Whipping motion of airplane composite fan blades due to bird strike

Composite fan blades made of CFRP have been developed and investigated to reduce the weight of aircraft engines. Aircraft fan blades are subjected to high-speed impact by foreign objects, such as bird strikes. Because CFRP has lower impact resistance than metal materials, it is necessary to focus on possible failure not only at the impact point but also at the tip and trailing edge of the fan blade. This paper developed a finite element analysis model of fan blade geometry and investigated the dynamic deformation that may induce peripheral fracture when a bird strike occurs on a composite fan blade. Natural vibration analysis and transient response analysis were performed to analyze the vibration behavior at the fan blade periphery. The natural vibration analysis showed that the vibration modes in the out-of-plane direction of the blade are of low order. In the transient response analysis, when a group of particles defined by the equation of state and the SPH method collided, a sudden deformation in the periphery, called a whipping motion, was observed immediately after the impact. The spanwise strain has a peak value at the trailing edge of the fan blade, while the chordwise strain has a peak value at the leading edge of the fan blade. Furthermore, the transient response analysis with the fan blades rotating showed an increase in the peak strain value. A comparison of the impact loads and displacements immediately below the impact indicated that the centrifugal force increased the geometric stiffness, which increased the reaction force due to the fan blade, increasing the peak value.