자료유형  

 학위논문

Control Number  

0017164410

International Standard Book Number  

9798346389217

Dewey Decimal Classification Number  

600

Main Entry-Personal Name  

Braga , Ricardo Braga Nogueira.

Publication, Distribution, etc. (Imprint  

[S.l.] : The Pennsylvania State University., 2024

Publication, Distribution, etc. (Imprint  

Ann Arbor : ProQuest Dissertations & Theses, 2024

Physical Description  

198 p.

General Note  

Source: Dissertations Abstracts International, Volume: 86-05, Section: B.

General Note  

Advisor: Yamamoto, Namiko.

Dissertation Note  

Thesis (Ph.D.)--The Pennsylvania State University, 2024.

Summary, Etc.  

요약Fiber-reinforced plastics (FRPs), particularly carbon fiber-reinforced plastics (CFRPs), are widely used in aerospace, automotive, and energy industries due to their excellent in-plane mechanical and multifunctional properties. However, CFRPs are prone to delamination due to relatively weaker interlaminar properties. Traditional reinforcement methods such as z-pinning and stitching improve out-of-plane properties but often compromise in-plane performance. Carbon nanotubes (CNTs) offer a promising solution by enhancing interlaminar properties without affecting in-plane characteristics due to their nanoscale and excellent intrinsic mechanical properties. Introducing vertically aligned CNTs within the interlaminar region of prepreg-based CFRPs allows for maximum transverse reinforcement, however, it has been a challenge to both maintain CNT alignment during laminate fabrication and characterize CNT alignment within fabricated laminates. The goal of this study was to bridge the knowledge gap that is currently present regarding how to introduce and quantify alignment of CNTs within prepreg-based CFRPs and evaluate mechanical enhancement through analysis of interlaminar shear strength (ILSS), crack morphology, and crack energy trends. To accomplish this goal, three research objectives were set.The first objective was to validate the effectiveness of magnetically aligned CNTs in toughening of epoxies while minimizing agglomeration. Mode I fracture toughness tests on CNT-epoxy nanocomposites with varying CNT content, magnetic field strengths, and epoxy viscosities were conducted. Scanning electron microscopy (SEM) and ultrasonic testing (UT) were used to characterize CNT morphology. A 72% increase in toughness was observed with 0.5 vol.% CNTs aligned at 180 G, with reduced agglomeration when compared to specimens made with higher magnetic fields (300 G). Differently from previous work, that focused mostly on CNT morphology and toughness trends with respect to one parameter, CNT content, the completion of the first objective allowed for better understanding CNT morphology trends relative to three parameters: magnetic field magnitude, CNT content, and matrix viscosity. In addition, UT was used for the first time as a potentially useful method to characterize mm-scale CNT morphology within nanocomposites.The second objective was to develop an hot press method to enable fabrication of aerospace-grade prepreg-based CFRP laminates with magnetically aligned CNTs. This involved improving CNT synthesis, magnetization, and functionalization processes and devising methods to fabricate B-staged CNT-epoxy films. These films were integrated into prepreg-based CFRPs using hot pressing, with the use of a load frame, and vacuum bagging. In addition, a method was developed to allow for integration of multiple B-staged CNT-epoxy films while minimizing ply sliding, which occurs due to epoxy bleeding from the B-staged films during laminate fabrication. The completion of the second objective enables the fabrication of aerospace-grade prepreg-based CFRP laminates integrated with magnetically aligned CNTs, with developed film fabrication methods for both coupon-sized lab testing and preliminary tests that would enable large-scale commercial manufacturing of B-staged CNT-epoxy films using a doctor blade technique. In addition, a MATLAB/ImageJ code was developed to assess laminate quality, including quantification of void, matrix, and fiber content, without the need of user input.The third objective was to evaluate the effects of introducing both randomly oriented and magnetically aligned CNTs into aerospace-grade prepreg-based CFRPs. Laminates were fabricated with one film at the midplane containing 0.1 vol.% and 0.5 vol.% of CNTs. Short beam shear (SBS) testing was conducted to compare the ILSS trends related to magnetic field application applied at different parts of the fabrication cycle, and relative to changing CNT content. It was found that having CNTs pre-aligned within B-staged films prior to laminate fabrication increases agglomeration and hinders maximum reinforcement capability. Laminates with three films containing 0.5 vol.% of CNTs were fabricated, and three-point bending tests indicated an improvement of ~ 6.5% in the mean ILSS for specimens containing aligned CNTs when compared to specimens with randomly oriented CNTs. Due to the introduction of a lower strength epoxy into the prepreg-based CFRP laminates and limitations with the SBS test method, though, the ILSS of laminates fabricated with B-staged films, with and without CNTs, decreased when compared to a prepreg-only baseline. However, fracture behavior differences between specimens fabricated with and without CNTs were apparent from assessing the load versus displacement plots, which indicated much sharper drops in load for specimens fabricated without CNTs. Laminates and CNT-epoxy films within the laminates were characterized using optical microscopy, and CNT presence and alignment were confirmed with a vibrating sample magnetometer (VSM). In addition, a fracture energy study was conducted to quantify fracture energy dissipation for the fabricated laminates by assessing the post-fracture work to total work ratio with respect to a range of percentage load drop from the point of initial fracture. Laminates containing aligned CNTs and randomly oriented CNTs exhibited approximately a 30% increase in the post-fracture work to total work ratio when compared to prepreg-only baseline specimens for the larger part of the analyzed load drop range.In summary, the completion of this work yielded new knowledge regarding 1) the effects of CNT content, magnetic field magnitude, and matrix viscosity on the morphology and toughness of CNT-epoxy nanocomposites, 2) the evaluation and demonstration of UT as a potential method to assess multi-scale CNT structures within CNT-epoxy nanocomposites, 3) the development of a scalable process that enables magnetically aligned CNT integration to prepreg-based CFRPs through the use of B-staged CNT-epoxy films, 4) the evaluation of the effectiveness of magnetically aligned CNTs in reinforcing interlaminar properties of CFRPs by assessing interlaminar shear strength results, analyzing crack morphology, and studying crack energy trends, 5) the verification of CNT presence and quantification of CNT alignment through the use of a VSM, and 6) the development of a fully automated MATLAB/ImageJ code to quantify void, matrix, and fiber content of CFRP laminates. Finally, recommended future work regarding integration of magnetically aligned CNTs to CFRPs include 1) fabricating B-staged films using an epoxy system of similar mechanical properties to those in the prepregs it is to be introduced to allow for direct comparison of aligned CNT effects with respect to the prepreg baseline, 2) studying the possibility of introducing CNTs in the intralaminar region of prepregs by using a high-gradient magnetic field, and 3) further developing the processes discussing in this work for large-scale applications. In addition, investigating how to tailor multifunctional properties of CFRPs by controlling CNT morphology within laminates can be explored.

