• Geomechanics and Engineering
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• 제25권1호
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• pp.49-58
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• 2021

The resistance of soil to the tractive force of flowing water is one of the essential parameters for the stability of the soil when directly exposed to the movement of water such as in rivers and ocean beds. Biopolymers, which are new to sustainable geotechnical engineering practices, are known to enhance the mechanical properties of soil. This study addresses the surface erosion resistance of river-sand treated with several biopolymers that originated from micro-organisms, plants, and dairy products. We used a state-of-the-art erosion function apparatus with P-wave reflection monitoring. Experimental results have shown that biopolymers significantly improve the erosion resistance of soil surfaces. Specifically, the critical shear stress (i.e., the minimum shear stress needed to detach individual soil grains) of biopolymer-treated soils increased by 2 to 500 times. The erodibility coefficient (i.e., the rate of increase in erodibility as the shear stress increases) decreased following biopolymer treatment from 1 × 10-2 to 1 × 10-6 times compared to that of untreated river-sands. The scour prediction calculated using the SRICOS-EFA program has shown that a height of 14 m of an untreated surface is eroded during the ten years flow of the Nakdong River, while biopolymer treatment reduced this height to less than 2.5 m. The result of this study has demonstrated the possibility of cross-linked biopolymers for river-bed stabilization agents.

• Journal of the Korean Wood Science and Technology
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• 제39권5호
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• pp.429-436
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• 2011

The selected physical and mechanical properties of non-certificated LVL circulated in domestic lumber market were investigated and compared to relevant standards. The tested LVL passed the moisture content and the soaking delamination rate limit as per domestic (KS) and Japanese standard (JAS). The evaluated mechanical properties were flatwise/edgewise bending strength, modulus of elasticity (MOE), horizontal shear and compressive strength. The 30 mm-thick LVL showed significantly higher bending strength than that of the 25 mm-thick LVL. The modulus of elasticity (MOE) showed same tendency in the results of bending strength. The edgewise bending strength and MOE were higher than that of flatwise bending strength and MOE. The horizontal shear strength values were also showed similar results to bending strength values. The tested results were compared each other and each products were graded according to JAS 701 grade specification. The failure mode of LVL in bending test showed the similar failure mode of solidwood that failed in a simple tension manner (splintery tension). The glue line failure was severe in 25 mm-thick specimens due to concentration of shear stress in layer discontinuity containing small voids and starved glue lines. In horizontal shear strength test, failure mode of LVL showed the typical horizontal shear failure. Compressive specimens failed with fiber crushing in company with apparent delamination that splitted along the length of the specimens. From the results, the complete bonding between lamination and consistency in thin veneer layer were considered as a critical factor in the mechanical properties of LVL. Moreover, the standard test procedure and specification for non-certificated LVL should be required to check the performance of uncertificated materials.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2006년도 춘계 학술발표회 논문집
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• pp.455-465
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• 2006

In this study, the effect of scour was evaluated by regional and geotechnical characteristics and back data were accumulate for the design against scour through the local erosion characteristics evaluation of the Inchon coast. The erosion characteristics for the undisturbed soil samples collected near the main locations at the Incheon 2nd bridge, the Hwangyeong bridge, and a coast road in Songdo, are determined quantitatively through the scour rate tests. On the basic soil properties test, the bed around the Inchon coast chiefly consists of fined grained soils, and the soil samples were classified as silty clay(ML) or clay(CL) under the Unified Soil Classification System. On the scour rate test, the critical shear stress increases when the undrained shear strength increases as of the general trend of fine grained soils, and the average scour rate for the maximum velocity by 100 year flood is 173mm/hr at the Incheon 2nd bridge, 67mm/hr at the Hwangyeong bridge and 10mm/hr at a coast road in Songdo, respectively. Comparing to the scour rate of coarse grained soil, that of the bed around the Inchon coast is turned out to be very low. Therefore, the relative ability of the bed around the Inchon coast to resist erosion is assumed to be very high.

• 폴리머
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• 제37권1호
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• pp.61-65
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• 2013

본 실험에서는, 양극산화 처리된 탄소섬유의 표면변화가 탄소섬유강화 복합재료의 기계적 계면특성을 통하여 살펴보았다. 양극산화 처리된 탄소섬유의 표면특성은 FTIR, XPS, 그리고 SEM을 통하여 알아보았다. 복합재료의 기계적 계면특성은 층간전단강도(interlarminar shear strength; ILSS)와 임계세기인자(critical stress intensity factor; $K_{IC}$) 그리고 임계변형속도에너지(critical strain energy release rate; $G_{IC}$)를 통하여 고찰하였다. 실험결과 양극산화에 의한 각각의 표면 처리된 탄소섬유는 표면특성의 변화를 가져오며, 복합재료의 ILSS, $K_{IC}$, 그리고 $G_{IC}$같은 기계적 계면특성은 탄소섬유의 양극산화를 통하여 향상되어진다. 전해질이 20% 황산/질산(3/1)일 때 다른 전해질보다 기계적 물성의 가장 큰 향상을 보였다. 이는 양극산화로 탄소섬유와 매트릭스 사이의 계면결합력의 향상때문이라 판단된다.

