Modeling progressive damage accumulation in thin walled composite beams for rotor blade applications

In the present study, models of the key damage modes in composite materials such as matrix cracking, debonding/delamination and fiber breakage are included in a thin walled composite beam analysis for helicopter rotor blade applications. The effects of transverse shear, elastic couplings and restrained warping are also included while modeling the thin walled composite beams. 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. The beam analysis is used to investigate the effect of damage on the various properties of thin walled composite beams such as out-of-plane stiffness, in-plane stiffness and torsion stiffness and deflections such as bending slopes and twist under an applied load. A two-cell airfoil section with [0/±45/90]s family of laminates having stiffness properties equivalent to a stiff in-plane hingeless rotor blade is considered. It is found that the bending and torsion stiffness loss due to matrix cracking is about 6–12% and 25–30%, respectively, and due to debonding/delamination is further 6–8% and 40–45%, respectively. Most of the bending stiffness loss is observed in the fiber breakage damage mode. It is also observed that the combination of the static tip bending and torsion response can be used to predict length of the damaged part of the thin walled composite beams, damage location and damage level.