Performance Assessment of Concrete Crack Repairing Materials using PZT Transducers

Department of Urban and Environmental Engineering (Urban Infrastructure Engineering)Concrete is a widely used material in construction of civil infrastructure engineerings such as dams, houses, bridges, and energy plants. Due to shrinkage, rapid dry of the concrete, and overload, cracks are usually generated on the concrete structures and can possibly cause durability-related issues and structural damages. Thus, the concrete crack is an important indicator of potential durability degradation and damage, and the crack should be monitored and repaired through regular maintenance. Indeed, identifying and repairing the concrete cracks using healing materials is important. While most research efforts to date have been devoted to investigation of crack locations and sizes and effective repair, few are evaluating the repairing performance. Therefore, to find an effective nondestructive evaluation (NDE) method for assessing the repairing performance of different healing materials is necessary. Meanwhile, the electro-mechanical impedance (EMI) employing the Piezoelectric Ceramic Lead Zirconate Titanate (PZT) is widely used in structural health monitoring (SHM) as an NDE method in the civil engineering field. The PZT-based EMI is usually applied to detect and locate structural damage in operation. This study used PZT EMI to extract the impedance, which was used as the damage indicator to evaluate the repairing performance of three different materials of the healing cement material from Intchem company, superabsorbent polymer (SAP), and epoxy. A comparison study on the different computation methods of damage index (the root-mean-square deviation (RMSD), the shift of resonance frequency (SRF) and the mean absolute percentage deviation (MAPD)) is also conducted. Results show that the increase of crack depth level and the completing process of repairing crack can be carried out by the change rates of the impedance (admittance) and the shifts of the resonance frequency of PZT sensor in the selected frequency range clearly. .ope

Low-Cost Piezoelectric Sensors for Time Domain Load Monitoring of Metallic Structures During Operational and Maintenance Processes

The versatility of piezoelectric sensors in measurement techniques and their performance in applications has given rise to an increased interest in their use for structural and manufacturing component monitoring. They enable wireless and sensor network solutions to be developed in order to directly integrate the sensors into machines, fixtures and tools. Piezoelectric sensors increasingly compete with strain-gauges due to their wide operational temperature range, load and strain sensing accuracy, low power consumption and low cost. This research sets out the use of piezoelectric sensors for real-time monitoring of mechanical strength in metallic structures in the ongoing operational control of machinery components. The behaviour of aluminium and steel structures under flexural strength was studied using piezoelectric sensors. Variations in structural behaviour and geometry were measured, and the load and μstrains during operational conditions were quantified in the time domain at a specific frequency. The lead zirconium titanate (PZT) sensors were able to distinguish between material types and thicknesses. Moreover, this work covers frequency selection and optimisation from 20 Hz to 300 kHz. Significant differences in terms of optimal operating frequencies and sensitivity were found in both structures. The influence of the PZT voltage applied was assessed to reduce power consumption without signal loss, and calibration to μstrains and loads was performed.This research was funded by Basque Government, grant number KK-2019/00051-SMARTRESNAK and by the European Commission, grant number 869884- RECLAIM

Damage identification in structural health monitoring: a brief review from its implementation to the Use of data-driven applications

The damage identification process provides relevant information about the current state of a structure under inspection, and it can be approached from two different points of view. The first approach uses data-driven algorithms, which are usually associated with the collection of data using sensors. Data are subsequently processed and analyzed. The second approach uses models to analyze information about the structure. In the latter case, the overall performance of the approach is associated with the accuracy of the model and the information that is used to define it. Although both approaches are widely used, data-driven algorithms are preferred in most cases because they afford the ability to analyze data acquired from sensors and to provide a real-time solution for decision making; however, these approaches involve high-performance processors due to the high computational cost. As a contribution to the researchers working with data-driven algorithms and applications, this work presents a brief review of data-driven algorithms for damage identification in structural health-monitoring applications. This review covers damage detection, localization, classification, extension, and prognosis, as well as the development of smart structures. The literature is systematically reviewed according to the natural steps of a structural health-monitoring system. This review also includes information on the types of sensors used as well as on the development of data-driven algorithms for damage identification.Peer ReviewedPostprint (published version

