Stress and strain distribution pattern investigation in multi-layer elastic hand prosthesis, inspired by the human skin structure

One of the very important issues in designing hand prosthesis is to consider their cover or cortex. The purpose of this research is to design a cover to have a similar behavior, as much as possible, to the human natural skin, in power transmission and deformation pattern. A layer made of Lorica®, which has similar properties to natural skin, has been added to the conventional cover which composed of three layers. Using finite element analysis Software, ANSYS V.15, the new four-layered cover has been investigated on three dimensional model of the hand prosthetics with different thickness for the outer layer, and the pattern of deformation and internal stresses in the prosthesis are measured. Optimal thickness of the outermost layer is evaluated due to stress and strain distribution and their transformation to prosthesis metallic core. The relationship between the thickness of this layer and the distribution of stress and deformation of the cover is not linear and direct and the thickness of 1.5mm shows better results among the measured values in this section. In this study, the fourth layer was added to improve the frictional and elastic properties of formerly used prosthetic covers, and its effects on stress and strain distribution in the prosthesis was investigated. It is determined that due to lack of linear correlation between the thickness and stress distribution, the optimal thickness of each layer must be selected based on design limitation like the ability of embedding tactile sensors in future for the minimum thickness.