Doctoral Dissertations

Date of Award

5-2019

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Mechanical Engineering

Major Professor

Uday Vaidya

Committee Members

Chad Duty, Amit Naskar, Ahmed Hassen, Vincent Paquit

Abstract

In the wake of lightweight and specific strength, composite materials are increasingly used for few decades. In order to meet the industry production rates, a novel mixing method has been developed in this work that provides more control on fiber length and homogeneity in wet-laid (WL) carbon fiber (CF) mats. The WL process has been adopted from papermaking industries to produce non-woven CF fiber mats.This work investigates the production of CF mats in three main phases; (a) First, the mixing regime of the WL method is explored to optimize the process of fiber dispersion. Experimental and theoretical computational fluid dynamics (CFD) studies have been conducted to understand the different factors of the process, in order to obtain the most optimal time of production. Mats produced are imaged through the Back Light Scattering (BLS) technique and computationally analyzed using a Matlab generated code to determine the fiber density distribution through pixel counts and compare the improved results of the mixing method developed in this work to the traditional propeller mixing. Processing time was reduced by 60% to produce a mat on laboratory scale with optimal characteristics; (b) Second composites were made from mats produced by each of the two mixing methods presented in the first part of the work. An object oriented finite element analysis (OFF) investigated the isotropic nature of the composites. The mechanical properties of these composites were evaluated in tensile, flex and inter laminar shear (ILSS). Tensile data showed improvement in standard deviation between samples collected from plates made with mats produced through the innovated mixing method when comparing them to composites made with the mats produced through the traditional method; and (c) Third, the in-plane permeability of the mats was analyzed in respect to changes in the fiber length and mats grammage per square meter (gsm) and a link between local permeability in response to changes in complex geometries is investigated.The novel mixing method for fiber distribution in WL discussed in this work presents an innovation in composites production, leading to improved production rate of nonwoven CF mats, ease of production and reproducibility of composites.

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