Skin tissue has often been considered as linear, elastic, and incompressible. Thereby, a Young’s modulus or a tangential modulus was often characterized by a Poisson’s ratio close to 0. 5 [1–9]. In the present study, a hyperelastic model, based on the microstructure, with consideration of the anisotropy was chosen. The choice of this Holzapfel model was performed in order to compare numerical simulation with microstructural because this model assumes an affine transformation [34]. The result of the sensitivity analysis showed a high dependence on the geometry and loading. An unsymmetric geometry and loading allowed to be very sensitive to all parameters of the Holzapfel model. For this reason, questions may arise concerning the accuracy of the identification of mechanical parameters in several studies. Nevertheless, it is still important to note that the choice of geometry and loading will be dependent on the adopted behavior. Therefore, this sensitivity analysis is essential to design experiments for an optimal parameter identification. Concerning the displacement field measurement, the subimages are quite large ( 128 pixels). This large area could be explained by the fact that the camera has a resolution smaller than the graphite powder size. Moreover, graphite powder is difficult to fix on mouse skin and in addition, at large scale, some graphite powder came off. Nevertheless the choice of graphite powder was performed because, unlike painting, graphite powder does not alter the sample. 8.5 Conclusion This study proposed a sensitivity analyse as an approach to design the experiment (i.e. loading and shape). This methodology allows us to determine an alternative loading which is more efficient to characterize the Holzapfel properties. The next step will consist of identifying the Holzapfel parameters. Thus, the orientation index of fibers could be deduced and compared with SHG measurements. a b c d e f g h i 20 0 ε ×× (%) -20 -40 40 20 0 ε ×× (%) -20 -40 40 20 0 ε ×× (%) -20 -40 40 20 0 ε yy (%) -20 -40 10 0 ε xy (%) -10 10 0 ε xy (%) -10 10 0 ε xy (%) -10 40 20 0 ε yy (%) -20 -40 40 20 0 ε yy (%) -20 -40 Fig. 8.6 εxx in the first line, εyy in the second and εxy in the third for an experimental loading of 10–0%, 10–10 %and 10–20 % 8 A Numerical Study of a Biaxial Sollicitation to Set-Up the Displacement Field Measurement of Ex Vivo Mouse Skin 59
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