Intelligent Crack Detection in Building Structures using Coupled Ultrasonic Guided Wave and Acoustic Emission Sensing

Wind energy plays a pivotal role in the transition to renewable energy sources. However, the reliability of wind turbine blades (WTBs) is often compromised by damage. This urges the increasing need for advanced Structural Health Monitoring (SHM) techniques to ensure the durability and reliability of WTBs. The current study investigates the application of the Ultrasonic Guided Wave (UGW) technique as a nondestructive evaluation (NDE) method for the early detection and localisation of multiple damages in composite WTBs. In this research, a network of three piezoelectric patches is strategically positioned on the blade’s surface to excite guided waves and capture the scattered signals. The study focuses on localising the damages, such as impact damage, surface cracks and their combination. Finite Element (FE) modelling is utilised to simulate wave propagation in the complex composite WTB. A novel damage index mapping approach, based on signal energy difference and time-of-flight (ToF) analysis, is employed to approximate defect locations. The proposed methodology effectively demonstrates the capability to detect and locate the various damage types with significant accuracy. This research contributes to the advancement of intelligent SHM systems for wind energy applications, facilitating autonomous, data-driven maintenance strategies for efficient damage assessment.

Despite proven effectiveness and accuracy in laboratories, the existing damage assessment based on guided ultrasonic waves (GUWs) or acoustic emission (AE) confronts challenges when extended to real-world structural health monitoring (SHM) for railway tracks. Central to the concerns are the extremely complex signal appearance due to highly dispersive and multimodal wave features, restriction on transducer installations, and severe contaminations of ambient noise. It remains a critical yet unsolved problem along with recent attempts to implement SHM in bourgeoning high-speed railway (HSR). By leveraging authors' continued endeavours, an SHM framework, based on actively generated diffuse ultrasonic waves (DUWs) and a benchmark-free condition contrast algorithm, has been developed and deployed via an all-in-one SHM system. Miniaturized lead zirconate titanate (PZT) wafers are utilized to generate and acquire DUWs in long-range railway tracks. Fatigue cracks in the tracks show unique contact behaviours under different conditions of external loads and further disturb DUW propagation. By contrast DUW propagation traits, fatigue cracks in railway tracks can be characterised quantitatively and the holistic health status of the tracks can be evaluated in a real-time manner. Compared with GUW- or AE-based methods, the DUW-driven inspection philosophy exhibits immunity to ambient noise and measurement uncertainty, less dependence on baseline signals, use of significantly reduced number of transducers, and high robustness in atrocious engineering conditions. Conformance tests are performed on HSR tracks, in which the evolution of fatigue damage is monitored continuously and quantitatively, demonstrating effectiveness, adaptability, reliability and robustness of DUW-driven SHM towards HSR applications.

We present a structural health monitoring (SHM) system based on the passive method of acoustic emission (AE) and the active methods of electromechanical impedance (EMI) and guided ultrasonic wave (GUW) methods. As all these methods can be deployed with the use of wafer-type piezoelectric transducers bonded or embedded to the structure of interest, this paper describes a unified SHM system where AE, EMI, and GUW are integrated in the same hardware/software unit. We assess the feasibility of this multi-modal monitoring in a large flat aluminum plate with six transducers. AE events are simulated by exciting a tone burst or using the conventional pencil-lead break test and the detected signals are processed with a source localization algorithm to identify the position of the source. For the active sensing, damage is simulated by adding a small mass to the plate: the raw waveforms are processed with a delay-and-sum algorithm to create an image of the plate whereas the electrical admittance of each transducer is analyzed using the statistical index of the root mean square deviation. The results presented in this paper show that the proposed system is robust, mitigates the weaknesses of each technique considered individually, and can be developed further to address the challenges associated with the SHM of complex structure

Acoustic Emission (AE) and Guided Ultrasonic Waves (GUWs) are non-destructive testing (NDT) methods in several industrial sectors for, e.g., proof testing and periodic inspection of pressure vessels, storage tanks, pipes or pipelines and leak or corrosion detection. In materials research, AE and GUW are useful for characterizing damage accumulation and microscopic damage mechanisms. AE and GUW also show potential for long-term Structural Health and Condition Monitoring (SHM and CM). With increasing computational power, even online monitoring of industrial manufacturing processes has become feasible. Combined with Artificial Intelligence (AI) for analysis this may soon allow for efficient, automated online process control. AI also plays a role in predictive maintenance and cost optimization. Long-term SHM, CM and process control require sensor integration together with data acquisition equipment and possibly data analysis. This raises the question of the long-term durability of all components of the measurement system. So far, only scant quantitative data are available. This paper presents and discusses selected aspects of the long-term durability of sensor behavior, sensor coupling and measurement hardware and software. The aim is to identify research and development needs for reliable, cost-effective, long-term SHM and CM with AE and GUW under combined mechanical and environmental service loads.

