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Experimental Analysis of High Temperature Shape Memory Polymers for Deployable Structures

ElMaoud, Mohamad Youssef
A Master of Science thesis in Mechanical Engineering by Mohamad Youssef ElMaoud entitled, “Experimental Analysis of High Temperature Shape Memory Polymers for Deployable Structures”, submitted in June 2019. Thesis advisor is Dr. Wael Abuzaid and thesis co-advisor is Dr. Maen Alkhader. Soft and hard copy available.
Shape Memory Polymers (SMP) continue to capture interest of the aerospace industry due to their unique properties. Compared to shape memory alloys, this class of smart materials is lighter in weight and can undergo significantly larger recoverable deformations. However, the recovery stresses, and therefore the loads that can be supported, are inferior compared to shape memory alloys. This limitation has triggered efforts to develop Shape Memory Polymer Composites (SMPC), using SMP epoxy resins, with the ability to overcome the aforementioned drawback. However, the focus has been on SMPs with low transformation temperatures below 100°C. On the other hand, certain aerospace applications require shape memory polymers with higher transformation temperatures to prevent undesirable actuation upon heat exposure. Moreover, and despite significant work on characterizing mechanical and recovery properties of shape memory polymers, the literature lack full field characterization of recovery properties, in particular at elevated temperatures. In this work, a high temperature thermoset epoxy SMP (Tg ~ 130°C), named EPON SMP, is thoroughly investigated. The study provides comprehensive experimental analysis of the mechanical and shape memory properties of the aforementioned high temperature epoxy SMP. In addition, this study uses a full-field characterization technique, Digital Image Correlation (DIC), to provide further insight on localization, heterogeneity and local recovery of shape memory strains. Furthermore, the study evaluates the recovery properties of SMP samples programmed at different loading conditions (i.e. bending, tensile) and proposes shape-recovery evaluation methods that can be later implemented on other SMPs. The EPON SMP samples were successfully manufactured and evaluated in this work. Stress free shape recovery was observed for SMP samples programmed at different loading conditions (i.e. bending, tensile). Moreover, the recovery rate was found to be dependent on programmed strain level and recovery temperature. Furthermore, the SMP displayed less shape recovery while under stress. Degradation in the SMP’s ductility was observed at elevated temperatures. In addition, the effects of thermal stresses and strains were quantified and observed to be highly significant in the SMP programming and shape recovery processes.
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