상대적으로 높은 기능수행수준을 제공한다는 것을 확인하였다. 그러나 강재받침교량도 하부구조 강성을 조정하면 요구되는 기능수행수준을 만족할 수 있으므로, 연성파괴메커니즘의 확보가 불가능한 경우 지진격리교량을 대안설계로 고려하는 것이 합리적인 내진설계과정이라는 것을 제시하였다.

• 한국주조공학회지
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• 제24권1호
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• pp.52-59
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• 2004

Microstructure and mechanical properties of ductile cast iron were investigated in terms of diameter change of samples that gives rise to modify the microstructure due to different cooling rate in the continuous casting process. The chemical composition used in this study was GCD 400 grade. From the microstructural observation, we have found a large number of graphite with small size in diameter which is comparable to the microstructure of the sample produced by conventional sand casting. The major reason of this would he due to high cooling rate. In the sample with 26 mm in diameter, the microstructure was composed of pearlite, iron carbide, and graphite. In the samples with 60 and 100 mm in diameter, however, we have observed a dissimilar microstructure that consisting of ferrite and graphite. Concerning the mechanical property, the sample with 26 mm in diameter showed higher hardness and strength compared to those samples with 60 and 100 mm in diameter. The result obtained for ductility appeared a reversal. Much more works such as inoculation, process design and chemical composition would be required in order to have a sound product even in a small diameter of samples.

• 소성∙가공
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• 제24권4호
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• pp.293-298
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• 2015

A safety vent is crucial to protect its user from unpredictable explosions caused by increasing internal pressure of the lithium-ion batteries. In order to prevent the explosion of the battery, a safety vent rupture is required when the internal pressure reaches a critical value. In conventional manufacturing, the cap plate and the safety vent are fabricated separately and subsequently welded to each other. In the current study, a manufacturing process including a backward extrusion and coining process is suggested to produce an integral safety vent which also has the benefit of increasing production efficiency. FE simulations were conducted to predict the rupture pressure and to design the safety vent using a ductile fracture criterion and the element deletion method. The critical value, C, in the ductile fracture criterion was obtained from uniaxial tensile tests with an annealed sheet of 1050-H14 aluminum alloy. Rupture tests were preformed to measure the rupture pressure of the safety vent. The results met the required rupture pressure within 8.5±0.5 kgf/cm². The simulation results were compared with experimental results, which showed that the predicted rupture pressures are in good agreement with experimentally measured ones with a maximum error of only 3.9%.

• Journal of Mechanical Science and Technology
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• 제19권11호
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• pp.1988-1997
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• 2005

This study is concerned with structural integrity evaluations for the interference-fit flywheels in reactor coolant pumps (RCPs) of nuclear power plants. Stresses in the flywheel due to the shrinkage loads and centrifugal loads at the RCP normal operation speed, design overspeed and joint-release speed are obtained using the finite element method (FEM), where release of the deformation-controlled stresses as a result of structural interactions during rotation is considered. Fracture mechanics evaluations for a series of cracks assumed to exist in the flywheel are conducted, considering ductile (fatigue) and non-ductile fracture, and stress intensity factors are obtained for the cracks using the finite element alternating method (FEAM). From analysis results, it is found that fatigue crack growth rates calculated are negligible for smaller cracks. Meanwhile, the material resistance to non-ductile fracture in terms of the critical stress intensity factor (K$_{IC}$) and the nil-ductility transition reference temperature (RT$_{NDT}$) are governing factors for larger cracks.

• Structural Engineering and Mechanics
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• 제75권5호
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• pp.559-569
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• 2020

In the present study, the fracture toughness of U-shaped notches made of aluminum alloy Al7075-T6 under combined tension/out-of-plane shear loading conditions (mixed mode I/III) is studied by theoretical and experimental methods. In the experimental part, U-notched test samples are loaded using a previously developed fixture under mixed mode I/III loading and their load-carrying capacity (LCC) is measured. Then, due to the presence of considerable plasticity in the notch vicinity at crack initiation instance, using the Equivalent Material Concept (EMC) and with the help of the point stress (PS) and mean stress (MS) brittle failure criteria, the LCC of the tested samples is predicted theoretically. The EMC equates a ductile material with a virtual brittle material in order to avoid performing elastic-plastic analysis. Because of the very good match between the EMC-PS and EMC-MS combined criteria with the experimental results, the use of the combination of the criteria with EMC is recommended for designing U-notched aluminum plates in engineering structures. Meanwhile, because of nearly the same accuracy of the two criteria and the simplicity of the PS criterion relations, the use of EMC-PS failure model in design of notched Al7075-T6 components is superior to the EMC-MS criterion.