• 한국해안해양공학회지
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• 제4권1호
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• pp.26-33
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• 1992

파-흐름의 공존장에서 실트질 점토의 부상특성을 연구하기 위해 조파수조에 흐름발생장치를 설치하며 파낭만 존재하는 경우, 순류 및 역류가 존재하는 경우에 대해서 장적물의 부상실험을 하였다. 역류가 작용할 때가 순류가 작용할 때보다 부상량이 훨씬 많았는데 이는 역류가 작용할 때는 저면에 난류성분이 발달하지만, 순류가 작용할 때는 진동류 효과가 감소하기 때문이다. 파-흐름의 공존장에서 실트질 점토의 부상양계저면전단응력은 $ au$$_{c}$~0.045 N/$m^2$인 것으로 추정되었다. 초기부상률과 저면전단응력과의 관계식 및 초기부상률과 측정된 유의파고와의 관계식이 도출되었는데, 초기부상률과 저면전단응력과의 관계는 상당히 분산되어 나타났으나, 초기부상률과 측정된 유의파고와의 관계는 상관성이 양호하게 나타났다. 파동하에서 장적물의 농도가 거의 평형상태에 도달했을 때에 농도의 연직경사로부터 산정된 장적물의 연직확산계수는 저면에서 수심의 1/2 지점까지는 지수형태로 증가하는 양상을 나타냈으나, 그 이상부터는 수심에 관계없이 거의 일정하게 나타났다.다.

• 한국도로학회논문집
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• 제19권2호
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• pp.97-102
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• 2017

PURPOSES : Emulsified asphalt is critical for road construction. The objective of applying asphalt emulsion as an adhesive is to prevent the phenomenon of debonding between the upper and lower layers. The quantity and veriety of bituminous material can be varied according to the type of pavement and site conditions. The objective of this study is to reveal the optimum application rates of the emulsified asphalt materials by types of tack-coats using Interface Shear Strength(ISS). METHODS : In the research, emulsified asphalt was paved on the surface of the divided mixture. The specimens of paving asphalt emulsion were utilized to evaluate the bond strength of tack-coat materials. In the evaluation process, NCHRP Report 712 was utilized to investigate the Interface Shear Strength, which reflects the bond capacity of asphalt emulsion. Then, the optimum residual application rates by tack-coat types were determined using regression analysis. RESULTS :As a consequence of squared R values investigated from 0.7 to 1 as part of the regression analysis, the tendency of predicted ISS values was compared with the results. The optimum residual application rates of AP-3, RS(C)-4, QRS-4, and BD-Coat were determined to be $0.78{\ell}/m^2$, $0.51{\ell}/m^2$, $0.53{\ell}/m^2$, and $0.73{\ell}/m^2$, respectively, utilizing 4th regression analysis. CONCLUSIONS :Based on the result of this study, it was not feasible to conclude whether higher residual application of tack-coat material leads to improved bond capacity. Rather, the shearing strength varies depending on the type of pavement.

• Korea-Australia Rheology Journal
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• 제21권4호
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• pp.269-280
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• 2009

The drop formation dynamics of a shear thinning, elastic, yield stress ($\tau_o$) fluid (Carbopol 980 (poly(acrylic acid)) dispersions) in silicone oil has been investigated in a flow-focusing microfluidic channel. The rheological character of each solution investigated varied from Netwonian-like through to highly non-Newtonian and was varied by changing the degree of neutralization along the poly (acrylic acid) backbone. We have observed that the drop size of these non-Newtonian fluids (regardless of the degree of neutralisation) showed bimodal behaviour. At first we observed increases in drop size with increasing viscosity ratio (viscosity ratio=viscosity of dispersed phase (DP)/viscosity of continuous phase (CP)) at low flowrates of the continuous phases, and thereafter, decreasing drop sizes as the flow rate of the CP increases past a critical value. Only at the onset of pinching and during the high extensional deformation during pinch-off of a drop are any differences in the non-Newtonian characteristics of these fluids, that is extents of shear thinning, elasticity and yield stress ($\tau_o$), apparent. Changes in these break-off dynamics resulted in the observed differences in the number and size distribution of secondary drops during pinch-off for both fluid classes, Newtonian-like and non-Newtonian fluids. In the case of the Newtonian-like drops, a secondary drop was generated by the onset of necking and breakup at both ends of the filament, akin to end-pinching behavior. This pinch-off behavior was observed to be unaffected by changes in viscosity ratio, over the range explored. Meanwhile, in the case of the non-Newtonian solutions, discrete differences in behaviour were observed, believed to be attributable to each of the non-Newtonian properties of shear thinning, elasticity and yield stress. The presence of a yield stress ($\tau_o$), when coupled with slow flow rates or low viscosities of the CP, reduced the drop size compared to the Newtonian-like Carbopol dispersions of much lower viscosity. The presence of shear thinning resulted in a rapid necking event post onset, a decrease in primary droplet size and, in some cases, an increase in the rate of drop production. The presence of elasticity during the extensional flow imposed by the necking event allowed for the extended maintenance of the filament, as observed previously for dilute solutions of linear polymers during drop break-up.

