Mechanical origin of shape memory performance for crosslinked epoxy networks

Abstract

The mechanical principle of microstructural change governing the shape formation and restoration process of shape memory epoxy (SME) was analyzed on a subcontinuum scale. A series of processes to program and operate the microstructure of highly crosslinked networks across the phase transition temperature range was implemented in molecular dynamics simulations. This elucidated the mechanisms by which the chemical composition of resins and crosslinkers, the degree of orientation of each chain, and the topology of the entire network characterize the shape memory behavior of the system. The strategy for analyzing the mechanical behavior of molecules by classifying them into translation, rotation, and deformation based on the classical kinematic framework was particularly effective in clarifying the structure–property relationship. The results showed that, during the shape programming process, each molecular component of the SME was rearranged to different levels depending on its stiffness, forming local residual stresses. The principle leading to shape recovery as the subsequent thermal load removes residual stress and the resulting change in the mechanical anisotropy of the entire system were also successfully comprehended.