Acoustic Emission Monitoring of CFRP Laminated Composites ...

4 Chapter 1. Introduction
Subjected to Cyclic Fatigue. 17
The ISI feature is the timing between two
sequential hits, and the hit pattern feature is essentially a technique for
fusing AE features, extracted from each AE hit, and for nding and locating
patterns which appear within the fused data representation. The
trough-to-peak pattern feature is made by using a variant of the ISI feature
as a input to the hit pattern feature. Furthermore, four Entropy-based features
are studied in order to assess whether they are useful for condition
monitoring CFRP subjected to multiaxial cyclic loading. The results of
this study were presented in AE Entropy for Condition Monitoring CFRP
Subjected to Cyclic Fatigue. 19
The study of these features and the results
form another contribution of this thesis.
The main contribution of this thesis is a methodology for processing,
presenting, and quantifying AE data for the purpose of identifying and
tracking the locations of multiple AE sources. The locations are determined
relative to the phase of a reference signal. This methodology was presented
in Monitoring The Evolution of Individual AE Sources in Cyclically loaded
16, 20
FRP Composites. The results show that the tracking of AE sources
can be used to facilitate early damage diagnosis and failure prognosis. The
methodology is neither limited to AE signals nor to periodic reference
signals. It can be used to study changes, or artifacts, in other signals using
either periodic or aperiodic reference signals.
Other contributions are an AE-based failure criterion 14 and a probabilitybased
approach for providing an early warning of imminent failure. 17
These
two contributions are based on a 10% displacement failure criterion, which
is used in this study.
1.3 Outline
The thesis is divided into 6 chapters, including this introduction chapter.
Chapter 2 provides an introduction to bre-reinforced composites, their
construction and properties. It also presents a detailed review of the cause
and eect of the various defects and damage mechanisms which can be
found in bre-reinforced polymer (FRP) composites.
The subject of Chapter 3 is acoustic emissions (AE). The chapter starts
with a background and literature section. The section, which is based on
NDT Methods for Evaluating Carbon Fiber Composites , 21
opens with a