Acoustic Emission (AE) refers to the generation of transient elastic waves produced by a sudden redistribution of stress in a material. When a structure is subjected to an external stimulus (change in pressure, load, or temperature), localized sources trigger the release of energy, in the form of stress waves, which propagate to the surface and are recorded by sensors. With the right equipment and setup, motions on the order of picometers (10 -12 m) can be identified. Sources of AE vary from natural events like earthquakes and rockbursts to the initiation and growth of cracks, slip and dislocation movements, melting, twinning, and phase transformations in metals. In composites, matrix cracking and fiber breakage and debonding contribute to acoustic emissions. AE’s have also been measured and recorded in polymers, wood, and concrete, among other materials.

1. ACOUSTIC EMISSION TESTING
-By
O L K ARAHVINTH
20082606

2. PRINCIPLE
 Acoustic Emission may be defined as a transient elastic wave generated
by the rapid release of energy within a material.
 When a structure is subjected to an external stimulus (change in
pressure, load, or temperature), localized sources trigger the release of
energy, in the form of stress waves, which propagate to the surface and
are recorded by sensors. This occurs when a small surface displacement of
a material is produced.

3. HISTORY & FACTS
 Probably the first practical use of AE was by pottery makers. As early as
6,500 BC, potters were known to listen for audible sounds during the
cooling of their ceramics, to asses the quality of there products.
 Probably the first observation of AE in metal was during twinning of pure
tin as early as 3700 B.C.
 The first documented observations of AE appear to have been made in the
8th century by Arabian alchemist Jabir ibn Hayyan. He described the
“harsh sound or crashing noise” emitted from tin. He also describes iron as
“sounding much” during forging.
 In 1936, Friedrich Forster and Erich Scheil (Germany) conducted
experiments that measured small voltage and resistance variations caused
by sudden strain movements caused by martensitic transformations.
 Today, AE Non-Destructive Testing used practically in all industries around
the world for different types of structures and materials.

4. TESTING PROCESS
Materials "talk" when they are in trouble: with Acoustic
Emission equipment you can "listen" to the sounds of
cracks growing, fibers breaking and many other modes of
active damage in the stressed material.

5. 1. DETECTION OF AE
 Sources of AE include many
different mechanisms of
deformations and fracture whilst
the detection process remains the
same.
 As a crack grows a number of
emissions are released.
 When the AE wave front arrives at
the surface of a test specimen
minute movements of the surface
molecules occur.
 The function of AE sensors is to
detect this mechanical movement
and convert it into a useable
electric signal.

6. 2. PROCESSING OF AE
SIGNALS
 The small voltage generated by the
sensor is amplified and the raw
radio frequency (RF) signal is
transferred to the computer.
 Based on user defined
characteristics, the RF signal is split
into discrete waveforms.
 These waveforms are then
prescribed by characteristics such
as amplitude, rise time, absolute
energy based on a user defined
threshold.

7. 3. DISPLAYING AE
SIGNALS
 The collected waveforms can then
be displayed in two ways.
 One, function of waveform
parameters.
 Two, as the collected waveform
itself.
 Most AE tests currently only record
the waveform parameters and
ignore the collected waveform,
mainly due to the large amount of
computing memory it uses.

8. 4. LOCATING AE
SIGNALS
 The automated source location
capability of AE is perhaps its most
significant attraction as a non-
destructive testing (NDT)
technique.
 The predominant method of source
location is based on the
measurement of time difference
between the arrival of individual AE
signals at different sensors in an
array.

9. DIFFERENT FROM OTHER NDT
TECHNIQUES
 The first difference pertains to the origin of the signal. Instead of
supplying energy to the object under examination, AET simply listens for
the energy released by the object. AE tests are often performed on
structures while in operation, as this provides adequate loading for
propagating defects and triggering acoustic emissions.
 The second difference is that AET deals with dynamic processes, or
changes, in a material. This is particularly meaningful because only active
features (e.g. crack growth) are highlighted. The ability to discern
between developing and stagnant defects is significant. However, it is
possible for flaws to go undetected altogether if the loading is not high
enough to cause an acoustic event. Furthermore, AE testing usually
provides an immediate indication relating to the strength or risk of failure
of a component. Other advantages of AET include fast and complete
volumetric inspection using multiple sensors, permanent sensor
mounting for process control, and no need to disassemble and clean a
specimen.

10. AE SOURCE LOCATION
TECHNIQUES
Locating the source
of significant
acoustic emissions is
often the main goal
of an inspection.

