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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.
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Chapter 31
Implementation of the Surface Response to Excitation Method
for Pipes
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
31.1 Introduction
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 [116]. 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
[1722]. 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
e-mail: abagh004@fiu.edu
H. Fekrmandi • D. McDaniel
Applied Research Center, Florida International University, 10555 W Flagler Street, Miami, FL 33174, USA
M. Unal
Department of Mechatronics Engineering, Faculty of Technology, Marmara University, Istanbul, Turkey
V.Y. Senyurek
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
261
plate-like structures [2328]. 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
identification.
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.
31.2 Method
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.
VBfðÞ¼Bm*n,VDfðÞ¼Dm*n ð31:1Þ
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
Eq. (31.2).
SSDj¼1,...,n¼X
i¼m
i¼1
Bij Dij

2ð31:2Þ
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 [2328]. 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
30
25
20
15
10
5
0
25000 50000 75000 100000 125000 150000
Frequency (Hz)
Voltage (mV)
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.
31.5 Conclusion
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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Surface Response to Excitation Method (SuRE) is an active structural health monitoring (SHM) method. SuRE method was implemented by exciting the surface of a plate with a piezoelectric element. The propagation of the created surface waves were monitored with one or more sensors. These sensors could be piezoelectric elements or noncontact sensors such as laser scanning vibrometer. During the experiments, one of the piezoelectric elements excited the block at the 20-400 KHz range while the signals of other piezoelectric elements were recorded and their spectrums were calculated. The reference spectrums of sensors were obtained when the block had no defect. However, in the presence of defect the spectrum deviates from reference response. SuRE method quantifies these changes by calculating sum of square of differences (SSD). It is shown that SuRE method is able to effectively detect the defects.
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In this study surface response to excitation (SuRE) method with a neural network was used for structural health monitoring of an aluminum beam. SuRE method excited and monitored the elastic guided waves on the structure. The frequency-transfer function was captured over a range of high frequencies (20-200 kHz) using a low cost Digital Signal Processor (DSP) system. For magnitude estimation, the amplitude of the received signal for each frequency value is calculated. With the magnitude estimation, the frequency domain spectrum response is calculated. Using an aluminum plate as the experimental surface, load in different points of the beam were applied and the response signals organized in a database. With the experimental data, a neural network is trained with the Levenberg-Marquardt algorithm and then trained with the scaled conjugated gradient algorithm.. The study indicated that the SuRE method may be used as a low cost alternative to detect surface changes.
Article
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Surface response to excitation (SuRE) method was originally developed for structural health monitoring (SHM) applications. SuRE was used to evaluate the performance of completed milling operations. The method generates surface waves on the plate and studies the spectrum changes at selected points to detect defects and change of compressive forces. In this study, the length, depth, and width of a slot were changed step by step. The surface of the aluminum plate was excited in the 20–400 kHz range with a piezoelectric element. A laser scanning vibrometer was used to monitor the vibrations at the predetermined grid points after the dimensions of the slot were changed methodically. The frequency spectrums of measured vibrations were calculated by using the Fast Fourier Transformation (FFT). The sums of the squares of the differences (SSD) of the spectrums were calculated to evaluate the change of the spectrums. The SuRE method was able to determine if the dimensions were changed in each case at all the selected points. The scanning laser vibrometer is not feasible to be used at the shop floor. However, the study demonstrated that a piezoelectric element attached to any of the grid points would be able to evaluate the completed machining process.
Article
Full-text available
The Surface Response to Excitation (SuRE) method excites the surface of the structure with a piezoelectric element. The generated vibrations at critical points on the surface are measured with other piezoelectric elements, a laser vibrometer or other sensors. Then the magnitude of the transfer function between the excitation and the sensory signal is monitored. The performance of the SuRE method was evaluated using a low cost Digital Signal Processor (DSP) system, spectrum analyzer, and laser vibrometer. The accuracies of the Teager–Kaiser (TKA), Goertzel, RMS and average of the positive values algorithms were evaluated for magnitude estimation. The SuRE method was employed successfully for detection of compression loads by using the DSP system. Existence of composite coating was inspected using a spectrum analyzer. Finally, the method was used to detect localized loads on an aluminum plate with a laser vibrometer. The study indicated that the SuRE method may be used as a low cost alternative to impedance method. The inconvenience of using separate sensor(s) is the disadvantages of the SuRE method respect to the imped- ance method. The main advantages are requirement of simpler and cheaper instrumenta- tion for data analysis, defect location estimation capability when multiple sensors are used, faster data acquisition at low noise environments, and allowing non-contact sensors such as laser vibrometers for measurement of surface response.
