Date of Award

Spring 2019

Document Type

Open Access Thesis

Department

Mechanical Engineering

First Advisor

Ramy Harik

Abstract

High-performance composite structures not only require a reliable fabrication process when creating primary structures, but also a high fidelity and repeatable bonding process for the assembled components. During the assembly process, surface contaminants are a major concern as they have the potential to compromise the bond quality resulting in poor bond strength, low failure load, and undesirable failure modes of the adhesively bonded structures. This is further complicated by composite materials inherently possessing low surface energy and thus exhibiting low adhesive property. Therefore, detecting and removing contaminants on the pre-bond composite surface is an active research topic in pursuit of a safer operation of composite structures.

In this research, composite panels were fabricated with Hexcel IM7/8552 carbon fiber using an automated fiber placement (AFP) machine by IMT®. An atmospheric pressure air driven plasma discharge by Plasmatreat® was utilized to treat the surface of the composite material. Atmospheric Pressure Plasma Jet (APPJ) treatment effects of carbon fiber reinforced polymers (CFRPs) were investigated with surface characterization methods as well as with double cantilever beam (DCB) tests. A water contact angle (WCA) measurement for assessment of surface energy, X-ray photoelectron spectroscopy (XPS) to understand surface elemental composition, scanning electron microscopy (SEM) to observe surface morphological changes, and atomic force microscopy (AFM) to analyze surface topographical changing were used to determine the effects of the APPJ treatment. Two composite laminates were bonded with Metlbond1515 3M, and DCB testing was performed to two groups of these bonded laminates to differentiate the bond performance between (1) pristine P and (2) treated T composite laminates. Mode I interlaminar fracture toughness was calculated for each test while failure modes were also assessed. A thorough test plan was conducted and experimental results were analyzed. The analysis demonstrated that APPJ treatment has a positive effect on the CFRP bonding effectiveness through the functionalization of the composite surface.

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