Vibration frequency control of a polymer beam using embedded shape-memory-alloy fibres

The possibility to actively change the natural vibration frequencies of a composite beam by. electrically activating a series of embedded shape-memory-alloy fibres is investigated. A model system composed of an epoxy matrix with prestrained shape-memory-ahoy fibres is used. The natural frequencies of vibration of the composite are measured in a clamped beam configuration. When electrically heated, the fibres undergo a reverse martensite to austenite transformation. Since this transformation is restrained by the constraints of both the matrix and the clamping device, a recovery force is generated. This force produces an increase of the natural frequency of vibration of the whole composite beam. Vibration frequency changes of more than 50% are obtained. The glass-to-rubber transition of the matrix affects the reversibility of the effect. The role of the matrix thermal expansion is discussed.