• Journal of Welding and Joining
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• 제32권4호
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• pp.75-79
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• 2014

This paper has an aim to study the effect of PWHT(for 140min. at $600^{\circ}C$) on FCAW weld metal properties (tensile, charpy impact and CTOD value) of YS 460 MPa steels for ship and offshore structures. On the basis of these study, it was found that strength was decreased and elongation was increased by PWHT. These phenomenon resulted from the reduction of acicula ferrite volume fraction by grain growth. Also, Charpy impact and CTOD value were decreased by PWHT. These phenomenon resulted from grain growth. Because the grain boundary grown by PWHT can play a role as crack initiation site and make the crack propagate more easily. Although weld metal properties were decreased by PWHT, tensile and impact properties could meet the class societies requirements for welds of YS 460 MPa steel, but decrease of fracture toughness need to be consider seriously.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2005년도 춘계 학술발표회 논문집
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• pp.151-158
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• 2005

For the safety analysis of large structures such as nuclear containment buildings, we conventionally prefer to use analytical approach using finite element method rather than empirical test. Therefor, this paper is mainly focused to develop low-order solid finite element model with the elasto-plastic material model for the safety analysis of nuclear containment building. Drucker-Prager failure criteria in uncracked concrete and maximum tensile stress criteria in cracked concrete are used to model the constitutive behavior of concrete. The concrete material model takes into account the aspects of tensile strain, compression strength reduction of concrete and shear transfer to improve the accuracy of the finite element analysis. Finally, numerical simulation to compare the performance of the developed model with experimental results is employed. The numerical results in this study agree very well with the experimental data.

• 한국지구물리탐사학회:학술대회논문집
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• 한국지구물리탐사학회 2003년도 Proceedings of the international symposium on the fusion technology
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• pp.233-237
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• 2003

For Taejon LNG Pilot Cavern being constructed to verify the technical aspects for storing LNG in lined rock cavern, various numerical studies were carried out to estimate the temperature profile and to understand thermo-mechanical behaviour in the rock around the cavern. With the help of Claesson's analytical solution and numerical models, the extent of zero degree isotherm and possible boil-off rate of gas to be stored were estimated. Even though the tensile stress by cooling down is very large compared to the tensile strength of the rock, it has been shown that possible rock yielding might bring about the dramatic reduction of the stress.

• KCI Concrete Journal
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• 제11권3호
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• pp.29-43
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• 1999

The effects of superplasticizers on fresh and hardened concrete were investigated. The experimental program included tests on the workability and slump loss, bleeding, setting time, air content, compressive, tensile and flexural strength, permeability, shrinkage, freeze-thaw durability and creep deformation. Properties of superplasticized concrete were compared with those of conventional and base concretes. Superplasticizers were observed to have an appreciable fluidifying action in fresh concrete. They permitted a significant water reduction while maintaining the same workability. Bleeding of superplasticized concrete was much lower than that of conventional concrete of the same consistency. This indicates that the use of superplasticizers did not affect the tendency of segregation of fresh concrete. The compressive, tensile, and flexural strengths of superplasticized concrete were significantly higher than those of conventional concrete. The permeability and drying shrinkage and creep of superplasticized concrete were less than those of conventional concrete, but there were no significant differences between base and superplasticized concrete. Compared with base concrete, non-air-entrained superplasticized concrete had slightly higher freeze-thaw durability. and superplasticized concrete with an appropriate amount of entrained air Eave even better resistance to freezing and thawing.

• 한국안전학회지
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• 제21권5호
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• pp.17-21
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• 2006

In this study, SPCC cross-tension type specimens produced under various spot welding conditions were tensile and fatigue tested. Decrease of 2 kA in normal current condition of 10 kA caused a large amount of reduction in both static joining strength and fatigue life. And 2 kA increase resulted in increase of static joining strength and an increase in low cycle regime but a decrease in high cycle regime, revealing the fact that fatigue strength rather than static joining strength would be a major factor during design process in view of the body endurance. As a results of estimating the fatigue lifetimes of various types of spot weld specimens. equivalent stress intensity factor is the proper parameter for predicting the lifetimes of various types of specimens. which can be expressed as ${\Delta}K_{eq}(N/nm^{1.5})=11550N^{-0.36}_{f}$.

• 콘크리트학회지
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• 제2권1호
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• pp.91-100
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• 1990

초기 균열을 갖는 대부분의 구조 부재의 있어서, 부재의 크기가 중가함에 따라 일반적으로 강도가 감소하는 현상을 보인다. 이를 크기효과라고 하며, 특히 콘크리트는 유리, 철과같은 구조 재료와는 달리 초기균열이 없는 경우에도 이러한 크기효과를 나타낸다는 것이 실험에 의해 나타나고 있다. 기존의 크기효과 법칙을 따르면 크기가 배우 큰 콘크리트 부재는 응력을 거의 받을 수 없는 것으로 나타나나, 실험에 의하면 강도의 감소율이 현저하게 감소되어 기존의 크기효과 법칙과 큰 차이를 보인다. 따라서, 본 논문에서는 콘크리트 구조물의 비선형 파괴역학에 근거하여 비유사 균열이 존재하는 경우에 대한 크기효과식을 유도하여 기존의 할열인장강도, 전단강도 및 압축강도 실험치에 대한 회귀분석을 통하여 보다 나은 모델식을 제시하였다.

