Identification of Microscopic Damages in CFRP Laminates with Chirped FBG Sensors (original) (raw)
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Journal of the Japanese Society for Experimental Mechanics, 2012
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...
Detection of Flow Separation on Aerofoil by FBG Cantilever Sensor
Journal of The Japan Society for Aeronautical and Space Sciences, 2008
The use of the Fiber Bragg Grating (FBG) cantilever sensor was attempted for the detection of flow separation. This optical sensor detects a shift of the wavelength of the reflected light corresponding to the amount of strain caused in the optical fiber. We successfully examined the sensing of the direction of flows. In the next stage, this sensor was installed at trailing edge of an aerofoil, to investigate the performance of the sensor and the characteristics of the flow separation. As a result, it is found that this sensor could catch the changing of the flow direction due to flow separation.
2022
Carbon fiber is a brittle material and its tensile strength is strongly influenced by defects, which are often assessed by the shape parameter of the Weibull distribution. Therefore, the shorter the gauge length is, the higher the tensile strength is. The usual tensile test is conducted with a gauge length of 25 mm and the tensile strength at short gauge is derived using Weibull distribution. However, it is reported that the shape parameter changes when the gauge length is less than 1mm. The objective of this work is to attempt to evaluate the short gauge tensile strength of carbon fiber in tests under optical microscope observation. The shorter the gauge length was, the more test results of fiber separation from adhesive or fiber breakage in adhesive were observed. It is found that the test of short gauge of 0.2 mm requires careful specimen preparation to avoid shear stress due to misalignment of fiber and loading axes. Weibull shape parameters of the tensile strengths at the gauges from 50mm to 1mm were almost the same as the usual tensile test. However, the values for the 0.5 mm and 0.2 mm gauges were higher than those for the longer gauges.