Page 60 - Engineered Interfaces in Fiber Reinforced Composites

Chapter 3

MEASUREMENTS OF INTERFACE/INTERLAMINAR
PROPERTIES

3.1. Introduction

A number of experimental techniques have been devised to measure the
mechanical properties of the fiber-matrix and laminar interfaces in composites.
These techniques in general can be classified into two different methods depending
on the nature of specimens employed and the scale of testing (Kim et al., 1994): one
involves the testing of single fiber (or multiple fibers in some cases) microcomposites
in which individual fibers are embedded in specially constructed matrix blocks of
various shapes and sizes; and the other uses bulk laminate composites to measure
the interlaminar/intralaminar properties. Much of the discussion presented in this
chapter follows that given in our recent publications (Kim and Mai, 1991, 1993;
Kim et al., 1994). The relative advantages and limitations of these testing techniques
are critically assessed with respect to specimen preparation, and interpretation of
data.
Given a combination of fiber and matrix, it is desirable that the testing method
will provide a reproducible and reliable means of not only measuring the interface
adhesion but also allowing the failure mode at the interface region to be studied.
One important requirement of these tests, whether the microcomposite tests or the
bulk composite tests, is that the mechanics model developed for data reduction must
be consistent with the actual failure mechanisms. But more often than not,
particular failure is assumed to have taken place without confirmation in
experiments. This practice not only makes the interface properties obtained
doubtful, but it also degrades the whole value of the test method. As will be shown
later in the chapter, this may also explain why there is an extremely large data
scatter in the test results for apparently the same materials tested in different
laboratories. Efforts are being continued to improve the quality and accuracy of
experimental data and to develop better mechanics models underpinning these
testing methods.

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