Effects of incidence angle in bird strike on integrity of aero-engine fan blade

The possibilities of blade deformation and even fracture, the need for subsequent containment and reduction in thrust and power supply make bird strikes to aero-engine fan blades very serious events. Due to the different bird-plane flight paths and the different types of turbofan engines, the incidence angle between the bird and the engine fan blade can vary within a wide range. The present explicit non-linear three-dimensional finite-element analyses examine in detail the effect of the incidence angle when a canonical 4-lb bird strikes a typical engine fan blade, using the commercial code LS-DYNA. Both the bird and the blade are simulated in a Lagrangian framework. The homogenised fluidic constitutive equation of the bird follows the Brockman hydrodynamic model, while the blade is modelled as a viscoplastic material of the Perzyna type. It was found that normal incidence results in maximum impact forces and plastic strains leading to severe deformation. For the case in which the incidence angle is equal to or larger than 60 degrees, the impact forces are significantly reduced, and the blade deformation remains within the elastic range. In addition, this work also provides a theoretical calculation for the bird Hugoniot pressure by assuming it as a high-speed soft-body impactor, thus providing a means for obtaining a quick conservative upper bound solution.