Determination of the WYPiWYG strain energy density of skin through finite element analysis of the experiments on circular specimens

Skin is a biological material which mechanical behavior has large variations depending on the individual and the location of the specimen in that individual, among other factors. Large differences are also encountered in measurements between in vivo and in vitro specimens. Then, optimal characterization of the skin for simulation (for example) of surgical procedures requires that all experiments to characterize the material behavior be performed on the same specimen and in vivo if possible. Recent experiments on circular discs (Groves et al., 2013 [16]) permit this characterization using a single specimen as we show in this paper, and may constitute a good starting point for ulterior characterization in vivo. However, because in these tests deformations are not homogeneous, the determination of the material behavior is not as direct as with tensile or biaxial tests, so finite element analysis is needed to propose a procedure to determine the material behavior. In this work we perform an analysis of the experiments using finite elements obtaining an insight which permits a very simple iterative procedure to determine the stress-strain behavior of the material and, thereafter, the corresponding What-You-Prescribe-Is-What-You-Get (WYPiWYG) stored energy densities.