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Choi, Kyoungjun,Nam, Sooji,Lee, Youngbin,Lee, Mijin,Jang, Jaeyoung,Kim, Sang Jin,Jeong, Yong Jin,Kim, Hyeongkeun,Bae, Sukang,Yoo, Ji-Beom,Cho, Sung M.,Choi, Jae-Boong,Chung, Ho Kyoon,Ahn, Jong-Hyun,Pa American Chemical Society 2015 ACS NANO Vol.9 No.6
<P>Preventing reactive gas species such as oxygen or water is important to ensure the stability and durability of organic electronics. Although inorganic materials have been predominantly employed as the protective layers, their poor mechanical property has hindered the practical application to flexible electronics. The densely packed hexagonal lattice of carbon atoms in graphene does not allow the transmission of small gas molecules. In addition, its outstanding mechanical flexibility and optical transmittance are expected to be useful to overcome the current mechanical limit of the inorganic materials. In this paper, we reported the measurement of the water vapor transmission rate (WVTR) through the 6-layer 10 × 10 cm<SUP>2</SUP> large-area graphene films synthesized by chemical vapor deposition (CVD). The WVTR was measured to be as low as 10<SUP>–4</SUP> g/m<SUP>2</SUP>·day initially, and stabilized at ∼0.48 g/m<SUP>2</SUP>·day, which corresponds to 7 times reduction in WVTR compared to bare polymer substrates. We also showed that the graphene-passivated organic field-effect transistors (OFETs) exhibited excellent environmental stability as well as a prolonged lifetime even after 500 bending cycles with strain of 2.3%. We expect that our results would be a good reference showing the graphene’s potential as gas barriers for organic electronics.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2015/ancac3.2015.9.issue-6/acsnano.5b01161/production/images/medium/nn-2015-01161h_0009.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn5b01161'>ACS Electronic Supporting Info</A></P>
Mijin Choi,Hwee Kwon Jung,Stuart G. Taylor,Kevin M. Farinholt,Jung-Ryul Lee,Gyuhae Park 한국비파괴검사학회 2016 한국비파괴검사학회지 Vol.36 No.2
This paper presents the results obtained using time-series-based methods for structural damage assessment. The methods are applied to a wind turbine blade structure subjected to fatigue loads. A 9 m CX-100 (carbon experimental 100 kW) blade is harmonically excited at its first natural frequency to introduce a failure mode. Consequently, a through-thickness fatigue crack is visually identified at 8.5 million cycles. The time domain data from the piezoelectric active-sensing techniques are measured during the fatigue loadings and used to detect incipient damage. The damage-sensitive features, such as the first four moments and a normality indicator, are extracted from the time domain data. Time series autoregressive models with exogenous inputs are also implemented. These features could efficiently detect a fatigue crack and are less sensitive to operational variations than the other methods.
Choi, Mijin,Jung, Hwee Kwon,Taylor, Stuart G.,Farinholt, Kevin M.,Lee, Jung-Ryul,Park, Gyuhae The Korean Society for Nondestructive Testing 2016 한국비파괴검사학회지 Vol.36 No.2
This paper presents the results obtained using time-series-based methods for structural damage assessment. The methods are applied to a wind turbine blade structure subjected to fatigue loads. A 9 m CX-100 (carbon experimental 100 kW) blade is harmonically excited at its first natural frequency to introduce a failure mode. Consequently, a through-thickness fatigue crack is visually identified at 8.5 million cycles. The time domain data from the piezoelectric active-sensing techniques are measured during the fatigue loadings and used to detect incipient damage. The damage-sensitive features, such as the first four moments and a normality indicator, are extracted from the time domain data. Time series autoregressive models with exogenous inputs are also implemented. These features could efficiently detect a fatigue crack and are less sensitive to operational variations than the other methods.