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Jang Daeik,Yang Beomjoo,Cho Giljae 한국탄소학회 2024 Carbon Letters Vol.34 No.3
In the present study, the effects of electrodes type (copper, steel or CFRP) and design (plate or mesh) on electrical stability of conductive cement as exposed to various weathering conditions were investigated. To fabricate these composites, multi-walled carbon nanotube and carbon fiber were added to the cement composites by 0.6 and 0.4% by cement mass. Seven different types of electrodes were embedded to the samples, and their electrical stability was examined during the curing period. In addition, the fabricated samples were exposed to water ingress and cyclic heating conditions. Then, the compressive strength of the samples was evaluated to observe the interfacial bonding between the cement paste and electrodes. Based on the experimental results, it was found that the samples showed different electrical stability even their mix proportion was same. Thus, it can be concluded that the type and design of the electrodes are important in measuring the electrical properties of the conductive cement composites. Specifically, an improved electrical stability of electrodes is required when they are exposed to various weathering conditions.
Jang, Han Gyeol,Yang, Beomjoo,Khil, Myung-Seob,Kim, Seong Yun,Kim, Jaewoo Elsevier 2019 Composites Applied science and manufacturing Vol.125 No.-
<P><B>Abstract</B></P> <P>In spite of active studies on multi-walled carbon nanotube (MWCNT)-incorporated polymer, MWCNTs of different thickness and lengths have been employed. Here, the effects of MWCNT morphology, specifically its length, on the mechanical, thermal, and electrical properties of MWCNT/polymer composites were examined in comparison with theoretical modeling. Field-emission scanning electron microscopy and micro-computed tomography observations revealed that short MWCNTs were dispersed more uniformly than long MWCNTs in a polyamide 6 (PA6) polymer. Correlation of this result with the tensile performance revealed that at low MWCNT concentrations the long-MWCNT/PA6 composite showed superior tensile properties since the effect of length was dominant. However, at high MWCNT concentrations, the short-MWCNT/PA6 showed superior tensile properties to the long-MWCNT/PA6 due to the better dispersion of the former. The thermal conductivity gradually improved with increasing MWCNT concentration, showing larger improvement for the long-MWCNT/PA6, while the electrical conductivity reached percolation threshold at 1 wt% for both MWCNTs.</P>
Haile, Bezawit F.,Jin, D.W.,Yang, Beomjoo,Park, Solmoi,Lee, H.K. Elsevier 2019 Construction & building materials Vol.229 No.-
<P><B>Abstract</B></P> <P>Ultra-high-performance concrete (UHPC), a multi-level cementitious composite that has properties influenced by constituents existing at different length scales, requires the combination of different modeling strategies to capture and understand its effective property. A multi-level (six levels) micromechanics-based homogenization is proposed to investigate the elastic mechanical properties of UHPC. Molecular dynamics and micromechanical theories based on Eshelby’s inclusion model are adopted to investigate the effects of the properties of the various constituents, such as the fiber type, volume fraction, orientation, geometry, including the size and volume fraction of coarse aggregates on the elastic mechanical properties of UHPC. Experimental investigations incorporating a compressive strength test, scanning electron microscopy, and mercury intrusion porosimetry tests were conducted to validate the model. The proposed multi-level homogenization scheme is able to quantitatively prove the importance of each constituent and provide a modeling tool capable of facilitating a thorough investigation of the mechanical properties of UHPC.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A multi-level micromechanics based homogenization scheme is developed. </LI> <LI> A combined Molecular dynamics simulation and micromechanics models were adopted. </LI> <LI> Effects of fiber type, geometry, orientation and interface are parametrically studied. </LI> <LI> Compressive strength test, MIP and SEM analysis were conducted. </LI> <LI> Model input parameters were obtained from literature and the experimental program. </LI> </UL> </P>
Eem, Seunghyun,Choi, In-Kil,Yang, Beomjoo,Kwag, Shinyoung Korean Nuclear Society 2021 Nuclear Engineering and Technology Vol.53 No.3
In 2011, an earthquake and subsequent tsunami hit the Fukushima Daiichi Nuclear Power Plant, causing simultaneous accidents in several reactors. This accident shows us that if there are several reactors on site, the seismic risk to multiple units is important to consider, in addition to that to single units in isolation. When a seismic event occurs, a seismic-failure correlation exists between the nuclear power plant's structures, systems, and components (SSCs) due to their seismic-response and seismic-capacity correlations. Therefore, it is necessary to evaluate the multi-unit seismic risk by considering the SSCs' seismic-failure-correlation effect. In this study, a methodology is proposed to obtain the seismic-response-correlation coefficient between SSCs to calculate the risk to multi-unit facilities. This coefficient is calculated from a probabilistic multi-unit seismic-response analysis. The seismic-response and seismic-failure-correlation coefficients of the emergency diesel generators installed within the units are successfully derived via the proposed method. In addition, the distribution of the seismic-response-correlation coefficient was observed as a function of the distance between SSCs of various dynamic characteristics. It is demonstrated that the proposed methodology can reasonably derive the seismic-response-correlation coefficient between SSCs, which is the input data for multi-unit seismic probabilistic safety assessment.