The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform

Fumio Koyama - One of the best experts on this subject based on the ideXlab platform.

  • Wavelength tuning of hollow waveguide DBR lasers
    2013 Conference on Lasers and Electro-Optics Pacific Rim (CLEOPR), 2013
    Co-Authors: Hideaki Yamakawa, Takahiro Sakaguchi, Fumio Koyama
    Abstract:

    We demonstrate the wavelength tuning of hollow-waveguide DBR laser with variable air Core. Wavelength tuning of 8.2nm was obtained with a Core-Thickness change of 0.68μm. A novel design for wide continuous tuning is also presented.

  • tunable stop band hollow waveguide bragg reflectors with tapered air Core for adaptive dispersion compensation
    Applied Physics Letters, 2006
    Co-Authors: Yasuki Sakurai, Akihiro Matsutani, Fumio Koyama
    Abstract:

    We propose a tunable stop-band hollow waveguide Bragg reflector with a variable tapered air Core for an adjustable dispersion-compensation device. The tapered air-Core structure gives us chirped Bragg reflection. The precise control of tapered air-Core Thickness and angle enables us to achieve the dynamic tuning of both stop-band width and center wavelength of Bragg reflection. We demonstrate center-wavelength tuning of 20.1nm corresponding to 1.3% of propagation constant change and stop-band expansion up to 5nm. Also, we demonstrate dispersion tuning operation either in negative or positive dispersion ranges with delay-time difference of about 10ps.

  • fabrication and characterization of hollow waveguide optical switch with variable air Core
    Optics Express, 2005
    Co-Authors: Changhwan Bae, Fumio Koyama
    Abstract:

    We demonstrate a novel hollow waveguide optical switch composed of an multi-mode interference (MMI) coupler with a variable air Core. The numerical simulation and experiment of the proposed optical switch is carried out for investigating the operation of the switch. Switching operation can be obtained by the mechanical displacement of the air Core of an MMI hollow waveguide. A hollow waveguide consists of Au mirrors deposited on two GaAs substrates for optical confinement. The measured result shows a possibility of switching of about 85% optical power fraction with a switch length of 1.1 mm and small displacement (ΔDCore=3 µm) of an air Core Thickness. The measured insertion losses of a 1.1 mm long hollow waveguide with 12 and 9 µm air Core are 5.4 dB and 5.7 dB respectively.

  • air Core Thickness dependence of propagation loss of slab hollow waveguide
    Japanese Journal of Applied Physics, 2004
    Co-Authors: Yasuki Sakurai, Toru Miura, Fumio Koyama
    Abstract:

    We present the Core Thickness dependence of the propagation loss and the polarization dependence loss (PDL) of hollow waveguides of various air Core Thicknesses. The addition of phase-control layers to GaAs/AlAs multilayer mirrors enables us to reduce the PDL by one order of magnitude. The propagation loss and the PDL of a 5 µm air Core hollow waveguide are 2.8 dB/cm and 1.7 dB/cm, respectively, which are currently limited by the reflectivity (0.998) of the GaAs/AlAs multilayer mirrors.

  • tunable hollow waveguide distributed bragg reflectors with variable air Core
    Optics Express, 2004
    Co-Authors: Yasuki Sakurai, Fumio Koyama
    Abstract:

    We demonstrate a tunable hollow waveguide distributed Bragg reflector consisting of a grating loaded slab hollow waveguide with a variable air-Core. The modeling shows that a change in an air-Core Thickness enables a large shift of several tens of nanometers in Bragg wavelength due to a change of several percents in a propagation constant. We fabricated a slab hollow waveguide Bragg reflector with 620 µm long and, 190 nm deep 1st-order circular grating composed of SiO2, exhibiting strong Bragg reflection at 1558 nm with an air-Core Thickness of 10 µm for TM mode. The peak reflectivity is 65 % including fiber coupling losses, the 3 dB bandwidth is 2.8 nm and the grating-induced loss is less than 0.5 dB. We demonstrate a 3 nm wavelength tuning of the fabricated hollow waveguide Bragg reflector by changing an air-Core Thickness from 10 µm to 7.9 µm.

Shankar Kalyanasundaram - One of the best experts on this subject based on the ideXlab platform.

