Microstructure‑Strengthening Interrelationship of an Ultrasonically Treated Hypereutectic Al–Si (A390) Alloy

Soo‑Bae Kim,Young‑Hee Cho,Jae‑Gil Jung,Woon‑Ha Yoon,Young‑Kook Lee,Jung‑Moo Lee 대한금속·재료학회 2018 METALS AND MATERIALS International Vol.24 No.6

Ultrasonic melt treatment (UST) was applied to an A390 hypereutectic Al–Si alloy in a temperature range of 750–800 °Cand its influence on the solidification structure and the consequent increase in strength was investigated. UST at such a hightemperature, which is about 100 °C above the liquidus temperature, had little effect on the grain refinement but enhanced thehomogeneity of the microstructure with the uniform distribution of constituent phases (e.g. primary Si, α-Al and intermetallics)significantly refined. With the microstructural homogeneity, quantitative analysis confirmed that UST was found tosuppress the formation of Cu-bearing phases, i.e., Q-Al5Cu2Mg8Si6, Al2Cuphases that form in the final stage of solidificationwhile notably increasing the average Cu contents in the matrix from 1.29 to 2.06 wt%. A tensile test exhibits an increasein the yield strength of the as-cast alloy from 185 to 208 MPa, which is mainly associated with the solute increment withinthe matrix. The important role of UST in the microstructure evolution during solidification is discussed and the mechanismcovering the microstructure-strengthening interrelationship of the ultrasonically treated A390 alloy is proposed.

Effect of Ultrasonic Melt Treatment on Solidification Microstructure of Al–5Ti–1B Alloy Containing Numerous Inoculant Particles

Soo‑Bae Kim,Jae‑Gil Jung,Young‑Hee Cho,Su‑Hyeon Kim,Kwangjun Euh,Jung‑Moo Lee 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.7

The effect of ultrasonic melt treatment (UST) on the solidification microstructure of an Al–5Ti–1B alloy containing highvolumefractions of Al3Tiand TiB2particles is investigated for various UST times with different melt holding times. Theas-cast Al–5Ti–1B alloy is composed of TiB2and polygonal Al3Tiparticles (present prior to UST), plate-like Al3Tiparticles,and Al grains (formed during UST and/or solidification). The UST causes a size reduction and homogeneous distributionof the TiB2-agglomerated region containing many submicron-sized TiB2particles pushed to the grain boundaries. The USTslightly decreases the size and improves the distribution of polygonal Al3Tiparticles enriched in the TiB2-agglomeratedregion. Unlike the TiB2and polygonal Al3Tiparticles, which exhibit a minor refining effect, the plate-like Al3Tiparticlesshow a significant refinement with UST application. The UST has a significant effect on the size distribution of Al grains byinducing the formation of medium-sized grains at the expense of small and large grains; however, it only has a slight effecton grain refinement. The degree of microstructure modification increases with increasing UST time but decreases with meltholding time after UST. The mechanisms for the refinement and dispersion of the TiB2and Al3Tiparticles and Al grains arediscussed considering fragmentation, nucleation, and growth behaviors induced by the UST and subsequent solidification.

점토굴착 사면의 거동에 관한 원심모형실험 및 수치해석

최민수,정길수,박병수,유남재 강원대학교 산업기술연구소 2005 産業技術硏究 Vol.25 No.B

This paper is the results of experimental and numerical works on analyzing the geotechnical engineering behavior and characteristics of excavated clay slope formed by the method of excavated replacement which is one of treatments in soft soil ground. For the centrifuge model tests, models of excavated clay slope were prepared by remolding the marine clayey soil sampled from the field. Tests were performed with changing the slope to investigate the behavior of them. On the other hand, numerical analyses were carried out to analyze the change of safety factor against instability of slope with time. Changes of pore water pressure, shear strength and displacement were also investigated. As results of centrifuge model tests with slopes of 1:1.5 and 1:3 using the confining body of simulating the effect of excavation, for the case of 1:1.5, slope failure occurred right after remove the confining body whereas relatively small displacements within the range of 3.2mm, implying to maintain the stability of slope, were observed for the case of 1:3 slope. From the results of numerical analyses using the software of PLAXIS to investigate the stability of slope after excavation, the minimum safety factor against slope failure was 1.28 for the case of 1:3 slope. The further researches in the future are required with considerations of build up of static pore water pressures during acceleration of centrifuge, depth of excavation influencing the behavior of the slope and permeability of the slope since excavation of the slope was not simulated well resulted from the limitations of apparatus at the stage of excavation during the centrifuge tests.

