• Geomechanics and Engineering
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• v.22 no.2
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• pp.173-185
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• 2020

Calcareous soil is originated from marine biogenic sediments and weathering of carbonate rocks. The formation history for calcareous sediment includes complex physical, biological and chemical processes. It is preferably selected as the major fill materials for hydraulic reclamation and artificial island construction. Calcareous sands possess inter pores and complex shape are liable to be damaged at normal working stress level due to its fragile nature. Thus, the engineering properties of calcareous soil are greatly affected by its high compressibility and crushability. A series of triaxial shear tests were performed on calcareous sands derived from South China Sea under different test conditions. The effects of confining pressure, particle size, grading, compactness, drainage condition, and water content on the total amount of particle breakage for calcareous soil were symmetrically investigated. The test results showed that the crushing extent of calcareous sand with full gradation was smaller than that a single particle group under the same test condition. Large grains are cushioned by surrounding small particles and such micro-structure reduces the probability of breakage for well-graded sands. The increasing tendency of particle crushing for calcareous sand with a rise in confining pressure and compactness is confirmed. It is also evident that a rise in water content enhances the amount of particle breakage for calcareous sand. However, varying tendency of particle breakage with grain size is still controversial and requires further examination.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.216.1-216.1
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• 2013

PZT 박막은 강유전 특성과 압전소자 특성을 나타내는 물질로 DRAM (dynamic random acess memory)과 FRAM (ferroelectric RAM) 등의 기억소자용 capacitor와 MEMS (micro electro mechanical system) 소자의 압전 물질로 사용하기 위한 연구가 진행중에 있다. 하지만 이러한 연구에서는 PZT 박막의 전기적 특성 향상을 주목적으로 연구가 진행되어 왔다. 특히, 박막 공정중 발생하는 plasma에 의한 PZT의 전기적 특성 변화가 박막 표면의 물리적 변화에 기인할 것으로 추정하고 있지만 이에 대한 구체적인 연구는 미비하다. 이 연구에서는 plasma에 의한 PZT 박막 표면의 물리적 특성 변화를 연구하기 위하여 PZT 박막을 sol-gel을 이용하여 Si 기판위에 약 100 nm의 두께로 증착하였으며, 이후 최대 300 W의 Ar plasma로 plasma power을 증가시켜 각각 10분간 plasma처리를 실시하였다. PZT 박막 표면의 nano-mechanics 특성을 분석하기 위하여 Nano-indenter와 Kelvin Probe Force Microscopy (KPFM)을 사용하여 surface hardness, surface morphology를 확인하였고 특히, surface potential 분석을 통하여 PZT 박막 표면의 plasma에 의한 박막 극 표면의 전기적 특성 변화를 연구하였다. 이 연구로 plasma에 의한 PZT 박막은 표면으로부터 최대 43 nm 깊이에서의 hardness는 최대 5.1 GPa에서 최소 4.3 GPa의 분포로 plasma power 변화에 의한 특성은 측정 불가능하였다. 이는 plasma에 의한 영향이 시료 극 표면에 국한되어 나타나기 때문으로 추정되며 이를 보완하기 위하여 surface potential을 분석하였다. 결과에 의하면 plasma power가 0 W에서 300 W로 증가함에 따라 potential이 30 mV에서 -20 mV로 감소하였으나 potential의 분산은 100 W에서 최대인 17 mV로 측정되었으며, 이때 RMS roughness역시 가장 높은 20.145 nm로 측정되었다. 특히, 100 W에서 potential에서는 물결 모양과 같은 일정한 패턴의 potential 무늬가 확인되었다.

• Advances in Computational Design
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• v.7 no.4
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• pp.321-343
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• 2022

Museum buildings display artefacts for public education and enjoyment, ensuring their long-term safety and the comfort of visitors by following strict indoor environment control protocols using mechanical Heating, Ventilation and Air Conditioning (HVAC) systems to keep the (environmental) variables at a fixed comfort level. Maintaining this requires constant supply of energy currently mostly sourced from the combustion of fossil fuels which exacerbates climate change. However, a review on the effects of the indoor environmental variables on museum artefacts as well as museum visitors revealed that there is no specific point at which artefact deterioration occurs, and that there are wide ranges of conditions that guarantee the long-term safety of artefacts and human comfort. Visits to museum buildings in hot-humid tropical climate of Nigeria revealed that strict indoor environmental practices were adopted. Even when appropriate micro-climatic conditions are provided for artefacts, mechanical HVAC systems remain necessary for visitor comfort because almost no consideration is given to natural ventilation. With the current global push towards energy management, this paper reviewed passive environmental control practices, architectural design strategies, and discusses the adaptation of double skin façade with jali screens, and the notion of smart materials, which can satisfy the range of requirements for the long-term safety of artefacts and levels of human comfort in buildings in hot-humid tropical climate, without mechanical HVAC systems. This review would inspire more discussions on passive, energy efficient, smart and climate responsible popular architecture, challenging current thinking on the impact of the more accepted representative architecture.

