• Geomechanics and Engineering
• /
• 제21권4호
• /
• pp.315-326
• /
• 2020

The long-term behavior of rockfill material used in the construction of infrastructures such as dams is of great significance. Because of concerns about the application of weak rockfill material in dam construction, further experimental studies on the behavior of these materials are required. In this study, laboratory experiments were performed to investigate the one-dimensional deformation and particle breakage of the weak rockfill material under stress. A one-dimensional compression apparatus was designed and developed for testing of rockfill materials of different maximum particle sizes (MPSs). The compression tests were performed under dry, wet and saturated conditions on samples of rockfill material obtained from a dam construction site in Iran. The results of the experiments conducted at the specimen preparation stage and the 1D compression tests are presented. In weak rockfill, the effect of the addition of water on the behavior of the material was uncertain as there were both an increases and decreases observed in particle breakage. Increasing the MPS of the weak rockfill materials increased particle breakage, which was similar to the behavior of strong rockfill material. In all of the MPSs examined, the settlement of specimens under wet conditions was higher than that observed under dry conditions. Also, the greatest deformation occurred during the first hour of loading.

• 한국지반공학회논문집
• /
• 제29권8호
• /
• pp.5-14
• /
• 2013

굵은 자갈 이상의 대입경 입자를 포함하는 조립질 지반재료는 댐, 제방, 철도 등 대형 지반구조물의 성토 및 채움재료로 널리 사용되며, 이러한 구조물의 동적 해석을 위해서는 축조재료의 변형특성에 대한 엄밀한 평가가 필수적이다. 본 연구에서는 대입경 조립재료의 동적 변형특성 평가를 위하여 지름 200mm, 높이 400mm의 공시체에 대한 시험이 가능하도록 개발된 대형 공진주시험기를 활용하여 댐 축조용 사력재의 최대전단탄성계수, 전단탄성계수감소곡선 및 감쇠비를 평가하였으며, 재료의 최대입경과 균등계수와 같은 입도분포특성이 재료의 변형특성에 미치는 영향을 확인하였다. 재료의 입경이 동적 변형특성에 미치는 영향을 평가한 결과, 동일한 균등계수에서 평균입경의 범위에 따른 전단탄성계수감소곡선에 차이가 발생함을 확인하였다. 동일한 최대입경에 대하여 균등계수를 달리하는 경우 균등계수에 따라 최대전단탄성계수의 구속압 영향계수가 증가함을 확인하였다. 결과적으로 조립재료의 입도 특성 중 최대입경은 전단탄성계수감소곡선을, 균등계수는 미소변형영역의 구속압 영향계수에 대한 영향요소임을 확인하였으며, 조립재료의 동적 변형특성을 엄밀히 평가하기 위한 대형 공진주시험기의 효용성을 확인하였다.

• Geomechanics and Engineering
• /
• 제31권5호
• /
• pp.461-476
• /
• 2022

Research studies on the scale effect on triaxial strength of intact rocks are scarce, being more common those in uniaxial strength. In this paper, the authors present and briefly interpret the peak and residual strength trends on a series of triaxial tests on different size specimens (30 mm to 84 mm diameter) of an intact granitic rock at confinements ranging from 0 to 15 MPa. Peak strength tends to grow from smaller to standard-size samples (54 mm) and then diminishes for larger values at low confinement. However, a slight change in strength is observed at higher confinements. Residual strength is observed to be much less size-dependent. Additionally, this study introduces preliminary modelling approaches of these laboratory observations with the help of three-dimensional particle flow code (PFC3D) simulations based on bonded particle models (BPM). Based on previous studies, two modelling approaches have been followed. In the first one, the maximum and minimum particle diameter (D_max and D_min) are kept constant irrespective of the sample size, whereas in the second one, the resolution (number of particles within the sample or ϕ_v) was kept constant. Neither of these approaches properly represent the observations in actual laboratory tests, even if both of them show some interesting capabilities reported in this document. Eventually, some suggestions are provided to proceed towards improving modelling approaches to represent observed scale effects.

