148. STRUCTURE AND MECHANICAL BEHAVIOR OF HIGH IMPACT RESISTANT BIOLOGICAL MATERIALS: HORNS AND HOOVES

Department: Mechanical & Aerospace Engineering
Research Institute Affiliation: Graduate Program in Materials Science and Engineering
Faculty Advisor(s): Joanna M. McKittrick

Primary Student
Name: Wei Huang
Email: w7huang@ucsd.edu
Phone: 858-263-5350
Grad Year: 2018

Abstract
Tubular structure are one of the most impact resistant and energy absorbent structural designs and although studied for many years, remains an attractive research interest. Among the biological materials that have tubular structures, horns and hooves are excellent examples of impact resistant structures that have evolved for fighting or galloping of bovidae and equidae, respectively. Microstructures and mechanical behavior of the bighorn sheep (Ovis Canadensis) horn and African zebra (Equus burchelli) hoof were studied to examine mechanisms of impact resistant. Hooves and horns are composed of α-keratin crystalline intermediate filaments embedded in an amorphous matrix. Both have a tubular structure and a surrounding laminated structure. Optical and electronic microscope images showed the shape of tubule cross section in both horn and hoof are ellipses, ~ 80μm (major axis) and ~ 40 μm (minor axis). However, the porosity in the horn is ~7%, while in the hoof is ~3.5%. The intertubular lamellae area is much larger in the hoof than that in the horn. Since anisotropy is an important factor in material properties, mechanical properties of horns and hooves were evaluated in three orthogonal directions (longitudinal, transverse and radial). Quasi-static compression test results showed strength and Young?s modulus were much higher in longitudinal and transverse direction than that in radial direction, while the radial direction was more energy absorbent because of the tubule collapse. Comparing horn and hoof structures, although the porosity in horn is two times that of the hoof, the compressive yield strength and Young?s modulus are higher in the horns in all the three directions, which demonstrated that horn structure was more energy absorbent in a quasi-static load. To determine how porosity affects the mechanical properties of tubular structures, 3D printed models of two different tubular densities (7% and 3.5%) were fabricated. At the same time, quasi-static and dynamic simulation of these two kinds of tubular models were carried out using finite element analysis, which showed a more uniformly distributed stress in transverse direction, leading to a higher stiffness. Kolsky bar dynamic test results as well as further finite element analysis on the tubular models will be presented. This work is supported by funding provided by a Multi-University Research Initiative through the Air Force Office of Scientific Research (AFOSR-FA9550-15-1-0009).

Industry Application Area(s)
Aerospace, Defense, Security | Civil/Structural Engineering | Materials

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