Finite Element Modeling of a Thermoplastic Polyurethane Ball for Rolling Seismic Isolation

ABSTRACT The Elastomeric‐Ball Pendulum (EBP) system, which consists of an elastomeric ball rolling on a spherical concrete surface, has been proposed as an isolation system for lightweight structures. Experimental tests have shown that the mechanics of such a rolling ball are remarkably complicated because the vertical load changes the shape of the ball from spherical to oval, without recovering the original spherical shape as the ball rolls. To better understand this behavior, this study performs finite element (FE) analysis of a rolling thermoplastic polyurethane (TPU) ball, particularly focusing on the rate‐dependent behavior of the elastomer. It considers a sophisticated, yet necessary, constitutive law that combines hyperelastic and viscoplastic components. The model is validated against published experimental results and is the first of its kind to capture both creep and cyclic behaviors reasonably well. Only rolling on a flat surface is considered to focus on the rolling mechanism and material deformation. The FE analyses demonstrate that it is the inner part of the ball (i.e., toward the center) that mainly contributes to the change of shape from spherical to oval, while the outer part (i.e., toward the surface) mainly contributes to energy dissipation during rolling. Additional parametric analyses are performed to examine the effect of an inner steel core on the rolling behavior. A series of simulations shows that the coefficient of rolling friction increases sublinearly with rubber thickness and vertical load, while the rolling velocity has a minor influence on the behavior of the system. The results contribute to the understanding of nonlinear phenomena in rolling isolation using elastomeric materials, offering a foundation for improving the design and efficiency of such seismic isolation systems.