Modal-based damage detection of a composite helicopter main rotor blade

Abstract

This work presents experimental results for structural health monitoring method based on modal properties. The test subject is a composite helicopter main rotor blade, which is a highly flexible, slender beam that can display unusual dynamic behavior with orthotropic properties. A damage method detection based on the coordinate modal assurance criterion (COMAC) was implemented and evaluated on a real-size helicopter main rotor blade. This method uses the global modal properties of the system to identify and locate damaged based on a sensor network. Additionally, simpler methods of tracking changes and detecting damage are evaluated, such as natural frequency tracking and modal assurance criterion (MAC). A test setup was built to carry out an experimental modal analysis on the main rotor blade. For that purpose, a total of 55 uniaxial accelerometers were used for the sensor network along the blade in a way to measure the most significant vibration modes and an electrodynamic shaker was used to excite the system. Vibration modes and natural frequencies were identified by means of a least squares fit (PolyMAX), with damage being simulated on the blade by attaching a small mass to it, changing its global properties this way. Experimental results for the damage detection techniques are shown and a comparison between the methods is also made. © 2012 AIAA.