Vibrational properties of adaptive polymer matrix composites with embedded shape-memory alloy wires

Incorporating pre-strained shape memory alloy (SMA) wires into a polymer matrix allows the development of new "smart" materials, which can change their vibration frequency in a reversible way with temperature changes. During heating, the pre-strained martensitic wires can not recover their original shape during the reverse transformation to the austenitic phase and act against the stiffness of the matrix. As a result, transformation recovery stresses are generated in the composite leading to a shift in the resonance vibration frequency. A series of composites have been fabricated using thin NiTiCu wires embedded in a hard epoxy matrix reinforced with Kevlar fibres. It was found that the stress generated in the "activated" composite results in a frequency shift, which increases with the volume fraction of the embedded SMA wires and decreases with increasing composite thickness. It was also observed that the frequency shift had a linear dependence with stress for all tested samples regardless whether the stress was induced by phase transformation or by straining the specimen at room temperature. This study was made in the frame of the ADAPT Brite/EuRam project.