Modeling damage in rotorcraft flexbeams using wave mechanics

The application of wave propagation analysis to detect damage in rotorcraft flexbeams in the form of transverse cracks and delaminations is discussed. The approach used involves examining the local scattering properties of structural discontinuities in the frequency domain to assess the effect of damage on the modal response of the structure. A model using a simulated cantilevered beam is used to illustrate the performance of the wave model approach for dynamic detection of damage in the form of transverse cracks imparted to composite rotorcraft flexbeams. Experimental validation is carried out on a graphite/epoxy (AS4/3501-6) cantilever beam test specimen with (0/90)(s) ply orientation in vacuum at various RPM levels. Damage in the form of a transverse crack, which extends across the entire width of the specimen is imparted at depths of 25, 50 and 75% of the beam thickness to the test specimen. A piezoelectric actuator mounted near the root is used to excite the structure dynamically to help locate and determine the extent of damage. The resonant frequencies and scattering properties are used as performance metrics to compare the experimental behavior against the analytical predictions from the wave modeling.