Scholarly Communications Project


Interfacial Adhesion Evaluation of Uniaxial Fiber-Reinforced-Polymer Composites by Vibration Damping of Cantilever Beam

by

Weiqun Gu

PhD Dissertation submitted to the Faculty of the Virginia Tech in partial fulfillment of the requirements for the degree of

Ph.D

in

Materials Engineering Science Program

Approved

Guo-Quan Lu, Chair
Stephen L. Kampe, Co-chair
Alex O. Aning
Ronald G. Kander
Alfred C. Loos
H. Felix Wu

February 17, 1997
Blacksburg, Virginia


Abstract

The performance of fiber-reinforced composites is often controlled by the properties of the fiber-matrix interface. Good interfacial bonding (or adhesion), to ensure load transfer from matrix to reinforcement, is a primary requirement for effective use of reinforcement properties. Thus, a fundamental understanding of interfacial properties and a quantitative characterization of interfacial adhesion strength can help in evaluating the mechanical behavior and capabilities of composite materials. A large number of analytical techniques have been developed for understanding interfacial adhesion of glass fiber reinforced polymers. Common adhesion tests include contact angle measurements, tension or compression of specially shaped blocks of polymer containing a single fiber, the single fiber pull-out test, single-fiber fragmentation test, short beam shear and transverse tensile tests, and the vibration damping test. Among these techniques, the vibration damping technique has the advantage of being nondestructive as well as highly sensitive for evaluating the interfacial region, and it can allow the materials industry to rapidly determine the mechanical properties of composites. In this work, we contributed a simple optical system for measuring the damping factor of uniaxial fiber-reinforced-polymer composites in the shape of cantilever beams. A single glass fiber- and three single metallic wire-reinforced epoxy resin composites were tested with the optical system. The fiber- (wire-) matrix interfacial adhesion strength measurements were made by microbond test. A reasonable agreement was found between the measured interfacial adhesion strength and micromechanics calculations using results from vibration damping experiments. The study was also extended to multi-fiber composites. The interfacial damping factors in glass-fiber reinforced epoxy-resin composites were correlated with transverse tensile strength, which is a qualitative measurement of adhesion at the fiber-matrix interface. Four different composite systems were tested. For each system, glass fibers with three different surface treatments were used at three different volume fractions. The experimental results also showed an inverse relationship between damping contributed by the interface and composite transverse tensile strength for all of the multi-fiber composites.

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