Journal of AE, Volume 25, 2007 (ca. 26 MB) - AEWG

STRUCTURAL INTEGRITY EVALUATION USING
ACOUSTIC EMISSION
KANJI ONO
Department of Materials Science and Engineering
University of California, Los Angeles, California 90095-1595
Abstract
This paper reviews various approaches used in acoustic emission (AE) testing of structures
so that further improvements can be realized in this important application of AE technology.
Since the late 1950s, many successful AE tests of structures have been completed. Yet, the
spread of AE technology is underwhelming. To achieve a wider use of AE, we attempt to organize
and reexamine the AE methodology applied to structural integrity monitoring in four steps.
1. AE Sources: Primary sources of brittle fracture, micro- or macro-cracks in contrast to secondary
sources of friction or fretting, rust, etc. 2. Evaluation Tools: Kaiser effects, arising from the
irreversibility of AE, allow the detection of prior loading level and of damage states. Related indices
are also useful. 3. Source Location: This approach identifies the area of integrity loss. 4.
Source Characterization: Combined AE parameters give good insight to the flaw types, but many
other methods, including signal amplitude, signal frequency, waveform and wave propagation
analysis and moment tensor analysis, can be useful. Avenues for better AE technology utilization
are suggested. These include: to accumulate basic data on structures with standardized procedures,
to devise combinatorial approach between localized damage evaluation and long-range
detection and to develop regional or global database under international cooperation. The final
goal of determining the structural integrity is attainable only with systematic approach with damage
quantification via NDT and with the use of fracture mechanics.
Keywords: Structural Integrity; AE Methodology, AE Sources, Source Characterization
1. Introduction
Acoustic emission (AE) testing of structures began in California in the midst of the space
race [1]. From the early years, R&D activity was high; 400+ papers on this topic were compiled
for 1970-72 period [2]. By now the methodology has well-established commercial basis in most
industrialized countries. Yet, we are far from the goal of providing quantitative answers regarding
the integrity and remaining lifetime of structures. Current status of AE testing of structures is
reviewed here to advance this important application of AE technology.
The basic AE testing strategy is to detect AE signals globally from the entire structure under
test using above-normal loading (or pressure), to identify their locations, to group them (clustering)
and to rank the groups comparing the collective AE characteristics with empirical database
[3-5]. The key issue is the presence or absence of critical intense sources in the structure. During
the past 40+ years, many AE tests of structures have successfully utilized this strategy. Most often,
AE has been used as an alternative to internal inspection of tanks and pressure vessels. However,
details remained inaccessible in proprietary reports and meaningful assessment has been
unavailable. Some recent articles give valuable insight to industrial AE practices [6-8]. The
strategy of AE testing relies on the presumed principle that active defects produce AE in asymptotically
increasing number with rising load. We also assume larger defects give stronger AE.
J. Acoustic Emission, 25 (2007) 1 © 2007 Acoustic Emission Group