All ETDs from UAB

Advisory Committee Chair

Thomas Attard

Advisory Committee Members

Nasim Uddin

Vinoy Thomas

Document Type

Thesis

Date of Award

2016

Degree Name by School

Master of Science in Civil Engineering (MSCE) School of Engineering

Abstract

The brittle nature of carbon fiber reinforced polymers (widely used in retrofitting and rehabilitation of damaged structures) stems from the mechanical properties of its binding polymer. Often, amorphous, 3-D cross-linked, thermoset resins are used as the matrix of the CFRP composite. Due to highly cross-linked arrangement of molecules, stiff epoxy matrix results in various brittle failure modes of the composite, manifested through crack propagation and fiber breakage. Various approaches to improve toughness of epoxy resins have been investigated with the intention of increasing the overall toughness of FRP composites. Rubber- and thermoplastic-toughening methods have been shown to increase fracture toughness considerably, but large amounts of epoxy-toughening agent content has been shown to inhibit certain properties such as a decrease in solvent resistance and substantial loss of stiffness. In addition, studies show that an increase in the matrix toughness does not necessarily result in overall toughness and to the composite or improved impact resistance of the FRP composite. An interfacial polymerization product, formulated on epoxy-Polyurea (elastomer) time-based reaction, is a viable alternative to brittle failure modes in fibrous composite systems. An interfacial reaction between amorphous block-copolymer (elastomer, i.e., Polyurea) containing rigid and soft segments along its molecular chain and highly cross-linked amorphous binding polymer (“epoxy”) provides enhanced overall energy dissipating properties to the composite system. The outcome integration of high-strength sustainability and large ductility in carbon- or aramid-fibrous-based epoxy-Polyurea systems, featuring tunable energy dissipation that appears to circumvent shortcomings of traditional FRP systems, such as lack of fracture toughness, damping, and impact resistance. The purpose of this thesis-level research focuses on first- and second- pass understanding of the physics of time-dependent critical processing parameters, specifically the epoxy curing time, tc, prior to its reaction with the pre-polymerized Polyurea in the design of impact resistant structural composite systems. The test results of low- and high- velocity impacted (LVI and HVI) structural shells and panels, designed with various tc, are discussed in terms of energy dissipation capacity, glass transition temperature, Tg, obtained via Thermomechanical Analysis (TMA), and resistance to penetration of 5 types of caliber (handgun) ammunition.

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