Determining modulus of elasticity using finite element analysis and non-destructive testing: Are aquatic animal whiskers stiffer?

Approximating the stiffness of biological materials can give important insights into how structures deform and when they may fail. Some samples may be too precious to test to destruction, or too fine to position accurately for conventional material testing, which makes it challenging to obtain approximations of material stiffness. Using two-dimensional scans, non-destructive bending tests, and finite element (FE) modeling, we show that we can approximate the modulus of elasticity of samples by fitting FE model data to that of experimental bend tests. We demonstrate our protocol on representative whiskers from three species of Carnivorans, including a terrestrial red fox, semi-aquatic Eurasian otter, and aquatic phocid grey seal. Grey seal whiskers had the highest approximated modulus of elasticity (0.5-19 GPa), followed by Eurasian otter (0.5-13 GPa) and red fox (0.1-1.5 GPa). We suggest that, as in many other biological structures, adaptations in both the shape and material stiffness of the whisker contribute to how it bends when loaded. Specifically, a larger base radius and higher material stiffness both act to increase whisker flexural rigidity in the aquatic grey seal. This protocol has broad applications in comparative biology and provides a way to determine shape and material stiffness information for various flexible specimen types.