• 대한금속재료학회지
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• 제50권2호
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• pp.136-145
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• 2012

Resistance spot welding of TRIP780 steels was investigated to enhance understanding of weld fracture mode after tensile shear testing (TST) and L-shape tensile testing (LTT). The main failure mode for spot welds of TRIP780 steels was partial interfacial fracture (PIF). Although PIF does not satisfy the minimum button diameter (4${\surd}$t) for acceptable welds, it shows enough load carrying capacity of resistance spot welds for advanced high strength steels. In the analysis of displacement controlled L-shape tensile test results, cracks initiated at the notch of the faying surface and propagated through the interface of weldments, and finally, cracks change path into the sheet thickness direction. Use of the ductility ratio and CE analysis suggested that the occurrence of PIF is closely related to high hardness and brittle welds, which are caused by fast cooling rates and high chemical compositions of TRIP steels. Analysis of the hold time and weld time in a welding schedule demonstrated that careful control of the cooling rate and the size of a weld nugget and the HAZ zone can reduce the occurrence of PIF, which leads to sound welds with button fractures (BFs).

• 철학연구
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• 제141권
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• pp.187-202
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• 2017

본 논문의 목적은 필연성과 개연성을 기준으로 연역논증과 귀납논증을 구별할 때 제기되는 몇 가지 문제점을 구체적으로 살펴보면서 현대논리학에서의 연역-귀납 개념과 아리스토텔레스의 쉴로기스모스-에파고게 개념의 차이를 명료하게 밝히는 것이다. 첫째, 현대논리학에서는 연역논증을 타당한 연역논증과 타당하지 않은 연역논증으로 구별하지만 아리스토텔레스에게는 타당하지 않은 쉴로기스모스라는 표현이 없다. 따라서 아리스토텔레스의 관점에서 보면 타당하지 않은 연역논증을 귀납논증으로 간주해야 하는 문제가 발생하지 않는다. 둘째, 현대논리학에서는 연역논증과 귀납논증 간에 심각한 불균형이 존재하지만 아리스토텔레스의 관점에서 보면 그러한 불균형이 존재하지 않는다. 현대논리학에서 연역논증과 귀납논증 간에 심각한 불균형이 존재하게 되는 이유는 연역논증의 경우에 결론이 잘 수립되는지를 확인하기 위해서 논증의 논리적 형식만 검토하면 되지만 귀납논증의 경우에는 결론이 얼마만큼의 개연성을 가지고 도출되는지를 확인하기 위하여 논증의 형식 이외에 부가적인 정보가 필요하기 때문이다. 그러나 아리스토텔레스에게는 연역논증과 귀납논증의 논리적 형식이 동일하기 때문에 그러한 불균형이 존재하지 않는다. 다만 연역논증은 언어로부터 언어에로(명제로부터 새로운 명제에로) 이동하는 논증인 반면에 귀납논증은 경험적 관찰로부터 언어에로(감각적 지각으로부터 명제에로) 이동하는 논증이라는 차이가 있을 뿐이다. 셋째, 현대논리학에서는 전제(들)이 실제로 참인 명제이든 거짓인 명제이든 참인 명제라고 가정하지만 아리스토텔레스는 그렇게 가정하지 않는다. 쉴로기스모스는 개념적으로 참인 명제로부터 출발하고 에파고게는 경험적으로 참인 명제로부터 출발한다.

• Advances in concrete construction
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• 제8권3호
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• pp.173-185
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• 2019

This article presents a comparative study of the effect of steel layouts on the seismic behavior of transition steel-concrete composite connections, both experimental and analytical investigations of concrete filled steel tube-reinforced concrete (CFST-RC) and steel reinforecd concrete-reinforced concrete (SRC-RC) structures were conducted. The steel-concrete composite connections were subjected to combined constant axial load and lateral cyclic displacements. Tests were carried out on four full-scale connections extracted from a real project engineering with different levels of axial force. The effect of steel layouts on the mechanical behavior of the transition connections was evaluated by failure modes, hysteretic behavior, backbone curves, displacement ductility, energy dissipation capacity and stiffness degradation. Test results showed that different steel layouts led to significantly different failure modes. For CFST-RC transition specimens, the circular cracks of the concrete at the RC column base was followed by steel yielding at the bottom of the CFST column. While uncoordinated deformation could be observed between SRC and RC columns in SRC-RC transition specimens, the crushing and peeling damage of unconfined concrete at the SRC column base was more serious. The existences of I-shape steel and steel tube avoided the pinching phenomenon on the hysteresis curve, which was different from the hysteresis curve of the general reinforced concrete column. The hysteresis loops were spindle-shaped, indicating excellent seismic performance for these transition composite connections. The average values of equivalent viscous damping coefficients of the four specimens are 0.123, 0.186 and 0.304 corresponding to the yielding point, peak point and ultimate point, respectively. Those values demonstrate that the transition steel-concrete composite connections have great energy dissipating capacity. Based on the experimental research, a high-fidelity ABAQUS model was established to further study the influence of concrete strength, steel grade and longitudinal reinforcement ratio on the mechanical behavior of transition composite connections.