11. 1. MULTIPLE CHANNEL SOURCE
LOCATION TECHNIQUE
 AE systems are capable of using multiple
sensors/channels during testing,
allowing them to record a hit from a
single AE event.
 As hits are recorded by each
sensor/channel, the source can be
located by knowing the velocity of the
wave in the material and the difference
in hit arrival times among the sensors, as
measured by hardware circuitry or
computer software.
 Source location techniques assume that
AE waves travel at a constant velocity in
a material. By properly spacing the
sensors in this manner, it is possible to
inspect an entire structure with
relatively few sensors.

12. 2. LINEAR LOCATION
TECHNIQUE
 One of the commonly used
computed-source location
techniques is the linear location
principle
 Linear location is often used to
evaluate struts on truss bridges.
 When the source is located at the
midpoint, the time of arrival
difference for the wave at the two
sensors is zero.
 Whether the location lies to the
right or left of the midpoint is
determined by which sensor first
records the hit. This is a linear
relationship and applies to any
event sources between the sensors.

13. 3. ZONAL LOCATION
TECHNIQUE
 As the name implies, zonal location
aims to trace the waves to a specific
zone or region around a sensor.
 Zones can be lengths, areas or volumes
depending on the dimensions of the
array.
 The source can be assumed to be within
the region and less than halfway
between sensors.
 When additional sensors are applied,
arrival times and amplitudes help
pinpoint the source zone.

14. 4. POINT LOCATION
 In order for point location to be
justified, signals must be detected in a
minimum number of sensors: two for
linear, three for planar, four for
volumetric.
 Accurate arrival times must also be
available.
 The velocity of wave propagation and
exact position of the sensors are the
necessary criteria.
 Equations can then be derived using
sensor array geometry or more complex
algebra to locate more specific points of
interest.

15. INSTRUMENTATION
Typical AE apparatus consist of the following
components:
Sensors used to detect AE events.
Preamplifiers amplifies initial signal. Typical
amplification gain is 40 or 60 dB.
Cables transfer signals on distances up to 200m to
AE devices. Cables are typically of coaxial type.
Data acquisition device performs filtration, signals’
parameters evaluation, data analysis and charting.

16. SENSOR
 AE sensors respond with amazing
sensitivity to motion in the low
ultrasonic frequency range (10 kHz -
2000 kHz). Motions as small as 10-12
inches and less can be detected.
 These sensors can hear the
breaking of a single grain in a metal,
a single fiber in a fiber-reinforced
composite, and a tiny gas bubble
from a pinhole leak as it arrives at
the liquid surface.
 The transducer element in an AE
sensor is almost always a
piezoelectric crystal, which is
commonly made from a ceramic
such as lead zirconate titanate
(PZT).

17. APPLICATIONS
1. WELD MONITORING
 During the welding process,
temperature changes induce
stresses between the weld and
the base metal.
 These stresses are often
relieved by heat treating the
weld.

18. 2. BUCKET TRUCK
INTEGRITY
EVALUATION
 Accidents, overloads and
fatigue can all occur when
operating bucket trucks or
other aerial equipment.
 If a mechanical or structural
defect is ignored, serious
injury or fatality can result.

19. 3. BRIDGES
 Bridges contain many welds, joints
and connections, and a combination
of load and environmental factors
heavily influence damage
mechanisms such as fatigue cracking
and metal thinning due to corrosion.
 Acoustic Emission is increasingly being
used for bridge monitoring
applications because it can
continuously gather data and detect
changes that may be due to damage
without requiring lane closures or
bridge shutdown.
 In fact, traffic flow is commonly used
to load or stress the bridge for the AE
testing.

20. 4. AEROSPACE
STRUCTURES
 Most aerospace structures consist
of complex assemblies of
components that have been design
to carry significant loads while
being as light as possible.
 AET has been used in laboratory
structural tests, as well as in flight
test applications.
 NASA's Wing Leading Edge Impact
Detection System is partially based
on AE technology.

21. OTHER APPLICATIONS
 Petrochemical and chemical: storage tanks, reactor vessels,
offshore platforms, drill pipe, pipelines, valves, hydro-treater
etc.
 Electric utilities: nuclear reactor vessels, piping, steam
generators, ceramic insulators, transformers, aerial devices.
 Fiber-reinforced polymer-matrix composites, in particular
glass-fiber reinforced parts or structures (e.g. fan blades)
 Material research (e.g. investigation of material properties,
breakdown mechanisms, and damage behavior)
 Real-time leakage test and location within various
components (small valves, steam lines, tank bottoms)

22. ADVANTAGES
 High sensitivity.
 Early and rapid detection of defects, flaws,
cracks etc.
 Real time monitoring
 Cost Reduction
 Minimization of plant downtime for
inspection, no need for scanning the whole
structural surface.

