All ETDs from UAB

Advisory Committee Chair

Uday K Vaidya

Advisory Committee Members

Amol S Vaidya

Haibin Ning

Vinoy Thomas

Document Type

Thesis

Date of Award

2015

Degree Name by School

Master of Science in Materials Engineering (MSMtE) School of Engineering

Abstract

Polymer composites are used in numerous industries due to their high specific strength and high specific stiffness. Such composites have markedly different properties than both the reinforcement and the matrix. Of the several factors which govern the final property of the composite, the interface is the single most factor that influences the stress transfer mechanism from the fiber to the matrix. The interface bond strength is also influenced by the surface treatments applied to the fiber during spinning and weaving. The present study is an effort to characterize and model the fiber-matrix interface in polymer matrix composites. Finite element models were developed to study the interfacial behavior during pull out of a single fiber in continuous fiber reinforced polymer composite. Three-dimensional (3D) unit cell cohesive damage models for the fiber/matrix interface debonding were employed to investigate effect of interface/sizing coverage on the fiber. Furthermore a 2-D Axi-symmetric model was also used to analyze sensitivity of interface stiffness, interface strength, friction coefficient, and fiber length via a parametric study. A 2-D axi-symmetric model was also used to study the shear stress distribution across the fiber-interface-matrix zone. It was determined that the force required to debond a single fiber from a matrix is three times more if there is full distribution of the sizing on the fiber. Parametric study indicated that cohesive strength was the most influential factor in debonding. Moreover the stress distribution model showed debonding mechanism of the interface. It was observed that the interface debonded first from the matrix and remained in contact with fiber even when the fiber was completely pulled out. Atomic force microscopy (AFM), X-ray photoelectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and contact angle analyses were performed on seven different carbon fiber surfaces. AFM images along with surface roughness showed that roughness and mechanical properties remained same for most of the fibers, this was deduced to be due to usage of same sizing. This was also validated by FT-IR, XPS and, scanning electron microscopy (SEM) and wettability. AFM as a surface analysis technique to quantify the characteristics of the fiber/matrix interface was implemented successfully. This study reaffirmed the belief that a combination of surface imaging tools like atomic force microscopy, x-ray photoelectron spectroscopy and finite element analysis, the interface and interphase of fiber reinforced composites can be characterized easily. Implementation of these techniques will result in easier ways to understand the fiber matrix bonding in comparison of existing methods.

Included in

Engineering Commons

Share

COinS