Implementation of the Surface Response to Excitation Method
A. Baghalian, S. Tahakori, H. Fekrmandi, M. Unal, V.Y. Senyurek, D. McDaniel, and I.N. Tansel
Abstract The Surface response to excitation (SuRE) method was developed to detect the defects and loading condition
changes on plates without using the impedance analyzer. The SuRE method excites the surface with a piezoelectric exciter.
Generally, sweep sine wave is continuously applied and surface waves are monitored with (a) piezoelectric element(s) or
noncontact sensor(s). The change of the spectral characteristics is quantiﬁed by using the sum of the squares of the
differences (SSD) to detect the defects. In this study, the SuRE method was implemented for detection of the defects in
pipes. The surface of a pipe was excited with a continuous sweep sine wave and the dynamic response of the pipe on selected
points were monitored by using a scanning laser vibrometer. The study shows that the SuRE method can be used effectively
for detection of damage and estimation of its severity in pipe like structures.
Keywords SHM • Pipe monitoring • SuRE method • Sensor networks • Guided waves
Wave transmission technology and impedance based SHM methods are among the most successful guided wave-based SHM
techniques that have been used for detecting defects in pipes. Wave transmission SHM techniques work based on monitoring
propagations of excited waves through measuring reﬂections and/or transmission of guided waves [1–16]. Successful
application of these techniques in SHM of pipes highly depends on identifying appropriate guided wave modes and
frequencies for each application. In some applications, there is limited or no knowledge regarding the structure’s material
properties, which makes proper mode and frequency selection an even more troublesome task.
In methods that fall under the category of Impedance methods, a PZT transducer is bonded to a target structure and is used
to simultaneously excite the structure with high-frequency waves and also to acquire electric impedance of a structure
[17–22]. Assuming that the PZT impedance is invariant, since the mechanical impedance of the PZT and the host structure
are coupled together, any changes in the measured electrical impedance by PZT can be correlated with the change of the host
structure’s mechanical health; therefore, by analyzing the electromechanical coupling relationship between PZT ceramic
and body structure the damage condition of the structure can be monitored. In practice, an impedance analyzer such as HP
4194A that costs about $40,000 is used for characterization of the piezoelectric element when implementing the Impedance
method. However, not all capabilities of such an analyzer are necessary; therefore, some researchers have substituted the
impedance analyzer with an ampliﬁer-based turnkey circuit which is capable of measuring and recording electric impedance
of a PZT; where the cost of parts required to make one test device was less than $10.
In a variation of the impedance approach, dynamic characteristics of a structure are monitored using a second piezoelec-
tric element that is also mounted on the surface of the structure. This approach is called the Surface Response to Excitation
(SuRE) method and it has been successfully applied to assess the state of the health in plates and also for load monitoring in
A. Baghalian (*) • S. Tahakori • I.N. Tansel
Mechatronics Research Laboratory, Department of Mechanical and Materials Engineering,
Florida International University, 10555 W Flagler Street, Miami, FL 33174, USA
H. Fekrmandi • D. McDaniel
Applied Research Center, Florida International University, 10555 W Flagler Street, Miami, FL 33174, USA
Department of Mechatronics Engineering, Faculty of Technology, Marmara University, Istanbul, Turkey
Department of Electrical and Electronics Engineering, Faculty of Technology, Marmara University, Istanbul, Turkey
#The Society for Experimental Mechanics, Inc. 2017
W.C. Ralph et al. (eds.), Mechanics of Composite and Multi-functional Materials, Volume 7,
Conference Proceedings of the Society for Experimental Mechanics Series, DOI 10.1007/978-3-319-41766-0_31
plate-like structures [23–28]. The basic concept of the SuRE method is to apply high-frequency sweep sine wave to excite a
piezoelectric element that is attached to surface of a target structure to monitor dynamic characteristics through acquiring the
frequency response using another sensor, which contain critical information regarding state of the health of the structure.
The sensor could be a piezo electric disk or laser vibrometer. In this method, SSD is used as damage metric for damage
The purpose of this paper is to examine the effectiveness of SuRE-based structural health monitoring by using noncontact
sensors in pipe monitoring. In this paper, the same philosophy of continuous comparison of frequency by frequency pattern
of responses is followed; however, the second piezoelectric sensor is substituted with a scanning laser vibrometer.
Circumferential and longitudinal defects have been created and the SSD damage metric was used to detect the presence
and estimate the severity of the damages. The study shows that the SuRE method can be used effectively for detection and
estimation of severity of both types of damages in pipe like structures.
The SuRE method is an active structural health monitoring technique in which the surface of a structure is excited over a
certain frequency range through using surface bonded piezoelectric elements. Typically, one piezoelectric element is used
for excitation and one or more piezoelectric or other type of transducer could be used to acquire the response of the system.
