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Multi-scale Composite Materials with Increased Design Limits

Suberu, Bolaji A
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1377868507

Abstract Details

2013, MS, University of Cincinnati, Engineering and Applied Science: Mechanical Engineering.
Laminated composite materials have gained wide use in a vast range of high strength engineering applications due to the high specific strength and stiffness of composites. However, composites have a critical limitation which is their susceptibility to matrix micro cracking and delamination which can lead to premature failure at stress levels significantly below the tensile strength of the composite. Laminated composites also have low through-the-thickness strength and conduction properties which are important for aerospace vehicles and the military defense industry. These fundamental weaknesses in FRPC can be mitigated by the use of (CNTs) as a secondary reinforcement phase due to its excellent mechanical, electrical and thermal properties. In addition, the nano-reinforcement architecture will add significant multifunctionality to laminated composites. In this thesis, different reinforcement architecture are being investigated to improve the structural properties of laminated composite materials. The first approach investigated to improve the interlaminar and flexural strength of composites was to reinforce the laminate interlayers using a short and dense CNT array. The CNT arrays toughen the matrix rich regions. A vertically aligned carbon nanotube (VACNT) laminated composite which consists of Multiwalled Carbon Nanotube (MWCNT) arrays are transferred unto IM7/977-3 carbon fiber prepreg and plies are stacked up to create a hybrid laminated composite material. A complete wetting of the short MWCNT array by the epoxy from the prepreg was sufficient to create a new interface which yielded higher interlaminar properties. Mechanical and SEM characterization of these composite materials was performed under different loading conditions which include interlaminar and in-plane shear, bending, and in-plane tension. The second phase of reinforcement in this work was to improve the interlaminar shear properties of the laminated composite without reducing its in-plane tensile properties using a procedure that is minimally invasive to the carbon fiber prepreg. This process consists of using long CNT array posts to mechanically interlock all the plies together in order to impart a better load transfer mechanism than the previous approach. Micron-sized pin-holes are gently pressed into the prepreg layup and long CNT array posts are manually inserted into these pin holes prior to consolidation process. Also, mechanical and SEM characterization is performed on these composite samples under shear and in-plane tensile loading to determine the effect of pin-hole insertion density on the composite strength. Lastly, fiber reinforced laminated composites exhibit high mechanical properties in-plane but micro-sized matrix pockets in these materials occur as a result of ineffective close packing of the carbon fibers due to their large diameters and one size of fiber. This section proposes future work where laminated composites are redesigned and manufactured to create a high volume fraction composite (HVFC) which consists of micron diameter CNT threads integrated in-plane with seven micron diameter carbon fibers. Through-the-thickness reinforcement with long CNT posts is proposed to be used with the longitudinal reinforcement. To further improve the load transfer mechanism between the CNT forms and resin matrix, CNTs will be functionalized using plasma annealing system. We believe nano scale reinforcement will be the future of composite materials.
Mark Schulz, Ph.D. (Committee Chair)
Jude Iroh, Ph.D. (Committee Member)
Vesselin Shanov, Ph.D. (Committee Member)
David Thompson, Ph.D. (Committee Member)
177 p.
Mechanics
multi-scale composite; Nano composite; Carbon nantube post; carbon nanotube arrays; functionalization; mechanical properties

Recommended Citations

Citations

  • Suberu, B. A. (2013). Multi-scale Composite Materials with Increased Design Limits [Master's thesis, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1377868507

    APA Style (7th edition)

  • Suberu, Bolaji. Multi-scale Composite Materials with Increased Design Limits. 2013. University of Cincinnati, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1377868507.

    MLA Style (8th edition)

  • Suberu, Bolaji. "Multi-scale Composite Materials with Increased Design Limits." Master's thesis, University of Cincinnati, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1377868507

    Chicago Manual of Style (17th edition)

ucin1377868507
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This open access ETD is published by University of Cincinnati and OhioLINK.