Subject Added Entry-Topical Term  

Mechanical properties.

Subject Added Entry-Topical Term  

Viscosity.

Subject Added Entry-Topical Term  

Nanocomposites.

Subject Added Entry-Topical Term  

Carbon.

Subject Added Entry-Topical Term  

Magnetic fields.

Subject Added Entry-Topical Term  

Aluminum.

Subject Added Entry-Topical Term  

Pressure distribution.

Subject Added Entry-Topical Term  

Laminates.

Subject Added Entry-Topical Term  

Sealing compounds.

Subject Added Entry-Topical Term  

Contact angle.

Subject Added Entry-Topical Term  

Visualization.

Subject Added Entry-Topical Term  

Thin films.

Subject Added Entry-Topical Term  

Shear strength.

Subject Added Entry-Topical Term  

Crack propagation.

Subject Added Entry-Topical Term  

Condensed matter physics.

Subject Added Entry-Topical Term  

Electromagnetics.

Subject Added Entry-Topical Term  

Materials science.

Subject Added Entry-Topical Term  

Mechanics.

Subject Added Entry-Topical Term  

Nanotechnology.

Added Entry-Corporate Name  

The Pennsylvania State University.

Host Item Entry  

Dissertations Abstracts International. 86-05B.

Electronic Location and Access  

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Control Number  

joongbu:656970