Identification of damage in its early stage can have a great contribution in decreasing the maintenance costs and prolonging the life of valuable structures. Although conventional damage detection techniques have a mature background, their widespread application in industrial practice is still missing. In recent years the application of Machine Learning (ML) algorithms have been more and more exploited in structural health monitoring systems (SHM). Because of the superior capabilities of ML approaches in recognizing and classifying available patterns in a dataset, they have demonstrated a significant improvement in traditional damage identification algorithms. This review study focuses on the use of machine learning (ML) approaches in Ultrasonic Guided Wave (UGW)-based SHM, in which a structure is continually monitored using permanent sensors. Accordingly, multiple steps required for performing damage detection through UGWs are stated. Moreover, it is outlined that the employment of ML techniques for UGW-based damage detection can be subtended into two main phases: (1) extracting features from the data set, and reducing the dimension of the data space, (2) processing the patterns for revealing patterns, and classification of instances. With this regard, the most frequent techniques for the realization of those two phases are elaborated. This study shows the great potential of ML algorithms to assist and enhance UGW-based damage detection algorithms.

Corrosion of steel bars in reinforced concrete structure will reduce the bearing capacity of the structure, which will cause damage to the structure and cause great casualties and economic losses. In this paper, the same specimen was monitored by using the ultrasonic guided wave (UGW) and acoustic emission (AE). The variation trend of the cumulative number of acoustic emission impacts and the amplitude variation trend of ultrasonic guided waves were obtained in the process of monitoring steel corrosion. By analysing the curve of cumulative number of impacts and the curve of the amplitude of ultrasonic guided wave changing with time, it can be accurately obtained that the corrosion of steel reinforcement can be divided into three stages, so that the feasibility of monitoring the corrosion process of steel reinforcement can be verified by ultrasonic guided wave and acoustic emission.

