For actuation purposes active hybrid structures made of fiber reinforced polymers (FRP) and shape memory alloys
(SMA) enable substantial savings concerning weight, space and cost. Such structures allow realizing new functions
which are more or less impossible with commonly used systems consisting of the structure and the actuator as separated
elements, e.g. morphing winglets in aeronautics. But there are also some challenges that still need to be addressed. For
the successful application of SMA FRP composites a precise control of temperature is essential, as this is the activating
quantity to reach the required deformation of the structure without overloading the active material. However, a direct
measurement of the temperature is difficult due to the complete integration of SMA in the hybrid structure. Also the
deformation of the structure which depends on the temperature, the stiffness of the hybrid structure and external loads is
hard to determine. An opportunity for controlling the activation is provided by the special behavior of the electrical
resistance of SMA. During the phase transformation of the SMA - also causing the actuation travel - the resistance drops
with rising temperature. This behavior can be exploited for control purposes, especially as the electrical resistance can be
easily measured during the activation done by Joule heating. As shown in this contribution, theoretical modelling and
experimental tests provide a load-independent self-sensing control-concept of SMA-FRP-hybrid-structures.
Sebastian Nissle, Moritz Hübler, and Martin Gurka, "Modeling of electric resistance of shape memory alloys: self-sensing for temperature and actuation control of active hybrid composites," Proc. SPIE 9801, Industrial and Commercial Applications of Smart Structures Technologies 2016, 98010A (Presented at SPIE Smart Structures and Materials + Nondestructive Evaluation and Health Monitoring: March 21, 2016; Published: 16 April 2016); https://doi.org/10.1117/12.2219077.
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