모래다짐말뚝과 널말뚝으로 처리된 연약점토지반의 거동

유남재,정길수,박병수,김경수 강원대학교 산업기술연구소 2006 産業技術硏究 Vol.26 No.B

Centrifuge model experiments were performed to investigate the confining effects of the sheet piles, installed to the sides of soft clay ground treated with sand compaction piles, on the bearing capacity and concentration ratio of composite ground. For the given g-level in the centrifuge model tests, replacement ratio of SCP and the width of surcharge loads on the surface of ground with SCP, the confining effects of installing the sheet piles on the edges of SCP ground on the bearing capacity, change of stress concentration ratio and failure mechanism were investigated. Kaolin, one of typical clay mineral, and Jumunjin standard sand were used as a soft clay ground and sand compaction pile irrespectively. As results of experiments, lateral confining effect by inserting the model sheet piles fixed to the loading plate was observed. For the strip surcharge loading condition, the yielding stress intensity in the form of the strip surcharge loads tends to increase with increasing the embedded depth of sheet piles. The stress concentration ratio was found not to be influenced consistently with the embedded depth of sheet piles whereas the effect of stress intensity on stress concentration ratio shows the general trend that values of stress concentration ratio are relatively high at the initial stage of loading and tend to decrease and converge to the certain values. For the failure mechanism in the case of reinforced with sheet piles, displacement behavior related to the punching failure, settlement right beneath the loading plate occurred since the soil was confined with sheet piles, was observed.

계약에 대한 8세기 예언자들의 침묵 : 아모스 호세아를 중심으로

서길원 목원대학교 신학연구소 1997 신학과 현장 Vol.7 No.-

아모스나 호세아는 ‘계약’이나 ‘율법’에 관하여 침묵한다. 그들이 이스라엘의 파멸을 선포한 것은 계약의 파괴 때문이 아니고, 이스라엘이 야훼의 구원행위를 잊어버리고 진실하게 사랑하지 못했기 때문이다. 예언자들은 야훼와 이스라엘의 관계를 법적인 계약관계로 보지 않고 ‘역동적인 사랑의 관계’로 파악했다. 이와 같은 예언자 운동이 있은 후에 깨어진 야훼와의 관계를 회복하고 재정립하기 위해서 야훼와 이스라엘의 관계를 법적인 계약의 관계로 이해하고 이 계약을 유지하기 위해 이스라엘 백성들이 지켜야 할 기본적인 지시와 규정이 정리되어 율법서가 되었다. 이런 면에서 예언자들은 고대 계약이나 율법 전통에 서서 그것을 해석한 사람들이 아니고 도리어 깨어진 관계를 회복하고 새롭게 긍정적인 관계로 나아가도록 길을 열어준 자들 즉 6-7세기에 등장한 계약 및 율법사상이 있게 한 자들이다. 계약사상의 출현은 8세기 예언자들의 멸망선언 이후, 이들의 예언이 적중되어갈 무렵, 즉 이스라엘의 야훼신앙이 완전한 위기에 처하게 되었을 때 새로운 가능성과 희망을 위해 나타났다. 국가 멸망에 처한 이스라엘은 절망하거나 야훼를 원망하거나 포기하지 않고 새로운 가능성을 모색하였는데 그것이 바로 계약신학이다. 이로써 이스라엘은 예언자들에게 정당성을 부여하고 또 자신들은 새로운 가능성을 갖게 된 것이다. 이처럼 계약 신학의 발견은 위기극복을 위한 야훼 하나님의 또 한번의 은총의 사건이었고 8세기 예언자들은 이 은총이 나타나도록 길을 열어 준 사람들이다.

