Global Structural Health Monitoring Research Articles

Performance Evaluation of Structural Health Monitoring System Applied to Full-Size Composite Wing Spar via Probability of Detection Techniques.

Probability of detection (POD) is an acknowledged mean of evaluation for many investigations aiming at detecting some specific property of a subject of interest. For instance, it has had many applications for Non-Destructive Evaluation (NDE), aimed at identifying defects within structural architectures, and can easily be used for structural health monitoring (SHM) systems, meant as a compact and more integrated evolution of the former technology. In this paper, a probability of detection analysis is performed to estimate the reliability of an SHM system, applied to a wing box composite spar for bonding line quality assessment. Such a system is based on distributed fiber optics deployed on the reference component at specific locations for detecting strains; the attained data are then processed by a proprietary algorithm whose capability was already tested and reported in previous works, even at full-scale level. A finite element (FE) model, previously validated by experimental results, is used to simulate the presence of damage areas, whose effect is to modify strain transfer between adjacent parts. Numerical data are used to verify the capability of the SHM system in revealing the presence of the modeled physical discontinuities with respect to a specific set of loads, running along the beam up to cover its complete extension. The POD is then estimated through the analysis of the collected data sets, wide enough to assess the global SHM system performance. The results of this study eventually aim at improving the current strategies adopted for SHM for bonding analysis by identifying the intimate behavior of the system assessed at the date. The activities herein reported have been carried out within the RESUME project.

Structural Health Monitoring of Fatigue Cracks for Steel Bridges with Wireless Large-Area Strain Sensors.

This paper presents a field implementation of the structural health monitoring (SHM) of fatigue cracks for steel bridge structures. Steel bridges experience fatigue cracks under repetitive traffic loading, which pose great threats to their structural integrity and can lead to catastrophic failures. Currently, accurate and reliable fatigue crack monitoring for the safety assessment of bridges is still a difficult task. On the other hand, wireless smart sensors have achieved great success in global SHM by enabling long-term modal identifications of civil structures. However, long-term field monitoring of localized damage such as fatigue cracks has been limited due to the lack of effective sensors and the associated algorithms specifically designed for fatigue crack monitoring. To fill this gap, this paper proposes a wireless large-area strain sensor (WLASS) to measure large-area strain fatigue cracks and develops an effective algorithm to process the measured large-area strain data into actionable information. The proposed WLASS consists of a soft elastomeric capacitor (SEC) used to measure large-area structural surface strain, a capacitive sensor board to convert the signal from SEC to a measurable change in voltage, and a commercial wireless smart sensor platform for triggered-based wireless data acquisition, remote data retrieval, and cloud storage. Meanwhile, the developed algorithm for fatigue crack monitoring processes the data obtained from the WLASS under traffic loading through three automated steps, including (1) traffic event detection, (2) time-frequency analysis using a generalized Morse wavelet (GM-CWT) and peak identification, and (3) a modified crack growth index (CGI) that tracks potential fatigue crack growth. The developed WLASS and the algorithm present a complete system for long-term fatigue crack monitoring in the field. The effectiveness of the proposed time-frequency analysis algorithm based on GM-CWT to reliably extract the impulsive traffic events is validated using a numerical investigation. Subsequently, the developed WLASS and algorithm are validated through a field deployment on a steel highway bridge in Kansas City, KS, USA.

Online structural integrity monitoring of high-performance composite rocket motor casing

Solid rocket motor (SRM) is one of the significant sub-systems for aerospace launch vehicles. The requirements of high range and high payload capabilities in aerospace systems demand the usage of high specific strength and high specific stiffness materials for rocket motor casings to minimize the inert weights. The present state-of-the-art technology is to realize stages of missile systems/launch vehicles with Composite Rocket Motor Casing (CRMC) to have a high-performance factor. CRMC is being designed with a marginal Factor of Safety (FOS) and mostly for a one-time use during its service life. CRMC is pressure tested to verify leak containment and its ability to sustain the Maximum Expected Operating Pressure (MEOP). Acoustic Emission Testing (AET), an online and global Structural Health Monitoring (SHM) technique along with strain and dilation measurement is used for observing the dynamic behavior of CRMC during the pressure test. Conventional Non-destructive Testing (NDT) such as Ultrasonic (UT) and Radiographic testing (RT) are employed to identify the type of defects. This unique capability of monitoring the dynamic behavior of active defects during real-time is of great significance for the acceptance of CRMC. The evolution of such an online system requires, first, identification of an appropriate process and next its adoption to meet the challenges posed by composite materials. There are various steps involved in the online SHM of CRMC. In this paper, various test practices, requirements, test parameters along with the details of strain and dilation measurements are given. This online inspection methodology and strain-dilation measurement during the Proof Pressure Test (PPT), along with a series of other inspection methods form the basis of CRMC acceptance for further use.

