Author

Na Yeon Lee

Advisor

Williams, Lakiesha N.

Committee Member

Horstemeyer, Mark F.

Date of Degree

1-1-2016

Document Type

Dissertation - Open Access

Abstract

This dissertation proposes engineering principles for stress wave dissipation found in woodpeckers. From the experimental study of a woodpecker’s beaks via electron microscopy and mechanical testing, the three main design factors were pointed out. First, a woodpecker’s beak has wavy lines inside of the beak for local shearing. The waviness of wavy lines found in the woodpecker’s beaks was 1 while chicken’s was 0.3, and toucan’s was 0.05. Second, the woodpecker showed elongated the keratin scales to the pecking direction with a dimension ratio of 3.67 (width/height) while chicken’s and toucan’s were 3 and 1, respectively. Third, a woodpecker’s beak bone was less porous for structural strength. The porosity of a woodpecker’s beak bone was about 9.9 % while chicken’s and toucan’s were 42.3 % and 61.5 %, respectively. Also, by using computational simulations, unique geometries including hyoid apparatus and suture interfaces found in woodpeckers were investigated to assess their damping capabilities. Surrounding a woodpecker’s head, the hyoid apparatus composed of core cartilage and muscle encasing a core cartilage. The spiral and thinning geometry of the hyoid apparatus converted the normal waves into shear waves. Then shear waves generated lateral displacement of the hyoid bone, and lateral displacement brought strain energy into surrounding muscle, in which energy loss occurred by viscoelastic behavior of the muscle. Quantitatively, as the stress wave traveled from the anterior to the posterior end of the hyoid apparatus, its pressure decreased 75 % and the impulse decreased 84 %. Suture interfaces, which is another unique feature observed from woodpecker’s beak, was investigated for their geometrical effects on the dynamic impact mitigation. A sinusoidal pattern of suture interfaces induced wave scattering at its boundary causing conversion of longitudinal waves into shear waves. The suture gap also brought pressure decay by storing strain energy in its viscoelastic material. As a result, a bar with a suture interface attenuated stress waves about 37 % more than a bar with a flat interface. Based on the results and ideas presented herein, one can develop bio-inspired material for energy absorbing.

URI

https://hdl.handle.net/11668/18316

Share

COinS