Hybrid High-Strength Carbon-Fiber/Epoxy Composites Reinforced with Self-Healing Nanofibers at Interfaces (ND NASA EPSCoR Seed Grant $28,610, 4/16/2011-4/15/2012) Xiangfa Wu, PhD. NDSU Mechanical Engineering NASA space mission highly relies on spacecrafts made of lightweight composites (i.e., carbon fiber reinforced polymer composites) with high specific strength and stiffness and superior damage tolerance Goal of proposed research - Development of a novel interfacial self-healing strategy for aerospace polymer composites with low-cost, low-weight penalty, and easy incorporation into existing manufacturing process of high-strength polymer composites - Formulation of reliable route for healing-agent encapsulation at nanoscale(two orders below existing ones) and processing of concept-of-proof hybrid multiscale polymer composites with self-healing interfaces - Exploration of potential interfacial self-healing mechanism for controlled manufacturing Interfacial failure

Relevance to NASA Research is directly related to NASA interests in developing high-strength lightweight polymer composites with high damage tolerance and damage self-repairing function in low cost. Proposed novel hybrid multiscale composites are expected to remarkably enhance the damage tolerance and fatigue lifetime, substantially reduce the structural maintenance cost, and increase the integrity and reliability of the resulting composite structures. As an example, if an antenna of the space station was made of such high-strength advanced composites with damage self-repairing function, it could be possible to save huge maintenance fees relating shuttle launches and space walk.

Accomplishments Successful fabrication of continuous core- shell nanofibers loaded with liquid healing agent by coelectrospinning Successful fabrication of proof-of-concept carbon-fiber/epoxy composites reinforced with self-healing core-shell nanofibers at interfaces Reliable mechanical characterization of self- healing effect in stiffness recovery (up to 100% recovery) after damage Exploration of interfacial toughening & self- healing mechanisms via SEM fractography (Dzenis, 2008) (Wu et al., 2012)

Collaborations - Dr. Bin Chen, NASA Ames Research Center, CA - Dr. Alexander L. Yarin, Univ. of Illinois-Chicago, IL - Dr. Hao Fong, South Dakota Sch. of Mines & Tech., SD Research Assistants Involved - Zhengping Zhou (Ph.D. student, ongoing); - Arifur Rahman (M.S., 2/12); - Robert Jensen (M.S., 8/11); - Youhao Zhao (undergraduate, summer 2011) Publications 1. X.F. Wu, A. Rahman, & Z.P. Zhou, “Hybrid high-strength carbon-fiber/epxoy composites reinforced with ultrathin toughening and self-healing core-shell fibers at interfaces,” NDSU Technology Transfer Office, February 2, 2012 (Invention Disclosure). 2. Z.P. Zhou, X.F. Wu, X.Q. Gao, L. Jiang, Y. Zhao, & H. Fong, “Parameter-dependency of conic angle of nanofibers during electrospinning,” J. Phys. D: Appl. Physi. 44, (2011) (6 pages). 3. S. Sinha-Ray, D. Pelot, Z.P. Zhou, A. Rahman, X.F. Wu, & A.L. Yarin, “Encapsulation of self-healing materials by coelectrospinning, emulsion electrospinning, solution blowing and intercalation,” J. Mater. Chem. 22, (2012). 4. Q. Chen, L.F. Zhang, M.K.Yoon, X.F. Wu, R.H. Arefin, & H. Fong, “Epoxy composites reinforced and/or toughened with electrospun SiO 2 nanofibers,” J. Appl. Polym. Sci. 124, (2012). 5. X.F. Wu, A. Rahman, Z..P. Zhou, D. Pelot, S. Sinha-Ray, B. Chen, & A. L. Yarin, “Polymer composites with engineered self-healing interfaces by electrospun core-shell nanofibers,” (under review) Collaborations, Student Involvement & Publications

AFOSR: Novel high-strength multiscale polymer composites with engineered self- healing interfaces ($613,317) (submitted, PI; co-PI: A.L. Yarin, UIC) NSF CMMI: Continuous nano-scaled carbon fibers with superior mechanical properties and their innovative composites with exceptionally high performances (co-PI) ($334,198) (submitted, co-PI; PI: H. Fong, SDSMT) DARPA (under preparation) Future Plans for Proposals