抄録
The combined contraction of about thirty kinds of facial muscles induces numerous types of facial expression and wrinkling. It induces permanent wrinkling in the human face due to aging and induces serious problems to the human face from the viewpoint of beauty science. Lanir and Fung (1993, 1974) studied a constitutive model of rabbit skin by in vitro experiments using cut-out speciments, and the pipette suction method (Sato 1997) has been applied to obtain the uniaxial load-displacement curves for blood vessels of living humans. There has been no method for obtaining multi-axial load-displacement curves for skin in living humans, however. This paper presents the design and development of a convenient automatic loading and sensing system for obtaining in vivo multi-axial load-displacement curves for the facial skin of a living human. The basic concept of the system is that since there is no edge in the facial skin of living humans, an axial end of the follow cylinder, attached to the sensor subsystem, is pressed on the skin surface. Since it generates a disc-like subregion of skin, fixed at the circular boundary, it is used as the test region. The end of the loading bar is pasted on a point near the center of the disc skin surface, and force and displacement are applied on it by moving the bar in the vertical and rotational directions. Once the load-displacement curves are obtained through a series of experiments for various directions (x-x, y-y, x-y, ...), then by combining the experimental load-displacement curves with those of FEM computer modeling, one can determine the constitutive parameters in the multiaxial stress-strain relations of facial skin, using the least squares method, so that the gap between the experimental and the calculated curves can be minimized by varying the physical parameters in the constitutive model. The results for identification were compared with those obtained by experiment for various directions, and those obtained from FEM simulation coincided well with those obtained by experiment in every direction. After the constitutive parameters were identified, another type of experiment with a different loading condition was carried out and compared with results obtained by calculations using identified material parameters, in order to verify the applicability of the method developed. Satisfactory coincidence between them was obtained.