In order for the increased use of fiber-reinforced composite structures to be financially feasible, employment of reliable and economical systems to detect damage and evaluate structural integrity is necessary. This task has traditionally been performed using off-line non-destructive testing (NDT) techniques. Safety enhancement programs and cost minimization schemes for repairs, however, have substantially increased the demand for real time integrity monitoring systems, i.e. structural health monitoring (SHM) systems, in the past few years. The real time feature imposes an additional constraint on SHM systems to be fast and computationally efficient. Among the existing approaches fulfilling these requirements, guided ultrasonic wave (GUW)-based methods are of particular interest, since they provide the possibility of finding small size defects, both at the surface and internal, and covering relatively large areas with reasonable hardware costs. Next to theses appealing features, there are certain complexities in utilizing GUWs for SHM of fiber-reinforced composites, that mainly arise from the multi-layer, anisotropic, and non-homogeneous nature of the material. In addition, the multi-mode character of GUWs further increases the complexity of the SHM problem in these materials. It is believed that computationally efficient methods for simulation of GUWs in composite structures can substantially contribute to the field of SHM. Such numerical tools do not only improve the understanding of the propagation of ultrasonic waves and their interaction with different damage types and boundary conditions, but can also make model-based damage identification techniques feasible in the context of on-line SHM. In this dissertation an improved framework for simulation of GUWs in composite structures is developed. The improvements are mainly brought about through the use of (i) physical constraints that reduces the dimensionality of the problem, (ii) improved approximation bases for spatial and temporal discretization of the governing equations, and (iii) efficient mathematical tools to enable the possibility of parallel computation. The formulated approach is a wavelet-based spectral finite element method (WSFEM), which offers the possibility of complete decoupling of the spatial and temporal discretization schemes, and results in parallel implementation of the temporal solution. Although the concept of the WSFEM was introduced a few years prior to this research, to the author's best knowledge, no general framework was proposed for dealing with 2D and 3D problems with inhomogeneity, anisotropy, geometrical complexity, and arbitrary boundary conditions. These issues are addressed in this dissertation in multiple steps as described below. 1- Improvement of the temporal discretization using compactly-supported wavelets, by computing the operators of the wavelet-Galerkin method over finite intervals, and demonstrating about 50% reduction in the number of sampling points, with the same accuracy, compared to the conventional wavelet-based approach. 2- Extension of the existing formulation of the 1D WSFEM based on an in-plane displacement field to 1D waveguides based on a 3D displacement field. In the 1D finite element formulation, spectral shape functions are employed which satisfy the governing equations, in which shear deformation and thickness contraction effects are also incorporated. The minimum number of elements for modeling 1D waveguides is used in this approach. 3- Formulation of a novel 2D WSFEM in which frequency-dependent basis functions are suggested for spatial discretization. Contrary to the conventional WSFEM, the presented scheme discretizes the spatial domain with 2D elements and does not require extra treatments for non-periodic boundary conditions. Superior properties of the formulation are shown in comparison with some time domain FEM schemes. 4- Generalization of the WSFEM and extension to 3D geometries. It is demonstrated that the standard spatial discretization schemes can be combined with the wavelet-Galerkin approach, to fully parallelize the temporal solution. A higher-order pseudo-spectral finite element method, i.e. spectral element method (SEM), is further adopted to attain spectral convergence properties over space and time. The developed WSFEM is subsequently employed in the passive time reversal (TR) method, which is a model-based approach for detection of load and damage location, and operates based on the time invariance of linear elastodynamic equations. It is shown that using the passive TR scheme, the problem of load and damage detection, which is essentially an inverse problem, can be solved in the form of a forward problem, thereby alleviating uniqueness and stability issues. A number of case studies and examples, numerical and experimental, are presented throughout this dissertation to better demonstrate the applicability of the proposed framework.

In this paper, an integrated nondestructive evaluation / structural health monitoring (NDE / SHM) system based on the use of acoustic emission (AE), electromechanical impedance (EMI) and guided ultrasonic waves (GUWs) is presented. The system is integrated into a single hardware/software unit and is driven by a few graphical user interfaces created in the laboratory. The feasibility of this multi-modal monitoring approach is assessed by monitoring an aluminum plate with an array of six wafer-type piezoelectric transducers. AE events are generated with the pencil-lead break technique whereas damage is simulated in the form of permanent magnets attached to the plate. The waveforms associated with the AE are processed using a source localization approach, whereas the GUWs and EMI data are processed using simple metrics based on cross-correlation. The results presented here show that the proposed system is robust and the three NDT methods complement each other very well.

Developing robust Structural Health Monitoring (SHM) solutions for large structures, particularly in the aerospace sector, remains challenging due to the volume, variability, and complexity of the data involved. One very promising solution is based on active ultrasonic guided waves (UGW) which are signals emitted and received by a set of transducers bonded to the structure to monitor. However, existing SHM algorithms cannot solve the aforementioned challenges under the current paradigm of path-by-path processing of the raw UGW signals. To move forward, a new paradigm is introduced in this work. This new approach exploits the intrinsic multi-dimensional tensorial nature of SHM UGW data through Canonical Polyadic Decomposition (CPD) and couples it with the Single Atom Convolutional Matching Pursuit Method (SACMPM). This redefines classical sparse decomposition techniques building accurate and efficient wave propagation models tailored to SHM applications. A unique UGW database where regular ground-based measurements have been carried out on an actual A380 running flight test is described in order to challenge the proposed paradigm shift. The efficiency of the coupling between SACMPM and CPD is illustrated here with respect to their ability to compress UGW information, and extract meaningful information from UGW signals in a physically informed manner. Additionally, a CPD-based damage localization algorithm is enriched using a SACMPM decomposition. Extracted physically informed features can thus be efficiently used for physically informed data driven damage monitoring approaches. The proposed paradigm shift thus demonstrates a strong potential for scalable, transferable, and reliable UGW SHM solutions, bridging the gap between laboratory experiments and real-world deployment. This paradigm shift is also expected to inspire further research and innovative ideas, leading to breakthroughs in the adoption of active UGW signals for SHM applications.