• Composites Research
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• 제35권4호
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• pp.277-282
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• 2022

본 연구에서는 저가 재료인 전분과 물 기반의 현탁액을 이용하여 과속방지턱에 응용 가능한 스마트 소재를 개발하고 물성을 평가하였다. 유변물성측정기를 이용하여 전단율에 따른 점도 및 전단력을 측정하여 전분 농도별 전단농화 발생 현상을 확인하였다. 물체의 낙하 시험과 5-25 km/h의 주행 속도로 충격 후 진동을 측정한 자전거 주행 시험을 통해 거시적인 전단농화현상을 확인하였고, 과속방지턱의 적용 가능성을 확인하였다. 점도 측정 결과, 초기에 전단담화 구간에 이어 전단농화가 발생하였고, 전단농화 현상을 유발하는 임계 변형률은 농도가 증가함에 따라 감소하였다. 또한 전분 농도 증가에 따라 점도와 전단력이 크게 증가하였다. 낙하시험과 자전거 주행시험 결과 현탁액이 단시간에 고체 상태로 바뀌었고 충격 에너지가 유체에 흡수되었다. 유체의 농도와 가하는 충격(속도)이 증가할수록 전단농화현상이 쉽게 발생하였다. 최종적으로 물과 전분 기반의 비뉴턴 유체로 5-25 km/h 범위에서 구동하는 스마트 과속방지턱 재료의 개발을 제안하였다.

• 대한토목학회논문집
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• 제28권1B호
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• pp.125-135
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• 2008

본 연구의 목적은 금강하구의 표층에 분포하는 점착성 퇴적물의 침식매개변수를 정량적으로 산정하는 것이다. 또한 본 연구는 침식매개변수들의 금강하구역 내에서의 지엽적 계절적 변화에 대한 조사와 타 지역 분석 결과와의 비교/분석을 통한 공간적 변화에 대한 조사를 포함한다. 점착성 퇴적물의 침식특성은 기본적으로 퇴적물 자체의 물리 화학적 특성에 의해 크게 영향을 받으므로, 본 연구는 또한 퇴적물의 이러한 기본특성이 침식특성에 미치는 영향에 대한 정성적 분석을 포함한다. 침식실험은 전북대 환형수조를 이용하여 균일저면 조건하에서 수행되었으며, 저면밀도와 바닥전단응력을 변화시키면서 총 16회의 실험이 수행되었다. 실험결과에 따르면, 금강하구역 점착성 퇴적물은 저면밀도 $1.14{\sim}1.38g/cm^3$ 범위에서 침식한계전단응력(${\tau}_{ce,s}$)은 $0.19{\sim}0.41N/m^2$, 침식률 계수(${\varepsilon}_{M,s}$)는 $54.26{\sim}7.70mg/cm^2{\cdot}hr$ 범위의 값을 갖는 것으로 나타났다. 또한 산정된 침식 매개변수들은 타 지역 점착성 퇴적물과 비교시 정량적으로 그 값이 크게 다른 것으로 나타났으나, 금강하구역 내에서의 지엽적/계절적 변화는 미미한 것으로 나타났다.

• 터널과지하공간
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• 제20권5호
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• pp.344-351
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• 2010

닫힌 균열을 따라 발생하는 전단거동을 Mode II 크랙의 시작과 진행으로 묘사할 수 있다. 파괴역학 이론에서는 순수 Mode II 재하에서 일반적으로 고유물성으로 인식되는 에너지 방출율(GII, Engergy Release Rate)이 한계점($G_{IIC}$)에 도달했을 때 전단거동이 시작된다고 예측한다. 지난 몇 년간 퍼듀대학의 암반공학그룹은 한계 에너지 방출률($G_{IIC}$)의 구속응력(normal stress)과 닫힌 균열의 거칠기에 대한 관계를 실험적으로 접근해왔다. 먼저 많은 실험들이 아크릴 재료를 대상으로 실행되었는데, 이는 광탄성(Photoelastic) 방법을 이용한 균열 끝(fracture tip)의 응력 집중 영역을 시각화하는 것을 가능케 해 주었다. 그 다음 실험 연구는 비교적 낮은 압축강도를 지닌 균질한 석고에 시행되었고, 최근에는 더 높은 압축강도를 지닌 재료를 대상으로 실험연구를 수행하였다. 그 예로 시멘트로 만든 시료 불록에 직접 전단 실험을 하였는데, 이전의 실험들과 마찬가지로 불연속면의 최대마찰각(Peak Friction Angle)이 잔류 마찰각(Residual Friction angle)과 비슷할 때만이 $G_{IIC}$가 재료의 고유물성으로 간주 될 수 있다는 점을 확인할 수 있었다. 그렇지 않은 경우에 한계 에너지 방출율($G_{IIC}$)은 구속응력과 함께 증가한다.