Numerical study for identifying damage in open-hole composites with embedded FBG sensors and its application to experiment results

Yashiro, S.,Murai, K.,Okabe, T.,Takeda, N. The Korean Society for Composite Materials 2007 Advanced composite materials Vol.16 No.2

This study proposes two new approaches for identifying damage patterns in a holed CFRP cross-ply laminate using an embedded fiber Bragg grating (FBG) sensor. It was experimentally confirmed that the reflection spectrum from the embedded FBG sensor was significantly deformed as the damage near the hole (i.e. splits, transverse cracks and delamination) extended. The damage patterns were predicted using forward analysis (a damage analysis and an optical analysis) with strain estimation and the proposed damage-identification method as well as the forward analysis only. Forward analysis with strain estimation provided the most accurate damage-pattern estimation and the highest computational efficiency. Furthermore, the proposed damage identification significantly reduced computation time with the equivalent accuracy compared to the conventional identification procedure, by using damage analysis as the initial estimation.

Characterization of tensile damage progress in stitched CFRP laminates

Yoshimura, Akinori,Yashiro, Shigeki,Okabe, Tomonaga,Takeda, Nobuo The Korean Society for Composite Materials 2007 Advanced composite materials Vol.16 No.3

This study experimentally and numerically investigated the tensile damage progress in stitched laminates. In particular, it focused on the effects of stitching on the damage progress. First, we experimentally confirmed that ply cracks and delamination appeared under load regardless of stitching. We then performed damage-extension simulation for stitched laminates using a layer-wise finite element model with stitch threads as beam elements, in which the damage (ply cracks and delamination) was represented by cohesive elements. A detailed comparison between observation and the simulated results confirmed that stitching had little effect on the onset and accumulation of ply cracks. Furthermore, we demonstrated that the stitch threads significantly suppressed the extension of the delamination.

Marcasite iron sulfide as a high-capacity electrode material for sodium storage

Voronina, Natalia,Yashiro, Hitoshi,Myung, Seung-Taek The Royal Society of Chemistry 2018 Journal of materials chemistry. A, Materials for e Vol.6 No.35

<P>Iron sulfides have attracted significant attention as promising electrode materials for sodium-ion batteries (SIBs) owing to their low electronegativity, high theoretical capacity, and cost-effectiveness. However, the large size of sodium ions generally induces severe volume changes and sluggish sodium kinetics in iron sulfide electrodes, which have prevented their practical application in SIBs. Herein, an orthorhombic marcasite FeS2 was successfully synthesized under solvothermal conditions and subsequently modified using electro-conductive carbon. This report is the first to use marcasite FeS2 as an electrode material in Na cells. The FeS2/carbon composite exhibited a high Na-storage capacity with stable capacity retention in Na cells; specifically, a discharge capacity of 385 mA h g<SUP>−1</SUP> (over 85% of the initial capacity) was retained after 200 cycles at 100 mA g<SUP>−1</SUP>. The following related Na-storage mechanism was proposed: FeS2 + 2Na<SUP>+</SUP> + 2e<SUP>−</SUP> → FeS + Na2S on sodiation (reduction), and this reaction occurs reversibly on desodiation (oxidation). The FeS2 cathode in the Na cells delivered a high energy density of approximately 620 W h kg<SUP>−1</SUP> even after 200 cycles, which is comparable to that of commercial cathode materials for lithium-ion batteries.</P>

Effect of Power Mode of Plasma Anodization on the Properties of formed Oxide Films on AZ91D Magnesium Alloy

Lee, Sung-Hyung,Yashiro, Hitoshi,Kure-Chu, Song-Zhu Materials Research Society of Korea 2018 한국재료학회지 Vol.28 No.10

The passivation of AZ91D Mg alloys by plasma anodization requires deliberate choice of process parameters due to the presence of large amounts of structural defects. We study the dependence of pore formation, surface roughness and corrosion resistance on voltage by comparing the direct current (DC) mode and the pulse wave (pulse) mode in which anodization is performed. In the DC plasma anodization mode, the thickness of the electrolytic oxide film of the AZ91D alloy is uneven. In the pulse mode, the thickness is relatively uniform and the formed thin film has a three-layer structure. The pulse mode creates less roughness, uniform thickness and improved corrosion resistance. Thus, the change of power mode from DC to pulse at 150 V decreases the surface roughness (Ra) from $0.9{\mu}m$ to $0.1{\mu}m$ and increases the corrosion resistance in rating number (RN) from 5 to 9.5. Our study shows that an optimal oxide film can be obtained with a pulse voltage of 150 V, which produces an excellent coating on the AZ91D casting alloy.

