Switchable Shape Memory Alloys Thermal Materials

Materials and systems are being designed and developed to meet complex operational requirements while being kept lightweight, efficient, and robust. Multifunctional and thermally switchable systems are needed to respond to the operational processes of space launch and exploration, most of which are transient. Active and passive systems, as well as novel systems that combine active and passive functions, have been identified and are being developed along two lines of research investigation: switchable systems and transient heat spreading. The approach is to build thermal functionality into structural elements in order to revolutionize the way high-energy space systems are designed. The potential industrial and consumer applications are numerous. The key to proving any such application is understanding thermal performance of the total system, along with the thermal behavior of the constituent materials under relevant conditions. The goal for this project was to develop 2-way switchable thermal systems for use in systems that function in cold to hot temperature ranges using different alloy designs for SMA system concepts. In this project, Kennedy Space Center (KSC) will specifically address designs of two proof of concept SMA systems with transition temperatures in the 65-95°C range and investigate cycle fatigue and "memory loss" due to thermal cycling. Shape memory alloys applies to a group of materials that demonstrate the ability to return to some previously defined shape when subjected to the appropriate thermal procedure. Generally, these materials can be plastically deformed at some relative lower temperature, and then upon exposure to some higher temperature will return to their original shape prior to the deformation. Materials that exhibit this property are referred to as one-way shape memory; some materials also undergo shape change upon re-cooling, and are referred to as 2-way shape memory. Generally, an alloy undergoes a transformation from the austenite phase to the martensitic upon strain below the transformation temperature, which is then reversed upon heating, returning to the parent phase. The only two alloys that have achieved any level of commercial exploitation are the nickel titanium (NiTi) alloys and the copper-base alloys, particularly copper-aluminum-nickel (CuAlNi) and copper zinc aluminum (CuZnAl). In training and testing of these SMAs there are indications that they are susceptible to cycle fatigue depending upon conditions of use. In this project, two different novel designs previously developed are being enhanced and evaluated for cycle fatigue of the 2-way SMAs effects for use in intelligent thermal systems. Knowing the effective, efficient lifetime of each system, it will then be possible to design and optimize a system to a specific application in the future. More »