  • finite element modelling of Core Thickness effects in aluminium foam composite sandwich structures under flexural loading
    Composite Structures, 2008
    Co-Authors: Millicent Styles, Paul Compston, Shankar Kalyanasundaram
    Abstract:

    This paper models the flexural behaviour of a composite sandwich structure with an aluminium foam Core using the finite element (FE) code LS-DYNA. Two Core Thicknesses, 5 and 20 mm, were investigated. The FE results were compared with results from previous experimental work that measured full-field strain directly from the sample during testing. The deformation and failure behaviour predicted by the FE model compared well with the behaviour observed experimentally. The strain predicted by the FE model also agreed reasonably well with the distribution and magnitude of strain obtained experimentally. However, the FE model predicted lower peak load, which is most likely due to a size effect exhibited by aluminium foam. A simple modification of the FE model input parameters for the foam Core subsequently produced good agreement between the model and experimental results.

  • the effect of Core Thickness on the flexural behaviour of aluminium foam sandwich structures
    Composite Structures, 2007
    Co-Authors: Millicent Styles, Paul Compston, Shankar Kalyanasundaram
    Abstract:

    The effect of Core Thickness on the deformation mechanism of an aluminium foam Core/thermoplastic composite facing sandwich structure under 4-point bending was investigated. Full field strain analysis and visual observations show a number of failure mechanisms between the different Core Thicknesses. High strain concentrations were observed in each sample Thickness corresponding to the particular region of failure. The thinner samples exhibited skin wrinkling and fracture, and some Core cracking and crushing while the thicker samples failed due to Core indentation. Increasing the skin Thickness eliminated the incidence of Core indentation. Instead, significant Core shear cracking was observed.

Heinz Palkowski - One of the best experts on this subject based on the ideXlab platform.

  • mechanical properties and forming behaviour of laminated steel polymer sandwich systems with local inlays part 1
    Composite Structures, 2014
    Co-Authors: Mohamed Harhash, Olga Sokolova, Adele Carrado, Heinz Palkowski
    Abstract:

    Abstract Steel/polymer/steel sandwich materials (SMs) with varying Core Thickness were produced using the roll bonding technology. At constant skin Thickness, the effect of the Core Thickness change on the mechanical properties, particularly their specific stiffness and strength, was investigated. Additionally, the SMs were locally reinforced with steel inlays to improve their behaviour against dimension changes or the degradation of the Core in case of local loading or joining. The effect of the reinforcement (RE) on the strain distribution under deep drawing conditions was studied. Strains were measured using photogrammetry. To take into account the influence of anisotropy in this sense, an essential anisotropy evaluation was carried out for the SMs to assess their forming behaviour. The results revealed an adequate agreement between the measured mechanical properties of SMs and the estimated values following the rule of mixtures. Up to a Core volume fraction of approx. 0.37, the specific stiffness and strength values of the SMs are only slightly reduced compared to the monolithic steel material. The deformation analysis shows a significant influence of the inserted REs on the strain distribution and failure and consequently the position of cracking, occurring at the bottom/edge region in front of the RE.

  • forming limit diagram of steel polymer steel sandwich systems for the automotive industry
    2014
    Co-Authors: Mohamed Harhash, Adele Carrado, Heinz Palkowski
    Abstract:

    Steel/polymer/steel sandwich materials (SMs) are considered an innovative substitute to the commercial steel sheets in the automotive industry due to weight-saving potential and enhanced damping properties. Deep-drawing steel and thermoplastic Core are used as the skin and Core sheets, respectively. The mono-materials and SMs were characterized via tensile test, deep drawing and flow limit curves (FLC) determination. The mechanical properties of the tested SMs showed a good matching with the mixture rule regardless the skin/Core sheet Thickness. Varying the skin/Core sheet Thickness has a remarkable effect on the thinning behavior under deep drawing; the Core Thickness increases the cracking probability. In case of using SMs with different skin-Thickness, it is better to position the thin skin sheet in contact with the punch. The Core Thickness exhibited no significant effect on the FLC results. The thicker-Core SMs are subjected to failure at lower strains in the stretching region of the FLC.

  • deep drawing properties of lightweight steel polymer steel sandwich composites
    Archives of Civil and Mechanical Engineering, 2012
    Co-Authors: Olga Sokolova, Ma Kuh, Heinz Palkowski
    Abstract:

    Abstract Due to the wide range of different properties – such as high strength, stiffness, high damping capacity, vibration resistance and the lightweight – metal/polymer/metal sandwich composites find their application as various body-parts in the automotive industry. Nevertheless the forming potential of layered sandwiches under different loading is not well studied. In this research the formability of 316L/PP–PE/316L sandwich composites with different sample size and Core Thickness was studied for the deep drawing process using two flat punches of different size and shape. It could be stated that the forming behaviour of the three layered sandwiches is strongly influenced by the geometry of the punch and the Core Thickness. The results were analysed photogrammetrically and metallographically.

Millicent Styles - One of the best experts on this subject based on the ideXlab platform.

