Doctor of Philosophy (PhD)
This study explored the development of a new self-healing Polystyrene Shape Memory Polymer (PSMP) based syntactic foam for service life extension in structural polymeric composites. The objective was to self-heal structural-length scale damage in an autonomous, efficient, timely and repeatable manner at the molecular-length scale. Self-healing is achieved through a novel two step close-then-heal (CTH) self-healing scheme, designed to mimic the natural biological process of wound healing in humans. A new methodology to fabricate three-dimensional (3-D) fiber reinforced shape memory polymer syntactic foam for structural applications was developed. The effect of impact energy on the ability for the 3-D fiber reinforced PSMP syntactic foam (PSMP-SF) panels to seal cracks and mitigate impact was investigated in terms of the number of impacts to complete perforation. It was found that by restoring surface dents and closing internal crack, perforation was delayed (from 9 impacts to 16 impacts at 32 J impact energy) and (from 5 impacts to 7 impacts at 42 J impact energy). A new self-healing particulate composite was developed by incorporating co-polyester thermoplastic particles (6% by volume) within the PSMP matrix. The self-healing behavior of the composite was studied on single edge notched bend (SENB) specimens through three-point bending tests. Miscibility between the PSMP and the CP was validated through differential scanning calorimetric (DSC) analysis. It was found that the composite can heal structural-length scale damage at the molecular level in 20 minutes at 150 °C. Measured in terms of fracture load, a repeatable healing efficiency of 65% was obtained. The effect of thermoplastic content on self-healing efficiency and fracture toughness of the new self-healing particulate composite was investigated. It was found that the healing efficiency increased with thermoplastic content. However, the fracture toughness of the composite decreased in the same direction. The healing efficiencies at 3% and 9% CP volume fraction were respectively 50% and 75%. A new biomimetic self-healing syntactic foam was developed and shown to heal structural-length scale damage with a healing efficiency of 50% based on fracture load in three-point bending test. Repeated impact and self-healing tests revealed excellent impact tolerance and superior impact mitigation capabilities.
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Nji, Jones, "A Biomimic Self-healing Shape Memory Polymer Based Syntactic Foam for Smart Structural Composites" (2011). LSU Doctoral Dissertations. 177.