Interferometric Optical Fiber Measurements of Internal Strain in Adhesive Joints
Strain inside adhesive lap joints has been measured using imbedded optical fiber sensors. Cylindrical glass-on-glass optical fibers with 125-micron outer diameters and an 0.85-micron single mode cutoff wavelength have been imbedded within expoxy lap joints between metal substrates. Strain integrated along the length of one imbedded fiber has been determined by interierometrically measuring the strain-induced phase modulation of multiple optical modes supported within the optical guide for 0.633-micron transmission. Differential measurements of the strains integrated along two fibers imbedded in different orientations within the lap joints have also been obtained using differential interferometric techniques modified due to the multimode nature of the waveguides. Results are compared with analytical predictions. Limitations of the imbedded fiber technique are considered. Extensions of the technique to local measurements of strain along the length of the imbedded fiber and measurements of the internal local strain tensor are discussed.
KeywordsOptical Fiber Radial Strain Optical Guide Interferometric Fiber Optical Fiber Waveguide
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