• Earthquakes and Structures
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• 제15권6호
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• pp.617-627
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• 2018

After earthquakes FRP sheets are often used for the rehabilitation of damaged Reinforced Concrete (RC) beamcolumn connections. Connections with minor to moderate damage are often dealt with by applying FRP sheets after a superficial repair of the cracks using resin paste or high strength mortar but without infusion of thin resin solution under pressure into the cracking system. This technique is usually adopted in these cases due to the fast and easy-to-apply procedure. The experimental investigation reported herein aims at evaluating the effectiveness of repairing the damaged beam-column connections using FRP sheets after a meticulous but superficial repair of their cracking system using resin paste. The investigation comprises experimental results of 10 full scale beam-column joint specimens; five original joints and the corresponding retrofitted ones. The repair technique has been applied to RC joints with different joint reinforcement arrangements with minor to severe damage brought about by cyclic loading for the purposes of this work. Aiming at quantitative concluding remarks about the effectiveness of the repair technique, data concerning response loads, loading stiffness and energy absorption values have been acquired and commented upon. Furthermore, comparisons of damage index values and values of equivalent viscous damping, as obtained during the test of the original specimens, with the corresponding ones observed in the loading of the repaired ones have also been evaluated and commented. Based on these comparisons, it is deduced that the technique under investigation can be considered to be a rather satisfactory repair technique for joints with minor to moderate damage taking into account the rapid, convenient and easy-to-apply character of its application.

• Wind and Structures
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• 제29권4호
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• pp.247-270
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• 2019

Wind-resistant design of existing cooling tower structures overlooks the impacts of rainfall. However, rainstorm will influence aerodynamic force on the tower surface directly. Under this circumstance, the structural response of the super-large cooling tower (SLCT) will become more complicated, and then the stability and safety of SLCT will receive significant impact. In this paper, surrounding wind fields of the world highest (210 m) cooling tower in Northwest China underthree typical wind velocities were simulated based on the wind-rain two-way coupling algorithm. Next, wind-rain coupling synchronous iteration calculations were conducted under 9 different wind speed-rainfall intensity combinations by adding the discrete phase model (DPM). On this basis, the influencing laws of different wind speed-rainfall intensity combinations on wind-driving rain, adhesive force of rain drops and rain pressure coefficients were discussed. The acting mechanisms of speed line, turbulence energy strength as well as running speed and trajectory of rain drops on structural surface in the wind-rain coupling field were disclosed. Moreover, the fitting formula of wind-rain coupling equivalent pressure coefficient of the cooling tower was proposed. A systematic contrast analysis on its 3D distribution pattern was carried out. Finally, coupling model of SLCT under different working conditions was constructed by combining the finite element method. Structural response, buckling stability and local stability of SLCT under different wind velocities and wind speed-rainfall intensity combinations were compared and analyzed. Major research conclusions can provide references to determine loads of similar SLCT accurately under extremely complicated working conditions.

• 한국식품과학회지
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• 제54권2호
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• pp.141-146
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• 2022

본 연구는 생리활성물질이 풍부한 아로니아를 활용하여 가공식품 개발에 필요한 기초 연구 데이터를 제공하기 위해 아로니아와 설탕의 배합비율별 프리저브 잼을 제조한 뒤 그 품질 특성과 항산화 활성을 조사하였다. 배합비율에 따라 아로니아의 함량이 낮아질수록 당도는 높아졌으며 수분함량은 낮아지는 경향을 나타내었다. 강도와 최대응력은 아로니아 함량이 줄어들고 설탕의 함량이 증가할수록 높은 값을 나타내었다. 잼의 비율별 항산화 활성은 아로니아 함량 70%에서 DPPH radical 저해율이 가장 높았다. 총 페놀 함량, TEAC, FRAP, ORAC의 값은 모두 아로니아 함량에 따라 비례적으로 증가하는 경향을 나타내었다. 관능평가에서 단맛과 식감이 모두 강하다고 평가된 아로니아 함량 30%에서는 오히려 종합적 선호도에서 가장 낮게 나타났으며 아로니아 함량 40%에서 가장 높은 선호도를 나타내었다. 본 연구에서는 아로니아와 설탕 배합비율에 따른 품질 특성과 항산화 연구를 진행하였으며 국산 아로니아를 활용한 제품의 개발에 기초 자료로서 활용될 것으로 기대된다.

