The nonlinear finite element analysis and plantar pressure measurement for various shoe soles in heel region

The most influential factor contributing to foot and shoe comfort is underfoot cushioning. The shock absorbing ability of footwear in the heel area is of particular importance in reducing the impact load during athletic activities and in therapeutic footwear prescribed for heel pain. Furthermore, foot care for foot problem patients is an important part of treatment and educational programs. Therefore, a well-designed sport shoe which can provide comfort and protection is essential. In order to design a functional shoe, biomechanics and other new technologies should be considered, and the design process should be examined in the biomechanics laboratory over and over. The design process requires too much time and effort since the entire experimental and test work can only be done after the prototype is manufactured. Therefore, this study tried to introduce the Finite Element Method (FEM) into the shoe design process by building a three-dimensional FE model with various shoe soles and loading conditions. The material properties of shoe materials were tested using an Instron Testing Machine. An in-shoe pressure insole was used to measure the plantar pressure in different ambulation conditions with various shoe constructions. The subject for this study was a healthy young male without any foot problem. The average plantar pressures obtained from approximately 50 steps in the heel region for each of the various conditions were collected. The results showed that the mean peak plantar pressure of the running situation was significantly higher than that of the walking situation as predicted, and that the insole could provide better cushioning compared to the other shoe constructions. The stress strain relationship for shoe materials was approximated better by a second-order nonlinear curve according to the Instron test. The results of the finite element method suggested that only the second-order nonlinear stress strain curve could correctly describe the shoe material, which also confirmed a potential valuable role for FEM in designing functional shoes.