땀복착용시 환기역치운동이 직장온, 산소섭취량 및 발한에 미치는 영향

신길수,김수근 圓光大學校 附設 體力科學硏究所 2001 體力科學硏究 Vol.24 No.-

The purpose of this study is to investigate the effect of wearing sweat suit on rectal temperature, oxygen uptake and sweating rate during ventilatory threshold exercise. 14 healthy students served as subjects in the experimental chamber which was controlled 22±1℃, 60±10%RH and no wind. The experimental clothes were Sweat Suit(SS) and General Suit(GS), SS was the product of R sports wear company which was consisted of long-sleeved jumper(100% polyester) and full length trousers(100% polyester) and GS were consisted of long sleeved shirt(100% cotton) and full length trousers(100% cotton). The subject were same socks and shoes in both experimental clothes SS and GS. The subject reported at the experimental chamber at the same time on each experimental day, exchanged their clothes to the experimental clothes SS or GS, wore all sensors for the physiological measurements and had a rest in a sitting posture about 10min. After rest, the subject carried out 20 min VT exercise on the treadmill and during the exercise rectal temperature, VO2, and evaporative weight loss were measured continuously and compared between two experimental clothes SS and GS. The major findings were as follows; Firstly, the increased in rectal temperature during 20min exercise was higher in experimental clothes SS than in GS. Secondly, VO2 were a little bit higher SS and GS. Thirdly, the evaporative weight loss(sweat rate) was greater in SS than GS. These results indicate that the thermophysiological responses and sweating rate differs according to the wearing suit even though the subjects performed same exercise.

마이셀 용액에서의 Diethyl Vinyl Phosphates의 산촉매 가수분해 반응에 관한 연구

유영길,이수민,김일광 圓光大學校 基礎自然科學硏究所 1982 基礎科學硏究誌 Vol.1 No.1

For the acid catalyzed hydrolysis of diethy1 viny1 phosphate and diethy1 isopropeny1 phosphate, the rate constants for diethy1 isopropeny1 phosphate is greater than that for diethy1 viny1 phosphate. Consistently, methy1 group has more effect of electron donating than proton. Both anionic and cationic detergents enhance the reaction rate respectively. Especially it shows that anionic micelles stabilization between micelles and viny1 phosphates, diethy1 isopropeny1 phosphate is less effective than diethy1 viny1 phosphate because of the steric hindrance.

고분자 희석용액의 분자론적 특성에 관한 연구(제1보)

서길수,배광수 嶺南大學校 工業技術硏究所 1982 연구보고 Vol.10 No.1

. The shear rate dependence of viscosity and primary normal stress for a dilute solution of elastic dumbbells joined by a spring has been studied for steady shearing flow. Assumption that Frenkel model can be applied to describe the spring force of elastic dumbbell has been estabished. Hydrodynamic interaction has been neglected. Giesekus expression for the stress tensor has been used. So as to calculate the expectation value of stress tensor, the differential equation of distribution function has been solved by use of perturbation method. Material functions, viscosity and normal stress, have been integrated through the orthogonal relationships of spherical harmonics. Although the crudeness of the model, the results have been qualitatively in agreement with the experimental data in the small range of shear.

수평배수재 배열의 진공압밀효과에 대한 수치해석

박병수,정길수,이종호,유남재 강원대학교 산업기술연구소 2003 産業技術硏究 Vol.23 No.A

This paper is results of numerical works of investigating effects of horizontal drain arrangements on vacuum consolidation. Extensive numerical analyses were carried out to find the appropriate arrangements of horizontal dram of vacuum consolidation. Commercially available program of CRISP. well know-n to be good to modelling the behavior of clay- material, was used Cam-clay model, based on the Critical State of Soil Mechanics(CSSM), was used to simulate the geotechnical engineering behavior of clay. Model test results carried out previously in the laboratory w-ere compared with numerically estimated results and it was found that results about consolidational settlement with times were in good agreements. Based on this confirmation. parametric numerical study was performed to investigate effects of horizontal drain arrangements on vacuum consolidation with changing the vertical and horizontal spacings between drains for the given soil properties and vacuum. The effect of distance of drain located in top layer from the surface of the ground on the settlement due to vacuum was also investigated. As a results of numerical analyses. appropriate arrangements of horizontal drain to maximize the consolidation settlement due to vacuum were found. The mechanism of vacuum consolidation about the vacuum pressures being transferred to the effective stresses around drains was also evaluated.

PBD가 설치된 연약지반의 원심모형실험에 관한 연구

정길수,박병수,전상현,유남재 강원대학교 산업기술연구소 2006 産業技術硏究 Vol.26 No.A

This study is the results of experimental and numerical study on the consolidational behavior of multi-layered soft soil ground installed with plastic board drains (PBD). Centrifuge model tests with a marine clay sampled from field were performed to investigate the consolidational behavior of multi-layered ground where a dredged soil was placed on the soft clay ground and PBDs were installed. Test results were compared with those of numerical analyses, using the 2-D equivalent model previously proposed. From test resuts, it was found that the amount of consolidation settlement occurred in the original ground due to embankment surcharge loads was in the range of 38% of total settlement in the whole ground. From the results of cone penetration tests executed after finishing the centrifuge model tests, the cone resistance was found to increase with depth. The measured water contents inbetween PBDs were in the ranges of 38~50% and their values tended to increase with increasing the distance between PBDs.