Developing robust Structural Health Monitoring (SHM) solutions for large structures, particularly in the aerospace sector, remains challenging due to the volume, variability, and complexity of the data involved. One very promising solution is based on active ultrasonic guided waves (UGW) which are signals emitted and received by a set of transducers bonded to the structure to monitor. However, existing SHM algorithms cannot solve the aforementioned challenges under the current paradigm of path-by-path processing of the raw UGW signals. To move forward, a new paradigm is introduced in this work. This new approach exploits the intrinsic multi-dimensional tensorial nature of SHM UGW data through Canonical Polyadic Decomposition (CPD) and couples it with the Single Atom Convolutional Matching Pursuit Method (SACMPM). This redefines classical sparse decomposition techniques building accurate and efficient wave propagation models tailored to SHM applications. A unique UGW database where regular ground-based measurements have been carried out on an actual A380 running flight test is described in order to challenge the proposed paradigm shift. The efficiency of the coupling between SACMPM and CPD is illustrated here with respect to their ability to compress UGW information, and extract meaningful information from UGW signals in a physically informed manner. Additionally, a CPD-based damage localization algorithm is enriched using a SACMPM decomposition. Extracted physically informed features can thus be efficiently used for physically informed data driven damage monitoring approaches. The proposed paradigm shift thus demonstrates a strong potential for scalable, transferable, and reliable UGW SHM solutions, bridging the gap between laboratory experiments and real-world deployment. This paradigm shift is also expected to inspire further research and innovative ideas, leading to breakthroughs in the adoption of active UGW signals for SHM applications.

This article is dedicated to the study of the issues of legal regulation of relations, the object of which is temporary structures for business activities (hereinafter referred to as Temporary Structures). The study of the problems of legal regulation of relations involving Temporary Structures is relevant in today’s conditions, as the current legislation does not provide sufficient legal means for clear regulation in this area of social relations, which in turn creates a number of legal conflicts in the regulation of legal relations involving Temporary Structures. Particular attention in the article is devoted to the issues of legal regulation of social relations related to the use of Temporary Structures as movable property in the sense of civil law, as an object of ownership rights, and to legal liability for violations of the procedure for establishing Temporary Structures, etc. The article analyzes the norms of the Civil Code of Ukraine, the Law of Ukraine «On the Regulation of Urban Development Activities», the Procedure for the Placement of Temporary Structures for Entrepreneurial Activities, which define the concepts and characteristics of Temporary Structures, the procedure for their placement in cases specified by current Ukrainian legislation, as well as the features and limits of exercising property rights in relation to the latter. Special attention was paid to the analysis of the norms of current legislation that would classify the Temporary Structure into the appropriate category of things in civil law, as well as determine its legal status as an object of ownership. The author emphasized the study of the institution of liability for violation of the established legal order regarding the placement and use of the Temporary Structure. During the research, it was found that the mechanism for legal regulation of relations regarding the use of Temporary Structures is imperfect, as it does not contain legal means that would establish the legal liability of a person for violation of the established rules regarding the use of Temporary Structures, nor does it classify the Temporary Structure into the category of things (movable or immovable property) and define it as an object of ownership as a whole. Based on the analysis of the norms of current legislation, the following conclusions have been drawn that allow us to assert that the mechanism of legal regulation of relations concerning the use of Temporary Structures does not contain a sufficient number of legal tools capable of defining the latter as a full-fledged object of social relations, since the norms of current legislation do not clearly define Temporary Structure as a movable property in the sense of civil law and do not classify it as an object of property rights. Regulation of relations where Temporary Structures are the object, taking into account the mentioned legal gaps, is carried out through judicial practice, which simultaneously creates legal uncertainty. It was also concluded that the mechanism of legal regulation of relations involving Temporary Structures needs significant improvement in terms of legal liability. After all, the current legislation does not contain any norm that would allow for the legal liability of persons who violate the requirements imposed on the use of Temporary Structures. Taking into account the conducted research, a general conclusion was made that the mechanism of legal regulation of relations, the object of which is a Temporary Structure, requires careful attention from the legislator, and therefore the only tool for improving it is the enshrinement at the legislative level of a complex of legal means that will eliminate the existing gaps that hinder participants in legal relations from fully exercising their rights in relation to such an object of legal relations as Temporary Structures.

