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.
In this contribution we present a new method as a “basic toolbox” for proper design of active composite structures. The characterization of the complete integrated active component is described, including the properties of the hosting composite material, the proper choice and characterization of the active material which is to be integrated and the interaction of both. The finite element model which was used to design the active component is presented. In order to improve prediction accuracy and functionality of this phenomenological modeling approach the behavior of the integrated active material, namely Shape Memory Alloy (SMA), is analyzed separately. New opportunities for additional functionalities are investigated: Two-way actuation due to the stiffness of the hosting composite structure is investigated as well as the possibility to introduce different maximum strain for actuation due to different pre-strains in the actuating material. An application-oriented finite element model able to predict the structure shape in hot and cold states enables more complex designs and demonstrates the potential of this new technology for various applications.
In this publication, major challenges occurring during integration of active elements made from shape memory alloys in fiber reinforced plastics are discussed. Tightly focused experimental tests with a properly chosen setup enable spatially resolved stress and temperature measurement, revealing important material characteristics which have to be considered for the design of integrated active elements. The detwinning process of the martensite during elongation of the shape memory alloy elements shows a nucleation, leading to critical inhomogeneous strain distribution. By investigating the strain rate-dependent behavior the nucleation mechanism is revealed. The measured local strain and actuation behavior of the active elements and its influence on the performance of hybrid structures is discussed. Also a clamped heating process is investigated to show how stress redistribution affects the processing of hybrid structures during a hot curing process.
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