Electromechanical Impedance Method Research Articles

Pipeline corrosion assessment using electromechanical impedance technique

Pipelines which transport and distribute petroleum products, oil, and gas, chemical substances, water, steam are vital to the economy. And these vital assets' health is adversely affected significantly by corrosion. Moreover, the corrosion of pipelines leads to periodical maintenance which often results in shutdown of operation and even leads to catastrophic failure of pipelines. Hence, an adequate monitoring system is required to detect and monitor corrosion in the pipelines. The Electromechanical Impedance Based method has emerged as the most promising non-destructive technique because of its ability to detect damage at an incipient level. This research work presents corrosion monitoring of mild steel pipelines using the Electromechanical Impedance Method (EMI). The corrosion monitoring was carried out for full surface corrosion and strip corrosion in mild steel specimens by simulating corrosion through the accelerated corrosion test. The variation in the conductance signature is used for the qualitative and quantitative evaluation of corrosion damage. The conductance of specimens is acquired using the LCR meter at regular intervals of time. Results indicate that the magnitude of conductance signature is decreased with an increase in the degree of corrosion. The quantification of corrosion amount is evaluated through Root Mean Square Deviation (RMSD), Moving Absolute Percent Deviation (MAPD), and Correlation Coefficient Deviation (CCD). All three matrices increase with the increase of the corrosion degree. The RMSD and CCD are consistent with the degree of corrosion. Among the three metrics, the MAPD has the most pronounced values and showed the highest sensitivity. The results from the study show promising development in SHM and illustrate the capability to quantify imminent corrosion in pipelines using damage indices.

Detecting fatigue in aluminum alloys based on internal friction measurement using an electromechanical impedance method

Detecting mechanical fatigue of metallic components is always a challenge in industries. In this work, we proposed to monitor the low-cycle fatigue of a 6061 aluminum alloy based on internal friction (IF) measurement, which is realized by a quantitative electromechanical impedance (Q-EMI) method using a small piezoelectric wafer bonded on the specimen. Large stress amplitude (230 MPa) was employed in the testing; thus, the fatigue life can always be below 105 cycles. It was found that except for the initial testing stage, the IF always increases steadily with the increasing fatigue cycles. Before the fatigue failure, the IF can reach 2.5–3.4 times the initial value, which is thought to be caused by the micro-cracks forming and growing. In comparison, the resonance frequency of the specimen just drops by about 2% compared with the initial value. Finally, a fatigue criterion based on IF measurement is suggested for aluminum alloys and it can also be extended to other metals.

Inverse analysis for damage detection in a rod using EMI method

The electro-mechanical impedance (EMI) method has been demonstrated to be a powerful tool to detect the small local damages in various engineering structures, due to its high-frequency vibration characteristics. However, this technique is difficult to accurately determine the degree and location of structural damages. In this paper, an inverse analysis combining the measured EMI signatures and the Transfer Matrix Method (TMM) is proposed to identify the damages in the steel rods. A milled groove is introduced into each steel specimen to simulate the local damage. By measuring the EMI signatures of the piezoelectric wafers bonded symmetrically on the upper and lower surfaces of the rectangular specimens respectively, the damage can be detected clearly, as well as natural frequencies being extracted in the relatively lower frequency range. The damage sizes and locations are further determined by connecting the frequency equations and any two measured natural frequencies. Tests on three samples show both damage sizes and locations are accurately detected, which indicates that the present method is quite feasible and effective for damage identification in the bar-type structures.

An Experimental Study of Damage Detection on Typical Joints of Jackets Platform Based on Electro-Mechanical Impedance Technique.

Many methods have been used in the past two decades to detect crack damage in steel joints of the offshore structures, but the electromechanical impedance (EMI) method is a comparatively recent non-destructive method that can be used for quality monitoring of the weld in structural steel joints. The EMI method ensures the direct assessment, analysis and particularly the recognition of structural dynamics by acquiring its EM admittance signatures. This research paper first briefly introduces the theoretical background of the EMI method, followed by carrying out the experimental work in which damage in the form of a crack is simulated by using an impedance analyser at different distances. The EMI technique is used to identify the existence of damage in the welded steel joints of offshore steel jacket structures, and Q345B steel was chosen as the material for test in the present study. Sub-millimetre cracks were found in four typical welded steel joints on the jacket platform under circulating loads, and root average variance was used to assess the extent of the crack damage.

