Date of Award

Spring 5-2022

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Mechanical & Aerospace Engineering

Program/Concentration

Aerospace Engineering

Committee Director

Oleksandr Kravchenko

Committee Member

Krishnanand Kapia

Committee Member

Miltos Kotinis

Abstract

In additive manufacturing, such as Automated Fiber Placement (AFP), defects often develop during the deposition and compaction of preimpregnated composite material, which reduce the strength of the resultant material. It is necessary to reduce defects and have good adhesion between plies to optimize the laminate performance and reduce delamination between composite layers. The aim of this work is to study the adhesion and deformation of preimpregnated (prepreg) composite material during the deposition and compaction stage in the composite forming process and how material parameters can be used to increase laminate strength. Two types of experimentation were performed on thermoset IM7/8552 prepreg samples: peel tests and unidirectional compaction experiments. For the T-peel testing, samples were subjected to varying temperatures, pressures, and contact times to simulate the layup conditions of an AFP roller and underwent peel testing to characterize the adhesion between the plies and to determine which experimental factor had the greatest effect on deposition by calculating the strain energy release rate. For the unidirectional experimentation, prepreg samples with varying geometries were subjected to isothermal compaction experiments for various times to study the strain and deformation of the material. It was determined that temperature had the greatest effect on the energy release rate and successful deposition of the prepreg material, while unidirectional samples with greater thicknesses but smaller widths had the greatest deformation and highest strain through the width and thickness. A MATLAB code was also developed based on laminate plate theory and free edge analysis to predict and study the stresses through a composite laminate and how σz stress is related to laminate strength. It was concluded that peel stress is related to the delamination of a composite and a lower laminate strength and can be controlled and minimized by changing material parameters such as ply thickness and stacking sequence.

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DOI

10.25777/3012-aw63

ISBN

9798834006886

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