Modeling multi-layer matrix cracking in thin walled composite rotor blades

Helicopter rotor blades are made of fiber-reinforced composite materials that are prone to matrix cracking. Matrix cracking precedes more serious damage mechanisms such as delamination and fiber breakage and is therefore a useful indicator of structural health. In the present study, the effect of matrix cracking on composite blade stiffness and deflections is investigated. A stiff inplane rotor blade with a rectangular box and two-cell airfoil section with [0/ +/- 45/90], family of laminates is considered. It is observed that the stiffness decreases rapidly in initial phase of matrix cracking and then becomes saturated. Study of the behavior of composite rotor blade from matrix cracking in single, two and complete lamina group show a bending stiffness loss of 6-12 percent and a torsion stiffness loss of 25-30 percent at the point where matrix cracking saturates, and more severe forms of damage such as debonding/delamination and fiber breakage begin.