Session: 04-13 SS: Active Hybrid Composites

Paper Number: 171914

171914 - Integration of Shape Memory Alloy Wires in Polymer Structures and Their Applications as Strain Sensors and Actuators 

Shape memory alloys (SMA) are thermosensitive materials that returns to its original shape after deformation and subsequent heating. This effect, known as pseudoplasticity, is based on a reversible phase transformation and can be used for actuation. Actuator systems based on SMA offer many advantages compared to conventional drives and have therefore already successfully established themselves on the market in many applications. A further area of applications are novel SMA-based strain sensors that can be integrated into or applied onto elastic polymer structures for structural health monitoring or damage detection. A large number of research activities also deal with the application of SMA elements in polymer structures in general and fibre reinforced polymers (FRP) in particular.

In this paper, we present various actuator and sensor applications of SMA in polymer structures, which were produced using a wide range of processing technologies. First, investigations into the integration of SMA actuators in thermoplastic injection moulding, extrusion and thermoforming will be presented. The results show that even mechanically blocked SMA wire actuators, which are moulded at temperatures above 200°C, can subsequently achieve several million actuation cycles without significant functional and structural fatigue.

Furthermore, thermoset FRP components with integrated SMA actuators are presented. As a result, verified finite element analyses (FEA) models of the hybrid material and functional demonstrators show the suitability of the technology. For example, a structurally integrated ventilation flap for automotive applications demonstrates the performance of the integrated SMA actuators. In addition, recent experimental and numerical investigations show the integration of thin plate-shaped SMA actuator elements into a thin glass-epoxy composite substrate. 

Further work also describes the use of the high elasticity and fatigue strength of embedded SMA as a strain sensor for FRP. The aim is to show that such sensors offer many advantages compared to conventional strain sensors made of CuNiMn, such as higher elasticity, higher fatigue strength, lower zero-point drift and higher sensitivity. To ensure accurate strain measurement and prevent damage to the sensor, it is recommendable to embed the strain sensors in the FRP structure. The strain-dependent change in resistance of the integrated SMA sensor can be correlated with the applied strain and the resulting gauge factor can be determined. The gauge factor of SMA sensors increases with strain and reaches a peak value during the stress-induced martensitic transformation, while the gauge factor of conventional strain sensors remains almost constant at a lower level.

Finally, planned approaches for the use of SMA in FRP to produce graded transition structures are presented. The aim here is to use partially exposed and pretrained SMA elements to set up the fibres of the FRP in order to achieve a better transition, e.g. to injection-moulded components.      

Presenting Author: Kenny Pagel Fraunhofer-Institute for Machine Tools and Forming Technology (IWU)

Presenting Author Biography: ..