Damping identification and localisation via Layer Method: Experimental application to a vehicle chassis focused on shock absorbers effects

This paper investigates the effects of the shock absorbers of a passenger body in white car on identified modal properties and damping matrices. The authors propose an experimental approach to evaluate the changes induced by localised dissipations on damping matrices and modal behaviour. The shock absorbers behave as localised viscous dampers; therefore, the global system results non-proportionally damped. The chassis dynamics is studied through experimental tests, e.g. roving hammer modal analysis. The chassis is tested in three different configurations to include or exclude the shock absorbers effects on the dynamic behaviour. A new approach to damping matrix identification is presented and applied to the chassis experimental data. The system viscous and hysteretic damping matrices are identified from the experimental data based on the inverse frequency response functions method combined with original physical and topological constraints able to describe the system mechanical properties. The effects of the suspension system on the first flexible modes are evaluated comparing the modal properties of the three experimental sets of mode shapes. A numerical method is developed to attenuate noise and to reduce the incompleteness of experimental data. Finally, the influence of localised dampers, their identification and spatial distribution are discussed.