Adaptive composites with embedded shape memory alloys

Shape memory alloys (SMA) offer the possibility of developing a new type of composites with embedded SMA-wires (SMA-composites) whose properties may be actively changed in response to environmental disturbances. Adaptive composite materials were fabricated by integrating pre-strained thin SMA wires as actuating elements in polymer matrix composites. Hybrid composite samples based on two types of wires were investigated : either containing NiTiCu wires in martensitic phase or NiTi wires in R-phase at room temperature. When electrically heated the SMA wires undergo a phase transformation and try to recover their shape. A stiff matrix or external clamping restrains the shape recovery related to the reversible phase transformation in the alloys and as a consequence a force is generated. This force is the origin of a change in the natural vibration frequency of the composite sample. The influence of the type of wire, as well as of the volume fraction of wires on the magnitude of the recovery force and resonance peak shift is discussed.