Experimental studying multi-impact phenomena exhibited during the collision of a sphere onto a steel beam

Abstract

The impact of sphere against the beam is one of the basic impact problems in flexible mechanical dynamics. A flexible steel beam supported at the two ends struck by a steel sphere was tested in this article. Multiple sub-impacts were observed during the falling impact process of the steel sphere. The test contact-impact durations of the sub-impacts were compared with that of the theoretic results derived from the Hertz contact law. It is confirmed that the Hertz contact law is still suitable to estimate the impact-contact duration of the first sub-impact. The difference between the test impact-contact durations of the subsequent sub-impacts and that of the theoretic results was explained theoretically by a revised impact theory in consideration of beam's vibration. The occurrence reason of the sub-impact was systematically discussed. It is concluded in this investigation that the sub-impacts are dominated by local contact-impact deformation, but influenced obviously by the global vibration of the flexible structure. When the sub-impacts occur, the coefficient of restitution shows strong uncertainty.