Chapter
In this study, an active structural health monitoring (SHM) system is developed for non-destructive defect identification in steel pipes, which is based on guided waves generated and collected using piezoelectric ceramics patches. Finite element models of the elastic wave propagation in steel pipes are devised to determine their characteristics and used to optimise wave mode and frequency. An experimental study is also conducted for the validation of the proposed structural health monitoring system and the numerical modelling. The obtained results can be employed to optimally design the online structural health monitoring system with an integrated piezoelectric actuator-sensor network for steel pipes.
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In this study the location of applied load on an aluminum and a composite plate was identified using two type of neural network classifiers. Surface Response to the Excitation (SuRE) method was used to excite and monitor the elastic guided waves on plates. The characteristic behavior of plates with and without load was obtained. The experiments were conducted using two set of equipment. First, laboratory equipment with a signal generator and a data acquisition card. Then same test was conducted with a low cost Digital Signal Processor (DSP) system. With experimental data, Multi-Layer Perceptron (MLP) and Radial Basis Function (RBF) neural network classifiers were used comparatively to detect the presence and location of load on both plates. The study indicated that the Neural Networks is reliable for data analysis and load diagnostic and using measurements from both laboratory equipment and low cost DSP.
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To improve the safety and reliability of pipeline structures, much work has been done using ultrasonic guided waves methods for pipe inspection. Though good for evaluating the defects in the pipes, most of the methods lack the capability to precisely identify the defects in the pipe features like welds or supports. Therefore, a novel guided wave based cross-sectional diagnostic imaging algorithm was developed to improve the ability of circumferential cracks identification in the pipe features. To ensure the accuracy of the imaging, an angular profile-based frequency selection method is presented. As validation, the approach was employed to identify the presence and location of a small circumferential crack with 1.13% cross sectional area (CSA) in the welding zone of a 48mm diameter type 304 stainless steel pipe. Accurate identification results have demonstrated the effectiveness of the developed approach.
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Cylindrical guided waves based techniques are effective and promising tools for damage detection in long pipes. The essential operations are generation and reception of guided waves in the structures utilizing transducers. A novel in-plane shear (d36 type) PMNT wafer is proposed to generate and receive the guided wave, especially the torsional waves, in metallic pipes. In contrast to the traditional wafer, this wafer will directly introduce in-plane shear deformation when electrical field is conveniently applied through its thickness direction. A single square d36 PMNT wafer is bonded on the surface of the pipe positioned collinearly with its axis, when actuated can predominantly generate torsional (T) waves along the axial direction, circumferential shear horizontal (C-SH) waves along circumferential direction, and other complex cylindrical Lamb-like wave modes along other helical directions simultaneously. While a linear array of finite square size d36 PMNT wafers was equally spaced circumferentially, when actuated simultaneously can nearly uniform axisymmetric torsional waves generate in pipes and non-symmetric wave modes can be suppressed greatly if the number of the d36 PMNT wafer is sufficiently large. This paper first presents the working mechanism of the linear d36 PMNT array from finite element analysis (FEA) by examining the constructive and destructive displacement wavefield phenomena in metallic pipes. Furthermore, since the amplitude of the received fundamental torsional wave signal strongly depends on frequency, a series of experiments are conducted to determine the frequency tuning curve for the torsional wave mode. All results indicate the linear d36 PMNT array has potential for efficiently generating uniform torsional wavefield of the fundamental torsional wave mode, which is more effective in monitoring structural health in metallic pipes.
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The use of ultrasonic guided waves for damage detection in pipes is continuously increasing. Generally longitudinal (axial symmetric) modes are excited and detected by PZT (Lead Zirconate Titanate) transducers in transmission mode for this purpose. In most studies the change in the received signal strength with the extent of damage has been investigated while in this study the change in the phase and the time-of-flight (TOF) of the propagating wave modes with the damage size is investigated. The cross-correlation technique is used to record the small changes in the TOF as the damage size varies in steel pipes. Dispersion curves are calculated to carefully identify the propagating wave modes. Differential TOF is recorded and compared for different propagating wave modes. Feature extraction techniques are used for extracting phase and time-frequency information. The main advantage of this approach is that unlike the recorded signal strength the TOF and the phase are not affected by the bonding condition between the transducer and the pipe. Therefore, if the pipe is not damaged but the transducer-pipe bonding is deteriorated then although the received signal strength is altered the TOF and phase remain same avoiding the false positive alarms of damage. Copyright © 2015 Elsevier B.V. All rights reserved.