KSGC Fellowship for Fulcher: Mechanical Characterization of Shape Memory Polymers for Reconfigureable Aerospace Structures

Shape memory polymers (SMPs) have been increasingly used on air and space vehicles (personal and commercial air vehicles, the interplanetary habitats, the International Space Station, unmanned air vehicles, etc.) to yield reconfigurable structures (morphing structures). However, the success of morphing air vehicles is cunently limited by the material systems that can provide both rapid reconfiguration and long-term durability. To date, shape memory polymers have not been fully tested to work in relevant environments (variable activation temperature, fuel and water swell, UV radiation, etc.) required for NASA missions. Failure of polymer materials in aggressive environments will have a direct impact on the reconfigurable ability of the aircrafts and fleet readiness for aerospace missions. It is thus critical to examine the shape recovery ability and mechanical properties on of SMPs conditioned at relevant service environments so that the true reconfigurable ability of the SMPs can be predicted. The present project is to characterize the shape recovery ability and mechanical properties of the SMPs prepared in simulated service environments designed to be ret1ective of anticipated performance requirements. The epoxy-based SMPs are conditioned by: (1) exposure to UV radiation for 125 cycles, (2) immersion in jet-oil at ambient temperature, (3) immersion in jet-oil at 49°C, and (4) immersion in water at 49°C. Novel high-temperahu'e indentation test will be used for in situ measurements of shape recovery ability and mechanical properties (temperature/time/rate dependent) of conditioned SNIPs. The high-temperature indentation test is particularly useful for assessing the complex, multiaxial deformation and tor examining the spatial dependent deformation as a result of environmental conditioning. The "hold-at-the-peak" method will be used to measure the elastic properties and the "constant-displacement-rate" method used to measure the viscous propeliies of the environmentally conditioned SI\tlPs. The main objective of the project is to access the shape recovery ability and mechanical properties (temperature/time/rate dependent) of SMPs conditioned at anticipated service environments. The project supports NASA's Earth Science Enterprise by directly addressing requirements for reliable and durable precise deployment for aerospace/space structures. This study will provide fundamental understanding on the functionality of shape memory polymers in actual operating conditions. The outcomes of this study will help the design and development of shape memory polymers for reconfigurable air vehicles and other NASA platforms. In addition, this project helps to build the tllture workforce vital to the NASA missions and subsequently contribute to the development of the Nation's science, technology, engineering, and mathematics (STEM) workforce of the future by attracting and training graduate and undergraduate students in aerospace discipline. This project further helps to strengthen our collaboration with NASA-Glenn Research Center - Polymer Branch, a world leader in developing advanced polymers and composites for aerospace and space applications.