• 한국기계가공학회지
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• 제18권3호
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• pp.66-73
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• 2019

Recently, FDM-type 3D printer technology has been developed, and efforts have been made to improve the output formability and characteristics further. Through this, 3D printers are used in various fields, and printer technologies are suggested according to usage, such as FDM, SLA, DLP, and SLM. In particular, the FDM method is the most widely used, and the FDM method technology is being developed further. The characteristics of the output are produced by the FDM-type 3D printer, which is determined by various factors, and particularly the perspective of the Inter-Layer Fill Factor, which is the volume ratio of the laminated material that exerts a direct influence. In this study, the Inter-Layer Fill Factor is theoretically obtained by presenting the internal space between each layer according to the laminate thickness as a cross-sectional shape model, and the cross section of the actual laminated sample is compared with the theoretical model through experiments. Then, the equation for the theoretical model is defined, and the strength change according to each condition (tensile strength of material, reduction slope, strength reduction rate, and output strength) is confirmed. In addition, we investigated the influence on the correlation and strength between laminate thickness and the Inter-Layer Fill Factor.

• Steel and Composite Structures
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• 제50권5호
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• pp.595-608
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• 2024

In this study, aluminum lathe waste was used by replacing aggregates in certain proportions in order to obtain expansive concrete using recycled materials. For this reason, five different aluminum wastes of 1%, 2%, 3%, 4% and 5% were selected and also reference without aluminum waste was produced. Based on the mechanical tests conducted, which included slump, compression, splitting tensile, and flexural tests, it was evident that the workability of the material declined dramatically once the volume ratio of aluminum exceeded 2%. As determined by the compressive strength test (CST), the CS of concrete (1% aluminum lathe wastes replaced with aggregate) was 11% reducer than that of reference concrete. It was noted that the reference concrete's CS values, which did not include aluminum waste, were greater than those of the concrete that contained 5% aluminum. When comparing for splitting tensile strength (STS), it was observed that the results of STS generally follow the parallel inclination as the CS. The reduction in these strengths when 1% aluminum is utilized is less than 10%. These ratios modified 18% when flexural strength (FS) is considered. Therefore, 1% of aluminum waste is recommended to obtain expansive concrete with recycled materials considering minimum loss of strength. Moreover, Scanning Electron Microscope (SEM) analysis was performed and the results also confirm that there was expansion in the aluminum added concrete. The presence of pores throughout the concrete leads to the formation of gaps, resulting in its expansion. Additionally, for practical applications, basic equations were developed to forecast the CS, STS, and FS of the concrete with aluminum lathe waste using the data already available in the literature and the findings of the current study. In conclusion, this study establishes that aluminum lathe wastes are suitable, readily available in significant quantities, locally sourced eco-materials, cost-effective, and might be selected for construction using concrete, striking a balance among financially and ecological considerations.

• 한국수소및신에너지학회논문집
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• 제18권4호
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• pp.391-398
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• 2007

The covalently cross-linked sulfonated polyetheretherketone (CL-SPEEK) membrane was prepared by four-step synthesis of sulfonation-sulfochlorination, partial reduction, lithiation, and cross-linking, and its electrochemical and mechanical properties were investigated for water electrolysis application. The prepared ion exchange membranes showed good electrochemical and mechanical properties; proton conductivity of 0.116 S/cm at $80^{\circ}C$, water uptake of 44.6%, ion exchange capacity of 1.75 meq/g-dry-memb., tensile strength of 64.25 MPa and elongation of 61.11%. The membrane electrode assembly (MEA) with homemade membranes were prepared by non-equilibrium impregnation-reduction (I-R) method. Especially, the electrochemical surface area (ESA) and roughness factor of CL-SPEEK electrolyte by cyclic voltammetry method were 23.46 $m^2/g$ and 307.3 $cm^2-Pt/cm^2$, respectively. The prepared MEA was used in the unit cell of water electrolysis and the cell voltage was 1.81 V at 1 A/$cm^2$ and $80^{\circ}C$, with platinum loadings of 1.31 mg/$cm^2$.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2005년도 추계 학술논문 발표대회
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• pp.39-42
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• 2005

This study investigates influence of organic fiber reinforced materials, affecting crack reduction of cement mortar using low grade natural sand(LNS). According to the test, for the properties of fresh mortar, the mortar using natural sand(NS) exhibited that flow value increased until adding most of fiber less than 1$\%$, except for Polyvinly alchol fiber(PVA), and then it decreased. Meanwhile, the mortar mixed with LNS showed that increase of fiber content decrease flow value, regardless of fiber type. Air content increased in the mortar adding nylon fiber(NY) and polypropylene fiber(PP), while it maintained or decreased in the mortar adding cellulose fiber(CL) and PVA. Compressive strength of the mortar does not affect during early age, but mortar using NS and adding 0.1$\%$ of fiber content increased the value, except for PP, at 28 age days, while the mortar mixed with LNS decreased. For the properties of tensile strength, mortar, using NS and adding individually PP and PVA, exhibited higher value. Especially 0.1$\%$ of NY provided the highest value. In addition, the mortar mixed with LNS resulted in improved tensile value as fiber content increased. It is demonstrated that mortar using LNS led to higher length change ratio than natural sand.