Civil & Environmental Engineering
Non-Destructive Testing of Wood-Based Composites Using Ultrasonic Stress Waves
Jean Carlo Vilalta, Undergraduate Research Assistant & Thomas Schumacher, Assistant Professor (Adviser)
Table 1. Estimated p-wave velocities for all specimens
Introduction and Background
Experimental Methodology
•
The test setup is illustrated in Figure 3. This setup is often referred to
as ‘pitch-catch’ where a piezoelectric transmitter creates a ultrasonic
stress wave on one side of the specimen that is measured on the
opposite face by a piezoelectric receiver. The fastest stress wave type
that exists in a solid is the so-called compression or p-(primary) wave
mode. For this study, a wave signal as shown in Figure 4 (black line)
with a peak frequency of 150 kHz was used as input signal and
repeated several times so that statistical variations of the
measurement and material could be established.
•
•
•
Wood and wood-based composites are more likely than other
materials to decay under certain environmental conditions and
exposure.
Non-destructive testing (NDT) is commonly used to determine the
properties of different materials such as metals, polymers, and
concrete, without varying their end-use capabilities.
NDT may be used to analyze physical and mechanical properties
of wood-based composites.
Specifically, ultrasonic NDT may be useful in the evaluation of
wood-based composites during the manufacturing process to
estimate glue line quality and to detect flaws (see Figure 1) to
accomplish quality control.
Waveform
Generator
Data
Acquisition
System
Signal
Preamplifier
Waveform
Amplifier
Receiver
Transmitter
Figure 1. Example of a ‘blow-out’ (large crack parallel to the surface
of the specimen) in a wood-based composite.
Computer using
wave recording
software
The objective of this study is to evaluate ultrasonic NDT
methods for the detection and visualization of flaws in
wood-based
such
as ‘blow-outs’
Objectives:composites
To detect (using
ultrasonic
NDT) any flawsand
or the
distribution
andwithin
quality
the specimens
glue line. otherwise
irregularities
theof
wood
undetectable by visual means.
Specimen
(a)
Figure 3. Experimental setup
Test Specimens
Results
Four engineered-wood-type specimens were tested and are shown in
Figure 2:
1) 0.75” thick, 16” x 3”, plywood (Figure 2.a)
2) 0.75” thick, 16” x 3”, oriented strand board (OSB) (Figure 2.b)
3) 0.75” thick, 16” x 16”, low-density particle board with a ‘blow-out’
(Figure 2.c)
4) 0.75” thick, 16” x 16”, low-density particle board (Figure 2.d)
Two parameters were determined from the recorded data using Matlab:
• The p-wave amplitudes Ap of the received signals (see Figure 4.a)
• The p-wave velocity cp using the time difference Dt and thickness d
between the transmitted and the received signal (see Figure 4.a)
(c)
Figure 2. Test specimens
(d)
Figure 5. Contour plots for p-wave velocities in (a) low density panel
and (b) panel with a blow-out board
Conclusions
The different specimens could be distinguished by the different pwave velocities. Using ultrasonic NDT, flaws in wood-based
composites such as ‘blow-outs’ can be quantified and localized.
Dt
Future Work
Ap
(a)
(b)
Figure 4. Example of transmitted (black) and received (red) signal
waveforms from (a) an integer area and (b) an area having a ‘blow-out’.
(b)
(b)
Change in time (s)
of wave arrival
d
cp 
Dt
(a)
Figure 5 shows an example of how the data can be represented using
a contour plot for the p-wave velocities for specimens 3) and 4):
It was found that the p-wave amplitudes from the OSB (Figure 2.b)
had a lower amplitude and a slower velocity than the plywood (Figure
2.a). This can be attributed to a lower density (more voids) of the OSB.
Continued evaluation of wood-based composites using ultrasonic
stress wave propagation and correlation with mechanical properties
such as density, glue line content and quality, and tensile and shear
strength.
Acknowledgments
This research work was sponsored by the University of Delaware
Research
Foundation
(UDRF)
Research
Experience
for
Undergraduates (REU) Summer Internship Program. Wood composite
specimens were provided by Arijit Sinha, Assistant Professor in Wood
Science at Oregon State University. The support is greatly appreciated.