Venu Gopal Madhav Annamdas

Application of Electromechanical Impedance Technique for Engineering Structures: Review and Future Issues

The recent advent of highly durable engineering materials and the advancement of latest structural design theories have made possible the fabrication of more efficient engineering structures. However, the safety and reliability of these structures remains the primary challenge and concern for engineers. Especially, for those structures which involve human traffic and huge investments such as the aerospace structures and bridges. Therefore, there is a compelling need to have high-quality online structural health monitoring (SHM) of such structures. The development of a real-time, in-service, and smart material-based SHM method has recently attracted the interest of a large number of academic and industrial researchers. In the recent past, piezoceramic (PZT) transducer has evolved as an efficient smart material, which is usually employed in electro mechanical impedance (EMI) and guided ultrasonic wave propagation techniques. In EMI technique, a PZT transducer interact with the host structure to result in unique health signature, as an inverse function of structural impedance, when it is subjected to high-frequency structural excitations in the presence of electric field. Using the self-actuating and sensing capabilities of PZT transducers, the EMI models attempted to detect loadings on, and damages in, the structures to be monitored. This article reviews some of the advancements in the field of PZT-based SHM made over the past two decades in engineering structures. This article also provides an insight into the possible future work and improvements required for PZT-based EMI technique.The recent advent of highly durable engineering materials and the advancement of latest structural design theories have made possible the fabrication of more efficient engineering structures. However, the safety and reliability of these structures remains the primary challenge and concern for engineers. Especially, for those structures which involve human traffic and huge investments such as the aerospace structures and bridges. Therefore, there is a compelling need to have high-quality online structural health monitoring (SHM) of such structures. The development of a real-time, in-service, and smart material-based SHM method has recently attracted the interest of a large number of academic and industrial researchers. In the recent past, piezoceramic (PZT) transducer has evolved as an efficient smart material, which is usually employed in electro mechanical impedance (EMI) and guided ultrasonic wave propagation techniques. In EMI technique, a PZT transducer interact with the host structure to result in un...

Influence of loading on the electromechanical admittance of piezoceramic transducers

Damage detection using electromechanical (EM) impedance in structural health monitoring (SHM) of engineering structures is rapidly emerging as a useful technique. In the EM impedance method, piezoceramic (PZT) transducers are either surface bonded to or embedded inside the host structure and are subjected to electric actuation. The EM admittance signatures of the PZT transducers, which consist of real and imaginary parts, serve as indicators to predict the health/integrity of the host structure. However, in real life, structural components such as slabs, beams and columns are constantly subjected to some form of external loading. The EM admittance signature obtained for such a constantly loaded structure is different from that obtained when damages are present in the structure. This paper presents an experimental and statistical investigation to show the influence of loading on EM admittance signatures. It is also observed that the susceptance signature is a better indicator than the conductance signature for detecting in situ stress in the host structure. This observation is further supported by a statistical analysis. This paper is expected to be useful for the non-destructive evaluation of engineering structures with external loading.

Applications of structural health monitoring technology in Asia

Asia is the largest and most populous continent in the world with over 45 million square kilometers of land mass and 4.5 billion people. Asia is characterized by numerous densely populated cities. Structural health monitoring is a non-issue for the underdeveloped countries where basic amenities of survival are more important. However, structural health monitoring is crucial for the developing countries, especially those with densely populated cities like Singapore, Mumbai, and Hong Kong, where any infrastructural failure could be devastating to their society and economy. Structural health monitoring of mechanical and aerospace structures is mostly similar worldwide, but of civil infrastructures could vary due to socio-economic, cultural, geographical, and governmental reasons across countries, and even across states within the same country. This article, which is an enhancement to the keynote paper of the International Workshop on Structural Health Monitoring (IWSHM 2015, Stanford University, USA), presents some of the better known structural health monitoring studies of key civil infrastructures in a few Asian countries. In addition, the authors’ research and applications of structural health monitoring technology carried out at the Nanyang Technological University for civil infrastructures in Singapore are presented. At the end, the authors also discuss recent work on energy harvesting using piezoelectric transducers as an alternative to wired structural health monitoring for automated and self-powered structural health monitoring.

