A Pocket AE DAS was used to measure simulated acoustic emissions from two thin plate specimens composed of homogeneous, isotropic materials. The first specimen was made of aluminum, and the second specimen was made of polyethylene. The results of the tests demonstrate not only the practical use of acoustic emission testing but also the effect of the material properties of the specimen on the raw data acquired by the DAS.

1. Acoustics Emission Lab
Report
NDE-ME 7820
Submitted by Pratik Saxena (gd8959)
Submitted On November 29, 2016.

2. ii
Table of Contents
Table of Figures ..................................................................................................ii
A. Objective......................................................................................................1
B. Theory/Background.......................................................................................1
C. Experiment ...................................................................................................2
D. Observations/Results.....................................................................................3
E. Discussion/Conclusion ..................................................................................4
F. References.............................................................................................................5
Table of Figures
Figure 1 – Typical Acoustic Emission Setup [1]...................................................1
Figure 2 – Aluminum & Polyethylene AE Test Setup...........................................2
Figure 3 – Input Screen for Basic Parameters for Polyethylene Beam....................3
Figure 4 – Acoustic Emission Results for Aluminum Beam Sample......................4
Figure 5 – Acoustic Emission Results for Polyethylene Beam Sample...................5

3. 1
A. Objective
The objective of the Acoustic Emission Laboratory experiment is to gain hands-on experience in using
the non-destructive evaluation (NDE) method of acoustic emission (AE) to detect and locate simulated
emission events in rectangular plate samples, where the simulated emission events are created by
striking the samples with a stylus [1].
B. Theory/Background
Acoustic emissions, also called stress wave emissions, are transient elastic waves in solids generated by
the rapid release of energy within a material during a micro or macro failure event, such as during crack
growth. Acoustic emission testing is a passive testing method since it does not require the addition or
introduction of energy into the test piece as part of the testing process. The energy of an acoustic
emission is on the order of attojoules (10-18
J). Thus, acoustic emission testing can be used to detect very
small events that would otherwise require very expensive and sensitive equipment to detect. A typical
acoustic emission test setup is illustrated in Figure 1.
Figure 1 – Typical Acoustic Emission Test Setup [2]
The location of an acoustic emission can be determined in a thin specimen by means of triangulation, in
which the difference in the time of flight (TOF) for the acoustic emission to reach each sensor is used to
calculate the position of the origin of the emission. This type of triangulation is less reliable in thick
samples, in which the depth of the origin of the emission can obscure the location of the emission when
using a planar array of sensors. The sensors are attached to the test specimen with the use of a couplant,
which is needed in order to remove air between the sensor and specimen because air has a very low
acoustic impedance, which impedes the transmission of the acoustic emission wave.

4. 2
C. Experiment
Aluminum and polyethylene thin plate specimens were used for this experiment. Dimensions of the thin
plate specimens were 127 mm length x 50 mm width and 95 mm length x 50 mm width, respectively.
Figure 2 – Aluminum and polyethylene AE Test Setup
The sample (aluminum or polyethylene) was attached to two transducers,which were connected to
Channels 1 and 2 of the Pocket AE acquisition system, as shown in Figure 2. A supersaturated aqueous
solution of glucose and fructose was used as a couplant between the transducers and each specimen to
ensure a continuous connection between the specimen and the sensor. Polyurethane foam was placed
under the sample not only to isolate the specimen from surrounding sources of acoustic energy but also to
prevent the emissions originating within the specimen from being absorbed by the surroundings rather
than the transducers.
Figure 3 – Input Screen for Basic Parametersfor Polyethylene Beam
Before conducting each test, the basic parameters of each specimen were measured and entered into the
Pocket AE data acquisition system (DAS). The parameters recorded were specimen length, width, and
thickness, as well as sensor to sensor distance and speed of sound in the specimen material. Figure 3
shows the input screen on the Pocket AE DAS. The velocity of sound waves in the specimen material
was pulled from a standard material properties table. Once the specimen parameters were entered and the
transducers were attached to the specimen, a single impact was applied to the specimen with a stylus.
This acoustic emission event yielded eight plots for each specimen. The transducers are denoted Channel
1, in blue, and Channel 2, in red, on all of the plots.

