Part I. Thermomechanical characteristics of shape memory alloys

Abstract

Shape memory alloys (SMAs) are a group of alloys that exhibit a phenomenon known as the shape memory effect, (SME). This effect gives the alloys the ability to “recover” their original shape by heating above a certain transition temperature. There is also a large recovery strain, of up to 8%, associated with the transition. Because of this unique property, a large research effort is currently being undertaken, directed towards the use of SMAs in the actuation of smart structures for shape control, vibration control and for damage mitigation. SMAs also have a very high damping capacity due to a superelastic effect. This property of SMAs is extremely useful in vibration damping as well as reducing impact damage in structures. As such there has been much interest in using SMA-composites in structures. With the possibility of using SMA-composites in real structures such as in aviation, high speed transport industry and the automotive industry, there is increasing demands on knowing how the composites will react under everyday conditions. This paper details an investigation into the thermomechanical behaviour of SMA wires, looking at the recovery stresses produced and the stress and strain behaviour with respect to temperature, as well as changes in resistance of the wires with pre-strain.