Thermoviscoplastic Modeling and Testing of Shape Memory Polymer Based Self-Healing Syntactic Foam Programmed at Glassy Temperature

Abstract

Traditionally, programming of shape memory polymer (SMP) material requires initial heating above the glass transition temperature (Tg), subsequent cooling below Tg and removal of the applied load. Therefore, the shape fixity process is inconvenient for some applications. Most recently, a new and effective approach, which programs glass transition activated SMPs directly at temperatures well below Tg,was introduced by Li and Xu [2011, “Thermomechanical Behavior of Shape Memory Polymer Programmed at Glassy Temperature: Testing and Constitutive Modeling,” J. Mech. Phys. Solids, 59(6), pp. 1231–1250. The 1D compression programming below Tg and free shape recovery were extensively investigated both experimentally and analytically. The current work extends this study into a shape memory polymer based self-healing syntactic foam, which was found to be capable of self-sealing structural scale damage repeatedly, efficiently, and almost autonomously [Li and John, 2008, “A Self-Healing Smart Syntactic Foam Under Multiple Impacts,” Compos. Sci. Technol., 68(15–16), pp. 3337–3343.]. A structural-relaxation constitutive model featuring damage-allowable thermoviscoplasticity was then developed to predict the nonlinear shape memory behavior of the SMP based syntactic foam programmed at glassy temperatures. After validated by both 1D (compression) and 2D (compression in longitudinal direction and tension in transverse direction) tests, the constitutive model was used to evaluate the effects of several design parameters on the thermomechanical behavior of the SMP based syntactic foam. It is concluded that the model is a useful tool for designing and training this novel self-healing composite.

Recent progress in shape memory polymer: New behavior, enabling materials, and mechanistic understanding

“…For example, when both time-temperature dependent structural relaxation (or physical aging) and stress relaxation are were considered, Choi et al [265] showed that the initial shape recover speed can be improved. Li and co-workers [266] also used the thermoviscoealstic model to investigate a SMP based syntactic form. It is known that water (or solution) can be used as a means for shape memory effect [52,267], because small molecules, such as water, can serve as plasticizers to decrease the glass transition temperature, or effectively increase the relaxation time, effects included in models by Xiao and Nguyen [268] and Lu and coworkers [269,270].…”

Temperature and rate dependent thermomechanical modeling of shape memory polymers with physics based phase evolution law

“…It is noted that programming does not necessarily need the temperature event. Programming can also be conducted at glassy state, which is termed as cold-programming, as long as the SMP can be stressed to beyond yielding (Li, 2014;Li and Zhang, 2013;Li and Shojaei, 2012;Li and Xu, 2011;Xu and Li, 2011). The recovery process, depending on the application where the recovery strain or stress is important, can be either under free or constrained boundary conditions, respectively.…”

Strength Analysis of Syntactic Foams Using a Three-Dimensional Continuum Damage Finite Element Model

“…As an excellent core material for sandwich structures, the com pressive and flexural behaviors of syntactic foams have received wide attentions [2,4,8,[18][19][20][21][22][23][24][25][26]. Similar to other porous materials, syntactic foams show a typical stress-strain behavior with three regions under compression, including elastic deformation region, plateau region, and consolidation region.…”