The Experts below are selected from a list of 3825 Experts worldwide ranked by ideXlab platform

Yoji Okabe - One of the best experts on this subject based on the ideXlab platform.

  • damage detection in aircraft composite materials using a built in broadband ultrasonic propagation system
    Journal of System Design and Dynamics, 2011
    Co-Authors: Yoji Okabe, Keiji Fujibayashi, Mamoru Shimazaki, Hideki Soejima
    Abstract:

    As one of structural health monitoring systems, the authors developed a broadband ultrasonic propagation system using macro fiber composite (MFC) actuators and fiber Bragg grating (FBG) sensors. This system can send and receive broadband Lamb waves efficiently in a specific direction, and the MFCs and FBGs can be integrated into composite laminates because of their flexibility and high fracture strain. In this research, this system was applied to detect an interlaminar Delamination in carbon fiber reinforced plastic (CFRP) laminates. One MFC and one FBG were bonded on each surface of the CFRP laminate to generate and receive the symmetric modes and the anti-symmetric modes separately for identification of the multiple modes of Lamb waves in the laminate. Then we investigated the mode conversion of Lamb waves at both tips of a Delamination in the middle of the thickness of the laminate, through an experiment and finite element analysis (FEA). On the basis of the knowledge about the mode conversion, an index to evaluate the Delamination Length was proposed using velocity changes by the mode conversions. From the results of experiments and FEA for the laminates with an artificial Delamination, this new index was found to be effective to evaluate the Delamination progress in the laminate quantitatively.

  • Delamination detection in composite laminates using dispersion change based on mode conversion of lamb waves
    Smart Materials and Structures, 2010
    Co-Authors: Yoji Okabe, Keiji Fujibayashi, Mamoru Shimazaki, Hideki Soejima, Toshimichi Ogisu
    Abstract:

    A new ultrasonic propagation system has been constructed using macrofiber composite (MFC) actuators and fiber Bragg grating (FBG) sensors. The MFCs and FBGs can be integrated into composite laminates because of their small size and high fracture strain. The developed system can send and receive broadband Lamb waves. In this research, this system was used to detect Delamination damage in composite laminates. First, the multiple modes of Lamb waves in a carbon-fiber-reinforced plastic (CFRP) quasi-isotropic laminate were identified by transmitting and receiving the symmetric and antisymmetric modes separately. Then, the mode conversions at both tips of a Delamination were investigated through an experiment and a two-dimensional finite element analysis (FEA). A new Delamination detection method was proposed on the basis of the mode conversions, and experiments were carried out on laminates with an artificial Delamination. When antisymmetric modes were excited, the frequency dispersion of the received A1 mode changed, depending on the Delamination Length owing to the mode conversion between the A1 mode and the S0 mode. This phenomenon was confirmed through the FEA and these results prove that this new method is effective in detecting a Delamination in CFRP laminates.

  • development of smart composite structures with small diameter fiber bragg grating sensors for damage detection quantitative evaluation of Delamination Length in cfrp laminates using lamb wave sensing
    Composites Science and Technology, 2005
    Co-Authors: Nobuo Takeda, Yoji Okabe, Junichiro Kuwahara, Seiji Kojima, Toshimichi Ogisu
    Abstract:

    The authors and Hitachi Cable, Ltd. have recently developed small-diameter optical fiber and its fiber Bragg grating (FBG) sensor for embedment inside a lamina of composite laminates without strength reduction. The outside diameters of the cladding and polyimide coating are 40 and 52 μm, respectively. First, a brief summary is presented for applications of small-diameter FBG sensors to damage monitoring in composite structures. Then, we propose a new damage detection system for quantitative evaluation of Delamination Length in CFRP laminates using Lamb wave sensing. In this system, a piezo-ceramic actuator generates Lamb waves in a CFRP laminate. After the waves propagate in the laminate, transmitted waves are received by an FBG sensor attached on or embedded in the laminate using a newly developed high-speed optical waveLength interrogation system. This system was applied to detect interlaminar Delamination in CFRP cross-ply laminates. When the Lamb waves passed through the Delamination, the amplitude decreased and a new wave mode appeared. These phenomena could be well simulated using a finite element analysis. From the changes in the amplitude ratio and the arrival time of the new mode depending on the Delamination Length, it was found that this system could evaluate the Delamination Length quantitatively. Furthermore, small-diameter FBG sensors were embedded in a double-lap type coupon specimen, and the debonding progress could be evaluated using the wavelet transform.

  • application of chirped fbg sensors for detection of local Delamination in composite laminates
    Smart Structures and Materials 2003: Smart Sensor Technology and Measurement Systems, 2003
    Co-Authors: Shinichi Takeda, Yoji Okabe
    Abstract:

    Chirped fiber Bragg (FBG) sensors were applied for the detection of Delamination in carbon fiber reinforced plastics (CFRP) cross-ply laminates. Reflection spectra from the embedded chirped FBG sensor were measured at various Delamination Lengths under static four-point bending test. The sensor were embedded into two different positions for the investigation of the relation between the spectrum and the direction of Delamination propagation. The spectrum changed sensitively depending on both the Delamination Length and the direction of the Delamination propagation. For confirmation of the measured results, the spectrum was simulated considering the strain distribution in the chirped FBG sensor theoretically. The change in the form of the measured spectrum was consistent with that of the calculated spectrum. Moreover, the area ratio of the two peaks in the spectrum and the spectrum width were proposed as effective indicators for the identification of the local Delamination.

