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C Galiotis - One of the best experts on this subject based on the ideXlab platform.
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effect of off axis matrix cracking on stiffness of symmetric angle ply composite laminates
International Journal of Fracture, 2006Co-Authors: Dionisios Katerelos, L N Mccartney, C GaliotisAbstract:Matrix cracking models developed for cross-ply composite laminates cannot easily be applied to more complicated geometries. In this paper a detailed analysis of the effect of matrix cracking on the longitudinal Young’s Modulus of a [0/45]s plate under uniaxial tension is attempted. The theoretical approach, based on a semi-analytical generalized plane strain model, is compared to experimental data obtained by microscopic strain measurements on a fiber sensor using the technique of Laser Raman Spectroscopy. The experimental results are in a good agreement with theoretical stiffness degradation predictions obtained using the semi-analytical model.
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Raman Spectroscopy assessment of stiffness reduction and residual strains due to matrix cracking in angle ply laminates
2006Co-Authors: Peter Lundmark, Janis Varna, Dionisios Katerelos, C GaliotisAbstract:Off — axis ply cracking in composite laminates and especially its effect on composites thermomechanical behaviour has been extensively studied in the case of cross — ply stacking sequence; see Katerelos and Galiotis [1], Joffe and Varna [2], and Katerelos et al. [3]. During the last decade, the extension of this research to more complex composite systems used in practice has been addressed and is still under development; see Crocker et al. [4], Katerelos et al. [5], Lundmark et al [6]. In the presented work a detailed analysis of the effects of evolved damage on the behaviour of a [0/45]s laminate under uniaxial tension is presented. Laser Raman Spectroscopy has been applied for the experimental measurements of the strain state variations due to damage within the specimens. Residual strain and stiffness reduction were derived using experimental Raman data, as a function of crack density increase and the results were compared with theoretical predictions using the model presented in [6]. Indicative conclusions on viscoelastic phenomena affecting the behaviour of angle — ply laminates were extracted.
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axial strain redistribution resulting from off axis ply cracking in polymer composites
Applied Physics Letters, 2004Co-Authors: Dionisios Katerelos, C GaliotisAbstract:The initial mode of damage in multidirectional composites is the accumulation of matrix cracks in the off-axis plies. Remote Laser Raman Spectroscopy, using aramid (Kevlar 49®) fibers as Raman strain sensors, has been employed to monitor the local strains in cracked crossply composites. The strain magnification in the 0° ply caused by 90° matrix cracking are measured at different levels of loading. A relationship between the values of strain magnification and the distance between the position of the fibers sensors vis-a-vis the crack front has been established. The effect of damage progression within the 0° plies on the remaining∕surviving glass fibers is modeled satisfactorily and verified against predictions on the basis of a generalized plane strain model by assuming that the 90° ply “expands” in relative size against the 0° ply thickness.
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strain redistribution in composite laminates resulting from off axis ply cracking
2003Co-Authors: Dionisios Katerelos, John Parthenios, C GaliotisAbstract:The initial mode of damage in multidirectional composites is the accumulation of matrix cracks in the off—axis plies. This kind of damage develops until reaching a so-called saturation point. Several other damage modes, such as delamination, may appear concurrently or just upon termination of the matrix cracking process due to joining and growth of these cracks. Remote Laser Raman Spectroscopy (ReRaM) has been employed to monitor the local strains in cracked cross—ply composites. The experiment involves the incorporation of an aramid (Kevlar 49®) fibre Raman strain sensor into the 0° ply and near the 0°/θ° interface of glass—fibre reinforced epoxy resin laminates. This type of laminate is transparent due to the matching of the refractive indices of glass fibres and epoxy resin. Thus, the changes in the longitudinal strain in the 0° ply, caused by transverse cracking in the θ° ply, are quantified.