Effect of Silane Coupling Treatment on the Joining and Sealing Performance between Polymer and Anodized Aluminum Alloy

Lee, Sung-Hyung,Yashiro, Hitoshi,Kure-Chu, Song-Zhu Materials Research Society of Korea 2021 한국재료학회지 Vol.31 No.3

In the fabrication of joined materials between anodized aluminum alloy and polymer, the performance of the metal-polymer joining is greatly influenced by the chemical properties of the oxide film. In a previous study, the dependence of physical joining strength on the thickness, structure, pore formation, and surface roughness of films formed on aluminum alloys is investigated. In this study, we investigated the effect of silane coupling treatment on the joining strength and sealing performance between aluminum alloy and polymer. After a two-step anodization process with additional treatment by silane, the oxide film with chemically modified nanostructure is strongly bonded to the polymer through physical and chemical reactions. More specifically, after the two-step anodization with silane treatment, the oxide film has a three-dimensional (3D) nanostructure and the silane components are present in combination with hydroxyl groups up to a depth of 150 nm. Accordingly, the joining strength between the polymer and aluminum alloy increases from 29 to 35 MPa, and the helium leak performance increases from 10-2-10-4 to 10-8-10-9 Pa ㎥ s-1.

Effect of carbon-sulphur bond in a sulphur/dehydrogenated polyacrylonitrile/reduced graphene oxide composite cathode for lithium-sulphur batteries

Konarov, Aishuak,Bakenov, Zhumabay,Yashiro, Hitoshi,Sun, Yang-Kook,Myung, Seung-Taek Elsevier Sequoia 2017 Journal of Power Sources Vol. No.

<P><B>Abstract</B></P> <P>A S/DPAN (dehydrogenated polyacrylonitrile) composite shows promising electrode performances as a cathode material for Li-S batteries though its electric conductivity is insufficient for high rate tests. In an attempt to enhance the electric conductivity, the S/DPAN composite is attached on reduced graphene oxide (rGO) sheets via self-assembling modification. As a result, the conductivity improves to ∼10<SUP>−4</SUP> S cm<SUP>−1</SUP>, and the S/DPAN/rGO composite thereby delivers approximately 90% of the theoretical capacity of sulphur at a rate of 0.2C (0.34 A g<SUP>−1</SUP>) over 700 mAh (g-S)<SUP>−1</SUP> even at 2C (3.4 A g<SUP>−1</SUP>). We first report on the CS bond between sulphur and DPAN in a composite that maintains the bond even after an extensive cycling test, as confirmed by time-of-flight secondary-ion mass spectroscopy (ToF-SIMS). These synergistic effects enable facile electron transport such that the S/DPAN/rGO composite electrode is able to maintain superior electrode performances.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Sulphur/polyacrylonitrile/reduced graphene oxide composite cathode is studied. </LI> <LI> The composite is synthesized via self-assembly process. </LI> <LI> Electric conductivity of the composite improves to ∼10<SUP>−4</SUP> S cm<SUP>−1</SUP> from ∼10<SUP>−12</SUP> S cm<SUP>−1</SUP>. </LI> <LI> The composite delivers a high capacity over 700 mAh (g-S)<SUP>−1</SUP> even at 2C (3.4 A g<SUP>−1</SUP>). </LI> <LI> The CS bond in the composite is kept even after extensive cycle test. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Fabrication and Characterization of Plasma Electrolytic Oxidation Coatings on Magnesium Alloys

Sung-Hyung Lee,Hitoshi Yashiro,Song-Zhu Kure-Chu 한국표면공학회 2018 한국표면공학회 학술발표회 초록집 Vol.2018 No.11

