Accession Number:

ADA324039

Title:

Modal Frequency Detection in Composite Beams Using Fiber Optic Sensors

Descriptive Note:

Master's thesis

Corporate Author:

AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH

Personal Author(s):

Report Date:

1997-04-18

Pagination or Media Count:

104.0

Abstract:

Extrinsic Fabry-Perot interferometric EFPI fiber optic sensors were used to determine the first five modal frequencies of laminated glassepoxy composite beams. EFPI fiber optic sensors and piezoelectric PZT ceramic sensor both found identical modal frequencies of the composite beams, however, EFPI fiber optic sensors showed more sensitivity and better signal-to-noise ratios. The analytical classical beam theory and a finite element model validated the EFPI modal frequency measurements. Several 8-ply glassepoxy composite beams, each 26.04 cm long and 2.33 cm wide were fabricated. Five damaged beams with specified delaminations as well as two different undamaged beams were tested for modal frequencies. Five different delaminations with sizes ranging from 1.27 cm to 6.35 cm long were incorporated in the midplane of the beams. Each modal frequency shifted with a change of delamination size and location. Classical beam theory was used to simulate modal frequency data sets for 1097 different prescribed delamination sizes and locations. These data sets were applied for training and testing a feedforward backpropagation neural network. Finally the neural network was tested against the EFPI fiber optic sensor modal frequency results. The delamination size and location predictions resulted from neural networks simulation had an average error of 5.9 and 4.7 respectively.

Subject Categories:

  • Laminates and Composite Materials
  • Optical Detection and Detectors
  • Fiber Optics and Integrated Optics

Distribution Statement:

APPROVED FOR PUBLIC RELEASE