• 한국화재소방학회논문지
• /
• 제12권2호
• /
• pp.61-68
• /
• 1998

가축사료 분진의 열적 안정성 실험결과 본 연구에서 사용한 시료 입도의 경우 발열개시온도 및 발열 량에는 별 차이가 없었으나, 숭온속도가 충가함에 따라 발열개시온도가 낮아지고, 입도가 미세해질수 록 분해열이 증가함을 알 수 있었다. 한편, 분위기 기체룰 조연성 기체인 Oz로 사용할 경우 불활성 기 체인 Nz를 사용하는 경우보다 발열개시온도는 현저히 낮아지며, 반면에 발열량도 20배 이상 중가하였 다. 또한 본 연구에서 사용한 시료중 비교적 미세업자가 대기중에 부유하기 쉽고, 외부에서 점화에너지 가 주어질 경우 공기중의 산소와 쉽게 순간적으로 반용하여 폭발하는 것올 볼 수 있다. 본 연구에서의 시료입도중 80/100 mesh의 경우 평균 최대폭발압력은 6.88 Kgf / cm2 로 구해졌다.

• 한국도로학회논문집
• /
• 제19권6호
• /
• pp.23-30
• /
• 2017

PURPOSES : In this paper, the applicability of DEM to a coarse graining method was evaluated by simulating a series of minicone tests for cement paste. METHODS : First, the fundamental physical quantities that are used in a static liquid bridge model were presented with three basic quantities based on the similarity principle and coarse graining method. Then, the scale factors and surface tensions for six different sizes of particles were determined using the relationship between the physical quantities and the basic quantities. Finally, the determined surface tensions and radii were utilized to simulate the fluidal behavior of cement paste under a minicone test condition, and the final shape of the cement paste with reference DEM particle radii was compared with the final shape of the others. RESULTS : The simulations with adjusted surface tensions for five different radii of particles and surface tension showed acceptable agreement with the simulation with regard to the reference size of the particle, although disagreement increases as the sizes of the particle radii increase. It seems reasonable to increase the particle radii by at least 0.196 cm considering the computational time reduction of 162 min. CONCLUSIONS : The coarse graining method based on the similarity principle is applicable for simulating the behavior of fluidal materials when the behavior of the materials can be described by a static liquid bridge model. However, the maximum particle radius should be suggested by considering not only the scale factor but also the relationship of the particle size and number with the radius of the curve of the boundary geometry.

• 한국세라믹학회지
• /
• 제51권2호
• /
• pp.127-131
• /
• 2014

Precipitated calcium carbonate(PCC) inorganic fillers for plastic offera higher replacement ratio with improved mechanical properties than any other inorganic fillers. Due to its secure economic feasibility, its fields of application areexpanding. For optimized PCC grain size and polymer replacement ratio, it is good to maintain at least $0.035{\mu}m$ grains and keep double the grain size of distance between particles, depending on the molecular weight and volume replacement rate of the polymer. PCC has unique characteristics, ie, with smaller grain size, dispersibility decreases, and if grain size is not homogenous, polymer cracking occurs. The maximum replacement ratio of PCC is approximately 30%, but in the range of 10 - 15% it produces the highest mechanical strength. When mixed with a biodegradable plastic like starch, it also improves initial environmental degradability.

• 한국광물학회지
• /
• 제21권3호
• /
• pp.271-281
• /
• 2008

조선시대에 녹색 광물 안료로 사용되었던 "뇌록(磊綠)"은 경북 포항시 장기면 뇌성산에서 제 4기 현무암질 화산쇄설암 내에 맥상 또는 공극충진상으로 산출되며, 주 구성광물은 셀라도나이트(celadonite)로 소량의 녹니석/스멕타이트 혼합층광물과 모데나이트 및 단백석을 함유한다. 뇌록의 원석인 뇌록석은 주로 수백 ${\mu}m\sim$수십 ${\mu}m$ 크기의 미세한 셀라도나이트라는 일종의 점토광물로 구성되어 있으며, 수 ${\mu}m$ 이하의 작은 입자들은 응집현상을 보여준다. 입자크기가 $71{\mu}m$ 이하로 감소하면서 그 착색율은 월등히 증가하였다. 은폐력은 입자 크기가 $0.2\sim0.3{\mu}m$일 경우 최대값을 나타내었으며, 초미분인 200 nm 이하에서 투명도가 최대값을 보였다. 내광성과 항균성은 일반안료와 비교했을 때 뛰어난 효과를 보여준다. 현존 단청 기술을 접목한 전색제 채색 실험 결과 $32{\mu}m$ 이하의 입도에서 가장 양호한 도색효과를 보여주고, 이상의 입도에서는 도색이 불가능하였다.