• Structural Monitoring and Maintenance
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• 제8권4호
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• pp.345-360
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• 2021

This paper presents an analytical approach to calculate the buckling load of the cylindrical ring structures subjected to both hydrostatic and hydrodynamic pressures. Based on the conservative law of energy and Timoshenko beam theory, a theoretical formula, which can be used to evaluate the critical pressure of buckling, is first derived for the simplified cylindrical ring structures. It is assumed that the hydrodynamic pressure can be treated as an equivalent hydrostatic pressure as a cosine function along the perimeter while the thickness ratio is limited to 0.2. Note that this paper limits the deformed shape of the cylindrical ring structures to an elliptical shape. The proposed analytical solutions are then compared with the numerical simulations. The critical pressure is evaluated in this study considering two possible failure modes: ultimate failure and buckling failure. The results show that the proposed analytical solutions can correctly predict the critical pressure for both failure modes. However, it is not recommended to be used when the hydrostatic pressure is low or medium (less than 80% of the critical pressure) as the analytical solutions underestimate the critical pressure especially when the ultimate failure mode occurs. This implies that the proposed solutions can still be used properly when the subsea vehicles are located in the deep parts of the ocean where the hydrostatic pressure is high. The finding will further help improve the geometric design of subsea vehicles against both hydrostatic and hydrodynamic pressures to enhance its strength and stability when it moves underwater. It will also help to control the speed of the subsea vehicles especially they move close to the sea bottom to prevent a catastrophic failure.

• Structural Engineering and Mechanics
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• 제81권6호
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• pp.715-728
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• 2022

A new type of buckling-restrained braces (BRBs) with a longitudinally profiled steel plate working as the core (LPBRB) is proposed and experimentally investigated. Different from conventional BRBs with a constant thickness core, both stiffness and strength of the longitudinally profiled steel core along its longitudinal direction can change through itself variable thickness, thus the construction of LPBRB saves material and reduces the processing cost. Four full-scale component tests were conducted under quasi-static cyclic loading to evaluate the seismic performance of LPBRB. Three stiffening methods were used to improve the fatigue performance of LPBRBs, which were bolt-assembled T-shaped stiffening ribs, partly-welded stiffening ribs and stiffening segment without rib. The experimental results showed LPBRB specimens displayed stable hysteretic behavior and satisfactory seismic property. There was no instability or rupture until the axial ductility ratio achieved 11.0. Failure modes included the out-of-plane buckling of the stiffening part outside the restraining member and core plate fatigue fracture around the longitudinally profiled segment. The effect of the stiffening methods on the fatigue performance is discussed. The critical buckling load of longitudinally profiled segment is derived using Euler theory. The local bulging behavior of the outer steel tube is analyzed with an equivalent beam model. The design recommendations for LPBRB are presented finally.

• Geomechanics and Engineering
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• 제31권5호
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• pp.439-452
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• 2022

A forecast of slope behavior during catastrophic events, such as earthquakes is crucial to recognize the risk of slope failure. This paper endeavors to eliminate the significant supposition of predefined slip surfaces in the slope stability analysis, which questions the relevance of simple conventional methods under seismic conditions. To overcome such limitations, a methodology dependent on the slip line hypothesis, which permits an automatic generation of slip surfaces, is embraced to trace the extreme slope face under static and seismic conditions. The effect of earthquakes is considered using the pseudo-static approach. The current outcomes developed from a parametric study endorse a non-linear slope surface as the extreme profile, which is in accordance with the geomorphological aspect of slopes. The proposed methodology is compared with the finite element limit analysis to ensure credibility. Through the design charts obtained from the current investigation, the stability of slopes can be assessed under seismic conditions. It can be observed that the extreme slope profile demands a flat configuration to endure the condition of the limiting equilibrium at a higher level of seismicity. However, a concurrent enhancement in the shear strength of the slope medium suppresses this tendency by offering greater resistance to the seismic inertial forces induced in the medium. Unlike the traditional linear slopes, the extreme slope profiles mostly exhibit a steeper layout over a significant part of the slope height, thus ensuring a more optimized solution to the slope stability problem. Further, the susceptibility of the Longnan slope failure in the Huining-Wudu seismic belt is predicted using the current plasticity approach, which is found to be in close agreement with a case study reported in the literature. Finally, the concept of equivalent single or multi-tiered planar slopes is explored through an example problem, which exhibits the appropriateness of the proposed non-linear slope geometry under actual field conditions.

• 한국분무공학회지
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• 제28권1호
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• pp.16-23
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• 2023

The objective of this numerical study is to investigate the effect of the shape and material of the blower blade for the electrified speed sprayer on the blowing performance. The shape of the blade was changed to the bonding angle, the number of blades, the width of the blade, and the blade length based on the existing model. In order to obtain the reliability of the numerical model, the analysis of the grid dependence was performed in the numerical analysis. The numerical analysis results were compared and analyzed in terms of the agricultural chemical penetration length characteristics, flow uniformity characteristics, and velocity distribution characteristics. Furthermore, the effect of material change on weight reduction and structural characteristics was also compared and analyzed. As a result of the analysis, it was found that the optimal condition was that the blade angle was 45°, the number of blades was 12, and the width was 115 mm, which was confirmed through a comparison of the inlet mass flow rate. As a result of the equivalent stress lower than the yield strength due to the material change from aluminum to steel compared to the existing steel, structural defects do not appear, and it is judged that the operation time compared to the battery capacity will be improved through the weight reduction of the blade.