A novel approach to enhancement of self-healing for chemical, mechanical damage, which is crucial to the life-time of composite materials is discussed. The key idea of the method is to encapsulating the healing agent within the core of polymer fibers. The experiments revealed that two parts of the healing agent (commercially available epoxy resin and hardener) are encapsulated in separate polymeric nanofibers. The fibers can be generated by a single-step dual coaxial nozzle or emulsion spinning via solution blowing or electrospinning. The core-shell fibers with the diameters in the 200-2600 nm range are encased in the PDMS (polydimethyl siloxane) matrix to form a self-healing composite material. Under fatigue conditions, the coreshell fibers inside the composite material are ruptured and the healing agents released into the surrounding matrix. Various fatigue conditions including repeated bending and stretching are used to damage the composites and the degree of self-healing is quantified after that. Also, an incision resembling a crack is pre-notched and crack propagation is studied. It is found that the presence of the self-healing agents in the fibers significantly retards crack propagation due to curing by the epoxy at the ruptured site. The stiffness of the composites is also measured for the samples containing self-healing fibers inside them before and after the fatigue tests. A novel theory of crack propagation is proposed, which explains the observed jump-like growth of subcritical cracks.
Biography: Minwook Lee completed his BS and MS in Mechanical Engineering from Korea University in 2008 and 2010. He pursued his PhD studies at Korea University in the School of Mechanical Engineering (2014), followed by postdoctoral studies at University of Illinois at Chicago in the department of Mechanical and Industrial Engineering (2014.1-2017.3). In 2017 Dr. Lee has been appointed as senior researcher in Institute of Advanced Composite Materials at KIST (Korea Institute of Science and Technology). His research interests include theoretical and experimental fluid mechanics, heat and mass transfer, spray dynamics, numerical simulations of multiphase flows, fracture and recovering of polymer composite materials and multifunctional micro-/nanofiber, etc. His present h-index (Scopus, 1/2018) is 16, and Dr. Lee is the author of 40 research papers, 25 domestic/PCT patents.