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interfacial studies on model composites by Laser Raman Spectroscopy
Composites Science and Technology, 1991Co-Authors: C GaliotisAbstract:Abstract A new technique for the determination of fibre strain in composites has been developed over the years. The strain-sensitive property of high-performance fibres is a vibrational frequency which can be measured by Laser Raman Spectroscopy (LRS). The application of this technique for performing interfacial studies on model short- and long-fibre composites will be reviewed in this paper. By subjecting these composites to various degrees of mechanical deformation a number of parameters, such as the transfer length, the stress transfer efficiency and the initiation of fibre debonding or matrix yielding, can be assessed. Finally, by simply balancing the tensile and the shear forces acting along the interface, the interfacial shear stress distribution at each level of applied load can be obtained.
Sangjae Kim - One of the best experts on this subject based on the ideXlab platform.
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hierarchical copper selenide nanoneedles grown on copper foil as a binder free electrode for supercapacitors
International Journal of Hydrogen Energy, 2016Co-Authors: Parthiban Pazhamalai, Karthikeyan Krishnamoorthy, Sangjae KimAbstract:Abstract In this communication, we demonstrated the use of CuSe2 nanoneedles grown on copper foil as a binder-free electrode for supercapacitors. Studies using X-ray diffraction, Laser Raman Spectroscopy and field emission scanning electron microscopy confirmed the formation of crystalline CuSe2 nanoneedles on the surface of copper foil. Cyclic voltammetry and electrochemical impedance Spectroscopy revealed the pseudocapacitive nature of the CuSe2/Cu electrode. The galvanostatic charge–discharge analysis showed that the CuSe2/Cu binder-free electrode delivered a high specific capacitance of about 1037.5 F/g at a constant current density of 0.25 mA/cm2.
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designing two dimensional nanoarchitectured mos2 sheets grown on mo foil as a binder free electrode for supercapacitors
Electrochimica Acta, 2016Co-Authors: Karthikeyan Krishnamoorthy, Parthiban Pazhamalai, Ganesh Kumar Veerasubramani, Sangjae KimAbstract:Abstract In this study, we demonstrated the preparation of nanoarchitectured MoS2 sheets grown on Mo foil via hydrothermal method and examined its use as a binder free electrode for supercapacitors. The formation of well crystalline MoS2 sheets on Mo foil was confirmed by Laser Raman Spectroscopy, Raman mapping, X-ray photoelectron Spectroscopy, and field emission scanning electron microscopic analyses. The cyclic voltammetric studies suggested that the charge-storage mechanism in the MoS2/Mo electrodes is due to the contribution of combined pseudocapacitance with electrochemical double layer capacitance. The MoS2/Mo electrodes delivered a specific capacitance of about 192.7 F/g from the galvanostatic charge-discharge analysis at a current density of 1 mA/cm2. The experimental results suggested that the prepared MoS2/Mo binder free electrode will be a suitable candidate for electrochemical energy storage devices.
Dionisios Katerelos - One of the best experts on this subject based on the ideXlab platform.
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effect of off axis matrix cracking on stiffness of symmetric angle ply composite laminates
International Journal of Fracture, 2006Co-Authors: Dionisios Katerelos, L N Mccartney, C GaliotisAbstract:Matrix cracking models developed for cross-ply composite laminates cannot easily be applied to more complicated geometries. In this paper a detailed analysis of the effect of matrix cracking on the longitudinal Young’s Modulus of a [0/45]s plate under uniaxial tension is attempted. The theoretical approach, based on a semi-analytical generalized plane strain model, is compared to experimental data obtained by microscopic strain measurements on a fiber sensor using the technique of Laser Raman Spectroscopy. The experimental results are in a good agreement with theoretical stiffness degradation predictions obtained using the semi-analytical model.
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Raman Spectroscopy assessment of stiffness reduction and residual strains due to matrix cracking in angle ply laminates
2006Co-Authors: Peter Lundmark, Janis Varna, Dionisios Katerelos, C GaliotisAbstract:Off — axis ply cracking in composite laminates and especially its effect on composites thermomechanical behaviour has been extensively studied in the case of cross — ply stacking sequence; see Katerelos and Galiotis [1], Joffe and Varna [2], and Katerelos et al. [3]. During the last decade, the extension of this research to more complex composite systems used in practice has been addressed and is still under development; see Crocker et al. [4], Katerelos et al. [5], Lundmark et al [6]. In the presented work a detailed analysis of the effects of evolved damage on the behaviour of a [0/45]s laminate under uniaxial tension is presented. Laser Raman Spectroscopy has been applied for the experimental measurements of the strain state variations due to damage within the specimens. Residual strain and stiffness reduction were derived using experimental Raman data, as a function of crack density increase and the results were compared with theoretical predictions using the model presented in [6]. Indicative conclusions on viscoelastic phenomena affecting the behaviour of angle — ply laminates were extracted.
