Free Vibration Studies of Woodpecker Inspired Layered Shock Absorbing Structure

Abstract

A woodpecker can drum the surface of a tree at a rate of 18 to 22 times per second with a deceleration of 1200g without experiencing any blackout or brain damage. A woodpecker is able to do this because of its unique head structure; beak, hyoid, spongy bone and skull bone with cerebrospinal fluid. Based on this concept, a bio inspired layered shock absorbing structure was fabricated. The three layer structure consists of steel as outer layer, aluminium as intermediate layer with viscoelastic material in between and a core containing gel/beads were used. The shock absorbing structure was then subjected to free vibration analysis by considering it as cantilever beam with fixed free boundary condition. The natural frequencies of the structure including the fundamental mode and higher modes were estimated using vibration measuring apparatus integrated with software. Experimental results of the shock absorbing layers were compared with numerical results estimated using commercial finite element package ANSYS. Noticeable variation in the frequency can be associated with the shell mode vibration of the cylindrical shape and delamination effect in the layered structure. The free vibration studies are useful in estimating the damping characteristics of woodpecker beak inspired layered structure and can find applications in hybrid shock absorber design.