Electrochemical Properties of Polyaniline-Coated Li-Rich Nickel Manganese Oxide and Role of Polyaniline Coating Layer

Cho, Dae-hyun,Yashiro, Hitoshi,Sun, Yang-Kook,Myung, Seung-Taek The Electrochemical Society 2014 Journal of the Electrochemical Society Vol.161 No.1

<P>Polyaniline is coated on Li[Li<SUB>0.2</SUB>Ni<SUB>0.2</SUB>Mn<SUB>0.6</SUB>]O<SUB>2</SUB> synthesized via co-precipitation. X-ray diffraction patterns exhibit that the polyaniline coating does not affect structural change of the Li[Li<SUB>0.2</SUB>Ni<SUB>0.2</SUB>Mn<SUB>0.6</SUB>]O<SUB>2</SUB>, and the resulting transmission electron microscopic images show the presence of coating layers on the surface of Li[Li<SUB>0.2</SUB>Ni<SUB>0.2</SUB>Mn<SUB>0.6</SUB>]O<SUB>2</SUB>. Electrochemical tests using coin type cells confirm that the surface modification by polyaniline is effective in maintaining capacity and retention upon cycling. The conducting coating character also assists improvement in rate capability. The polyaniline layer forms F-doped polyaniline during cycling, as is proved by time-of-flight secondary ion mass spectroscopy. Therefore, the presence of the polyaniline layers plays a role in lowering HF levels via scavenging F<SUP>−</SUP> from HF in the electrolyte, and this F–doped polyaniline layer also assists in protecting the Li[Li<SUB>0.2</SUB>Ni<SUB>0.2</SUB>Mn<SUB>0.6</SUB>]O<SUB>2</SUB> from HF attack upon cycling, resulting in improved electrochemical properties.</P>

Improvement of joining strength between aluminum alloy and polymer by two - step anodization

Sung-Hyung Lee,Hitoshi Yashiro,Song-Zhu Kure-Chu 한국표면공학회 2020 한국표면공학회지 Vol.53 No.4

In the manufacturing process of joining of aluminum alloy and polymer, the strength of the metal-polymer joining is greatly influenced by the nanostructure of the oxide film. In this study, we investigated the dependence of joining strength on the thickness, structure, pore formation and surface roughness of the formed film. After the two-step anodization process, the surface oxide layer became thinner and rougher resulting in higher joining strength with the polymer. More specifically, after the two-step anodization, the surface roughness, Ra increased from 2.3 to 3.2 ㎛ with pore of three-dimensional (3D) nanostructure, and the thickness of the oxide film was thinned from 350 to 250 ㎚. Accordingly, the joining strength of the aluminum alloy with polymer increased from 23 to 30 ㎫.

Electrochemical behavior and passivation of current collectors in lithium-ion batteries

Myung, Seung-Taek,Hitoshi, Yashiro,Sun, Yang-Kook Royal Society of Chemistry 2011 Journal of materials chemistry Vol.21 No.27

<P>This paper examines several metals that are commonly employed as current collectors of positive and negative electrodes for rechargeable lithium batteries. Current collectors must be electrochemically stable when in contact with the cell component during the potential operation window of an electrode. Various electrochemical techniques have been used to investigate the corrosion of current collector materials. In practice, continued corrosion of current collectors leads to a gradual increase in the internal resistance of cells, which causes the capacity to fade gradually. Corrosion of the current collector may induce a short-circuit, affecting its safety. Thus, the formation of thick and compact, protective passive film on the metal surface is highly important so as to ensure battery performance and safety. Depending on the salts and additives, different types of protective films are formed. The solubility of these surface layers in the electrolyte is a determining factor in the overall stability of the current collector. In this review, we introduce the electrochemical behavior and protective film formation processes of various metallic current collectors in representative electrolytes.</P> <P>Graphic Abstract</P><P>Formation of thick and compact, protective, passive film on the metal surface is highly important so as to ensure battery performance and safety. Depending on the salts and additives, different types of protective films are formed. The solubility of these surface layers in the electrolyte is a determining factor in the overall stability of the current collectors for Li-ion batteries. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c0jm04353b'> </P>