Investigation of electromechanical impedance and residual stress relation for samples machined by hot ultrasonic-assisted turning

Electromechanical impedance (EMI) method has been widely used in recent years to evaluate the condition of structures. In this method, piezoelectric sensors are added to the structure to examine material properties. The impedance/admittance signals are recorded with the aid of the impedance analyzer without any conversion. When there is any change in structures, differences occur in these signals. Thus, changes in structures can be easily determined. It is known that residual stress plays a vital role in materials in terms of crack initiation, breakage, fatigue life, etc. In contrast, the detection of residual stress is time-consuming and it requires experience. This study reveals the effect of cutting parameters on residual stress and electromechanical impedance/admittance values. Firstly, hot ultrasonic-assisted turning was performed for Ti6Al4V material. A parametric study was carried out with different cutting depth, feed rate, and cutting speed. In the second stage, residual stress values measured by X-Ray diffraction (XRD) method and impedance/admittance values measured by an impedance analyzer were compared. In this context, empirical equations with their values between stress/impedance–admittance values have been derived. In general, it has been observed that stress values are significantly associated with impedance/admittance values and the highest correlation was obtained with the reactance values.

A PZT-based electromechanical impedance method for monitoring the moisture content of wood

PurposeAt present, piezoelectric impedance technology has been used in the study of wood damage monitoring. However, little effort has been made in the research on the application of piezoelectric impedance system to monitor the change of wood moisture content (MC). The monitoring method of wood MC is used by piezoelectric impedance technique in this study.Design/methodology/approachOne piezoceramic transducer is bonded to the surface of wood specimens. The MC of the wood specimens increases gradually from 0% to 60% with 10% increments; the mechanical impedance of the wood specimen will change, and the change in the mechanical impedance of the structure is reflected by monitoring the change in the electrical impedance of lead zirconate titanate. Therefore, this paper investigates the relationship between wood MC change and piezoelectric impedance change to verify the feasibility of the piezoelectric impedance method for monitoring wood MC change.FindingsThe experiment verified that the real part of impedance of the wood increased with the increase of wood MC. Besides, the damage index root mean square deviation is introduced to quantify the damage degree of wood under different MC. At the same time, the feasibility and validity of this experiment were verified from the side by finite element simulation. Finally, MC monitoring by piezoelectric impedance technique is feasible.Originality/valueTo the best of the authors’ knowledge, this work is the first to apply piezoelectric ceramics to the monitoring of wood MC, which provides a theoretical basis for the follow-up study of a wide range of wood components and even wood structure MC changes.

A new data normalization approach applied to the electromechanical impedance method using adaptive neuro-fuzzy inference system

A new data normalization approach applied to the electromechanical impedance method using adaptive neuro-fuzzy inference system

Review of piezoelectric impedance based structural health monitoring: Physics-based and data-driven methods

Vibration based structural health monitoring methods are usually dependent on the first several orders of modal information, such as natural frequencies, mode shapes and the related derived features. These information are usually in a low frequency range. These global vibration characteristics may not be sufficiently sensitive to minor structural damage. The alternative non-destructive testing method using piezoelectric transducers, called as electromechanical impedance (EMI) technique, has been developed for more than two decades. Numerous studies on the EMI based structural health monitoring have been carried out based on representing impedance signatures in frequency domain by statistical indicators, which can be used for damage detection. On the other hand, damage quantification and localization remain a great challenge for EMI based methods. Physics-based EMI methods have been developed for quantifying the structural damage, by using the impedance responses and an accurate numerical model. This article provides a comprehensive review of the exciting researches and sorts out these approaches into two categories: data-driven based and physics-based EMI techniques. The merits and limitations of these methods are discussed. In addition, practical issues and research gaps for EMI based structural health monitoring methods are summarized.

