Detection of microscopic damages in composite laminates

Abstract Small-diameter fiber Bragg grating (FBG) sensors, of outside diameter 52 μm, have been developed by the authors and Hitachi Cable Ltd. for embedding inside a laminate without deterioration of the mechanical properties of the composite laminate. In this research, the small-diameter FBG sensor was embedded in the 0° ply of a CFRP cross-ply laminate for the detection of transverse cracks in the 90° ply. The reflection spectra from the FBG sensor were obtained at various tensile stresses. As a result of damage, the spectrum became broad and had some peaks with increase in the transverse crack density. Furthermore, theoretical calculation reproduced the change in the spectrum very well. These results show that small-diameter FBG sensors have the potential to detect the occurrence of transverse cracks through the change in the form of the spectrum, and to evaluate the transverse crack density quantitatively by the spectrum width.

[1]  M. Leblanc,et al.  Continuous arbitrary strain profile measurements with fiber Bragg gratings , 1998 .

[2]  Kara Peters,et al.  Experimental verification of response of embedded optical fiber Bragg grating sensors in non-homogeneous strain fields , 2000 .

[3]  Nobuo Takeda,et al.  Experimental characterization of microscopic damage progress in quasi-isotropic CFRP laminates: effect of interlaminar-toughened layers , 1998 .

[4]  Nobuo Takeda,et al.  Initiation and growth of delamination from the tips of transverse cracks in CFRP cross-ply laminates , 1994 .

[5]  L. McCartney.  Theory of stress transfer in a 0°—90°—0° cross-ply laminate containing a parallel array of transverse cracks , 1992 .

[6]  Nobuo Takeda,et al.  Development of small-diameter optical fiber sensors for damage detection in composite laminates , 2000, Smart Structures.

[7]  Michael A. Davis,et al.  Fiber grating sensors , 1997 .

[8]  Nobuo Takeda,et al.  Detection of transverse cracks in CFRP composites using embedded fiber Bragg grating sensors , 2000 .

[9]  Wei-Ping Huang.  Coupled-mode theory for optical waveguides: an overview , 1994 .

[10]  J. Alfredo Guemes,et al.  Measurement of strain distribution in bonded joints by fiber Bragg gratings , 1998, Smart Structures.

[11]  R. Dändliker,et al.  Determination of the individual strain-optic coefficients in single-mode optical fibres , 1988 .

[12]  George S. Springer,et al.  Strain and Temperature Measurement with Fiber Optic Sensors , 1996 .

[13]  Nobuo Takeda,et al.  In situ observation and probabilistic prediction of microscopic failure processes in CFRP cross-ply laminates , 1994 .

[14]  M. Yamada,et al.  Analysis of almost-periodic distributed feedback slab waveguides via a fundamental matrix approach. , 1987, Applied optics.