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Nancy Sottos with the University of Illinois, Urbana-Champaign |
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Date: April 28, 2003
Time: 10:30am
Location: NASA LaRC, Bldg 1192C, Rm 102
Speaker:Nancy Sottos with the University of Illinois, Urbana-Champaign
Subject:* "Autonomic Healing of Polymer Composites"
Additional Information: Presentation (PDF)
Inspired by biological systems, in which damage (e.g. bumps and cuts of soft tissue or fracture of the skeletal system) triggers an autonomic healing response, a polymer composite material that can heal itself when cracked has been developed. This seminar summarizes the recent demonstration of the self-healing concept for polymeric composite materials and investigates fracture mechanics issues consequential to the development and optimization of this new class of materials. The self-healing material under investigation is an epoxy matrix composite, which utilizes embedded microcapsules to store dicyclopentadiene (DCPD) as a healing agent and an embedded living catalyst. Grubbs’ Ruthenium catalyst is mixed into the epoxy monomer and becomes a suspended second phase in the specimen. The amount, size and properties of microcapsules are chosen to optimize the fracture properties of the bulk material and maximize the delivery of healing agent. The material has been developed such that the final material exhibits higher fracture toughness than the pure epoxy. When the composite cracks, the microcapsules rupture and release the healing agent into the damaged region through capillary action. As the healing agent contacts the embedded catalyst, polymerization is initiated which then bonds the crack face closed.
Of particular interest is the effect of microcapsules and catalyst on the stiffness and toughness of the epoxy resin. Topology of the fracture plane and its relationship to the failure modes of the healed material are investigated. Impact of thermal effects associated with cure and manufacture processes are related to fracture behavior of the virgin material and extent of healing. The process by which the microcapsules rupture and DCPD flows into the crack are also studied. Fracture tests were performed on the virgin material and on the material after healing, using tapered double-cantilever beam (TDCB) specimen, to assess the crack-healing efficiency of this composite material. Once healed, the self-healing polymer recovers as much as 90% of its virgin fracture toughness. Preliminary investigations of the inherent fatigue characteristics of the self-healing epoxy and its ability to extend component life will also be discussed.
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