In order to monitor the dynamic response of the system, Fast Fourier Transform (FFT) of the acquired signal is obtained.
This frequency spectrum remains unchanged as long as no change occurred on the structure. The frequency response matrix
of the system in intact and damaged states is shown in Eq. (31.1). The response at each frequency has the unit of voltage,
where f is frequency, B and D indicate the Baseline and Damage states, m is number of scanned frequencies, and n is the
number of sensory points in the network. In other words, every column in the matrixes represents the frequency response
spectrum of a certain sensory point over the acquired frequency range.
When damages occur or loads are applied on the structure of interest, the dynamic response of the structure changes. In the
SuRE method, for sensory points of j ¼1,...,n in the sensing network, SSD of the frequency response matrix of the
damaged part with respect to the pristine structure (baseline state) is used as the damage metric and is calculated, as shown in
SSD is an index to quantify changes in the frequency spectrum; damages and loads application on the structure affect
properties such as mass, damping and stiffness, which result in variation of the frequency response from its initial state.
31.3 Experimental Setup
In the present study, a disk-shaped piezoelectric transducer was permanently bonded to the surface of an Aluminum pipe
specimen and it was excited by an external signal generator over a broad frequency range. the pipe had an external diameter
of 26 mm, a wall thickness of 3 mm and a length of 226 mm. Responses at different points were sensed using the LDV (Laser
Doppler Vibrometer)—Polytec 3D Laser Scanning Vibrometer PSV400 [23–28]. The received signals were in the form of V
(f) curves (i.e., amplitude versus frequency).
The testing phase was broken into two main stages of damaged and pristine structure (baseline) tests; ﬁrst, the dynamic
response of the structure at different sensory points in a pristine state were acquired; then, to simulate defects with different
sizes and degrees of severity, circumferential and longitudinal defects were created using a tube cutter and milling machine,
respectively. The depth of the defect in the circumferential defect and the length of the defect in the longitudinal defect were
increased in three increments, in the course of experiments. After increasing the damage characteristics in each increment,
the response of the structure was acquired and the SSD vector was calculated. The schematic of experimental set up used in
this experiment is shown in Fig. 31.1.
262 A. Baghalian et al.
31.4 Results and Discussion
To implement the SuRE method, in the ﬁrst step, the response of the system to excitation in the situation of no-damage
(baseline) was acquired. To show repeatability of the procedure, the response was captured on two different days and each
time prior to data acquisition, the experimental setup was completely disassembled and once again assembled. The test was
repeated three times and the average of the acquired response of the system after the three different tries was used in analysis.
As it can be seen from Fig. 31.2, there is a very high match between responses acquired in the two sets of tests.
Fig. 31.1 Experimental set-up for implementation of SuRE method
Baseline Day 1
25000 50000 75000 100000 125000 150000
175000 200000 225000 250000
Baseline Day 2
Fig. 31.2 First baseline spectrum vs. second baseline spectrum
31 Implementation of the Surface Response to Excitation Method for Pipes 263
A complete circumferential cut was created in the pipe using a tube cutter and depth of cut was increased in three
increments, in steps of 0.5 mm. The dynamic response of the pipe in all sensory points was acquired. Using Eq. (31.2), SSD
values were calculated with respect to baseline frequency spectrums; the results for all sensory points are shown in Fig. 31.3.
As it can be seen from Fig. 31.3, the SuRE method was successfully able to distinguish between three damage states. As it is
shown in Fig. 31.3, by increasing the damage depth, the SSD value that is an indicative of damage presence and severity in
structure increases in all sensory points.
In another try it was aimed to study the effectiveness of the SuRE method in the detection of longitudinal defects and
distinguishing between different levels of severity. Therefore, the length of a longitudinal defect with a width of 1 mm was
increased in increments of 0.5 mm, in three steps. Using Eq. (31.2), SSD values were calculated with respect to frequency
response of the pristine pipe. Similar to Fig. 31.3, it can also be seen from Fig. 31.4 that increasing the length of the damage,
the SSD value monotonically increases in all sensory points.
Fig. 31.3 SSD values on sensory points after each increase in circumferential damage
Fig. 31.4 SSD values on sensory points after each increase in longitudinal damage
264 A. Baghalian et al.
For the ﬁrst time, the SuRE method is applied for pipe structural health monitoring using noncontact laser doppler sensors.
The differences between the FFT of the acquired signal in pristine and other damaged states were quantiﬁed by calculating
the corresponding sum of the squares of differences. The SSD damage metric in pipes shows steady and monotonic change
in value as the damage condition increases. Our case studies have demonstrated that SuRE method could be successfully
applied for SHM of pipes.
Acknowledgment The authors would like to thank The Scientiﬁc and Technological Research Council of Turkey (TUBITAK) for supporting
Dr. Muhammet Unal and Dr. Volkan Yusuf Senyurek’s research at the Florida International University.
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