Experimental study on a nonlinear vibration isolator based on a post-buckled inverted L-shaped beam

In this paper, the characteristics and the effectiveness of a nonlinear passive vibration isolator based on apost-buckled beam is investigated experimentally. The intended application is specifically isolation in thevertical direction where the isolator is required to be sufficiently stiff statically to bear the weight of theisolated mass. The isolator consists of two beams joined to form an inverted L-shape and the weight of theisolated mass is taken to act at the vertex. If the weight of isolated mass is larger than the buckling load of theL-shaped beam then the beam buckles in one of two modes, one of which is unstable. In this paper, the staticrestoring force of the unstable mode is measured and an appropriately selected coil spring is added tocounteract the negative stiffness of the beam. The resulting system presents a dramatically lower stiffness tosmall excursions about its equilibrium position in its buckled state but maintains its static load bearingcapability. Free vibration measurements are presented which show some amplitude dependency of the naturalfrequency for large amplitude motion. Low amplitude harmonic base excitation measurements are alsoconducted from which transmissibility measurements are obtained and compared with corresponding resultsfrom a Finite Element model. The fundamental resonance is about 80% lower than that achievable by acomparable linear isolator. However the potential improvement in isolation performance has not been fullyrealised in the prototype design due to the presence of higher frequency internal resonances of the isolator,mitigation of which is the focus of ongoing work