• Journal of the Korean Geosynthetics Society
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• v.15 no.4
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• pp.33-42
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• 2016

Discrete Element Method was conducted for rock and coarse-grained materials in development of granular mechanics and related numerical model due to analyze and apply micromechanical property. And it was verified that the analysis to consider bonding effect was insufficient. In this study, to overcome limits of existing method, it was conducted to analyze difference between indoor test result and bonding effect using $PFC^{3D)}$. For indoor test of mixed soil, uniaxial compression tests by curing time and by cement content were performed. And, DEM to suitable for each condition of indoor test was conducted. In the result of this study, in terms of geotechnics, it was verified that DEM can be used for application as numerical laboratory as well as prediction of micro and macro behavior about bonding effect of mixed soil.

• Tunnel and Underground Space
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• v.25 no.6
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• pp.487-495
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• 2015

The specification for selecting railway ballast in France is introduced in this study and the effectiveness of selection for railway ballast is studied for the case of a quarry located in northen France. The quality of railway ballast is, in general, estimated depending on the grain distribution and mainly of the resistance against abrasion. The resistance against abrasion is obtained by both Los Angeles abrasion test and Micro Deval test, which determine the ballast quality suitable whether for high speed railway or classical railway. This study analyzed the correlation between the abrasion index obtained from the abrasion tests for the aggregates sampled at three different stages among ballast production procedure at the quarry. A high correlation is determined between Los Angeles Abrasion index (LA) and Micro Deval index (MDA) and also between abrasion indices of different aggregates. Particularly, this correlation between the abrasion indices allows to estimate the quality of ballast at the final stage from the aggregates at the site in a quarry within the margin of error.

• Tunnel and Underground Space
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• v.22 no.2
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• pp.106-119
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• 2012

Roughness of rock joint has generally been characterized based upon geometrical aspects of a two-dimensional surface profile. The appropriate description of joint roughness, however, should consider the features of roughness mobilization at contact areas under normal and shear loads. In this study, direct shear tests were conducted on the replicas of tensile fractured gneiss joints and the influence of the shear direction on the shear behavior and effective roughness was examined. In this procedure, a joint surface was represented as a group of triangular planes, and the steepness of each plane was characterized using the concepts of the active and inactive micro-slope angles. The contact areas at peak strength which were estimated by a numerical method showed that the locations of the contact areas were mainly dependent on the distribution of the micro-slope angle and the shear behavior of joint was dominated by only the fractions with active micro-slope angles. Therefore, a three-dimensional coefficient for the quantification of rock joint roughness is proposed based on the distribution of active micro-slope angle: active roughness coefficient, $C_r$. Comparison of the active roughness coefficient and the peak shear strength obtained from the experiment suggests that the active roughness coefficient is the effective parameter to quantify the surface roughness and estimate the shear behavior of rock joint.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.10a
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• pp.227-230
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• 2009

In order to predict failure behavior of advanced high-strength steel sheets (AHSS) in hole expansion tests, damage model was developed considering surface condition sensitivity (with specimens prepared by milling and punching: 340R, TRIP590, TWIP940). To account for the micro-damage initiation and evolution as well as macro-crack formation, the stress triaxiality dependent fracture criterion and rate-dependent hardening and ultimate softening behavior were characterized by performing numerical simulations and experiments for the simple tension and V-notch tests. The developed damage model and the characterized mechanical property were incorporated into the FE program ABAQUS/Explicit to perform hole expansion simulations, which showed good agreement with experiments.

• Interaction and multiscale mechanics
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• v.5 no.1
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• pp.41-56
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• 2012

This study is focused on evaluation of the tensile properties of concrete exposed to acid rain environment. Acid rain environment was simulated by the mixture of sulfate and nitric acid in the laboratory. The dumbell-shaped concrete specimens were submerged in pure water and acid solution for accelerated conditioning. Weighing, tensile test, CT, SEM/EDS test and microanalysis were performed on the specimens. Tensile characteristics of the damaged concrete are obtained quantitatively. Evolution characteristics of the voids, micro cracks, chemical compounds, elemental distribution and contents in the concrete are examined. The deterioration mechanisms of concrete exposed to acid rain are well elucidated.

• Structural Engineering and Mechanics
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• v.32 no.5
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• pp.685-699
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• 2009

Current research and development of high performance concrete, together with study of phenomena that are pertinent to impact resistance, have lead to a new generation of barriers with improved properties to resist impact loads. The paper reviews major properties and mechanisms that affect impact resistance of concrete barriers as per criteria that characterize the resistance. These criteria are the perforation limit, penetration depth and the amount of front and rear face damage. From the long-known, single strength parameter that used to represent the barriers' impact resistance, more of the concrete mix ingredients are now considered to be effective in determining it. It is shown that the size and hardness of the aggregates, use of steel fibers and micro-silica have different effects on performance under impact and on the resistance. Additional pertinent phenomena, such as the rate and size effects, confinement and local versus global response, are pointed out with their reference to possible future developments in the design of impact resisting concrete barriers.

• Journal of Welding and Joining
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• v.30 no.6
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• pp.80-85
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• 2012

Fatigue cracks in structural components are the most common cause of structural failure when exposed to fatigue loading. In this respect, fatigue crack detection and structural health assessment are very important. Currently, various smart materials are used for detecting fatigue crack and measurement of SIFs(Stress Intensity Factors). So, this paper presented a measurement of SIFs using MFC(Micro Fiber Composite) sensor which is the one of the smart material. MFC sensor is more flexible, durable and reliable than other smart materials. The SIFs of Mode I(K I) as well as Mode II(K II) based on the piezoelectric constitutive law and fracture mechanics are calculated. In this study, the SIF values measured by MFC sensors are compared with the theoretical results.