Debonding damage detection of the CFRP-concrete interface based on piezoelectric ceramics by the electromechanical impedance method

Debonding in carbon fiber reinforced polymer (CFRP)-strengthened RC structures might always carry the risk of structural collapse. Several studies have focused on the debonding detection of CFRP-strengthened RC structures by nondestructive methods, which represents some limitations. Therefore, an electromechanical impedance (EMI) method based on piezoelectric ceramic (PZT) was applied to detect damage at the CFRP-concrete interface. First, different simulated interfacial defects in a CFRP sheet-wrapped concrete column were detected, and the feasibility of the method was validated. Then, the debonding process of a CFRP plate strengthened RC beam under four-point loading was monitored by the EMI method. Two damage indices, the root mean square deviation (RMSD) and the mean absolute percentage deviation (MAPD), were used to quantify the degree of damage at the CFRP-concrete interface. It is verified that these two damage indices obtained from the EMI method can clearly capture the process of damage development. Moreover, compared to the wave-based method, the EMI method is more sensitive to incipient concrete and debonding damage, which confirms the practicability of the EMI method for on-site applications.

Performance of Linear Mixed Models to Assess the Effect of Sustained Loading and Variable Temperature on Concrete Beams Strengthened with NSM-FRP.

Although some extended studies about the short-term behavior of NSM FRP strengthened beams have been carried out, there is a lack of knowledge about the behavior of this kind of strengthening under sustained loads and high service temperatures. Electromechanical impedance method formulated from measurements obtained from PZT patches gives the ability for monitoring the performance and changes experienced by these strengthened beams at a local level, which is a key aspect considering its possible premature debonding failure modes. This paper presents an experimental testing program aimed at investigating the long-term performance of a concrete beam strengthened with a NSM CFRP laminate. Long term performance under different levels of sustained loading and temperature conditions is correlated with EMI signatures processed using Linear Mixed-effects models. These models are very powerful to process datasets that have a multilevel or hierarchical structure as those yielded by our tests. Results have demonstrated the potential of these techniques as health monitoring methodology under different conditions in an especially complex problem such as NSM-FRP strengthened concrete structures.

Electrical admittance of a circular piezoelectric transducer and chargeless deformation effect

The electromechanical impedance (EMI) method is a promising technique for the sake of structural health monitoring. This method measures the electrical admittance of a piezoelectric transducer attached to a host structure. If the mechanical admittance of the host structure is retrieved from the measured electrical admittance, more information about the host structure can be obtained. For this purpose, an accurate analytical closed-form expression relating the electrical admittance of a piezoelectric transducer to the mechanical admittance of a host structure is needed. Although such expression is available in literature for a circular piezoelectric transducer (CPT), the authors found it erroneous. In this work, closed-form expressions of the mechanical impedance of a free CPT and the electrical admittance of a CPT attached to a host structure are re-defined. Following, the latter is validated by comparing its result with that of an experiment. Successful use of such expressions demands accurate values of the material properties of the transducer. Hereto an analytical-experimental procedure for material calibration of a CPT is proposed. Next, the procedure of detecting the natural frequencies of a host structure using the EMI method is discussed. Using 3D numerical simulations, it is demonstrated that some of the natural frequencies cannot be detected. In essence, the corresponding mode shapes of those natural frequencies impose a deformation onto a CPT which generates a non-significant electric charge.

Curve/Probabilistic Fitting of Damage Metrics for Al-7075 Materials Behavior by Using Electromechanical Impedance Method

The purpose of structural health monitoring is to provide information by making a simultaneous diagnosis of the status of the structure. Despite aging, environmental conditions and unforeseen circumstances, the construction should remain as specified in the design. Changing the environmental conditions causes the sensor and the host structure to change material properties. It is essential to take into account environmental conditions to prevent misdiagnosis. Therefore, the real cause of the change can be determined.In this study, the behavior of constrained piezoelectric wafer active sensor (PWAS)/Al 7075 was investigated by using electromechanical impedance method (EMI) under changing environmental conditions. Numerical studies on this material in the literature are limited and all the experimental/ numerical results are compensated for the temperature effect and analyzed using curve/probabilistic fitting approach for the first time. The sample used in the experimental work was modeled in ANSYS finite element program. In the experimental and numerical results, it has been observed that as the temperature decreases, the frequency shifts to the right and the amplitude increases. The experimental and simulation results were nearly the same. The temperature effect was compensated using the compensation algorithm for experimental and numerical studies. The results were compared using damage metrics. The experimental results analyzed using a curve/probabilistic fitting approach

