Numerical Evaluation of Recalling Elasticity due to Surface Roughness by Finite Element Modeling of Human Skin

Abstract

Among human sensations, tactile perception has an important role in physics and in living comfortably. It is already known that surface roughness greatly affects the feel of solid objects, but the mechanics of the relationship between feeling and physics, as well as their effects, are difficult to determine. This study, aims to clarify the numerical relationship between elastic tactile perception and surface roughness of a rigid body by designing various products with surfaces comfortable to touch. The finite element method (FEM) has been adopted for this clarification, and a numerical model of human skin with 3 layers, epidermis, dermis, and subcutaneous, has been developed to discuss the mechanical effects of touch movement. This skin model is used to evaluate the distribution of skin deformations during the process of touch movement, and the analysis of the tactile perception is done by discussing the distribution change due to touching objects. The change in distribution of deformation is mainly discussed in terms of pressure under the epidermis, and various patterns of distribution are inspected by changing the diameters and pitch ratio of a uniformly spread ball used as a plain surface. By comparing the relationship between distributions of rigid and elastic surfaces, similar distributions of pressure in the skin model were observed, and the relationships of the distribution are summarized to solve the mechanics of touch feeling. In this summarization, the maximum pressure and the maximum gradient of pressure distribution are adopted as parameters for the analysis. The analysis shows that it is numerically possible to represent the elasticity recalled by the rigid surface from its relationship with the elastic surface when they have the same maximum pressure and maximum inclination of pressure. The importance of maximum inclination of pressure for touch feeling is also shown here.