NiTi alloy wires were embedded during the infusion processing of woven carbon fibre reinforced plastic (CFRP)
composite plates with the purpose to passively increase their damping. Two types of NiTi wires, having the same
diameter of 203 μm, were considered, one superelastic at room temperature, the other one martensitic. For the first one, a
martensitic transformation was induced by applying a pre-strain of 2.5% before embedding the wires. The coexistence of
austenite and martensite should provide damping through the mobility of boundaries between the two phases. For the
second type of wires, the enhancement of damping was based on the presence of martensite.
The passive damping effect produced by the shape memory alloy (SMA) wires was evaluated from free vibration tests
on composite plates, neat or with 5% of volume fraction of SMA wires. Resonance frequency and damping ratio were
measured as a function of temperature. Improvement in damping was verified, at room temperature, for both types of
SMA wires and was observed to be dependent on vibration amplitude. For small-amplitude free vibrations, pre-strained
superelastic wires presented more interest as they provided a damping increase of around 87%. The effect however
depends on temperature.