Abstract:

：The sub-impacts are peculiar characteristic of impacts involving flexible structure. The contact time regularity and main influencing factors of the sub-impacts of a simply supported beam struck by a steel sphere are studied by the Hertz impact theory and the dynamic substructure method, and tested by a set of sub-impact experimental platform designed by ourselves. The sub-impact phenomenon is observed through the experimental tests and numerical simulations. The results demonstrate that the dynamic substructure method is an effective numerical tool to analyze elastic-plastic sub-impact behavior of simply supported beam struck by steel sphere. Research found that impact-contact time of the first sub-impact is coinciding well with the Hertz contact time in low velocity impact. This means that the first sub-impact is dominated by local contact deformation, and its mechanism can be explained by the Hertz impact theory. As the sub-impacts occur, the ratios of maximum amplitudes of the first-, second-and third-order vibrations to the maximum amplitudes of the beam vibrations and the phase angle of the first-order vibration will change obviously. A further study showed that the occurrence conditions of the sub-impacts are connected with the ratio of the sphere mass to the equivalent mass of the simply supported beam, initial impact velocity and impact position. It is also found that the occurrence conditions of the sub-impacts can be represented by a mass ratio threshold, and the sub-impact will occur as long as the mass ratio threshold is satisfied.

Key words: dynamic substructure method, experiment, Hertz impact theory, impact-contact time, sub-impact, beam