Mechanical instability in bat wing skin
Alyssa Skulborstad (University of Michigan), Nakhiah Goulbourne (University of Michigan)
Instability in Solids and Structures
Tue 2:40 - 4:00
Barus-Holley 190
The wing skin of bats is highly extensible, which distinguishes it from other natural flyers. This extensibility enables various wing conformations and flight modes. In order to mimic the functionality of the bat wing for applications such as micro-aerial vehicles, an understanding of its structure-property-function relationship is needed. Inherent to the skin is a structural instability arising from different natural states among the components. In the species Glossophaga soricina, pre-stretched spanwise elastin fibers embedded in a stiffer un-stretched matrix produce compressive loads and create a spanwise wrinkled skin configuration. In another species, Tadarida braziliensis, pre-stretched elastin fibers run in both the spanwise and chordwise directions producing a wrinkle pattern oriented at an angle to the two directions. In this study, we model the mechanics of the wing skin instability. Biological materials are highly complex and exhibit nonlinear and viscoelastic behavior; however, as a starting point, we idealize the structure as a stiffer neo-Hookean layer bonded to a softer pre-stretched neo-Hookean layer. Using a minimum energy approach, we determine the critical membrane forces and wave numbers for structure in terms of relative material properties and pre-stretches. These expressions are compared to the well known linear elastic results for a stiff film bonded to a compliant substrate. Uniaxial pre-stretch cases are analyzed to reproduce the sinusoidal wrinkle patter observed in G. soricina. Then, biaxial pre-stretch cases are assessed to reproduce various sinusoidal wrinkle orientations found in other bats, including T. braziliensis. This analysis gives insight into the fabrication of biomimetic synthetic skins and future work will include synthesis of such materials and comparison of their structural characteristics with those predicted by the model.