On the effect of progressive damage on composite helicopter rotor system behavior

Composite rotor blades are routinely used in modern helicopters. Damage in composite helicopter rotor blades is investigated in this work. Effects of the key damage modes in composite materials such as matrix cracking, debonding/delamination and fiber breakage on various properties of the composite rotor blade such as stiffnesses, frequencies, deflection, root forces, root moments and strains in forward flight are studied using an aeroelastic analysis. The composite rotor blade is modeled as a thin walled composite beam and includes the effect of transverse shear, elastic couplings and restrained warping. Matrix cracking is modeled at the laminate level and debonding/delamination and fiber breakage at the lamina level and included in the formulation by adjusting the A, B and D matrices for composite laminates. A stiff in-plane rotor blade with a two-cell airfoil section with [0/±45/90]s family of laminates is considered. An aeroelastic analysis of the helicopter rotor based on finite elements in space and time is used to study the effects of key damage modes in a composite rotor in forward flight.