Development of Mechanical Analysis System for Facial-Expression Wrinkling by the Finite Element Method

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This paper presents a method of finite element analysis for finite deformation of layered skin and under-skin tissues applicable to facial expression. The hyperelastic constitutive equation for skin and under-skin tissues are identified from experimental work in vitro by using strain-energy function. Green strain for finite deformation and the hyperelastic constitutive equation with incompresibility are linearlized in incremental form and the governing matrix equation are solved on each loading step. Some tensile tests on layered skin and under-skin tiessues with a hole,and indentation tests on similar specimens, have been carried out by two-axial tensile-test apparatus, within a vessel fulfilled by physiological salt water and compared with calculation results. It was shown that both results are well coincident with each other.Analysis and Experiments on forehead wrinkling have been carried out by using the finite element method.Wrinkling analysis, in which hyperelastic and large deformation formulations for skin structure are incrementally solved as buckling and post buckling problems,has been developed based on the finite element method. Physical nature of skin-structure,facial configuration and in plane distorsion of forehead skin by facial expression are measured in vivo state and used as data for numerical calculations. The calculation results for wrinkling are compared with experimental results on actual human and satisfactory coincidences between them are confirmed. Some kinds of in vitro wrinkling tests for rabbit skin structure are also examined and similar results to the above is obtained.