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axial strain redistribution resulting from off axis ply cracking in polymer composites
Applied Physics Letters, 2004Co-Authors: Dionisios Katerelos, C GaliotisAbstract:The initial mode of damage in multidirectional composites is the accumulation of matrix cracks in the off-axis plies. Remote Laser Raman Spectroscopy, using aramid (Kevlar 49®) fibers as Raman strain sensors, has been employed to monitor the local strains in cracked crossply composites. The strain magnification in the 0° ply caused by 90° matrix cracking are measured at different levels of loading. A relationship between the values of strain magnification and the distance between the position of the fibers sensors vis-a-vis the crack front has been established. The effect of damage progression within the 0° plies on the remaining∕surviving glass fibers is modeled satisfactorily and verified against predictions on the basis of a generalized plane strain model by assuming that the 90° ply “expands” in relative size against the 0° ply thickness.
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strain redistribution in composite laminates resulting from off axis ply cracking
2003Co-Authors: Dionisios Katerelos, John Parthenios, C GaliotisAbstract:The initial mode of damage in multidirectional composites is the accumulation of matrix cracks in the off—axis plies. This kind of damage develops until reaching a so-called saturation point. Several other damage modes, such as delamination, may appear concurrently or just upon termination of the matrix cracking process due to joining and growth of these cracks. Remote Laser Raman Spectroscopy (ReRaM) has been employed to monitor the local strains in cracked cross—ply composites. The experiment involves the incorporation of an aramid (Kevlar 49®) fibre Raman strain sensor into the 0° ply and near the 0°/θ° interface of glass—fibre reinforced epoxy resin laminates. This type of laminate is transparent due to the matching of the refractive indices of glass fibres and epoxy resin. Thus, the changes in the longitudinal strain in the 0° ply, caused by transverse cracking in the θ° ply, are quantified.
Kangnian Fan - One of the best experts on this subject based on the ideXlab platform.
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synthesis of novel core shell structured wo3 tio2 spheroids and its application in the catalytic oxidation of cyclopentene to glutaraldehyde by aqueous h2o2
Journal of Catalysis, 2005Co-Authors: Xinli Yang, Weilin Dai, Hui Chen, Yong Cao, Changwen Guo, Kangnian FanAbstract:Novel core-shell structured WO3/TiO2 spheroids were synthesized through a conventional incipient wetness impregnation method and systematically characterized by X-ray diffraction, N2 sorption, scanning electron microscopy, transmission electron microscopy, Laser Raman Spectroscopy, thermogravimetric and differential thermal analysis, X-ray photoelectron Spectroscopy, and NH3 temperature-programmed desorption. It was found that tungsten species are highly dispersed in the interlayer between the core and the shell layer of the TiO2 support and that there are interactions between the tungsten species and the TiO2 support that could provide abundant oxygen defect lattice. It is also found that the as-prepared WO3/TiO2 material is highly active as a catalyst for the selective oxidation of cyclopentene to glutaraldehyde with aqueous hydrogen peroxide as the green oxidant. Proper content and high dispersion of tungsten species, the interaction between the tungsten species and the support, as well as the medium strong acidity of the novel WO3/TiO2 catalyst all account for this material's high activity.
