Recently, there has been an explosion of research on exciting new fashionable (so-called "smart") materials that can react to stimuli such as temperature, chemical composition, light, and magnetic field by deforming and changing their shape. They have the potential to completely revolutionize the design of a wide variety of devices ranging from human adaptive exoskeletons/prosthetics, to morphable wings of aircrafts and energy harvesting applications. The global market for such "smart" material devices is growing at a rate of approximately 10% and is one of the areas where a significant competitive advantage of the US can be maintained. However, designers of "smart" components have been stymied by the lack of well-developed simulation tools to evaluate their designs and to control the devices during use. The proposed research addresses this need by establishing a rational scientific basis for the analysis of "smart" structural components based on a novel thermodynamical framework that combines aspects of Lagrangian mechanics together with newly developed simulation techniques (which are called discrete variational integrators).
The proposed research has the potential to transform the "smart" systems design landscape by bringing scientific predictive capabilities into the hands of designers of "smart" devices, allowing them to conceive and develop innovative structures and devices for a variety of applications. The research will also revamp selected structural mechanics courses in mechanical engineering to include a rational approach to designing with these materials. The research will motivate both graduate and undergraduate students to create innovative solutions to societal challenges with these materials.
The project deals with the development of models and techniques for simulating the response of "programmable materials" , We focused on models for Ionic polymers, Shape Memory Alloys and Shape Memory Polymers. Designers of "smart components" need simple accurate models to predict or verify their response in order to design efficient systems and this is what the proposed work set out to do. Since a majority of the response is by a combination of extension, bending and twisting of wires, we focused on these first: Through this project, At a higher level, we were able to show that it is the diverse behavior of these materials can be brought into a single framework if we systematically separate the non-dissipative aspects from the dissipative aspects. When we do so, we see that the mechanism of dissipation has a huge influence on the nature of the response. In Shape Memory alloys, the dissipation is due to the movement of transformation fronts. In Ionic Gels it is the deformation induced diffusion and in the shape memory polymers it is the breaking and reforming of chains. Computationally we are able to exploit this and create a "two step" scheme were we take a purely non-dissipative "shape change step" followed by a dissipative "internal redistribution" step. By using this technique, we were able to do the following: 1. We were able to develop a new way of modeling shape memory behavior (which was called a discrete thermodynamic Preisach model) which was very accurate for both mechanical and thermal loads while at the same time amenable to obtaining data from experiments. 2. We carried out the first large deformation torsion (or twisting) tests (both loading and unloading and complex paths) on wires and show how well the model is able to simulate this. 3 We developed a new way of quantifying functional degradation of sma wires under thermomechanical loads. 4. We were able to develop models for bending of sma wires which simply and accurately simulated the entire response 5. We modeled the bending of ionic polymer beams by using a new Hybrid Finite Element Method for the deformation coupled with a finite volume method for the fluid flow. We were able to show the difference in the response between Nafion and Flemionic polymers using this method 6. We developed a new thermoinelastic model for the behavior of shape memory polymers and were able to match the response of both epoxy based polymers as well as polyurethane based polymers. 7. We also developed models for the large deformation behavior of these polymers in a three dimension setting and compared the simulations to available experiments 8. We are able to develop a new composite by combining shape memory alloys and shape memory polymers and built several morphing devices out of it