The result of the earthquake causes a lateral force that occurs on the building structure. Loads caused by earthquake loads need to be calculated and designed based on standards, so that when an earthquake occurs, the structure of the building is still able to resist the resulting lateral forces. The calculated building structure has a height of 12 floors with structural elements consisting of columns, beams, and shear walls. This building structure is loaded with earthquake loads which refer to SNI 1726-2019 Procedures for Earthquake Resistance Planning for Building and Non-Building Structures. Based on the calculation of the existing building structure due to the earthquake load of SNI 1726-2019, it was found that the story drift and Demand–Capacity Ratio (DCR) in column and beam did not meet the planning standards. The building structure was remodeled using type X bracing retrofitting to determine the value of story drift and DCR. Building structure modeling with type X bracing consists of three model shapes varying the location of placement and the number of type X bracing per floor. The results show that the addition of type X bracing can reduce the story drift up to 32.77% for the x direction and 33.75% for the y direction. In the cross-section of the beam element, the reduction in internal forces can reduce the Demand–Capacity Ratio (DCR) value in the beam. The cross-section of column element, the internal force has decreased but for the column which is attached to the type X bracing system showed an increase in internal force which causes an increase in the DCR value.

Finite Element Analysis of Crack Growth for Structural Health Monitoring of Mooring Chains using Ultrasonic Guided Waves and Acoustic Emission

A novel optico-acoustic sensing system based on digital image correlation (DIC), guided ultrasonic waves (GUW), and acoustic emission (AE) and its application in detecting breaks on seven-wire steel strands is presented. The implementation of the emerging optical nondestructive testing (NDT) method of DIC in parallel with established acoustic NDT techniques enables the cross-correlation/validation of in situ recorded information related to progressive damage accumulation, which is the focal point of this research. To the authors' best knowledge, it is the first time that full field strain accumulations have been obtained on the surface of the seven-wire strands. Furthermore, acoustic waveforms and their extracted features are found complementary to full field strain measurements and prove capable to detect damage initiation in critical structural sites ('hot spots'). To demonstrate the potential of the novel NDT system, pristine and prenotched strands were loaded using a mechanical testing frame while simultaneously recording DIC, GUW, and AE data. The DIC and GUW were acquired and excited at specific load intervals to avoid overlapping of GUW with AE activity. The reported DIC results directly reveal strain accumulations at the notched areas prior to breaking, whereas AE waveforms and related features show sudden changes at time instances that correspond to wire breaks. In addition, the GUW signals show a decrease in their amplitude upon progressive load of the strands and wave speed variations. Detailed post-processing of the acoustic results was performed to cross-correlate recorded information from novel optico-acoustic sensing system and create methodologies for effective data filtering, alignment, synchronization, and fusion (through unsupervised pattern recognition techniques) that could lead to robust damage identification in structural health monitoring applications. The results demonstrate for the first time that the use of full field strains in correlation with acoustic techniques visually validates the damage source location and, in turn, enhances the damage predictive capabilities of each NDT method for prestressed and post-tensioned cables found in stay cable bridges. Copyright © 2013 John Wiley & Sons, Ltd.

In order to avoid the safety problems of the public building structure in the dense passenger flow environment, the structural health monitoring system is combined with the Building Information Modeling (BIM) method. This paper proposed a dynamic building information management system based on Structural Health Monitoring (SHM) information to ensure the security of its passenger flow information for a crowded exhibition hall. The continuous development of BIM (building information modeling) technology has greatly promoted the development of the construction industry. We can achieve real-time updating and visualization of sensor monitoring data and effectively manage different types of monitoring information as well as improve the controllability and safety of building structure monitoring by introducing BIM technology into structural health monitoring. A static building information model (BIM) was established to generate dynamic passenger flow information through video data learning, and provide a basis for structural health monitoring system for structural safety analysis and emergency response functions under dense passenger flow conditions. A dynamic building information management system suitable for structural health monitoring was built to display the dynamic network of traffic capacity in real time, so that the building information model is dynamic and predictable. The establishment for the combination mechanism of BIM and SHM system improved the data information circulation of BIM system. It could carry out dynamic health monitoring management and early warning control of building structures, realize information sharing in the process of health monitoring, and effectively improve the safety and operational efficiency of public building structures.