Date of Award

3-1-2021

Document Type

Thesis

Degree Name

Master of Science

Department

Department of Aeronautics and Astronautics

First Advisor

Marina B. Ruggles-Wrenn, PhD

Abstract

Carbon nanotubes (CNTs) exhibit outstanding mechanical properties, such as exceptionally high tensile stiffness and strength, combined with excellent electrical and thermal characteristics. This research investigates the mechanical properties and performance of a newly developed hybrid nano-engineered composite. The carbon fiber/polymer matrix composite incorporates a forest of vertically aligned CNTs, called NanoStitch, between the prepreg plies. Basic tensile properties of both material systems were investigated for both on-axis [0/90] and off-axis [±45] fiber orientations at room temperature. Tension-tension fatigue tests were performed with a frequency of 1.0 Hz and a ratio of minimum stress to maximum stress of R= 0.05. Fatigue run-out was set to 2x105 cycles. In addition to constructing fundamental fatigue S-N diagrams, strain accumulation and modulus change with cycles each fatigue test were examined. The presence of the NanoStitch reinforcement did not result in a decrease in tensile properties compared to the control PMC. For both 0/90 and ±45 fiber orientations the two material systems produced similar values of the tensile modulus and ultimate tensile strength. Likewise, the two material systems exhibit similar fatigue resistance. The presence of the NanoStitch reinforcement did not decrease the fatigue limit nor degraded cyclic life of the composite. Additionally, creep and recovery tests were performed to study the time-dependent deformation behavior of the nano-engineered composite with ±45 fiber orientation. The test results were analyzed in context of Schapery's nonlinear viscoelastic model. The model was successfully characterized and validated using experimental data. Thus it was determined that Schapery's viscoelastic deformation theory can be used to predict the off-axis deformation behavior of the hybrid nano-engineered composite.

AFIT Designator

AFIT-ENY-MS-21-M-306

DTIC Accession Number

AD1127936

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