• 대한기계학회논문집B
• /
• 제29권9호
• /
• pp.1013-1021
• /
• 2005

In this work, $TiO_2$ nanoparticles were synthesized using a N2-diluted hydrogen coflow diffusion flame. The effects of flame temperature on the crystalline structure and the size of formed nanoparticles were investigated. The maximum centerline temperature of the flame ranged from 1,920K for $H_2-only$ flame to 863k for $81\%\;N_2-diluted$ flame. The morphology and the crystal structure of $TiO_2$ nanoparticles were analyzed by a TEM and a XRD, respectively. The particle size distribution was also measured by using a scanning mobility particle size. (SMPS). The mean particle diameter was calculated from the TEM images depended on the flame temperature, having minimum at about 1,look. Based on the SMPS measurements, the mean particle diameter of $TiO_2$ nanoparticles at flame temperatures > 1,300K was smaller than that at flame temperatures < 1,300K. From the XRD analysis, it was evident that the anatase fraction increased with decreasing the flame temperature. The portion of anatase phase in $TiO_2$ nanoparticles might be greater than $80\%$ when the flame temperature was lower than 1,000K.

• 대기
• /
• 제17권4호
• /
• pp.407-420
• /
• 2007

Optical characteristics of aerosols in Seoul are investigated from the measurements of sky radiance by Skyradiometer at Yonsei University from December 2005 to November 2006. Aerosol optical depth (AOD) shows a maximum in June due to weak ventilation and particle growth by aging process and hygroscopic effect. Single scattering albedo (SSA) and Angstrom Exponent (AE) show the lowest value in spring due to the Asian dust. It is clear that coarse mode is dominant in spring and fine mode is dominant in summer from the volume size distribution measured in this study. The explanations on the changes of aerosol loadings are provided through the correlation between AOD and AE, while the pattern of wavelength dependency related to particle size is shown through the correlation between SSA and AE. Backward trajectory analysis by HYSPLIT provides information about origin of aerosol, which allows us to classify the case according to the source region and the path distance. Although the direction of backward trajectory traces back mostly to west, coarse mode particle is dominant in the case of long pathway and fine mode particle is dominant in the case of short pathway. This discrepancy is caused by the regional difference of emitted particles.

• 대한치과기공학회지
• /
• 제40권1호
• /
• pp.17-25
• /
• 2018

Purpose: When casting of ceramics, proper amount of deflocculant was added for disperse the particles in slip. In this study, examined the optimum amount of APMA(ammonium polymethaacrylate) water as deflocculant for casting the zirconia. Methods: The 100 g of zirconia powder were ball milled with 300 g zirconia ball, 90 g of distilled water, and APMA water in polyethylene pot for 24 hours. The amount of APMA water were added as deflocculant from 0.5 to 0.9 g at an intervals of 0.1 g. The viscosity of slip with no deflocculant showed 1362c.p. and the minimum viscosity with 580c.p. obtained when the slip contained 0.7% of deflocculant. Bar type specimens were casted with plaster mold and biscuit fired at $1100^{\circ}C$ for 1 hours. Biscuit fired specimens were finished with $60mm(L){\times}14mm(W){\times}10mm(H) bar$. Finished specimens were 2nd fired at $1500^{\circ}C$ for 1 hour. Results: Regardless the addition of deflocculant, all 2nd fired specimens showed 0% of apparent porosity and water absorption. The specimens with no deflocculant showed 24% of drying shrinkage and 27.4% firing shrinkage. On the other hand, The specimens with deflocculant showed 17.4% of drying shrinkage and 17.6% firing shrinkage regardless the amount of deflocculant. The maximum bulk density with $6.09g/cm^3$ obtained when the specimens casted with 0.7~0.9% of deflocculant contained slips. Bend strength of specimen with no deflocculant showed 680 MPa and the maximum bend strength with 814 MPa obtained when the specimen casted with 0.7% of diflocculant contained slip. Conclusion : It was found that the particle shape of the powder according to the dispersing agent is added, the particle size, sintering temperature and affect the particle size distribution, sintering time, sintering atmosphere, such a great influence on the sintering.