Acoustic Emission Monitoring for Concrete Structures:...
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Transcript of Acoustic Emission Monitoring for Concrete Structures:...
Applications of Acoustic Emission for Reinforced Concrete:
Acoustic Emission Monitoring for Concrete
Structures: Qualitative vs. Quantitative Methods
Thomas Schumacher (Presenter), Assistant Professor and
Lassaad Mhamdi, PhD Student
Tuesday, October 23, 2012
Civil & Environmental Engineering
• WHAT ARE ACOUSTIC EMISSIONS (AE)?
• SOURCES FROM CONCRETE STRUCTURES
• MEASUREMENT PROCESS
• ANALYSIS METHODS
• STRENGTHS AND
LIMITATIONS • CONCLUSIONS
OVERVIEW
• Acoustic Emission (AE) is the term used for transient elastic waves generated by the release of energy within a material or by a process (EN, 2000).
• Irreversible process • Passive technique (vs. UT) • Source parameters unknown
• Sensing via surface-mounted piezo-electric transducers
• Similarity to earthquakes, i.e. nano-seismic activity
• Frequency range of AE in concrete: ~10 to 500 kHz
Medium
Sensor
to DAQ
Source
External load
WHAT ARE AE?
• Primary sources
SOURCES FROM CONCRETE STRUCTURES
Rebar debonding (slip, pull-out)
Wire debonding/fracture Concrete crushing
Inclined cracks
Flexural cracks
Crack surface interaction
Rebar fracture
• Secondary sources
• Noise: impacts on road surface, electrical
MEASUREMENT PROCESS
( ) ( ) ( ) ( ) ( )= ∗ ∗ ∗M S DAQR t tf t tf t tf t S t
1
3
2
4 5
n sensors n signals
( )S t
( )R t
( )DAQtf t( )Stf t
( )Mtf t
Qualitative AE Analysis
Quantitative AE Analysis
OVERVIEW ANALYSIS METHODS
Event forming
Qualitative Quantitative
Estimation of source parameters (time,
location)
Estimation of source mechanisms Waveform analysis
Parameter extraction
Data analysis
Stored AE waveforms, R(t)
Sim
ple
forw
ard
proc
edur
es
Non
-line
ar in
vers
e pr
oced
ures
OVERVIEW ANALYSIS METHODS
Event forming
Qualitative Quantitative
Estimation of source parameters (time,
location)
Estimation of source mechanisms Waveform analysis
Parameter extraction
Statistical analysis
Stored AE waveforms, R(t)
• Kaiser Effect (Kaiser, 1950): Previous stress level needs to be exceeded in order for new AE to be produced
• Felicity Ratio (Fowler, 1986):
Source: ASTM E602 (1982)
QUALITATIVE METHODS
7 Source: Koeppel, 2002
• NDIS-2421 (Ohtsu et al., 2002):
• b-Value Analysis
(Gutenberg & Richter, 1952):
QUALITATIVE METHODS (CONT.)
8
Source: Ohtsu et al., 2002 • Historic-Severity Index (Fowler, 1989):
Source: Golaski et al., 2002
2 2.5 3 3.5 4 4.5
0
0.5
1
1.5
2
AE Magnitude [AdB/20]
log(
Cum
ulat
ive
AE H
its) [
-]
Frequency distribution of hit amplitudesEstimated b-value (slope of this line)± one standard deviation of dataData mean value
Sour
ce:
Schu
mac
her,
2008
• Others: AE Rate Process Analysis (Ohtsu et al., 2004)
• Waveform analysis (Grosse, 1996):
QUALITATIVE METHODS (CONT.)
