Behavior of Thermoset Shape Memory Polymer-Based Syntactic Foam Sealant Trained by Hybrid Two-Stage Programming

Recently, a shape memory polymer-based self-healing syntactic foam was proposed and tested as a sealant for expansion joints. The key for success is to train the foam by using a two-dimensional (2D) stress condition (compression in the horizontal or traffic direction and tension in the vertical direction) at a temperature above the glass transition temperature (Tg). However, for practical applications, programming a full-size slab of sealant with a 2D stress condition and under temperature control is not a trivial task. This study demonstrated that the programming with a one-stage 2D stress condition can be replaced by a sequential two-stage one-dimensional (1D) stress condition. To further simplify the programming process, 1D tension programming was conducted at a temperature above the Tg, followed by 1D compression programming at a temperature below the Tg (cold compression). The test results show that the hybrid programming leads to similar shape memory behavior as long as the prestrain level in the two programing is similar or the prestrain absolutely predominates in one direction. Otherwise, the sealant exhibits a two-stage recovery: it recovers first in the direction with larger prestrain, followed by the direction with smaller presrtain, regardless of the programming sequence.