Damage localization map using electromechanical impedance spectrums and inverse distance weighting interpolation: Experimental validation on thin composite structures

Piezoelectric sensors are widely used for structure health monitoring technique. In particular, electromechanical impedance techniques give simple and low-cost solutions for detecting damage in composite structures. The purpose of the method proposed in this article is to generate a damage localization map based on both indicators computed from electromechanical impedance spectrums and inverse distance weighting interpolation. The weights for the interpolation have a physical sense and are computed according to an exponential law of the measured attenuation of acoustic waves. One of the main advantages of the method, so-called data-driven method, is that only experimental data are used as inputs for our algorithm. It does not rely on any model. The proposed method has been validated on both one-dimensional and two-dimensional composite structures

Sensor validation of a Structural Health Monitoring Process for Aircraft Nacelle

This paper details the implementation process of an embedded structural health monitoring (SHM) system enabling condition-based maintenance of aircraft nacelles. One critical issue before being able to make use of such system is to ensure the effective bonding of the chosen actuators and sensors with their host structure, especially as the latter will be exposed to harsh environments and wide operational variability. In this work, we are concerned with the composite components of the nacelle and we use piezoelectric elements as both sensors and actuators. We propose an integrated approach that allows to validate a combination “Substrate—Glue—Piezoelectric” (SGP) and thus provides criteria to choose and size these assemblies. This validation scheme is based on the observation of the variations of the static capacity of the piezoelectric element after enduring various temperature and stress conditions when bonded to its host structure. Based on those SGP combinations, an active SHM strategy interrogating the structure by means of elastic wave propagation is currently being developed and preliminary results on samples representative of the nacelle are presented and discussed.Projet AIRCELLE (EPICE/CORALIE

Acoustic energy transmission in cast iron pipelines

In this paper we propose acoustic power transfer as a method for the remote powering of pipeline sensor nodes. A theoretical framework of acoustic power propagation in the ceramic transducers and the metal structures is drawn, based on the Mason equivalent circuit. The effect of mounting on the electrical response of piezoelectric transducers is studied experimentally. Using two identical transducer structures, power transmission of 0.33 mW through a 1 m long, 118 mm diameter cast iron pipe, with 8 mm wall thickness is demonstrated, at 1 V received voltage amplitude. A near-linear relationship between input and output voltage is observed. These results show that it is possible to deliver significant power to sensor nodes through acoustic waves in solid structures. The proposed method may enable the implementation of acoustic - powered wireless sensor nodes for structural and operation monitoring of pipeline infrastructure

Vibration Based Damage Identification in a Composite T-Beam Utilising Low Cost Integrated Actuators and Sensors

The development of integrated measurement systems for composite structures is\ud urged by the fact that a Structural Health Monitoring environment requires these systems to become an integral part of the structure. The feasibility of using low cost piezoelectric diaphragms for dynamic characterisation and vibration based damage identification in a composite T-beam structure is demonstrated. The dynamic behaviour is analysed by applying these basic electronic sound components for actuation and sensing. Impact induced damage at the skin-stiffener connection is detected and localized by applying the MSE-DI algorithm on the measured bending strain mode shapes