Integrative approach for transducer positioning optimization for ultrasonic structural health monitoring for the detection of deterministic and probabilistic damage location

The concept of structural health monitoring has been introduced to ensure structural integrity during the design lifetime of a structure. The main objectives of structural health monitoring are to detect, locate, quantify, and predict any damage that occurs during this lifetime of the structure so that effective and efficient maintenance and repair procedures can be performed. The location of structural damage events can be discretized as deterministic and probabilistic. A deterministic location specifies that the damage occurs in high-stress regions or other regions that can be predicted by the structural design, such as the most probable location for a fatigue crack. A probabilistic damage event is one where the location of the damage is independent of structural design parameters, such as hail impact, bird strike, and impact from ground vehicles. A structural health monitoring system should be able to handle both these damage occurrences. In our previous work, we optimized the transducer placement in Lamb wave–based structural health monitoring for the detection of a fatigue crack that emerges from a rivet hole. In this article, we demonstrate a combination of that method with a different sensor placement optimization method to add the capability to detect probabilistic damage location. First, we considered the ultrasonic wave attenuation in the structure and based on this attenuation, we created a fitness function. Since this fitness function is difficult to solve due to its combinatorial nature, we compared three common metaheuristic stochastic strategies: global random search, greedy algorithm, and genetic algorithm, for solving this problem. The results of this analysis were then integrated with the previously described deterministic approach, making a global structural health monitoring sensor placement strategy that balances the need to detect both pre-determined and random damage location occurrences. The analytical result of the study presented is validated by experiment.

A Perspective of Non-Fiber-Optical Metamaterial and Piezoelectric Material Sensing in Automated Structural Health Monitoring

Metamaterials are familiar in life sciences, but are only recently adopted in structural health monitoring (SHM). Even though they have existed for some time, they are only recently classified as smart materials suitable for civil, mechanical, and aerospace (CMA) engineering. There are still not many commercialized metamaterial designs suitable for CMA sensing applications. On the other hand, piezoelectric materials are one of the popular smart materials in use for about 25 years. Both these materials are non-fiber-optical in nature and are robust to withstand the rugged CMA engineering environment, if proper designs are adopted. However, no single smart material or SHM technique can ever address the complexities of CMA structures and a combination of such sensors along with popular fiber optical sensors should be encouraged. Furthermore, the global demand for miniaturization of SHM equipment, automation and portability is also on the rise as indicated by several global marketing strategists. Recently, Technavio analysts, a well-known market research company estimated the global SHM market to grow from the current US $ 1.48 billion to US $ 3.38 billion by 2023, at a compound annual growth rate (CAGR) of 17.93%. The market for metamaterial is expected to grow rapidly at a CAGR of more than 22% and the market for piezoelectric materials is expected to accelerate at a CAGR of over 13%. At the same time, the global automation and robotics market in the automotive industry is expected to post a CAGR of close to 8%. The fusion of such smart materials along with automation can increase the overall market enormously. Thus, this invited review paper presents a positive perspective of these non-fiber-optic sensors, especially those made of metamaterial designs. Additionally, our recent work related to near field setup, a portable meta setup, and their functionalities along with a novel piezoelectric catchment sensor are discussed.

