Characterization and Modeling of Dual Phase Thermoplastic Self Healing System for Fiber Reinforced Thermoset Composite Structures
The one characteristic that sets biological systems apart from human-engineered systems is its ability to heal itself repeatedly without any external intervention. In the last few decades, drawing inspiration from nature, there has been a tenacious drive towards the design and development of bio-mimetic multifunctional polymers and polymer matrix composites that possess the capability of repeatable self-healing. In this dissertation, bio-mimetic self-healing methods are explored for recover-ing the mechanical and structural performances of damaged ?ber reinforced thermoset polymer composite using thermoplastic healants. Speci?cally, repeatable Mode-I interlaminar fracture healing capabilities of thermoplastic polycaprolactone (PCL) particles and polyurethane shape memory polymer (SMP) ?brils in a thermoset unidirectional carbon/epoxy composite were investigated. During the bio-mimetic healing process, the polyurethane SMP ?brils were used to close the open crack through a thermally-activated contraction, and then the thermoplastic PCL was heated to heal the damage through melt intercalation into the crack. The chemical and thermal properties of the polymer composite and healants and interactions between the brittle epoxy and ductile healants were investigated. Further, repeatable Mode-II interlaminar shear fracture property recovery of unidirectional carbon/epoxy by a blend of the same biphasic healants was experimentally investigated. The shear crack growth phenomenon and mechanism of fracture toughness recovery were thoroughly investigated and contrasted with Mode-I failure. Finally, the real-time in-situ application of self-healing in ?ber-reinforced composite was accomplished by using a macro ?ber composite (MFC) actuator assisted healing. The parameters for generating stimulus (heat) from MFC without damaging it or the composite were calculated. Relative crack growth stability was also investigated during in-situ healing for virgin and healed cases by using R ? curve and crack growth rate phenomenon. For a comprehensive understanding of the healing mechanism and fracture behavior of the polymer composite, analytical and numerical models were generated using a bilinear cohesive law. The critical fracture parameters obtained from the analytical studies were thoroughly veri?ed with experimental results and ?nite element numerical simulations. It is envisioned that this work will provide a solid foundation for the future development and implementation of self-healing polymer composites in real life structural applications.