FIBER OPTIC DISTRIBUTED STRAIN SENSING USED TO INVESTIGATE THE STRAIN FIELDS IN A WIND TURBINE BLADE AND IN A TEST COUPON WITH OPEN HOLES

摘要

High resolution fiber optic strain sensing is used to make measurements of the distributed strainrnpresent in both a 9-meter CX-100 wind turbine blade with intentionally introduced defects and inrna laminated composite coupon test sample possessing three open holes. Commercially availablerntelecommunications-grade, low-bend-loss optical fiber was surface mounted along the spar caprnof the blade and on both faces of the coupon. The amplitude and phase of the light reflectedrnfrom the fibers are measured using a commercial Optical Frequency Domain Reflectometerrn(OFDR). Changes in the amplitude and phase of the backscattered light are used to determinernthe strain along the entire length of the fibers. The measurements taken of the strain in the bladernhave 2.5 millimeter spatial resolution, and the measurements of the strain in the coupon havern0.50 millimeter resolution. High-resolution distributed strain measurements reveal therncomplexly structured strain fields existing in these laminated composite materials.