Structural Health Monitoring for Multi-story Shear Frames Based on Signal Processing Approach

Non-destructive vibration-based global structural health monitoring and damage detection methods are divided into modal-based and signal-based methods. There is much research in these areas, but each one has some advantages and disadvantages. The combination of these two areas can greatly overcome these disadvantages and thus can enhance the robustness of the damage detection methods. This article presents a signal-modal-based structural health monitoring technique for multi-story shear buildings subjected to an earthquake event. The proposed method utilizes the combination of wavelet transform and FFT as signal processing tools and also Hilbert transform with the aim of final modal parameters extraction, in order to determine the existence, location, and extent of damage in the multi-story shear frames. In fact, extraction of final modal parameters from the acceleration response signals is desired. To demonstrate the capabilities of the proposed algorithm, numerical simulations are performed on a four-story two-bay and ten-story two-bay shear frame with different damage scenarios using OpenSees. The results show that this method can detect the occurrence, location, and severity of the damage with good accuracy even in different levels of multi-damage scenarios and also in the presence of measurement noise.

Experimental and numerical evaluation of structural dynamic behavior of Rialto Bridge in Venice

This paper presents part of the diagnostic activities performed for the subsequent major restoration work of the Rialto Bridge in Venice. The document analysis, the visual inspection, and the destructive tests on extracted masonry samples have proved to be the first important steps for an initial structural assessment and for the characterization of the materials. Moreover, the tensile stresses of the tie-rods, which connect the two sides of the shops structures, have been measured by means of dynamic tests. To study the local and the global dynamic behavior of the bridge structure and its overlying shops structures, a dynamic monitoring was performed. The data were acquired through ambient vibrations test to measure the dynamical properties (mode of vibration, frequencies, displacements, and damping ratios) of the historical construction using a modal identification of output-only systems. The main natural vibration sources were pedestrian traffic, wind, and wave-motion of the Grand Canal. Modal identification was carried out through poly-reference least square complex frequency-domain (pLSFC) estimator. Finally, of the variations of the boundary conditions and the structural interaction between the bridge and the shops, structures on the modal shapes are evaluated through a finite element model. The global structural health monitoring was carried out to define the real dynamic behavior of this important bridge.

Damage assessment in wind turbine technology

The economic efficiency of wind turbines WT is strictly dependent on their availability and reliability. This problem is most important in the case of offshore wind turbines OWT. There is a search for new materials, new manufacturing process, and new rules of structural designs. The aim of it, is to achieve far tighter safety margins than previously developed wind turbine solutions. Attention of many researchers is focused on the problem of WT/OWT reliability.In this paper Structural Health Monitoring (SHM) approach for wind turbines is presented. This approach is based on such topics as piezoelectric transducers, elastic waves propagation phenomenon, fibre Bragg gratings sensors, structural vibrations analysis. The combination of mentioned techniques allows to perform efficient both local and global SHM of the OWT.Research results presented in this paper are mainly related to fibre reinforced polymer materials FRPs due to fact that they are widely utilized in wind turbine blades manufacturing. However, certain results for metallic structures (tower structure) were also presented.Considered above investigations are intended to develop future SHM techniques that include sensors, hardware, software and methodologies of WT/OWT structural assessment.

FBG and FOPS for local and global structural health monitoring on a single fiber

Fiber Bragg grating (FBG) sensors and fiber optic polarimetric sensors (FOPS) have been widely researched and implemented for structural health monitoring (SHM). FBG essentially provides localized strain information, while FOPS gives a global indication of the structural health of materials. An FBG written on the polarization maintaining (PM) fiber can thus be used for both global structural monitoring and local strain sensing. However each sensor has to be used with its own hardware and processing. For gratings written on PM fibers two Bragg reflections, corresponding to two modes of polarization, are observed. While both Bragg wavelengths shift under longitudinal strain in unison, their relative peak amplitude does not change. In this paper, a novel concept is proposed which makes the peak amplitudes responsive to the longitudinal strain. This relative amplitude of both the peaks is used for the first time to determine the state of polarization (SOP) with no additional optical systems. With this additional information on SOP, PM–FBGs can be used for both, local and global SHM simultaneously. Further, a new design has been proposed which gives improved information on the damaged location in beam structures. This can be further extended to other complex geometries.

