Meeting Abstract
P1.141 Monday, Jan. 4 Poisson’s Ratio of Crustacean Exoskeleton CROFTS, SB*; SUMMERS, A; University of Washington; Universtiy of Washington croftss@u.washington.edu
The crustacean exoskeleton is constructed from a stacking plywood arrangement of the chitin fibers connected by cross-linking proteins and hardened by mineral deposits. When an animal out-grows its exoskeleton, it is shed and the new underlying exoskeleton is inflated and hardened through additional protein cross-linking and mineral deposition. This study examines how the structure of the chitin matrix of crustacean exoskeletons affects the material properties of the exoskeleton, specifically the Poisson’s ratio. The Poisson’s ratio describes how a material behaves along lengths perpendicular to a plane of deformation. Most materials have a positive Poisson’s ratio. This means, for example, that when a material is stretched along one axis, the perpendicular axes will shorten. In contrast, some manufactured materials have negative Poisson’s ratios, meaning that these materials expand in all dimensions when stretched, due to the arrangement of their microstructures. This microstructure arrangement appears to be similar to the stacking plywood/honeycomb pattern of the chitin matrix in the crustacean exoskeleton. To test the Poisson’s ratio we used store bought shrimp, Penaeus sp. Samples of exoskeleton were taken from the pleuron and tergum of abdominal segments one, two, and three. Samples were tested under tension using an MTS Synergie, and the change in length perpendicular to the tensile forces was measured with an extensometer. In contrast to previous studies on other crustacean exoskeletons, we found that the samples demonstrated a negative Poisson’s ratio. In industry, it has been shown that negative Poisson’s ratio materials have high energy absorption and high resistance to fracture. Therefore, a negative Poisson’s ratio in crustacean exoskeleton has some interesting ramifications for our understanding of crustacean ecology.
