Fundamental experiments of bird-strike, and derivation of empirical equations for damage

Abstract

Bird-strikes against aircrafts and against wind generator blades are urgent issues. In addition, their effects on flying cars are beginning to be highlighted. As it is assumed that birds vary in size, impact experiments using projectiles that take into account the characteristics and shapes of birds are unavoidable for material screening during their development stage. However, such kinds of experiments have not been sufficiently carried out. In this study, to elucidate the effect of the shape and the properties of projectiles on the impact behaviors of CFRPs, a fundamental study was done by three-dimensional measurement using various projectiles including a gelatin cylinder, rubber cylinders and rubber spheres for mainly two types of CFRPs with different laminate configurations (stackings) at the impact velocities below 370 m/s. The difference in the elapsed-time dependence of the largest displacement of deformation (vertex displacement) due to the stackings was slight, but the deformation behavior changed depending on the shape of the projectile, i.e. especially, large deformable or large-diameter projectiles resulted in a wider bottom area. To determine the penetration and delamination, the contacted area, related to the projectile’s diameter, should be considered. The deformation of CFRPs by a spherical projectile just after the impact could be described by a quartic/quintic-function and after a certain period of time (30–50 μs) by a quadratic-function. Empirical equations for the kinetic energies of penetration and delamination for aircraft structural grade CFRP were proposed.