ABSTRACT
Shape-memory polymers (SMPs) are an exciting class of materials that have the ability to store a temporary shape, possibly for long periods of time, and then recover a predetermined permanent shape when subjected to an environmental stimulus. We review the state-of-the-art with regard to the behavior of SMPs. Even though numerous environmental stimuli have recently been shown to effect shape-memory behavior, we focus on the most common driver for shape-memory behavior, i.e., temperature. After describing the basic thermomechanical behavior of SMPs, both in terms of macroscopic behavior and molecular mechanisms, we describe
CONTENTS
3.1 Introduction ..................................................................................................65 3.1.1 Brief History-Current Status .......................................................66 3.1.2 Macroscopic Response of SMPs-Thermomechanical ...............66 3.1.3 Macroscopic Response of SMPs-Environmental ...................... 69 3.1.4 Description of Mechanisms for Modeling ................................... 70
3.2 Modeling of Thermomechanical Behavior of SMPs ............................... 71 3.2.1 Backdrop for Modeling ................................................................... 71 3.2.2 Models Based on Storage Deformation ........................................72 3.2.3 Models Based on Phase Transition ................................................ 74 3.2.4 Models Based on Viscoelasticity ................................................... 82
3.3 Conclusions ................................................................................................... 87 References ............................................................................................................... 87
recent efforts to develop three-dimensional, large deformation constitutive models for SMPs. We classify the modeling approaches that have been developed and illustrate their capabilities in comparison to the thermomechanical response of various polymers during shape-memory cycles. To enable a rational engineering design using SMPs, constitutive models will ultimately have to be implemented in a nite element code. We describe one such implementation and illustrate the capabilities of such a modeling approach by simulating the behavior of a polymer sheet that folds into a cubic box during a shape-memory cycle.
