Multiple sub-impacts phenomenon and influences on responses of elastic-plastic beam

The multiple sub-impact phenomenon, consisting of more than one short contact event, has frequently been observed in experiments and simulations. The multiple sub-impact phenomenon and its influences on impact responses lack systematic study. Hence, this paper presents a parametric analysis method, an extended hybrid, numerical-analytical model (EHNA model). The nature of multiple sub-impact responses of elastic-plastic beams struck by elastic-plastic spherical impactors is investigated parametrically. The occurrence and disappearance of multiple sub-impacts are observed. Their threshold curves are obtained and expressed analytically for low-velocity impacts. A characterization diagram is proposed to characterize the region of multiple sub-impacts in the relative stiffness ratio-effective mass ratio plane. The characterization diagram can be used to quickly predict the state of multiple sub-impacts or the state of a single impact without solving the impact responses in detail. It is validated experimentally and numerically for impacts with wide ranges of initial velocity, beam size, constraint, material property and contact type. The influences of multiple sub-impacts on impact force response, impact impulse, and energy loss are parametrically investigated. The high influence zones and several influence features are observed. The wide multiple sub-impact region proves that the multiple sub-impact phenomenon is ubiquitous. The strong influences on flexible beam impacts indicate that multiple sub-impacts cannot be neglected for structural damage and structural dynamics.