Using a R-Phase SMA Methodology to Design an Energy Harvesting Unit With Tight Temperature Hysteresis

Shape memory alloys (SMA) are smart materials with the ability to remember a previous imprinted shape after plastic deformation. The shape memory actuator effect is induced by thermal energy. Its bases on crystalline transformation of NiTi-alloys from the austenitic B2 to the martensitic B19′ phase. Usually, SMA actuators show a large temperature hysteresis with high strokes and loads. A lot of technical applications are realizable with SMA-actuators, for example in automotive sector. Under special conditions an additional phase, the R-phase occurs in SMA. This transformation from the austenitic B2 phase to the R-phase is characterized by a very small temperature hysteresis. Compared to conventional transformation characteristic of B2 ⇒ B19′, the R-phase transformation has small stroke and load. Because of this the R-Phase transformation qualifies for temperature sensitive and autarkical applications in air-conditioning or heating systems. Today’s problem for engineers designing R-phase actuators is that a lot of rules and parameters need to be considered. This paper presents a methodology, which can be used as a guideline to support engineers designing R-phase actuators. The whole process from defining requirements to prototyping will be discussed for the development of an energy harvesting actuator, which uses a low thermal energy potential. This paper contribution is to fill this gap in product development methodologies for shape memory actuators.