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Papers by Shin-ichi Takeda

Journal of the Japanese Society for Experimental Mechanics, 2012

In this paper, the propagation behavior of elastic waves generated in CFRP laminates by pulsed la... more In this paper, the propagation behavior of elastic waves generated in CFRP laminates by pulsed laser was investigated both experimentally and analytically. First, the anisotropy in amplitudes of elastic waves generated by pulsed laser were measured experimentally. The anisotropic property was found to vary with different frequencies. Secondly, elastic wave propagation behavior was evaluated by finite element analysis. In this analysis, two cases in which CFRP has anisotropic and isotropic thermal expansion properties were compared with experimental results. As a result, tendency in analytical results of CFRP with anisotropic thermal property agreed well with the experimental results, which confirms that the anisotropic thermal expansion property of CFRP laminates causes the anisotropy in amplitudes of elastic waves generated in CFRP laminates by pulsed laser. Finally, the influence of coatings on anisotropic behavior of elastic waves generated in CFRP laminates by pulsed laser was i...

Journal of the Japan Society for Composite Materials, 2019

Proceedings of the 1992 Annual Meeting of JSME/MMD, 2002

Journal of the Japan Society for Composite Materials, 2012

Journal of the Japan Society for Composite Materials, 2005

Composites Part A: Applied Science and Manufacturing, 2011

ABSTRACT This study demonstrated fiber-optic-based life cycle monitoring of a representative carb... more ABSTRACT This study demonstrated fiber-optic-based life cycle monitoring of a representative carbon fiber reinforced plastic (CFRP) stiffened panel manufactured by vacuum assisted resin transfer molding (VARTM). A single optical fiber was embedded between the stiffeners and the skin during the laminate lay-up process and the formed fiber-optic network was then utilized to monitor the manufacturing process and subsequent impact tests. A Brillouin-based system with a spatial resolution of 10cm was utilized for distributed strain measurement. Strain changes induced during the manufacturing process and the impact tests were comprehensively presented and discussed. The internal state of the panel was successfully monitored throughout its life, confirming the effectiveness of life cycle monitoring by fiber-optic-based distributed sensing for developing highly-reliable composite structures.

Composites Part A: Applied Science and Manufacturing, 2004

Advanced Composite Materials, 2008

ABSTRACT FBG (Fiber Bragg Grating) sensors and optical fibers were embedded into CFRP dry preform... more ABSTRACT FBG (Fiber Bragg Grating) sensors and optical fibers were embedded into CFRP dry preforms before resin impregnation in VaRTM (Vacuum-assisted Resin Transfer Molding). The embedding location was the interface between the skin and the stringer in a CFRP-stiffened panel. The reflection spectra of the FBG sensors monitored the strain and temperature changes during all the molding processes. The internal residual strains of the CFRP panel could be evaluated during both the curing time and the post-curing time. The temperature changes indicated the differences between the dry preform and the outside of the vacuum bagging. After the molding, four-point bending was applied to the panel for the verification of its structural integrity and the sensor capabilities. The optical fibers were then used for the newly-developed PPP-BOTDA (Pulse-PrePump Brillouin Optical Time Domain Analysis) system. The long-range distributed strain and temperature can be measured by this system, whose spatial resolution is 100 mm. The strain changes from the FBGs and the PPP-BOTDA agreed well with those from the conventional strain gages and FE analysis in the CFRP panel. Therefore, the fiber-optic sensors and its system were very effective for the evaluation of the VaRTM composite structures.

Engine debris penetration tests were conducted to evaluate the large notch damage and residual st... more Engine debris penetration tests were conducted to evaluate the large notch damage and residual strength of composite stiffened panel. The damage mechanism was examined by progressive failure analysis based on Hashin’s failure criteria and cohesive zone model. The influence of delamination on the progressing notched damage path and initial failure load of the panel are investigated. The results reveal that typical damage path is characterized by fiber breakage perpendicular to the crack tips to be followed by skin/stringer interface damage. The numerical model has a potential capability to predict the debris penetration and residual strength of the damaged panel.