Doctor of Philosophy (PhD)


Mechanical Engineering

Document Type



Self-healing smart material systems have been introduced into the research arena and they have already been deployed into industrial applications. The Close-Then-Heal (CTH) healing mechanism for polymeric self-healing systems is addressed herein and then a new generation of Shape Memory Polymer (SMP) based self-healing system is proposed in this work. This system incorporates SMP fibers to close the cracks while the embedded Thermoplastic Particles (TPs) are diffused into the crack surfaces upon heating and provide a molecular level of healing. The SMP fiber manufacturing procedure is briefly addressed in this work in which the bobbin of SMP fibers are heat treated in a specific procedure and then they are wound to produce SMP fibers. The performance of the proposed healing system is highly dependent on mechanical responses of SMP fibers. The polyurethane SMP fibers are categorized as semicrystalline polymeric material systems. These semicrystalline SMP fibers are then constituted from two distinguishable phases, which are amorphous and crystalline polymers. Such a multiphase system can be evaluated through a multiscale analysis within the micromechanics framework in which the macroscopic mechanical responses are evolved through averaging the microscale mechanical fields. Then in this research the constitutive relation for each of the micro-constituents are utilized to compute the microscale mechanical fields and then these fields are correlated to the macroscopic field through the micromechanics framework. The cyclic viscoplastic and viscodamage of these fibers are of utmost importance for designing self-healing systems in which repeatability of the healing process and the healing efficiency for subsequent healing cycles are highly dependent on cyclic responses of these fibers. A new approach in measurement of cyclic damage of SMP fibers is proposed in this work in which the reduction in recoverable stress after each cyclic stress recovery is correlated to the damage. In this approach the damage is interpreted as failure of the polymeric bonds to recover their original shape (SM effect). In general the proposed self-healing scheme establishes a new generation of self-healing systems while the developed theoretical multiscale analysis provides a well-structured method to investigate the cyclic viscoplastic and viscodamage of the SMP fibers.



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Committee Chair

Li Guoiqang