Detecting Chordwise Cracks and Delaminations in Uncoupled Composite Rotoreraft Flexbeams Under Rotation

The appearance of cracks and delaminations caused by excessive vibratory and fatigue loads in composite rotoreraft flexbeams can lead to degradation in flap- wise and lagwise performance of the rotor blade. In addition, these types of damage in composite rotorcraft flexbeams under cyclic loading can result in rapid fatigue failure of these elements leading to catastrophic results. A novel detection strategy is evaluated which attempts to use the scattering of structural waves generated from piezoelectric actuators to locate damage. Previous approaches to damage detection have focused on using the modal response of the structure. The approach reported in this work relies primarily on more accurate local continuum mechanics descriptions of the structural dynamics. The method developed here exploits the wave propagation solution of uncoupled equations of motion for thin composite flexbeams under rotation. Local models of structural damage in the form of chordwise interply delaminations and notch cracks are developed by accounting for how waves scatter at structural discontinuities. The scattering matrix, which characterizes how incoming and outgoing waves scatter at a structural defect, is used as a performance metric to quantify damage. Finally, experimental validation of the structural damage modeling and damage identification strategy were carried out on [0/90]s graphite epoxy (Gr/Ep) beams in vacuum under rotation. To simulate local structural damage in rotoreraft flexbeam a teflon layer was inserted into specimen for the delaminated cases and a small notch was filed from specimen for the cracked cases.