Oehler, Stephen Daniel (2012-08). Developing Methods For Designing Shape Memory Alloy Actuated Morphing Aerostructures. Master's Thesis.
The past twenty years have seen the successful characterization and computational modeling efforts by the smart materials community to better understand the Shape Memory Alloy (SMA). Commercially available numerical analysis tools, coupled with powerful constitutive models, have been shown to be highly accurate for predicting the response of these materials when subjected to predetermined loading conditions. This thesis acknowledges the development of such an established analysis framework and proposes an expanded design framework that is capable of accounting for the complex coupling behavior between SMA components and the surrounding assembly or system. In order to capture these effects, additional analysis tools are implemented in addition to the standard use of the non-linear finite element analysis (FEA) solver and a full, robust SMA constitutive model coded as a custom user-defined material subroutine (UMAT). These additional tools include a computational fluid dynamics (CFD) solver, a cosimulation module that allows separate FEA and CFD solvers to iteratively analyze fluid-structure interaction (FSI) and conjugate heat transfer (CHT) problems, and the addition of the latent heat term to the heat equations in the UMAT to fully account for transient thermomechanical coupling. Procedures for optimizing SMA component and assembly designs through iterative analysis are also introduced at the highest level. These techniques are implemented using commercially available simulation process management and scripting tools. The expanded framework is demonstrated on example engineering problems that are motivated by real morphing structure applications, namely the Boeing Variable Geometry Chevron (VGC) and the NASA Shape Memory Alloy Hybrid Composite (SMAHC) chevron. Three different studies are conducted on these applications, focusing on component-, assembly-, and system-level analysis, each of which may necessitate accounting for certain coupling interactions between thermal, mechanical, and fluid fields. Output analysis data from each of the three models are validated against experimental data, where available. It is shown that the expanded design framework can account for the additional coupling effects at each analysis level, while providing an efficient and accurate alternative to the cost- and time-expensive legacy design-build-test methods that are still used today to engineer SMA actuated morphing aerostructures.