Experimental analysis of composite rotor blade models for damge identification

Abstract

The helicopter rotor system operates in a highly dynamic and unsteady environment leading to severe vibratory loads. Repeated exposure to this severe loading condition can induce damage in the composite rotor blades. These blades are generally made of fiber reinforced laminated composites and exhibit various competing modes of damage such as delamination, fiber matrix debonding, fiber breakage, fiber pull out and matrix cracking. There is a need to study the behavior of the composite helicopter rotor system under various key damage modes in composite materials, as this understanding can then be further used for developing a Structural Health Monitoring (SHM) system which will be able to predict these key damage modes in the helicopter from the measured data. An experimental study for understanding the combined influence of damages is carried out. Experimental analysis is carried out for non-rotating and rotating conditions. In the non-rotating conditions fundamental properties of composite rotor blade model viz. stiffnesses and natural frequencies in various directions are obtained. For the rotating conditions strains in various directions are measured for damaged and undamaged rotor blade models. Further, dynamic responses of undamaged and damaged blade are also obtained for rotating as well as non-rotating conditions.