Assessment of the Mechanics of the Shoe-Turf Release Phenomenon Over a Range of Normal Loads

Abstract The goal of this study was to develop a test methodology for use in studying cleat-turf mechanical interaction that permits laboratory testing, precision-controlled inputs, variation in normal load applied to the cleat, and imaging of the cleat-turf interaction. This new test method utilized a 6 DOF force/torque and position-controlled serial robotic test device to perform compress-then-shear tests between a cleated shoe surrogate and artificial turf samples. The test method proved to be highly repeatable in displacement-controlled inputs across variations in axial load. Force response data were also repeatable, but variations in shear response were indicative of inherent variability in turf construction. Precise identification of cleat-turf release was permitted through high-speed imaging and verified to occur at the time of peak horizontal force. A strong linear relationship was found between release shear force and normal force at time of release for both posterior and lateral shear test types under the loading regime investigated (R 2  = 0.96, R 2  = 0.97). This linear regression represents a “release traction” that can be used to help better understand how turf construction relates to cleat-turf interaction mechanics, which is necessary to optimize player safety and performance.