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Development of a rubber sole with an integral cushioning system for casual sport shoes

The footwear industry has been experiencing a rapid growth with a constant demand for new and comfortable models of footwear by its consumers. In response to this challenge, a sole with innovative cushioning system, dedicated to a casual segment of sports shoes and aimed at the female audience, was designed. This work reports the shoe sole design process and the study of its behavior under the action of loads equivalent to the human walk. The initial study of the foot and its role in the biomechanics of gait allowed identifying the regions that suffer the most pressure and need more cushioning. Based on that, the selected concept uses a system whose cushioning would be provided by the compression of the sole structure on the most affected areas of the foot during gait. The work focused on the bi- and three-dimensional design of the sole and cushioning system, using 3D scanners, 3D modeling and rendering software, and finite element analysis. In terms of material selection, through the application of loads to the heel and toe sole parts, simulating the human walk, and the use of different types of natural rubber and styrene-butadiene rubber materials, the von Mises stresses and the sample surfaces displacement were analyzed so that it was possible to suggest the most adequate materials and possible design changes. Samples with three rubber mixtures were produced and evaluated through impact tests. It was possible to verify that the most suitable rubber for the shoe sole would be the one that presented low rigidity and high yield strength. Ethylene vinyl acetate was also proposed as a shoe material, taking into account its low density. From the impact tests, it was concluded that the material with a better commitment between the damping and resilience properties is a natural rubber polymer-based mixture that was selected for the industrial production.