Electromechanical impedance based self-diagnosis of piezoelectric smart structure using principal component analysis and LibSVM

The long-term use of a piezoelectric smart structure make it difficult to judge whether the structure or piezoelectric lead zirconate titanate (PZT) is damaged when the signal changes. If the sensor fault occurs, the cases and degrees of the fault are unknown based on the electromechanical impedance method. Therefore, after the principal component analysis (PCA) of six characteristic indexes, a two-component solution that could explain 99.2% of the variance in the original indexes was obtained to judge whether the damage comes from the PZT. Then LibSVM was used to make an effective identification of four sensor faults (pseudo soldering, debonding, wear, and breakage) and their three damage degrees. The result shows that the identification accuracy of damaged PZT reached 97.5%. The absolute scores of PCA comprehensive evaluation for structural damages are less than 0.5 while for sensor faults are greater than 0.6. By comparing the scores of the samples under unknown conditions with the set threshold, whether the sensor faults occur is effectively judged; the intact and 12 possible damage states of PZT can be all classified correctly with the model trained by LibSVM. It is feasible to use LibSVM to classify the cases and degrees of sensor faults.

A new approach to monitor wear tracks propagation on-site with electromechanical impedance technique

Generally, the determination of the wear in the mechanical systems is done by checking the critical components in periodic maintenance or by monitoring the secondary indicators such as vibration, noise, and temperature. These indicators can only be recognized after the wear reaches a certain level. In this study, an approach has been carried out on the use of the electromechanical impedance (EMI) method. In this study, EMI measurements were carried out depending on the different test samples, representing a different amount of wear level and wear location of the AISI 1040 steel block. The test samples were worn out in a controlled laboratory environment. The impedance measurements were taken before and after wear tests for each sample. Different measurements were made, and damage metrics were calculated and compared with the reference measurement made; the amount of the wear could be monitored primarily using the Root Mean Square Deviation (RMSD) method without dismantling the system. The location of wear could be determined by Correlation Coefficient Deviation (CCD) technique. In this study, it has been demonstrated that it could be possible to monitor the progress of wear in sensitive mechanical systems periodically without disturbing the integrity of the machine system.

Early-age strength monitoring of the recycled aggregate concrete using the EMI method

At present, the recycled aggregate concrete (RAC) technology has served as an environment-friendly means to dispose the waste concrete. This paper mainly investigates the feasibility of the early-age strength monitoring of the RAC using the electro-mechanical impedance (EMI) method. Both the compressive test and EMI test utilizing the embedded piezoelectric smart aggregate (SA) transducers were conducted on the specimens with different recycled coarse aggregate (RCA) replacement ratios and loading ages. The compressive test results show the early-age strength of the RAC develops more slowly on the whole as the RCA replacement ratio increases. In addition, the EMI test results as well as the theoretical analysis show that the conductance resonant frequency (CRF) of the SA generally rises as the age goes on. By regression analysis, the linear relationship between the early-age strength of the RAC and the CRF increment was established. It validates the applicability of using the EMI method to monitor the early-age strength of the RAC in engineering practice.

Employing principal component analysis for assessment of damage in GFRP composites using electromechanical impedance

In the presented research authors investigated the electromechanical impedance (EMI) technique in the context of damage detection. The EMI method has been studied for considerable amount of time for detecting damage in metallic, composite, concrete, and other parts. Here, the focus is put on the GFRP (glass fibre reinforced polymer) composites. Both a beam and plate was investigated. The samples were prepared with simulated damage. Impact damage was introduced as well as delamination. Authors have developed a data processing tool based on principal component analysis (PCA). The PCA output served as a damage index. It allowed for sensor network data handling, differentiating the damage cases, and damage detection with missing some of the data. The obtained results are promising and show advantages over traditional EMI damage index – the RMSD. The proposed solution can be employed when only one sensor is used as well as when a sensor network is used. Both cases were reported in this work.

