Carbon nanofiller modified multifunctional glass fiber/epoxy laminated composite
Open Access
- Author:
- Zhu, Ye
- Graduate Program:
- Engineering Science and Mechanics
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- October 03, 2011
- Committee Members:
- Charles E. Bakis, Committee Chair/Co-Chair
Clifford J. Lissenden, Committee Member
Sulin Zhang, Committee Member
James H. Adair, Committee Member - Keywords:
- electrical conductivity
carbon nanotube
composite
fracture toughness - Abstract:
- The primary objective of the current research is to utilize carbon nanofillers to modify a glass fiber/epoxy laminated composite to achieve improvement in the mechanical properties as well as tailored electrical properties of the hybrid composite. Mechanical and chemical methods for uniformly dispersing multi-walled carbon nanotubes (CNTs) and carbon nanofibers (CNFs) in an epoxy material were investigated. A silane coupling agent carbon nanofiller functionalization scheme has been developed. The functionalization of nanofillers led to improved dispersion of nanofillers in the epoxy system. Carbon nanotubes and carbon nanofibers with different ranges of aspect ratios and surface functionalities were chosen to modify an S2-glass/epoxy laminated composite made by a filament winding method. The fillers were incorporated in the composite by one of two approaches: (1) impregnating the fiber tow with nanofilled resin during filament winding and (2) placing a nanofiller/epoxy interlayer between filament wound wet or dry fiber plies. Using the nanofiller interlayer approach for fabricating the hybrid composite resulted in a maximum of 95% improvement in the mode I interlaminar fracture toughness (IFT) and a maximum of 109% improvement in the mode II IFT relative to the baseline material with no fillers. Contrastingly, the approach of impregnating the fiber tow with nanofilled resin resulted in slight or no improvement in fracture toughness. Higher aspect ratio functionalized nanofillers added to the interlayer were proven to be more effective in improving fracture toughness than unfunctionalized fillers with lower aspect ratio. Applying electric field in the through-thickness direction of the laminate to assist alignment of nanofillers increased the mode I IFT by a maximum of 105% compared to that of the baseline material. Multidirectional glass fiber reinforced composite tubes were also fabricated using the two nanofiller placement approaches. Compressive strength and compression after indentation (CAI) strength were determined for nanofiller modified tubes as well as the control tubes without nanofillers. Using either one of the two nanofiller placement approaches, the compressive strength and CAI strength are improved, with the highest improvement achieved by adding 0.5 wt% short COOH-CNT in the matrix (21% improvement in compressive strength and 17% improvement in CAI strength relative to the baseline material with no filler). Carbon nanofillers were aligned and chained in liquid epoxy and the glass/epoxy material by application of an AC electric field. The effect of filler functionality, AC electric field frequency, and strength, and filler concentration on the electric field alignment efficiency and the composite resistivity were evaluated. Using unfunctionalized and high aspect ratio CNTs for modifying the epoxy were proven to be more effective in achieving high electrical anisotropy and low resistivity in the alignment direction by the electric field alignment method compared to that of functionalized fillers modified epoxy. Increasing the AC electric field increases material anisotropy, but only within a range of field strength. The material electrical anisotropy was highest at an AC field frequency of 1 kHz. Without the addition of nonconductive fillers into the two phase nanofiller/epoxy composites, an anisotropy ratio of electrical resistivity in the transverse direction to that in the alignment direction of greater than 30 was achieved. With the addition of nonconductive glass fibers, the electrical anisotropy ratio reduces as the volume percent of the glass fiber increases and it reaches 1 when the glass fiber volume fraction is greater than 20%. Glass fiber /epoxy composites with nanofillers were manufactured with an electric field applied during material fabrication for reduced resistivity in the through-thickness direction of the composite. Interlaminar fracture, compression, and compression after indentation tests were conducted on the hybrid composites while measuring the electrical resistance (ER). The ER signal was able to detect the onset of both delamination and compressive failure. In the case of delamination, the electrical resistance was correlated to the damage size by a third order polynomial.