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Title:Self-healing of delamination damage in glass/epoxy composites using catalyst functionalized fibers
Author(s):Hart, Kevin
Advisor(s):White, Scott R.
Department / Program:Aerospace Engineering
Discipline:Aerospace Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Grubbs' Catalyst
Double-Cantilever Beam
Abstract:The use of polymer matrix fiber-reinforced composites in structural applications is growing because of the excellent specific strength and stiffness of these materials. Their wide spread acceptance, however, has been limited in some areas because of susceptibility to damage from impact events in directions transverse to the direction of fiber reinforcement. Damage occurring from transverse impact events is multi-dimensional, difficult to predict and visually difficult to detect. This complexity leads to more expensive maintenance, which in many cases offsets the original benefits of these lightweight materials. As an alternative, self-healing polymers have been introduced as a way to autonomically repair damage in fiber-reinforced polymer composites, ultimately reducing maintenance costs associated with their use. In this work, self-healing applications are explored in 2D woven glass/epoxy composites for ultimate use in 3D woven composites. Initial work focuses on a new method for introducing self-healing components into low temperature cure 2D fiber-reinforced polymer composites. In these studies, glass fiber preforms are functionalized with second generation Grubbs’ catalyst using an evaporative crystallization technique for catalyst deposition. Preforms are then used in the manufacture of laminated 2D woven composites. Healing of interlaminar fracture damage is evaluated in these composites using double cantilever beam (DCB) specimens. Recovery of interlaminar fracture damage is initiated by the injection of liquid dicyclopentadiene (DCPD) onto the fracture surface of the functionalized fiber composites whereby the catalyst on the surface of the fibers triggers a ring opening metathesis polymerization (ROMP) reaction in the liquid monomer, healing the interlaminar damage. Recovery of up to 10% of critical strain energy release rates is observed. Minimal recovery is attributed, in part, to weak bonding between the polymerized DCPD and the surrounding materials. Tortuous crack paths limit interfacial fiber/matrix de-bond required to expose the catalyst coated fiber surface and also introduce crack blunting mechanisms that increase virgin critical strain energy release rates. In later work, optimization of the fiber functionalization technique is extended to high temperature cure glass/epoxy composites. Alternate methods for catalyst functionalization are examined and dip coating techniques are shown to more evenly and consistently deposit the catalyst on the fiber surface. Thermal and chemical stability of the second generation Grubbs’ catalyst is verified using pure polymer bullet samples. Optimization of fiber architectures is carried out and an 8-harness satin weave is chosen as the optimal system based on double cantilever beam testing. This fabric exhibited more stable crack propagation and greater interfacial fiber/matrix failure and fiber bridging during testing. Small model DCB specimens are used to qualitatively assess healing potential and results indicate that a high catalyst loading is required to demonstrate healing in high temperature cure glass/epoxy composites.
Issue Date:2012-05-22
Rights Information:Copyright 2012 Kevin Hart
Date Available in IDEALS:2012-05-22
Date Deposited:2012-05

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