Master of Science in Mechanical Engineering (MSME)
Shape memory polymers are smart materials that can be trained to hold a temporary shape through programming and regain their original shape upon heating. Since there discovery in the 1960s, much research has been devoted to the study of these polymers. Of particular interest in recent years is the study of self-healing shape memory polymers. In a previous study, it has been shown that in order for efficient healing to take place in self-healing shape memory polymers, confinement during healing is essential. Moreover, a two-step close-then-heal (CTH) approach to healing was suggested. It was shown that use of this CTH method on a shape memory particulate composite provided both structural (macro) and microscopic healing of the material. The present study aimed to further investigate the influence on confinement levels and local heating on healing efficiencies of a polystyrene based shape memory polymer with 6% by volume of thermoplastic particle additives (copolyester). After fabrication of the composite, the glass transition temperature was determined by DSC analysis of the material. Cylindrical specimens measuring 120 mm long and with a 10 mm diameter were used for testing. Each specimen underwent thermomechanical programming to a pre-strain level of 10 %. After programming each specimen then underwent a three-point flexural test to complete failure. The broken specimens were then healed at varying levels of confinement and at varying healing stresses. In this study three levels of confinement and three healing stresses were investigated: 50 %, 75 %, 100 % and 0 MPa, 7 MPa, and 12 MPa respectively. At least two specimens were used for each test. After healing the specimens again underwent a three-point flexural test to complete failure. Comparison of the post-programming ultimate strength to the post-healing ultimate strength provided a means of calculating the healing efficiency of the material under each testing condition. It was shown that as the level of confinement increased, so did the healing efficiency of the material. This was attributed mostly to the higher recovery stress produced by more activation of the polymer chains as more of the material is confined and heated. Also, in the case of 75 and 100 % confinement, the healing efficiency showed a steady increase as the healing stress applied increased. However, this trend was not seen in the case of 50 % confinement. The maximum average healing efficiency seen was 91.02 % and was obtained through healing at the maximum confinement level (100 %) and the maximum applied healing stress (12 MPa).
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Champagne, Jonah, "Effects of partial confinement and local heating on healing efficiencies of self-healing particulate composites" (2013). LSU Master's Theses. 3722.