PZT Sensor Arrays for Integrated Damage Monitoring in Concrete Structures

The broad objective of the work reported here is to provide a fundamental basis for the use of Lead Zirconate Titanate (PZT) patches in damage detection of concrete structures. Damage initiation in concrete structures starts with distributed microcracks, which eventually localize to form cracks. By the time surface manifestation in the form of visible cracking appears there may be significant degradation of the capacity of the structure. Early detection of damage, before visible signs appear on the surface of the structure is essential to initiate early intervention, which can effectively increase the service life of structures. Development of monitoring methodologies involves understanding the underlying phenomena and providing a physical basis for interpreting the observed changes in the parameters which are sensed. PZT is a piezoelectric material, which has a coupled constitutive relationship. In the case of the PZT patches bonded to a concrete structure, any sensing strategy requires developing an understanding of the coupled electromechanical (EM) response of the PZT-concrete system. The challenges associated with the use of PZT patches for damage monitoring in a concrete substrate include providing the following: a clear understanding of the fundamental response of the PZT patch when bonded to a concrete substrate; interpretation of the coupled response of the PZT patch under load induced damage; and development of an efficient, continuous monitoring methodology to sense a large area of the concrete substrate. Due to a lack of a fundamental basis, the use of PZT patches in concrete structures often involves inferring the measured response using model-based procedures. The work outlined in this thesis addresses the key issue of developing the theoretical basis and providing an experimental validation for PZT-based damage monitoring methodology for concrete structures. A fundamental understanding of response of the PZT patch when bonded to concrete substrate is developed. The outcome of the work is an integrated local and distributed sensing methodology for concrete structures by combining the electromechanical impedance and stress wave propagation methods using an array of bonded PZT patches. The work presented in this thesis is focused on using PZT patches bonded to a concrete substrate. A fundamental understanding of the coupled electromechanical behaviour of a PZT patch under an applied electrical excitation in an electrical impedance (EI) measurement, is developed. The influence of the substrate size and its material properties on the frequency dependent EI response of a PZT patch is investigated using concrete substrates of different sizes. The dynamic response of a PZT patch is shown to consist of resonance modes of the PZT patch with superimposed structural response. The resonance behaviour of the PZT patch is shown to be influenced by the material properties of the substrate. The size dependence in the EI response of a PZT patch bonded to a concrete substrate is produced by the dynamic behaviour of the structure. The size of the local zone of the concrete material substrate in the vicinity of the bonded PZT patch, which influences the frequency dependent EI response of the PZT patch is identified. For each resonant mode, a local zone of influence, which is free from the influence of boundary is identified. The dynamic response of the PZT resonant mode is influenced by the elastic material properties and damping within the zone of influence. The structural effects of the concrete substrate produced by the finite size of the specimen are separated from the material effects produced by the material properties and the material damping in the coupled EM response of the bonded PZT patch. The influence of size of the concrete substrate on the coupled impedance response of the PZT is identified with peaks of structural resonance, which are superimposed on the resonant peaks of the bonded PZT patch The EI response of the PZT patch when bonded to concrete for detecting load-induced damage from distributed microcrack to localized cracks within the zone of influence of the PZT patch is investigated. Using an approach which combines an understanding of the coupled EM constitutive behaviour of PZT with experimental validation, a methodology is developed to decouple the effects of stress and damage in the substrate on the coupled EM response of a PZT patch. The features in the EI signature of a bonded PZT patch associated with stress and damage are identified. An increasing level of distributed damage in the concrete substrate produces a decrease in the magnitude and the frequency of the resonant peak of the bonded PZT patch. The substrate stress produces a counter acting effect in the EI spectrum of the bonded PZT patch. A measurement procedure for the use of bonded PZT patches for continuous monitoring of stress-induced damage in the form of distributed microcracks in a structure under loading is developed. An integrated methodology for damage monitoring in concrete structures is developed by combining the EI method for local sensing and the stress wave propagation-based method in a distributed sensing mode. An array of surface mounted PZT sensors are deployed on a concrete beam. The EI measurements from individual PZT sensors are used for detecting damage within the local zone of influence. PZT sensor pairs are used as actuators and sensors for distributed monitoring using stress wave propagation. A stress-induced crack is introduced in a controlled manner. It is detected very accurately from the full-field displacement measurement obtained using digital image correlation. The crack opening profile in concrete produced by the fracture is established from the surface displacement measurements. From the measurements of bonded PZTs, the localized crack is detected in the zone of influence by EI. The change in compliance of the material medium due to a localized crack is small and it is reflected in the smaller change in the measured EI when compared to distributed damage. Stress wave based measurements sensitively detect crack openings on the order of 10m. The material discontinuity produced by a closed crack, after removal of the stress is also detected. A damage matrix is developed for stress wave based method which is independent of transmission path to assess the severity of damage produced by the crack in a concrete structure