Crushing of thin-walled spheres and sphere arrays

Due to its ideal material properties and very small but uniform wall thickness, ping pong balls are selected to study the plastic crushing behavior of thin-walled spheres and sphere arrays. In experiments, single spheres were compressed by point-load, rigid ball, rigid plate, rigid cap or double rigid balls. A number of bifurcation phenomena are identified and their effect on the crushing force is illustrated. It is noted that when two ping pong balls compress each other, the snap-through deformation randomly occurred in one of the balls while the other one remained undeformed or only deformed elastically. This fact allows us to conveniently employ a single ball's load-deformation relation for predicting the 1-D or 2-D array's load-deformation behavior. A very good agreement between the prediction and the experimental result is shown. If the ping pong balls are connected, the connection part, which can be simulated by a rigid cap, transforms the ball from a type I to a type II structure. Thus, when compressing a 1-D array of connected balls, the deformation will be localized in a ball until the force increases to a certain value, which crushes the next ball. Such a crushing force depends on the size of the connection part, as demonstrated in the case of compression by a rigid cap.