Current developments in fiber Bragg grating sensors and their applications

Whatever may be the material used to build the engineering structures, they are bound to undergo damage at some point in their lifetime. The damage could develop because of continuous usage, degradation, environmental factors, earthquakes or man-made disasters. Structural health monitoring (SHM) has emerged as an important area that has attracted intensive research attention in the recent time. Smart materials like piezoceramics (e.g. lead zirconate titanate or PZT) and fibre optical sensors (FOSs) based effective SHM tools are rapidly developing. Especially, the FOSs offer great potential as monitoring sensors due to their small size, immunity to electromagnetic interference, robustness and survivability in harsh environment. Conventional FOSs use phase modulation techniques for sensing. In spite of the above advantages, they are dependent heavily on source intensity fluctuations and coupling loses. However the fibre Bragg grating (FBG) sensors developed from FOSs are immune to source intensity fluctuations, thus addressing some potential problems of the conventional FOSs. This paper presents a review on the current development of FBG based monitoring techniques and their applications.

Monitoring concrete by means of embedded sensors and electromechanical impedance technique

This paper describes the use of embedded and surface bonded piezoelectric transducers (PZTs) to monitor concrete by means of the electromechanical impedance (EMI) method. The main objective of the present study is the design and utilization of a rugged and embeddable sensing system capable to monitor curing, stress and damage in concrete structures. Three concrete cylinders with in-house designed sensors were cast and tested. Surface bonded PZT were also used to compare the response of conventional PZT patch to the response of the embedded system. After the conventional 28-days curing, two cylinders were subjected to a compression test and the third cylinder was subjected to induced damage. The EM signatures were processed using a statistical index and a slope gradient. The results show that the sensing system and the EMI method are suitable to monitor curing progression and to detect applied stress, damage onset, and damage propagation.

Multiple piezoceramic transducers (PZT)-structure interaction model

Piezoceramic (PZT) transducers are extensively used for damage detection in electromechanical impedance (EMI) based structural health monitoring (SHM) of engineering systems. In the EMI methods, the PZT transducers are generally surface bonded or embedded inside the host structure, and then subjected to actuation so as to interrogate the structure for the desired frequency range. The interrogation results in the prediction of electro-mechanical admittance signatures. These signatures serve as indicator of the health/integrity of the structure. The existing PZT-structure interaction models consider the PZT transducer to be negligible in mass and thus ignored it. However, for multiple PZT-structure interaction, influence of the PZT mass becomes significant as there is significant increase in the number of PZT transducers. This paper presents a novel semi-analytical multiple PZT-structure interaction model which considers the mass influence of the multiple PZT transducers. The model involves numerical modelling, modal analysis and analytical formulation of admittance signature, and thus, is semi-analytical in nature. The numerical analysis serves to obtain the structure response for use as input to the analytical equations, so as to finally predict the admittance signature. The transducers and their host structure without restricting the PZT transducers to square shaped and electrically isotropic ones. Hence, it is expected to be applicable for the non destructive evaluation (NDE) of most engineering systems. The derived model is then experimentally verified using lab sized aluminium plate.

