All ETDs from UAB

Advisory Committee Chair

Uday K Vaidya

Advisory Committee Members

Selvum Pillay

John Johnstone

Alan Eberhardt

Mark Weaver

Document Type

Dissertation

Date of Award

2013

Degree Name by School

Doctor of Philosophy (PhD) School of Engineering

Abstract

Composite materials display excellent specific strength and stiffness, light-weighting benefits, and are effective replacements for metals which are typically heavy and susceptible to corrosion. Next generation transportation, military, infrastructure, and marine sectors are extensively using fiber reinforced composite materials for part replacement and structural applications. Producing these advanced composite structures can often result in extensive development time and material wastage. There is a need to understand composite laminate formability and implement predictive methodology during product design to minimize manufacturing costs. The overall objective of this research was to predict the formability of thick section, plain woven, thermoplastic matrix composite laminates by analyzing parts produced with the combined application of localized heat and pressure. This research dealt with (a) optimizing the manufacturing process for thermoformed laminates using a single, hemispherical cup and a design of experiment approach, (b) generating a global strain map of the formed laminate with continuum mechanics, and using this as a comparative tool to generate a predictive, analytical model built upon bilinearly blended Coons patches and cubic-splines, (c) constructing a finite element model capable of forming conditions to predict global temperature profiles of the laminate, and (d) developing a bi-component shear stress based mechanical relationship for an as-formed part which considered the predicted intraply shear from section (b) and the predicted temperature profile of section (c). Section (a) minimized the amount of cross-sectional variance within one millimeter and permitted the assumption of uniform thickness throughout the thermoforming process. The analytical model of section (b) produced results which were highly comparable to experimental trials. On average, there was a point to point difference of 2.5 millimeters with a standard deviation of 1.4 and a variation in intraply shear of 4.3 degrees with a standard deviation of 4. Thermal profiles of section (c) were determined from finite element analysis and able to match experimental tests for undeformed laminates within an average accuracy of 10°C. Section (d) summarized the predicted mechanical properties and produced a stress profile for a formed laminate.

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