• Advances in nano research
• /
• 제13권3호
• /
• pp.285-295
• /
• 2022

Creation of plastic deformation under seismic loads, is one of the most serious subjects in RC structures with steel bars which reduces the life threatening risks and increases dissipation of energy. Shape memory alloy (SMA) is one of the best choice for the relocating plastic hinges. In a challenge to study the seismic response of concrete moment resisting frame (MRF), this article investigates numerically a new type of concrete frames with nano fiber reinforced polymer (NFRP) and shape memory alloy (SMA) hinges, simultaneously. The NFRP layer is containing carbon nanofibers with agglomeration based on Mori-Tanaka model. The tangential shear deformation (TASDT) is applied for modelling of the structure and the continuity boundary conditions are used for coupling of the motion equations. In SMA connections between beam and columns, since there is phase transformation, hence, the motion equations of the structure are coupled with kinetic equations of phase transformation. The Hernandez-Lagoudas theory is applied for demonstrating of pseudoelastic characteristics of SMA. The corresponding motion equations are solved by differential cubature (DC) and Newmark methods in order to obtain the peak ground acceleration (PGA) and residual drift ratio for MRF-2%. The main impact of this paper is to present the influences of the volume percent and agglomeration of nanofibers, thickness and length of the concrete frame, SMA material and NFRP layer on the PGA and drift ratio. The numerical results revealed that the with increasing the volume percent of nanofibers, the PGA is enhanced and the residual drift ratio is reduced. It is also worth to mention that PGA of concrete frame with NFRP layer containing 2% nanofibers is approximately equal to the concrete frame with steel bars.

• 한국주조공학회지
• /
• 제29권6호
• /
• pp.270-276
• /
• 2009

After casting button-type small ingots of ternary Fe-Mn-S alloys which had three different Mn/S ratios (1, 5 and 70) in a vacuum arc furnace, the effect of the ratio on the sulfide formation was investigated. In case of the Mn/S ratio of 1, if alloy composition was located in an iron-rich corner on a Fe-Mn-S ternary phase diagram, only duplex MnS-FeS sulfide films were observed in the grain boundary. If the alloy composition was located in the miscibility gap area of the phase diagram, primary globular dendritic sulfides and dendritic sulfide slags were generated within the grain and tubular monotectic sulfides were also detected in the grain boundary. When the Mn/S ratio was 5, if the alloy composition was in the iron-rich corner, only bead-like sulfides were generated. On the other hand, if the composition was in the miscibility gap area, globular dendritic sulfides and dendritic sulfide slags were generated in the form of primary sulfide inclusions and rod-like eutectic sulfides were observed in the grain boundary. Especially, if the contents of Mn and S increased more in the miscibility gap area of the phase diagram, primary globular sulfides containing iron intrusions were observed. In case of Mn/S ratio of 70, if the contents of Mn and S was decreased in the Fe corner of the phase diagram, only bead-like sulfides were observed in the grain boundary. Despite the composition was outside the miscibility gap area of the phase diagram, if the contents of Mn and S increased, clusters of fine sulfide particles as well as fine spherical primary monophase sulfides were observed in the grain boundary.

• 한국패류학회지
• /
• 제30권4호
• /
• pp.353-361
• /
• 2014

동합금이 사육 생물에게 미치는 생리적 영향을 조사하기 위해 화학적 조성이 다른 5종류의 금속판을 넣은 수조에서 사육한 북방전복을 대상으로 성패와 치패의 생존율, 호흡 및 배설률 그리고 기관별 중금속 축적률을 조사하였다. 생존율은 치패와 성패가 각각 27-60%와 63-83%로 성패가 더 높게 나타났다. 합금 조성에 따른 생존율의 뚜렷한 차이는 나타나지 않으나 중금속 축적률 그리고 영양적인 스트레스 등을 고려하면 동합금망은 전복 양성을 위한 가두리로서는 적합하지 못할 것으로 사료된다.

• 한국재료학회지
• /
• 제12권1호
• /
• pp.16-20
• /
• 2002

In this study, the 95W heavy alloys of 3/7, 5/5 and 7/3 of Ni/Fe ratio were sintered at the temperature range between 1420 and $1480^{\circ}C$ for 1h and their microstructures were discussed for an effect of the ${\mu}$-phase $(Fe_7W_6)$ on the microstructure. The ${\mu}$-phase was observed in the only 95W-1.5Ni-3.5Fe alloy of 3/7 and it is thought to be formed and grown from the surface of the W particle. The W particle was surrounded with the ${\mu}$-phase and there were only the W particles and this phase without Ni-Fe-W matrix at the most part. The ${\mu}$-phase changed the interphase structure in the alloy and the grain growth of the W was suppressed because of interrupting the solution-reprecipitation of the W. The W content in the matrix was considered to be lowered due to the interruption of the solution-reprecipitation and the formation of the ${\mu}$-phase in the .

