Vibration isolation and design of automotive test benches

The design of two automotive test benches for fatigue and comfort assessment of cars is illustrated. The Vibration isolation of such test benches, designed to operate under arbitrary load histories in the frequency range 0-200 Hz, has been obtained with a fibre-reinforced concrete mass equipped with a dual suspension system. Because the imposed load histories are arbitrary, the eventuality that the resilient isolation mass of the bench may undergo resonant condition under harmonic excitation must be duly taken into account to exclude any fatigue damage under such extreme conditions. For this reason the research involved both the theoretical definition of the suspension system and the study of optimum concrete mixtures. Amongst the mixes considered, the two best, with polypropylene and steel fibre reinforcement respectively, were selected for the fashioning of two model benches, each of revealed very satisfactory behaviour when subsequently tested for fatigue under resonant conditions. The experimental behaviour of the real full-scale bench, constructed according to the guidelines stemming from the research, fully complies with the theoretical predictions, substantiating the methodological approach.