Coupled Finite element simulation of SMA-sheet for morphing applications

Abstract

In recent years, Shape Memory Alloys (SMA) have become increasingly available as sheet stock, offering a promising solution for morphing applications of large-scale aircraft structures. However, the utilization of SMA sheets presents several challenges compared to traditional SMA wires, which are commonly used in morphing structures concepts. While SMA wires are easy to handle and calculate, they often lack the necessary force to achieve significant deformations in stiff structures. In contrast, sheet SMA offers a more powerful alternative, but its deformation behavior and activation methods require further understanding. One of the primary challenges with using sheet SMA is the complex deformation behavior as well as nonhomogeneous strains and stresses within the sheet during the shape-memory effect (SME). With regards to SMA wires, these effects are well understood and activation through electrical heating is commonly used but can’t be transferred to sheet SMA. Non-uniform heating through Joule heating influences the transformation behavior in an unknown way. To address these challenges, coupled finite element (FE) methods to simulate the deformation behavior of sheet SMA in stiff morphing structures were used. By combining static structural simulations with thermo-electric simulations, non-uniform heating through electric heating was taken into consideration and its effects could be studied. A 3D material model for the SME developed by Auricchio was used. The simulation involved placing two identical SMA sheets on each side of an arbitrary flat carbon fiber reinforced plastic (CFRP) plate. Both sheets were prestrained and then bonded to the plate in order to use the one-way-effect. One sheet was heated and thus contracted due to the SME, while the other remained at room temperature. Therefore, a bending of the structure is achieved. The simulation results showed that significant deformations can be achieved, even with stiff structures. In the evaluation of the results, emphasize is put on stresses and strains within the bonding of the SMA sheets to the CFRP plate in order to gain requirements for later bonding methods. Elastic and transformation strains within the SMA sheets are analyzed to gain an understanding of the SMA material behavior. In conclusion, this presentation provides a first look into the possibilities and limitations of using sheet SMA for large-scale morphing applications. The research highlights the possibilities of using sheet SMA as well as the need for further investigation to overcome current challenges and unlock the full potential of this SMA sheets. A further outlook is given for the necessary steps until the simulated structure can be realized.