Hybrid micro-macro-mechanical constitutive model for shape-memory alloys

摘要

A substantial reduction in the size of control actuation systems employed in today's aerospace vehicles can enhance overall vehicle performance by reducing envelope volume requirements and inert weight. Functional materials such as shape memory alloys (SMA's) offer the opportunity to create compact, solid-state actuation systems by virtue of the material's ability to convert electrical energy to thermal energy to mechanical energy within its microstructure. A hybrid micro-macro-mechanical SMA model is developed for future closed-loop actuator development studies. The constitutive model is a combination of concepts originally presented by Likhatchev for microstructural modeling and Brinson for modeling of transformation kinetics. Global strain of the heterogeneous solid or polycrystal, where the grains are assumed to be randomly oriented, was calculated by averaging the elastic, thermal, stress-induced and autoaccomodation strains of each grain over the total material volume. The introduction of a frequency distribution function in the micromechanical model provided a convenient way to quantify texture. The model was successfully tested under constant temperature conditions and constant load-low frequency cycling conditions.