Damping capacity of thermoelastic martensite in shape memory alloys

Shape memory alloys attract increasing interest as materials that can be used for passive as well as active damping applications. The passive high damping capacity finds its origin in the thermoelastic martensitic phase due to the hysteretic mobility of martensite variants or different phase interfaces. The damping capacity increases with increasing amplitude of the applied vibration. Special interest exists moreover for damping extremely large displacements. This is realised by applying the mechanical hysteresis occurring during pseudoelastic loading. This aspect is nowadays very strongly studied as a tool for protecting buildings against earthquakes in seismic active regions. Active damping can be obtained in hybrid composites by controlling the recovery stresses or strains of embedded shape memory alloy wires. This controls the internal energy of a structure which allows controlled modal modification and tuning of the dynamic properties of structural elements. But also impact damage, acoustic radiation, dynamic shape control can be actively controlled. As a consequence, improved fatigue-resistance, better performance and a longer lifetime of the structural elements can be obtained. This paper overviews the specific damping properties and damping functional behaviour of shape memory alloys, with special emphasis on NiTi. It is illustrated by actual applications and applications under development.