Fatigue Monitoring of Double Surface Defects Using PZT Based Electromechanical Impedance and Digital Image Correlation Methods

Most of the engineering failures especially in mechanical and aerospace industry are due to the fatigue. Fatigue cracks and their propagation can be monitored by observing changes in the structural stiffness resulting from strength reduction as a function of the number of loading cycles. This monitoring can be observed using piezoceramic (PZT) transducer based electromechanical impedance (EMI) technique, and digital image correlation (DIC) system which uses variations on structural surface. The fatigue load usually aggravates the fracture if any defects pre-exist in the structure. The present work monitors multiple-crack emanating from electrode sparked multiple plane defects which are induced in to the specimens prior to the fatigue test, using EMI technique and DIC system. The fracture occurs much below the ultimate stress for the structures which already have defects as in the present case. EMI technique uses signature comparison of healthy and cracked state of the structure to depict crack growth. Initial detection of surface hair-line cracks from the corners of induced defects and their propagation till merging and subsequent failure were explained by signature variations and DIC techniques. Thus, a signal processing technique EMI, and image processing technology DIC were found to complement each other in prediction of early crack and their appearance on surface of the specimens.

Health monitoring of concrete structures using embedded PZT transducers based electromechanical impedance model

This paper presents an easy method of embedding piezoceramic transducer (PZT) and its implementation in electromechanical (EM) impedance based health monitoring of concrete structures. The basic principle used in this monitoring is to record EM admittance signatures acquired from the actuations of PZT transducer in the presence of electric field. Any deviations in these signatures during the monitoring period indicate disturbance/ damage in the structure. The PZT can be either surface bonded or embedded, however the important features of embedding PZT inside the host structure are durability and protection from surface finish, vandalism and environment attacks. The embedment of PZT in the structure is not as simple as surface bonding because there are several issues such as bonding between PZT and host structure. Moreover, it should withstand the curing pressures and temperatures of the host material. This paper is also expected to be useful for monitoring embeddable composite structures.

Evaluation of peak-free electromechanical piezo-impedance and electromagnetic contact sensing using metamaterial surface plasmons for load monitoring

Continuous structural health monitoring (SHM) and delayed SHM techniques can be contact/ contactless, surface bonded/embedded, wired/wireless and active/passive actuator-sensor systems which transfer the recorded condition of the structure to the base station almost instantaneously or with time delay respectively. The time between fatal crack initiation and its propagation leading to the collapse of key infrastructures such as aerospace, nuclear facilities, oil and gas is mostly short. Timely discovery of structural problem depends heavily on the scanning period in well-established techniques like piezoelectric (PZT) based electromechanical impedance (EMI) technique. This often takes much scanning time due to the acquisition of resonant structural peaks at all frequencies in the considered bandwidth; thus poses a challenge for its implementation in practice. On the other hand, recently developed strain sensors based on metamaterials and their breeds such as nested split-ring resonators, localized surface plasmons (LSP), etc, employ measurement of reflected or transmitted signal, with super-fast scanning in the order of at most 1/100th of the time taken by the EMI technique. This paper articulates faster measurements by reducing unnecessary resonant structural peaks and focusing on rapid monitoring using PZT and metamaterial plasmons. Our research adopted wired PZT and wireless LSP communications with impedance analyser and vector network analyser respectively. We present integrated and complementary nature of these techniques, which can be processed rapidly for key infrastructures with great effectiveness. This integration can result in both continuous and delayed SHM techniques based on time or frequency or both domains.

Crack monitoring using multiple smart materials; fiber-optic sensors & piezo sensors

ABSTRACT This article focuses on health monitoring of structures using multiple smart materials. In this research, two fiber-optic sensors, namely fiber Bragg grating (FBG) and fiber-optic polarimetric sensor (FOPS), are investigated for damage detection in the beam specimen. FBG is used for local strain measurement while FOPS is used for global strain measurement. Both FBG and FOPS show significant changes in the strain due to damages in the specimen. Also, at the center of the specimen, piezoelectric wafer active sensor (PWAS) is attached. The electromechanical admittance (EMA) signature of the specimen beam is recorded by PWAS. The changes in the amplitudes of the peaks obtained at various frequencies in this EMA signature are analyzed, and it is shown that the peak amplitudes respond differently to damages and to change in loading. Thus, multiple smart materials (FBG, FOPS, and PWAS) are used to get improved information on the health of the beam.