Deterioration of structural parameters due to corrosion in prestressed concrete identified by smart probe-based piezo sensor

In this paper, the deterioration of structural parameters namely equivalent stiffness, mass and damping due to corrosion in prestressed concrete (PC) structures using a smart probe-based piezo sensor (SPPS) via electro-mechanical impedance (EMI) technique is presented. The effectiveness of the SPPS was first demonstrated qualitatively by a change in the raw conductance signatures during the corrosion progression and different phases of corrosion (initiation, propagation, and cracking) was identified by the quantitative statistical damage indices. Assessment of material degradation under chloride-laden environment was done using equivalent structural parameters identified by SPPS from the raw admittance signatures and demonstrated the possibility to calibrate with the corrosion rates. Experimental results indicate that SPPS is very sensitive in capturing the changes during the corrosion progression and statistical metric-based method can identify the phases of corrosion. The identified structural parameters (stiffness, mass, and damping) are found to be effective in assessing the material degradation under corrosion in a realistic manner. Hence, it can be concluded that the SPPS via EMI method can be effectively employed in real-life scenarios for diagnosing the PSC structures subjected to corrosion.

Investigation of steel wire mesh reinforcement method for 3D concrete printing

3D concrete printing has received widespread attention and been developed for an increasing number of applications. However, a major challenge facing this technology is an effective way to introduce reinforcement into continuously deposited cementitious material. In this study, different layers of steel wire meshes (SWM) are employed to reinforce the 3D printed structures to improve mechanical capacities. Both destructive (bending, compression and splitting) and non-destructive (using electro-mechanical impedance) tests are employed to characterize the impact of this reinforcement method. The damage accumulation process is measured through the smart PZT patches based on the electro-mechanical impedance method. The results indicate that reinforced 3D-printed components with SWM change their failure modes from brittle to ductile. The peak loads are increased by 59.2–173.3% and the deflection capacity can be increased by more than 11 times than the non-reinforced one. Different mechanical responses of print and cast samples under compression are studied. The splitting tensile strength of wire mesh reinforced concrete is also measured, which is 43.7% higher than the non-reinforced sample. The calculating methods of the cracking moment and ultimate moment of steel wire mesh reinforced 3D printed concrete are presented. Comparison between the calculated and the experimental results verifies the effectiveness in predicting the ultimate moment. Experimental results show that it is feasible and effective to employ steel wire mesh for strength and toughness enhancement of 3D printed structures.

Methods for diagnosing defects in glued joints - a methods review

The paper presents the applications of glued joints in many industry branches. The advantages and disadvantages of glued joints as well as the methods of detecting weld damage are presented. The methods of damage analysis to the glued joints were divided and explained. The most important detection techniques are the X-ray method, the ultrasonic method, the Laser Ultrasound method, the guided wave method, the electromechanical impedance method and the active thermography method. The advantages and limitations that may allow for the proper selection of the research method depending on the diagnosed material and the conditions accompanying the study were indicated.

Crack Identification in Necked Double Shear Lugs by Means of the Electro-Mechanical Impedance Method.

This contribution investigates fatigue crack detection, localization and quantification in idealized necked double shear lugs using piezoelectric transducers attached to the lug shaft and analyzed by the electro-mechanical impedance (EMI) method. The considered idealized necked lug sample has a simplified geometry and does not includes the typical bearing. Numerical simulations with coupled-field finite element (FE) models are used to study the frequency response behavior of necked lugs. These numerical analyses include both pristine and cracked lug models. Through-cracks are located at 90 and 145 to the lug axis, which are critical spots for damage initiation. The results of FE simulations with a crack location at 90 are validated with experiments using an impedance analyzer and a scanning laser Doppler vibrometer. For both experiments, the lug specimen is excited and measured using a piezoelectric active wafer sensor in a frequency range of 1 kHz to 100 kHz. The dynamic response of both numerical calculations and experimental measurements show good agreement. To identify (i.e., detect, locate, and quantify) cracks in necked lugs a two-step analysis is performed. In the first step, a crack is detected data-based by calculating damage metrics between pristine and damaged state frequency spectra and comparing the resulting values to a pre-defined threshold. In the second step the location and size of the detected crack is identified by evaluation of specific resonance frequency shifts of the necked lug. Both the search for frequencies sensitive to through-cracks that allow a distinction between the two critical locations and the evaluation of the crack size are model-based. This two-step analysis based on the EMI method is demonstrated experimentally at the considered idealized necked lug, and thus, represents a promising way to reliably detect, locate and quantify fatigue cracks at critical locations of real necked double shear lugs.