  • Delamination detection in cfrp laminates with embedded small diameter fiber bragg grating sensors
    Composites Part A-applied Science and Manufacturing, 2002
    Co-Authors: Shinichi Takeda, Yoji Okabe
    Abstract:

    Newly developed small-diameter fiber Bragg grating (FBG) sensors were applied for the detection of the Delamination in carbon fiber reinforced plastic (CFRP) cross-ply laminates. Since the diameter of the FBG sensor was very small, the sensor was easily embedded into the 0° ply along the reinforcing carbon fibers. The reflection spectra from the FBG sensor were measured at various Delamination Lengths through four-point bending test. The form of the spectrum changed sensitively, as the Delamination Length increased. Moreover, the spectrum was calculated theoretically for confirmation of the measured spectrum. The calculated result reproduced the change in the measured spectrum very well. Then, we proposed the intensity ratio in the spectrum as an effective indicator for the prediction of the Delamination Length. This indicator has a potential to be applied to other laminate configurations.

Toshimichi Ogisu - One of the best experts on this subject based on the ideXlab platform.

  • Delamination detection in composite laminates using dispersion change based on mode conversion of lamb waves
    Smart Materials and Structures, 2010
    Co-Authors: Yoji Okabe, Keiji Fujibayashi, Mamoru Shimazaki, Hideki Soejima, Toshimichi Ogisu
    Abstract:

    A new ultrasonic propagation system has been constructed using macrofiber composite (MFC) actuators and fiber Bragg grating (FBG) sensors. The MFCs and FBGs can be integrated into composite laminates because of their small size and high fracture strain. The developed system can send and receive broadband Lamb waves. In this research, this system was used to detect Delamination damage in composite laminates. First, the multiple modes of Lamb waves in a carbon-fiber-reinforced plastic (CFRP) quasi-isotropic laminate were identified by transmitting and receiving the symmetric and antisymmetric modes separately. Then, the mode conversions at both tips of a Delamination were investigated through an experiment and a two-dimensional finite element analysis (FEA). A new Delamination detection method was proposed on the basis of the mode conversions, and experiments were carried out on laminates with an artificial Delamination. When antisymmetric modes were excited, the frequency dispersion of the received A1 mode changed, depending on the Delamination Length owing to the mode conversion between the A1 mode and the S0 mode. This phenomenon was confirmed through the FEA and these results prove that this new method is effective in detecting a Delamination in CFRP laminates.

  • development of smart composite structures with small diameter fiber bragg grating sensors for damage detection quantitative evaluation of Delamination Length in cfrp laminates using lamb wave sensing
    Composites Science and Technology, 2005
    Co-Authors: Nobuo Takeda, Yoji Okabe, Junichiro Kuwahara, Seiji Kojima, Toshimichi Ogisu
    Abstract:

    The authors and Hitachi Cable, Ltd. have recently developed small-diameter optical fiber and its fiber Bragg grating (FBG) sensor for embedment inside a lamina of composite laminates without strength reduction. The outside diameters of the cladding and polyimide coating are 40 and 52 μm, respectively. First, a brief summary is presented for applications of small-diameter FBG sensors to damage monitoring in composite structures. Then, we propose a new damage detection system for quantitative evaluation of Delamination Length in CFRP laminates using Lamb wave sensing. In this system, a piezo-ceramic actuator generates Lamb waves in a CFRP laminate. After the waves propagate in the laminate, transmitted waves are received by an FBG sensor attached on or embedded in the laminate using a newly developed high-speed optical waveLength interrogation system. This system was applied to detect interlaminar Delamination in CFRP cross-ply laminates. When the Lamb waves passed through the Delamination, the amplitude decreased and a new wave mode appeared. These phenomena could be well simulated using a finite element analysis. From the changes in the amplitude ratio and the arrival time of the new mode depending on the Delamination Length, it was found that this system could evaluate the Delamination Length quantitatively. Furthermore, small-diameter FBG sensors were embedded in a double-lap type coupon specimen, and the debonding progress could be evaluated using the wavelet transform.

Shinichi Takeda - One of the best experts on this subject based on the ideXlab platform.

  • application of chirped fbg sensors for detection of local Delamination in composite laminates
    Smart Structures and Materials 2003: Smart Sensor Technology and Measurement Systems, 2003
    Co-Authors: Shinichi Takeda, Yoji Okabe
    Abstract:

    Chirped fiber Bragg (FBG) sensors were applied for the detection of Delamination in carbon fiber reinforced plastics (CFRP) cross-ply laminates. Reflection spectra from the embedded chirped FBG sensor were measured at various Delamination Lengths under static four-point bending test. The sensor were embedded into two different positions for the investigation of the relation between the spectrum and the direction of Delamination propagation. The spectrum changed sensitively depending on both the Delamination Length and the direction of the Delamination propagation. For confirmation of the measured results, the spectrum was simulated considering the strain distribution in the chirped FBG sensor theoretically. The change in the form of the measured spectrum was consistent with that of the calculated spectrum. Moreover, the area ratio of the two peaks in the spectrum and the spectrum width were proposed as effective indicators for the identification of the local Delamination.

