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Polymer matrix composites have high strengths in tension. However, their compressive strengths are much lower than their tensile strengths due to their weak fiber/matrix interfacial shear strengths. We recently developed a new approach to fabricate composites by overwrapping individual carbon fibers or fiber tows with a carbon nanotube sheet and subsequently impregnate them into a matrix to enhance the interfacial shear strengths without degrading the tensile strengths of the carbon fibers. In this study, a theoretical analysis is conducted to identify the appropriate thickness of the nanocomposite interphase region formed by carbon nanotubes embedded in a matrix. Fibers are modeled as an anisotropic elastic material, and the nanocomposite interphase region and the matrix are considered as isotropic. A microbuckling problem is solved for the unidirectional composite under compression. The analytical solution is compared with finite element simulations for verification. It is determined that the critical load at the onset of buckling is lower in an anisotropic carbon fiber composite than in an isotropic fibfer composite due to lower transverse properties in the fibers. An optimal thickness for nanocomposite interphase region is determined, and this finding provides a guidance for the manufacture of composites using aligned carbon nanotubes as fillers in the nanocomposite interphase region.
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Near–fiber effects of UV irradiation on the fiber–matrix interphase: A combined experimental and numerical investigation
Characterization of the interphase region in carbon fiber reinforced polymer (CFRP) is challenging because of the length scale involved. The interpretation of measured load-displacement curves using indentation is affected by the lack of analytical solutions that account for the fiber constraint effect. A combination of AFM (Atomic Force Microscopy) based indentation and FE (Finite Element) simulations showed a gradient in the elastic modulus of the interphase evaluated along a radial line from the fiber. 3D FEA (Finite Element Analysis) indicated that fiber constraint effect is significant in the region less than 40 nm away from the fiber. Nonetheless, the apparent rise in elastic modulus due to fiber constraint is limited when compared to the gradient in the elastic modulus of the interphase. Additionally, this technique is used to demonstrate that UV irradiation causes a rapid decrease in the modulus of the region near the fiber due to photocatalytic degradation of carbon fiber but subsequently increases due to high cross-linking. Whereas, the modulus of the matrix at 8 mm away from the fiber decreased by 32% after 24 h of UV irradiation. This indicates that the response of epoxy to UV irradiation is influenced by the proximity to the reinforcement.
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- Award ID(s):
- 1649481
- PAR ID:
- 10088919
- Date Published:
- Journal Name:
- Materials & design
- ISSN:
- 0264-1275
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/https://doi.org/10.1016/j.matdes.2018.07.050
