Multiple Impact Phenomenon in Impact Hammer Testing: Theoretical Analysis and Numerical Simulation

As conducting an impact hammer testing during experimental modal analysis, the multiple impact phenomenon must be avoided. It is generally recognized that the multiple impact phenomenon is induced by the tester’s improper operation and can be avoided through more careful operation. This study theoretically and numerically investigates the whole process of the dynamical interaction between the hammer tip and the impacted structure and discovers the intrinsically physical mechanism of the multiple impact phenomenon. The determination of the interacting process comes down to solve two sets of governing differential equations alternately, and the effectiveness of the theoretical analysis is validated by numerical simulations. Four dimensionless parameters governing the interacting process are recognized in the theoretical framework. The critical stiffness ratio for a given impacted location and the critical impacted location for a given stiffness ratio are analytically determined. These results can guide impact hammer testing to avoid the occurrence of multiple impact by suggesting the hammer tip and impacted locations.