5. 3
D. OBSERVATIONS/RESULTS
The aluminum beam specimen was tested and the results are shown in Figure 4. The first plot shown, Hits
vs Time (Plot 1), shows the DAS measured two hits on Channel 2. For each test,only a single impact was
supposed to be applied to the specimen with a stylus. The indication of two hits recorded is likely due to
accidentally striking the specimen a second time with the stylus. The Amplitude vs. Time plot (Plot 2),
which shows the amplitudes of the emissions received by each transducer,supports this scenario. The
Voltage vs Time plots (Plot 3 and Plot 4 for Channel 1 and Channel 2, respectively) are very similar to
one another, indicating that each of the two sensors received similar inputs as a result of the acoustic
emissions. The Voltage vs. Time plots show the raw data recorded by the DAS, since each transducer
reads the impinging acoustic wave as a voltage generated by the piezoelectric crystal inside the
transducer. These plots show far less attenuation with time than the Voltage vs. Time plots shown for the
polyethylene specimen in Figure 5. This difference is likely due to differences in the inherent damping of
the materials, with the polymer polyethylene having a much higher damping coefficient than the metallic
aluminum, resulting in faster dissipation of the acoustic waves. The Power vs Frequency plots (Plot 5 and
Plot 6 for Channel 1 and Channel 2, respectively) are likewise very similar to one another. This result is
expected since the specimen is composed of one homogenous, isotropic material. The specimen was
struck in approximately the middle of its length between the two sensors,as indicated by the Amplitude
vs. X Position plot (Plot 8).
Figure 4 – Acoustic Emission Resultsfor AluminumBeamSample

6. 4
The polyethylene thin plate specimen was tested using the same procedure and the results are shown in
Figure 5. The Hits vs Time (Plot 1) plot indicates that the DAS measured four hits on Channel 1 and two
hits on Channel 2. Again, while only a single impact was supposed to be applied to the specimen with a
stylus, the indication of multiple hits recorded is likely due to accidentally striking the specimen multiple
times with the stylus. The Amplitude vs. Time plot (Plot 2) supports this scenario, with the amplitudes of
multiple strikes shown. The Voltage vs Time plots (Plot 3 and Plot 4, for Channel 1 and Channel 2,
respectively), show similar responses, though the maximum amplitude of the Channel 1 voltage response
is higher than that of Channel 2, while the total perturbation of the voltage signal for Channel 2 is greater
than that of Channel 1. The Power vs Frequency plots (Plot 5 and Plot 6, for Channel 1 and Channel 2,
respectively) show similar frequency responses,indicating that each of the two sensors received similar
inputs as a result of the acoustic emissions. This outcome is expected since the specimen is composed of
one homogenous, isotropic material. The specimen was struck at approximately one-third of its length
between the two sensors,closer to the sensor denoted Channel 1, as indicated by the Amplitude vs. X
Position plot (Plot 8).
Figure 5 – Acoustic Emission Results for Polyethylene Beam Sample
E. Discussion/Conclusion
A Pocket AE DAS was used to measure simulated acoustic emissions from two thin plate specimens
composed of homogenous, isotropic materials. The first specimen was made of aluminum, and the
second specimen was made of polyethylene. The results of the tests demonstrate not only the practical
use of acoustic emission testing but also the effect of the material properties of the specimen on the raw
data acquired by the DAS.

7. 5
F. References
[1] E. Ayorinde. Acoustic Emission. 2015. Wayne State University. Course handout.
[2] Non Destructive Testing by Acoustic Emission: Instrumentation. 2004. Euro PhysicalAcoustics
SA. [Online]. Available: < http://www.epandt.com/us/produits_ea_us.html >