  • finite element modelling of Core Thickness effects in aluminium foam composite sandwich structures under flexural loading
    Composite Structures, 2008
    Co-Authors: Millicent Styles, Paul Compston, Shankar Kalyanasundaram
    Abstract:

    This paper models the flexural behaviour of a composite sandwich structure with an aluminium foam Core using the finite element (FE) code LS-DYNA. Two Core Thicknesses, 5 and 20 mm, were investigated. The FE results were compared with results from previous experimental work that measured full-field strain directly from the sample during testing. The deformation and failure behaviour predicted by the FE model compared well with the behaviour observed experimentally. The strain predicted by the FE model also agreed reasonably well with the distribution and magnitude of strain obtained experimentally. However, the FE model predicted lower peak load, which is most likely due to a size effect exhibited by aluminium foam. A simple modification of the FE model input parameters for the foam Core subsequently produced good agreement between the model and experimental results.

  • the effect of Core Thickness on the flexural behaviour of aluminium foam sandwich structures
    Composite Structures, 2007
    Co-Authors: Millicent Styles, Paul Compston, Shankar Kalyanasundaram
    Abstract:

    The effect of Core Thickness on the deformation mechanism of an aluminium foam Core/thermoplastic composite facing sandwich structure under 4-point bending was investigated. Full field strain analysis and visual observations show a number of failure mechanisms between the different Core Thicknesses. High strain concentrations were observed in each sample Thickness corresponding to the particular region of failure. The thinner samples exhibited skin wrinkling and fracture, and some Core cracking and crushing while the thicker samples failed due to Core indentation. Increasing the skin Thickness eliminated the incidence of Core indentation. Instead, significant Core shear cracking was observed.

Elsayed Fathallah - One of the best experts on this subject based on the ideXlab platform.

  • numerical analysis of sandwich composite deep submarine pressure hull considering failure criteria
    Journal of Marine Science and Engineering, 2019
    Co-Authors: Mahmoud Helal, Huinan Huang, Defu Wang, Elsayed Fathallah
    Abstract:

    The pressure hull is the primary element of submarine, which withstands diving pressure and provides essential capacity for electronic systems and buoyancy. This study presents a numerical analysis and design optimization of sandwich composite deep submarine pressure hull using finite element modeling technique. This study aims to minimize buoyancy factor and maximize deck area and buckling strength factors. The collapse depth is taken as a base in the pressure hull design. The pressure hull has been analyzed using two composite materials, T700/Epoxy and B(4)5505/Epoxy, to form the upper and lower faces of the sandwich composite deep submarine pressure hull. The laminated control surface is optimized for the first ply failure index (FI) considering both Tsai–Wu and maximum stress failure criteria. The results obtained emphasize an important fact that the presence of Core layer in sandwich composite pressure hull is not always more efficient. The use of sandwich in the design of composite deep submarine pressure hull at extreme depths is not a safe option. Additionally, the Core Thickness plays a minor role in the design of composite deep submarine pressure hull. The outcome of an optimization at extreme depths illustrates that the upper and lower faces become thicker and the Core Thickness becomes thinner. However, at shallow-to-moderate depths, it is recommended to use sandwich composite with a thick Core to resist the shell buckling of composite submarine pressure hull.

  • numerical analysis of sandwich composite deep submarine pressure hull considering failure criteria
    Journal of Marine Science and Engineering, 2019
    Co-Authors: Mahmoud Helal, Huinan Huang, Defu Wang, Elsayed Fathallah
    Abstract:

    The pressure hull is the primary element of submarine, which withstands diving pressure and provides essential capacity for electronic systems and buoyancy. This study presents a numerical analysis and design optimization of sandwich composite deep submarine pressure hull using finite element modeling technique. This study aims to minimize buoyancy factor and maximize deck area and buckling strength factors. The collapse depth is taken as a base in the pressure hull design. The pressure hull has been analyzed using two composite materials, T700/Epoxy and B(4)5505/Epoxy, to form the upper and lower faces of the sandwich composite deep submarine pressure hull. The laminated control surface is optimized for the first ply failure index (FI) considering both Tsai–Wu and maximum stress failure criteria. The results obtained emphasize an important fact that the presence of Core layer in sandwich composite pressure hull is not always more efficient. The use of sandwich in the design of composite deep submarine pressure hull at extreme depths is not a safe option. Additionally, the Core Thickness plays a minor role in the design of composite deep submarine pressure hull. The outcome of an optimization at extreme depths illustrates that the upper and lower faces become thicker and the Core Thickness becomes thinner. However, at shallow-to-moderate depths, it is recommended to use sandwich composite with a thick Core to resist the shell buckling of composite submarine pressure hull.