23. STANDARDS
ASME - American Society of Mechanical Engineers
• Acoustic Emission Examination of Fiber-Reinforced Plastic Vessels, Article 11, Subsection A, Section V, Boiler and
Pressure Vessel Code
• Acoustic Emission Examination of Metallic Vessels During Pressure Testing, Article 12, Subsection A, Section V,
Boiler and Pressure Vessel Code
• Continuous Acoustic Emission Monitoring, Article 13 Section V
ASTM - American Society for Testing and Materials
• E569-97 Standard Practice for Acoustic Emission Monitoring of Structures During Controlled Stimulation
• E650-97 Standard Guide for Mounting Piezoelectric Acoustic Emission Sensors
• E749-96 Standard Practice for Acoustic Emission Monitoring During Continuous Welding
• E750-98 Standard Practice for Characterizing Acoustic Emission Instrumentation
• E976-00 Standard Guide for Determining the Reproducibility of Acoustic Emission Sensor Response
• E1067-96 Standard Practice for Acoustic Emission Examination of Fiberglass Reinforced Plastic Resin (FRP)
Tanks/Vessels
• E1106-86(1997) Standard Method for Primary Calibration of Acoustic Emission Sensors
• E1118-95 Standard Practice for Acoustic Emission Examination of Reinforced Thermosetting Resin Pipe (RTRP)
• E1139-97 Standard Practice for Continuous Monitoring of Acoustic Emission from Metal Pressure Boundaries
• E1211-97 Standard Practice for Leak Detection and Location Using Surface-Mounted Acoustic Emission Sensors
• E1316-00 Standard Terminology for Nondestructive Examinations
• E1419-00 Standard Test Method for Examination of Seamless, Gas-Filled, Pressure Vessels Using Acoustic Emission
• E1781-98 Standard Practice for Secondary Calibration of Acoustic Emission Sensors
• E1932-97 Standard Guide for Acoustic Emission Examination of Small Parts
• E1930-97 Standard Test Method for Examination of Liquid Filled Atmospheric and Low Pressure Metal Storage
Tanks Using Acoustic Emission
• E2075-00 Standard Practice for Verifying the Consistency of AE-Sensor Response Using an Acrylic Rod
• E2076-00 Standard Test Method for Examination of Fiberglass Reinforced Plastic Fan Blades Using Acoustic
Emission

24. ASNT - American Society for Nondestructive Testing
• ANSI/ASNT CP-189, ASNT Standard for Qualification and Certification of Nondestructive Testing Personnel.
• CARP Recommended Practice for Acoustic Emission Testing of Pressurized Highway Tankers Made of
Fiberglass reinforced with Balsa Cores.
• Recommended Practice No. SNT-TC-1A.
Association of American Railroads
• Procedure for Acoustic Emission Evaluation of Tank Cars and IM-101 tanks, Issue 1, and Annex Z thereto, “
Test Methods to Meet FRA Request for Draft Sill Inspection program, docket T79.20-90 (BRW) ,”
Preliminary 2
Compressed Gas Association
• C-1, Methods for Acoustic Emission Requalification of Seamless Steel Compressed Gas Tubes.
European Committee for Standardization
• DIN EN 14584, Non-Destructive Testing – Acoustic Emission – Examination of Metallic Pressure Equipment
during Proof Testing; Planar Location of AE Sources.
• EN 1330-9, Non-Destructive Testing – Terminology – Part 9, Terms Used in Acoustic Emission Testing.
• EN 13477-1, Non-Destructive Testing – Acoustic Emission – Equipment Characterization – Part 1,
Equipment Description.
• EN 13477-2, Non-Destructive Testing – Acoustic Emission – Equipment Characterization – Part 2,
Verification of Operating Characteristics.
• EN 13554, Non-Destructive Testing – Acoustic Emission – General Principles.
Institute of Electrical and Electronics Engineers
• IEEE C57.127, Trial-Use guide for the Detection of Acoustic Emission from Partial Discharges in Oil-
Immersed Power Transformers.

25. THANK YOU
AET 08.11.2011 OLK