Sour
ce: G
ross
e, 19
96
Magnitude Squared Coherence
Signal 1
Signal 2
• Data analysis of many extracted parameters/waveforms • Do not try to explain source mechanisms • Can be performed with as few as 1 sensors • Often implemented in commercial AE systems
• Relative measure, only
comparable for same conditions • Depend on selected acquisition
and threshold criteria:
SUMMARY QUALITATIVE METHODS
Source: Schumacher, 2008
OVERVIEW METHODS
Event forming
Qualitative Quantitative
Estimation of source parameters (time,
location)
Estimation of source mechanisms Waveform analysis
Parameter extraction
Statistical analysis
Stored AE waveforms, R(t)
Motivation of using quantitative methods: • Earthquakes studied for a long time, a variety of analysis tools exist • Earthquakes = AE, different scales
QUANTITATIVE METHODS
Adapted from: earthquakesandplates.wordpress.com
Source
Source: Schumacher, 2008
QUANTITATIVE METHODS (CONT.)
Source: Schumacher, 2008
• Estimation of source locations (Geiger, 1910):
Source: Schumacher, 2008
Moment Tensor Inversion (Aki & Richards, 1980): Seismic sources (and AE) can be represented by a model of equivalent forces.
• Radiation pattern inferred through measured surface displacements of p-wave:
• Simplification: Result: • Fracture type • Orientation of fracture planes • Moment magnitude
Source: Finck, 2005
QUANTITATIVE METHODS (CONT.)
=
Solve for using LSQ
Green’s functions
Source: Grosse & Ohtsu, 2008
• Example 1: explosive/implosive sources
• Example 2: pure vertical shear sources
QUANTITATIVE METHODS (CONT.)
Source: Grosse & Ohtsu, 2008
QUANTITATIVE METHODS (CONT.)
Absolute MTI
Methods
Relative MTI
Methods
Hybrid MTI
Methods
Calculation of Green`s functions for each single event
Limitations:
Accurate estimation of Green`s functions can be difficult Applications:
SiGMA-AE by M. Ohtsu
Calculation of Green’s functions not required for each event, but for cluster of events with common ray path
Limitations:
Dependence of the solution on the a-priori knowledge of the reference event
Applications:
Rel. MTI by Dahm & Grosse
Capitalize on the strengths of both the absolute and relative MTI methods Weighing scheme to
compensate for different types of systematic errors
More reliable and robust estimate of the moment tensor
Applications:
MTI Toolbox by L. Linzer
• MTI Methods developed for AE
• Visualization: Stereograph–focal mechanism diagram–Beach ball
QUANTITATIVE METHODS (CONT.)
Source: Wikipedia
Adapted from Suetsuga, 1994
N
E
N
E
D
x
y
z x
y
x
y
z x
y y
z
2D focal mechanism diagram
y
x
explosion implosion shear
• Others: Full waveform inversion (the ‘king discipline’)
QUANTITATIVE METHODS (CONT.)
Complete source-time function
Source: Grosse et al., 2001 Source: Katsaga et al., 2008
Possible in concrete?
• Try to relate observations with source mechanisms
• Require a network of sensors • Difficult to apply non-linear inverse procedures • Require reliable high-fidelity data with high signal-to-noise ratio • Challenging to apply in cracked media
SUMMARY QUANTITATIVE METHODS
Shigeishi et al., 2003
STRENGTHS AND LIMITATIONS
Qualitative Quantitative
• Strengths
• Limitations
– Simple procedures – Few sensors needed – Work even after concrete
cracks
– What do they physically represent?
– Relative result – Conditions need to be the
same
– Physically meaningful parameters that relate to source mechanism
– Absolute result
– Complicated procedures – Many sensors required – Difficult to apply in large
structures and once severe cracking has occurred
• Real-time feedback on fracture processes • Applied during testing/normal operation – no disturbance
• Local method (vs. global) – Use in targeted areas of concern
• Potential applications for monitoring of concrete structures: – Fracture of rebars and prestressing wires – Crack propagation monitoring – Location of mechanical noise during operation – Fracture monitoring during experiments
• Use of high-fidelity sensors crucial!
• Needs: long-term experience, standards
CONCLUSIONS
Source: Schumacher, 2007
Source: www.thestar.com
Civil & Environmental Engineering