Performance range of SMA actuator wires and SMA–FRP structure in terms of manufacturing, modeling and actuation

Abstract

In this contribution we present a comprehensive theoretical and experimental description of an active shape memory alloy (SMA) fiber reinforced composite (FRP) hybrid structure. The major influences on actuation performance arising from variations in the design and manufacturing process are discussed, utilizing a new phenomenological model to describe the actuating SMA material. The different material properties for the activated, respective the unactivated, SMA as well as the influence of different loading conditions or pre-treatment of the material are taken into account in this model. To validate our material model we performed new actuation experiments with an exemplary SMA-FRP structure, which we compared to finite element (FE) simulation results. Our FE-model is based on a material model for the actuating SMA elements derived from experiments and data on the actual microscopic geometry of the hybrid composite. Therefore it is able to predict very precisely the actuation behavior of a typical FRP structure for industrial use cases: a thin walled CFRP sheet with SMA wires attached to the top for performing a bending motion with a maximum deflection of approx. 25% of its length.

Active hybrid structures made of shape memory alloys and fiber-reinforced composites

“…For the purpose of a model-based design process for active hybrid structures, we developed a simplified phenomenological material model, based on experimentally derived stress-strain characteristics for SMA [25,38], which is qualitatively in good alignment with physically motivated microscopic models for SMA like, for example, the potential well-based models developed by Seelecke and Müller [30] and Heintze and Seelecke [31].…”

“…NiTi aus m ar Temperature-dependent actuation behavior of one-way SMA wire working against different spring stiffness [25].…”

“…This simplified material model can easily be implemented in finite element (FE) simulation [25], wherein the SMA wires are approximated with a layer of shell elements of type S4. The thickness and layer position is adjusted according to the cross section and the center of area of the modeled SMA wires.…”

“…For demonstration of load induced two-way actuation with SMA elements, a simple test structure was developed [25]. Resembling a typical aerospace or automotive application, a flat panel made out of CFRP was chosen.…”

New Developments

“…Sensing capabilities could increase the functionality of the airframe by enabling superior structure health monitoring (SHM) systems. A material integrated actuation, enabling fully controlled morphing structures, would offer completely new possibilities to optimise aerodynamics [33,34].…”