  • Delamination detection in cfrp laminates with embedded small diameter fiber bragg grating sensors
    Composites Part A-applied Science and Manufacturing, 2002
    Co-Authors: Shinichi Takeda, Yoji Okabe
    Abstract:

    Newly developed small-diameter fiber Bragg grating (FBG) sensors were applied for the detection of the Delamination in carbon fiber reinforced plastic (CFRP) cross-ply laminates. Since the diameter of the FBG sensor was very small, the sensor was easily embedded into the 0° ply along the reinforcing carbon fibers. The reflection spectra from the FBG sensor were measured at various Delamination Lengths through four-point bending test. The form of the spectrum changed sensitively, as the Delamination Length increased. Moreover, the spectrum was calculated theoretically for confirmation of the measured spectrum. The calculated result reproduced the change in the measured spectrum very well. Then, we proposed the intensity ratio in the spectrum as an effective indicator for the prediction of the Delamination Length. This indicator has a potential to be applied to other laminate configurations.

Junqian Zhang - One of the best experts on this subject based on the ideXlab platform.

  • Delaminations induced by constrained transverse cracking in symmetric composite laminates
    International Journal of Solids and Structures, 1999
    Co-Authors: Junqian Zhang, K P Herrmann
    Abstract:

    Abstract Transverse ply cracking and its induced Delaminations at the φ/90° interfaces in [. . . /φi/φm/90n] s laminates are theoretically investigated. Three cracked and delaminated model laminates, one five-layer model (FLM) laminate [SL/φm/902n/φm/SR] T and two three-layer model (TLM) laminates I and II, [φm/902n/φm] T and [S′L/902n/S′R] T, are designed to examine constraining mechanisms of the constraining plies of the center 90°-ply group on transverse crack induced Delaminations, where SL, SR, S′L and S′R are sublaminates [. . ./φi] T, [φi/. . .] T, [. . ./φi/φm] T and [φm/φi/. . .] T, respectively. A sublaminate-wise first-order shear laminate theory is used to analyze stress and strain fields in the three cracked and delaminated laminates loaded in tension. The extension stiffness reduction of the constrained 90°-plies and the strain energy release rate for a local Delamination normalized by the square of the laminate strain are calculated as a function of Delamination Length and transverse crack spacing. The constraining effects of the immediate neighboring plies and the remote plies are identified by conducting comparisons between the three model laminates. It is seen for the examined laminates that the nearest neighboring ply group of the 90°-plies primarily affects the stiffness reduction and also the normalized strain energy release rate, whereas the influences of the remote constraining layers are negligible.

  • strain energy release rate associated with local Delamination in cracked composite laminates
    Composites, 1994
    Co-Authors: Junqian Zhang
    Abstract:

    Abstract In the present paper the total strain energy release rate GT associated with Delaminations that initiate from a matrix crack in a symmetric composite laminate is calculated using the potential energy approach in elastic fracture mechanics and a two-dimensional finite element analysis. Two laminate stacking sequences, [ 0 2 90 4 ] s and [ ±25 90 4 ] s , are examined with a matrix crack in the 90° plies and Delaminations growing uniformly from the matrix crack tip in the 0 90 and − 25 90 interfaces, respectively. The finite element analysis indicates that the Gl component (opening mode Delamination) is reduced to zero for Delamination Length greater than one ply thickness; the shear mode (Mode II) dominates the growth of Delamination. The total GT increases with increasing Delamination Length, but eventually approaches a constant asymptotic value, which is close to the GT result calculated from the analytical model. Finally, the analytical and numerical calculations show that G for local Delamination decreases notably with increasing matrix cracking.

M Heidarirarani - One of the best experts on this subject based on the ideXlab platform.

  • effect of initial crack Length on the measured bridging law of unidirectional e glass epoxy double cantilever beam specimens
    Materials & Design, 2014
    Co-Authors: Mahmood M. Shokrieh, Mazaher Salamattalab, M Heidarirarani
    Abstract:

    Abstract In this paper, the effect of initial Delamination Length is experimentally investigated on obtaining the mode I bridging law of unidirectional E-glass/epoxy double cantilever beam (DCB) specimens manufactured by hand layup method. To this end, an experimental test set-up is established for accurate measurement of crack tip opening displacement (CTOD) using digital image processing method. DCB tests are performed for three different Delamination Lengths and the corresponding bridging laws are calculated using J -integral approach. Results showed that the maximum bridging stress, the shape of bridging law and energy dissipation in bridging zone are slightly affected by changing initial crack Length. In other words, the measured bridging law acts independent of initial Delamination Length. Therefore, the obtained bridging law can be used with the cohesive elements available in the commercial finite element software to simulate the Delamination propagation behavior in unidirectional DCB specimens.