Numerical and experimental investigation of the applicability of pellet impacts for impulse excitation

This work presents dynamic finite element simulations of various pellet impacts in order to investigate their applicability during impulse excitation in modal analysis. Compared to the classical impulse excitation with modal hammer, the approach of pellet shots provides shorter impact time and reduces the multi-hitting effect leading a wider relevant frequency range of the frequency response function (FRF). However, the estimation of the contact characteristics requires the complete understanding of the material behaviour of the investigated commercial airsoft pellets and steel bearing balls. The behaviour of the airsoft pellet shows elastic, yielding and viscous properties during the impact, whereas the deformation of the bearing ball is mostly elastic. The commercial FE software ABAQUS offers the two-layer viscoplastic model to capture the complex material behaviour of the airsoft pellet. Based on the FE simulations of both pellets an estimation is provided for the relevant frequency range, where the force spectrum is considered to be mostly constant and the FRF is proportional with the FFT of the output signal. In order to highlight the benefits and the applicability of the excitation with pellet shots experimental work has been carried out. The comparison of the measured FRFs shows that using this novel approach wide relevant frequency domain can be reached with excellent accuracy and repeatability, which could benefit in the modal analysis of structures with high natural frequencies.