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novel tungsten containing mesoporous hms material its synthesis characterization and catalytic application in the selective oxidation of cyclopentene to glutaraldehyde by aqueous h2o2
Applied Catalysis A-general, 2005Co-Authors: Xinli Yang, Weilin Dai, Hui Chen, Yong Cao, Kangnian FanAbstract:Tungsten-containing hexagonal mesoporous silica (HMS) has been synthesized by using dodecylamine as template at room temperature. The as-prepared novel material is very active as a catalyst for the selective oxidation of cyclopentene (CPE) to glutaraldehyde (GA) with environmentally benign hydrogen peroxide as the oxidant. Tungsten species could stably exist in the silica-based matrix of HMS up to a Si/W molar ratio of 30, as determined by X-ray diffraction (XRD), Laser Raman Spectroscopy, and FT-IR. Proper content of tungsten species and its high dispersion account for its high activity. Complete conversion of cyclopentene and very high yield of glutaraldehyde (∼76.3%) are obtained over the W-HMS catalyst with a Si/W molar ratio at 30. Furthermore, almost no tungsten species are leached into the reaction solution, enabling the catalyst to be employed for many reaction cycles without dramatic deactivation.
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novel heterogeneous w doped mcm 41 catalyst for highly selective oxidation of cyclopentene to glutaraldehyde by aqueous h2o2
Catalysis Letters, 2002Co-Authors: Hao Chen, Weilin Dai, Jingfa Deng, Kangnian FanAbstract:W-doped MCM-41 (W-MCM-41) has been reported as a novel heterogeneous catalyst for the selective oxidation of cyclopentene to prepare glutaraldehyde with environmentally benign aqueous hydrogen peroxide. It is found that tungsten species could stably exist in the silica-based matrix of MCM-41 up to a Si/W molar ratio of 40 by means of X-ray diffraction, Laser Raman Spectroscopy, scanning electron microscopy, etc. Proper content of tungsten species, high specific surface area and large mean pore size of the W-MCM-41 account mainly for its high catalytic activity in comparison with other W-containing heterogeneous catalysts. Complete conversion of cyclopentene and very high yield of glutaraldehyde (∼72%) are obtained over the W-MCM-41 catalyst with an Si/W molar ratio of 40. Furthermore, almost no tungsten species are leached into the reaction solution, enabling the catalyst to be employed for many reaction cycles without obvious degeneration. The correlation of the catalytic behavior with the special structural characteristics of the W-MCM-41 catalyst is also discussed through various characterization methods.
Parthiban Pazhamalai - One of the best experts on this subject based on the ideXlab platform.
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hierarchical copper selenide nanoneedles grown on copper foil as a binder free electrode for supercapacitors
International Journal of Hydrogen Energy, 2016Co-Authors: Parthiban Pazhamalai, Karthikeyan Krishnamoorthy, Sangjae KimAbstract:Abstract In this communication, we demonstrated the use of CuSe2 nanoneedles grown on copper foil as a binder-free electrode for supercapacitors. Studies using X-ray diffraction, Laser Raman Spectroscopy and field emission scanning electron microscopy confirmed the formation of crystalline CuSe2 nanoneedles on the surface of copper foil. Cyclic voltammetry and electrochemical impedance Spectroscopy revealed the pseudocapacitive nature of the CuSe2/Cu electrode. The galvanostatic charge–discharge analysis showed that the CuSe2/Cu binder-free electrode delivered a high specific capacitance of about 1037.5 F/g at a constant current density of 0.25 mA/cm2.
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designing two dimensional nanoarchitectured mos2 sheets grown on mo foil as a binder free electrode for supercapacitors
Electrochimica Acta, 2016Co-Authors: Karthikeyan Krishnamoorthy, Parthiban Pazhamalai, Ganesh Kumar Veerasubramani, Sangjae KimAbstract:Abstract In this study, we demonstrated the preparation of nanoarchitectured MoS2 sheets grown on Mo foil via hydrothermal method and examined its use as a binder free electrode for supercapacitors. The formation of well crystalline MoS2 sheets on Mo foil was confirmed by Laser Raman Spectroscopy, Raman mapping, X-ray photoelectron Spectroscopy, and field emission scanning electron microscopic analyses. The cyclic voltammetric studies suggested that the charge-storage mechanism in the MoS2/Mo electrodes is due to the contribution of combined pseudocapacitance with electrochemical double layer capacitance. The MoS2/Mo electrodes delivered a specific capacitance of about 192.7 F/g from the galvanostatic charge-discharge analysis at a current density of 1 mA/cm2. The experimental results suggested that the prepared MoS2/Mo binder free electrode will be a suitable candidate for electrochemical energy storage devices.