• 한국분말재료학회지
• /
• 제15권5호
• /
• pp.345-351
• /
• 2008

The effects of the dopant (Mn) ratio on the microstructure and thermoelectric properties of $FeSi_2$ alloy were studied in this research. The alloy was fabricated by a combination process of ball milling and high pressure pressing. Structural behavior of the sintered bulks were systematically investigated by XRD, SEM, and optical microscopy. With increasing dopan (Mn) ratio, the density and ${\varepsilon}-FeSi$ phase of the sintered bulks increased and maximum density of 94% was obtained in the 0.07% Mn-doped alloy. The sintered bulks showed fine microstructure of ${\alpha}-Fe_{2}Si_{5}$, ${\varepsilon}-FeSi$ and ${\beta}-FeSi_2$ phase. The semiconducting phase of ${\beta}-FeSi_2$ was transformed from ${\alpha}-Fe_{2}Si_{5}+{\varepsilon}-FeSi$ phase by annealing.

• 한국기계가공학회지
• /
• 제15권3호
• /
• pp.135-146
• /
• 2016

This study investigated the effect of the changes in metal characteristics due to the hot forging on SCR420HB applied to ensure the optimal production of the hot-forging ratio on the mechanical properties of an automotive automatic transmission gear. The microstructural changes in the forging ratio were investigated by adjusting the forging range into multiple ranges from alloy steel. This was done in order to set the optimum forging range given the manufacturing process conditions during the hot forging of alloy steel parts with a carbon content of more than 0.8% wt. The effects of the content change in the microstructure on the mechanical properties due to the use of the part were examined.

• 열처리공학회지
• /
• 제26권5호
• /
• pp.225-232
• /
• 2013

The influence of aging treatment, addition elements and rolling reduction ratio on the microstructure, mechanical, electrical and bendability properties of Cu-Ni-Si-P-x (x = Fe, Sn, Zn) alloys for connector material application was investigated. SEM/EDS analysis exhibited that Ni2-Si precipitates with a size of 20~100 nm were distributed in grains. Fe, Sn, Zn elemnets in Cu-Ni-Si-P alloy imporved the mechanical strength but it was not favor in increasing of electrical conductivity. As higher final rolling reduction ratio, the strength and electrical conductivity is increased after aging treatment, but it indicated excellent bendability. Especially, Cu-2Ni-0.4Si-0.5Sn-0.1Fe-0.03P alloy show the tensile strength value of 700MPa and the electrical conductivity was observed to reach a maximum of 40%IACS. It is optimal for lead frame and connector.

• 한국분말재료학회지
• /
• 제14권4호
• /
• pp.251-255
• /
• 2007

This work is to report not only the effect of rapid solidification of $MgZn_{4.3}Y_{0.7}$ alloys on the micro-structure, but also the extrusion behavior on the materials properties. The average grain size of the atomized powders was about $3-4{\mu}m$. The alloy powders of $Mg_{97}Zn_{4.3}Y_{0.7}$, consisted of I-Phase (Icosahedral, $Mg_{3}Zn_{6}Y_{1}$) as well as Cubic structured W-Phase ($Mg_{3}Zn_{3}Y_{2}$), which was finely distributed within ${\alpha}-Mg$ matrix. The oxide layer formed along the Mg surface was about 48 nm in thickness. In order to study the consolidation behavior of Mg alloy powders, extrusion was carried out with the area reduction ratio of 10:1 to 20:1. As the ratio increased, fully deformed and homogeneous microstructure could be obtained, and the mechanical properties such as tensile strength and elongation were simultaneously increased.

• Journal of Welding and Joining
• /
• 제7권1호
• /
• pp.28-35
• /
• 1989

The fatigue crack growth behavior in GTA butt welded joints of Al-Alloy 5052-H38 was examined using Single Edge Notched(SEN) specimens. It is well known that welding residual stress has marked influence on fatigue crack growth rate in welded structure. In the general area of fatigue crack growth in the presence of residual stress, it is noted that the correction of stress intensity factor (K) to account for residual stress is important for the determination of both stress intensity factor range(.DELTA.K) and stress ratio(R) during a loading cycle. The crack growth rate(da/dN) in welded joints were correlated with the effective stress intensity factor range(.DELTA.Keff) which was estimated by superposition of the respective stress intensity factors for the residual stress field and for the applied stress. However, redistribution of residual stress occurs during crack growth and its effect is not negligible. In this study, fatigue crack growth characteristics of the welded joints were examined by using superposition of redistributed residual stress and discussed in comparison with the results of the initial welding residual stress superposition.

• 한국주조공학회지
• /
• 제13권6호
• /
• pp.547-554
• /
• 1993

Aluminum alloy matrix composites reinforced with various amounts of $Al_2O_3$ short fibers have been produced by rheo-compocasting accompanied by hot pressing. When composites reinforced with fibers are produced by rheo-compocasting, S-L process is the most effective method for homogeneous dispersion of fibers. A sound composites with the improved orientation(3 dimension${\rightarrow}$2 dimension) of the fibers and increased volume fraction of them have been fabricated through the hot pressing of the casted composites. Fibers are broken down when rheo-compocasting, hot pressing, and $T_6$ treating. Among them fibers are broken down most heavily in the hot pressing. And even in the case of the composite reinforced with 30 vol% fibers, which showed the hardest fiber break down, aspect ratio(11.6) is higher than critical aspect ratio(10.7). The fiber strengthening effect in the composites has showed upto 573K. As the test temperature increases to the range of 573K, the effect has been higher. The fracture of composites is controlled by fiber from room temperature to 473K, but the fracture of composites is controlled by interface between fiber and matrix alloy above 473K.