Civil Engineering ETDs

Publication Date

7-11-2013

Abstract

Carbon fiber reinforced polymer (CFRP) composites have been utilized in rehabilitation and strengthening of civil infrastructure, and fabrication of aerospace, automotive and marine structural components. This is attributed to the high strength-to-weight ratio and durability of CFRP. However, for strengthening using externally bonded CFRP laminates, creep of epoxy adhesive at the CFRP interface can result in off-loading of the CFRP and inefficient structural strengthening. When the CFRP strengthened structure is subjected to sustained loads, creep of epoxy should be carefully considered and controlled. Moreover, utilization of CFRP in fabrication of such structural components is rapidly demanding the enhancement of the structural properties of CFRP composites. Since CFRP structural properties depend on both the fiber and matrix properties, enhancement in the properties of the matrix yields relative improvement of the structural properties of the CFRP composite. Moreover epoxy resin systems incorporating nanoclay (epoxy-clay nanocomposite) have recently been reported to generally display significant improvements in structural properties over neat epoxy. This research examines the possible control of creep of epoxy using nanoclay. A multi-scale investigation of creep behavior of the epoxy-clay nanocomposite was conducted including macrocreep behavior at the CFRP-steel interface by using double lap shear testing, followed by investigation of the nanocreep of an epoxy-clay nanocomposite using nanoindentation. In addition, a hybrid CFRP composite incorporating an epoxy-clay nanocomposite (NC-CFRP) was fabricated. The experiments showed nanoclay to have a significant effect on epoxy creep, and tensile, in-plane shear, and flexural properties of NC-CFRP. Moreover, nanoclay was proven to improve low-velocity impact responses as well as limit damage evolution. Microstructural, thermal and mechanical characterizations of the epoxy-clay nanocomposite were performed to explain the observed effects. Microstructural characterization included scanning electron microscope (SEM), X-ray diffraction (XRD), transmission electron microscope (TEM), and nuclear magnetic resonance (NMR) measurements. Thermal characterization involved thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) measurements. These measurements showed that intercalated and exfoliated nanoclay platelets have significantly different effects.

Keywords

Epoxy-clay nanocomposite, Carbon fiber reinforced polymer (CFRP) composites, Microstructural characterizations, Creep, Nanoindentation

Sponsors

US National Science Foundation (NSF)

Document Type

Thesis

Language

English

Degree Name

Civil Engineering

Level of Degree

Masters

Department Name

Civil Engineering

First Committee Member (Chair)

Maji, Arup

Second Committee Member

Lin-Shen, Y

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