Finite element modeling of oblique impacts of softballs

Abstract This study involved a finite element (FE) analysis of softballs for sliding and gripping oblique impacts across a range of angles and velocities. A temporal friction model was implemented that incorporated independently measured static and dynamic coefficients of friction. Normal impacts were used to calibrate material parameters to match ball stiffness and coefficient of restitution within 4% of experimental results, while oblique impacts were used to validate the friction model. The FE results were evaluated through comparisons with experimentally measured angular velocities, linear and rotational energy, and normal and tangential impact forces. Ball inhomogeneity was found to be important, where the model’s angular velocity was 13% and 3% higher than experiment for a homogeneous and inhomogeneous ball, respectively. Compared with constant-friction models, the temporal friction model reduced the mean normalized root-mean-square error in predicted angular velocity by 29% across gripping and sliding impacts and for the first time described both sliding and gripping behavior. Normal and tangential impact forces were within 2.5% and 6.1% of experimental measurements. The FE softball model demonstrated good agreement with experimental data, showing that ball mass distribution and temporal friction are important to describe shear deformation under oblique impacts.