The interdependence of functional properties of a football boot outsole during the shape optimisation process

The aim of this study was to investigate the relationship and interdependence of functional properties of the football boot outsole during the shape optimisation process. Sensitivity-based shape optimisation technique was applied to a football boot outsole to modify its thickness to have various functional properties. Three functional properties of the outsole, which are the midfoot and forefoot bending stiffness and torsional stiffness, were investigated. The midfoot and forefoot bending stiffness were measured via a three-point bending test. Torsional stiffness was measured via a bespoken mechanical test. The functional properties were evaluated by finite element models, representing the developed mechanical tests. Through the optimisation tasks, it was explored how much each functional property could be changed individually and also while minimising the influence of the other two functional properties. With the modification of the regions of the outsole to optimise for various individual target functional property values, the changes in the other two functional properties were observed. Lastly, the optimised outsoles from the finite element models were 3D printed and tested to determine the accuracy of the process. Within a permitted thickness limit, modifying the region associated with the torsional stiffness measurement influenced the other two functional properties the most. Especially, the midfoot bending stiffness was influenced more than the forefoot bending stiffness. On the other hand, the areas involved in the midfoot and forefoot bending stiffness measurements were independent of each other. The conclusions drawn in this study are limited to the particular outsole design, single outsole component and mechanical test utilised.