Composites Based on Shape Memory Materials

Abstract

Shape memory properties provide a very attractive insight into materials science, opening unexplored horizons and giving access to unconventional functions in every material class (metals, polymers, and ceramics). Since the discovery of shape memory materials (SMMs), there has been a continuous quest for ways to application of SMMs with the extraordinary properties. Two groups of materials have shown the shape memory effect: shape memory metal alloys (SMAs) and shape memory polymers (SMPs). The intermetallic alloys such as NiTi can be extremely compliant while retaining the strength of metals and can convert thermal energy to mechanical work. The unique properties of SMAs result from a reversible solid-to-solid phase transformation. Among the commercially available SMAs, NiTi alloys in the form of wires, ribbons, or particles are the most widely used because of their excellent mechanical properties and shape memory performance. Also, SMPs can rapidly change their shapes from a temporary shape to their original (or permanent) shapes under appropriate stimulus such as temperature, light, electric field, magnetic field, pH, specific ions, or enzyme. Thermally active SMP belongs to a kind of functional material that can hold a temporary deformation at a temperature below the switching temperature and recover the original shape when it is heated to a temperature above the switching temperature. The integration of SMMs into composite structures has resulted in many benefits, which include actuation, vibration control, damping, sensing, and selfhealing. The SMMs composite complexity that includes strong thermomechanical coupling, large inelastic deformations, and variable thermoelastic properties will have many applications in industry. Nonetheless, as SMMs are becoming increasingly accepted in engineering applications, a similar trend for SMM composites is expected in aerospace, automotive, and energy conversion and storage-related applications. Reinforcement of SMMs with particles and nanoparticles such as carbon nanotubes is new insight to find new extraordinary properties for SMAs.