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The application of shape memory alloys (SMA) for actuators is still limited to a couple of particular prototypes, and only a few commercial actuators are available. One of the main reasons is the lack in robustness regarding substantial fatigue and changes in boundary conditions. In order to improve the life time behavior and reduce the fatigue of SMA actuators, a self-sensing control strategy is presented. Based on resistance feedback, the heating power at full contraction is controlled in order to avoid overheating without reducing the operating voltage. This allows fast actuation without thermal overload of the SMA. The concept was proved experimentally. Life time tests show a considerable increase in life cycles and reduce of fatigue.

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Experimental determination of frequency response function of nonlinear systems is difficult when there exists more than one solution branch. Depending on the system at hand, various types of jump phenomena can be observed and in the example of the well‐known Duffing‐oscillator, it is not possible to experimentally determine the unstable solution branch if the system is excited by a harmonic force. In the present paper we investigate the Duffing‐oscillator and present a method, which allows to reformulate the equation of motion of the system with force‐excitation in the form of an equivalent self‐excited system. Considering the phase between force and response as the input variable, it is possible to evaluate the frequency of the systems vibration for any given phase shift. In the same way the corresponding response amplitude is determined. An experimental set‐up is presented, which is used to validate the performance of the method. Measurements of the backbone curve are performed and discussed on the background of theoretical predictions. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)