Shape memory behavior of cold-programmed carbon fiber reinforced CNT/epoxy composites

Abstract

Conventional shape memory programming involves, heating the material above the glass transition temperature (Tg), deforming to the desired shape, cooling below Tg and unloading to fix the temporary shape. However, for applications in large scale structures (e.g. deployable space structures), this process of deforming at high temperatures becomes a time, labor and energy expensive process. The reversible plasticity shape memory (RPSM) effect is an alternate programming approach wherein the material is plastically deformed (cold programmed) to a temporary shape at temperatures well below the transition temperature, preferably at room temperature. In this paper, the shape memory behavior of cold-programmed carbon-fiber reinforced carbon-nanotube (CNT)/epoxy laminates is investigated. The addition of carbon-fiber in a cold-programmable epoxy matrix resulted in significant changes in the glass-transition temperature and subsequently in the cold-programmability of the composites. So, in order to realize RPSM effect at room temperature, trials were made to optimize the glass transition region of the composites by varying the material constituents. Specimens of different laminate configurations with/without CNT reinforcement were fabricated to study the shape-memory behavior under flexure. The addition of 1 wt% CNT resulted in a slight increase in Tg but had no effect on the cold-programmability of the composites. Results reveal that all specimens show 100% shape-recovery. The laminate configuration had a considerable effect on the shape-fixity since the initial elastic recovery after unloading is dominated by the fiber reinforcement. CNT addition resulted in an improvement or no effect in shape-fixity and mechanical properties depending on the laminate configuration.