Three-dimensional finite element modeling of the shoe sole to investigate the impact of various geometries on foot heel stresses and energy absorption

The force applied to the foot is noticeable, and the foot is subjected to the limits of repetitive, prolonged muscular loading on a bone in some activities like sports that are not as heavily loaded in typical activities such as walking. Thus, it is mandatory that optimal footwear be designed with the lowest stress acting on the foot and maximum energy absorbed by the soles. In this study, the effects of some geometric features on the energy absorption of shoe soles were investigated using a finite element model (FEM). Auxetic structures showed some beneficial properties, including improved energy absorption. In addition, different types of holes in the midsoles of shoes were considered to reduce their weight. Therefore, this study investigated the effect of geometry by comparing auxetic shoes with re-entrant structures, shoes with weight-reducing holes with the same geometry as auxetic shoes, auxetic shoes with an auxetic structure similar to Nike RN 2017 shoes in the outsole, and shoes without auxetic structures and weight-reducing holes. A 3D finite element modeling was used to evaluate the effect of geometry on stress, displacement, and energy absorption. It was found that the strain energy of soles with re-entrant auxetic structures and with an auxetic structure in the outsole was 153 and 7% higher, respectively than that of plain soles. Similarly, adding weight-reducing holes increased the strain energy of the sole by almost 157%.