BILBO Network: a proposal for communications in aircraft Structural Health Monitoring sensor networks

In the aeronautical environment, numerous regulatory and communication protocols exist that cover interconnection of on-board equipment inside the aircraft. Developed and implemented by the airlines since the 1960s, these communication systems are reliable, strong, certified and able to contact different sensors distributed throughout the aircraft. However, the scenario is slightly different in the structural health monitoring (SHM) field as the requirements and specifications that a global SHM communication system must fulfill are distinct. The number of SHM sensors installed in the aircraft rises into the thousands, and it is impossible to maintain all of the SHM sensors in operation simultaneously because the overall power consumption would be of thousands of Watts. This design of a new communication system must consider aspects as management of the electrical power supply, topology of the network for thousands of nodes, sampling frequency for SHM analysis, data rates, selected real-time considerations, and total cable weight. The goal of the research presented in this paper is to describe and present a possible integration scheme for the large number of SHM sensors installed on-board an aircraft with low power consumption. This paper presents a new communications system for SHM sensors known as the Bi-Instruction Link Bi-Operator (BILBO).

Output-Only Structural Health Monitoring for Deepwater Risers: Experimental Study of Wavelet Modified SOBI and Distributed Force Index Algorithm

Risers are the conduits between the subsea wellhead and the drilling/production platform for development, production, gas lift or water injection purposes, which are also one of the most important and the most vulnerable components for deepwater floating platforms. To address the lack of appropriate global structural health monitoring (SHM) system for deepwater risers, this paper proposes a time-frequency domain approach using a wavelet modified second order blind identification (WMSOBI) method and combined distributed force change (CDFC) index. WMSOBI provides a reliable time-frequency domain identified modal properties of riser systems, even with large damping and under-determinate conditions. In addition, CDFC index generated from modal properties extracted by WMSOBI can accurately identify the damage location and damage level for both single and multiple crack scenarios. Details of experiments conducted on suspended pipe are presented. Both numerical and experimental verification are presented to validate the effectiveness of the proposed WMSOBI/CFDC algorithm and SHM system.

Static Monitoring and Non-Destructive Test of a Historic Damaged Palace

The City Hall of Mirandola was stricken and damaged by Emilia-Romagna earthquake sequence of May 2012. This paper presents the procedure for the structural monitoring control of a masonry historic building that presents a serious damage pattern. Structural monitoring was carried out with transducers installed to control the serious cracks that regards the main volumes of the building. The global structural health monitoring was useful to define the actual condition of the dynamic behavior of the damaged construction that are subjected to different mechanism. Ground penetrating radar allows to detect the depth of the cracks and the condition of the masonry. These researches are useful also for the structural future rehabilitation and to define the possible changes in the structural behavior.

Damage Assessment of Historic Buildings Hit by Earthquake

The Church of Gesù and the tower of the Cathedral were stricken and damaged by Emilia-Romagna earthquake sequence of May 2012. This paper presents the procedure for the structural identification of the most widespread types of religious monuments. The dynamic behavior was analyzed using the ambient vibrations test to measure the dynamical properties (mode of vibration, frequencies, displacements and damping ratios) of the constructions using a modal identification of output-only systems. The operational modal analysis OMA has been carried out to identify the modal characteristics through poly-reference Least Square Complex Frequency-domain (pLSFC) estimator. The global structural health monitoring was carried out to define the real dynamic behavior of the damaged constructions that are subjected to different mechanism. These researches are useful for the structural rehabilitation and to define the possible changes in the structural behavior.

SHM of Historic Damaged Churches

The paper shows the results of monitoring activities to check the structural response and the level of damage of two historic monument of LAquila: San Pietro di Coppito and Santa Maria Paganica, that were damaged by the main earthquake of April 2009. The diagnostics operation was planned and carried out in situ and in laboratory to verify the integrity of the residual stiffness of the structures and to define the mechanical parameters of the material. The mechanical characterization of materials was carried out through destructive tests on samples, taken directly on site, and micro-destructive tests through single and double flat jacks. To give a first qualitative assessment of overall was used sonic test (non-destructive test) on the main macro-structure. The global structural health monitoring (SHM) was carried out through ambient vibrations to define the real dynamic behavior in serviceability state and to calculate - via a modal identification of output-only systems-the dynamic parameters (mode of vibration, frequencies, displacements and damping ratios). The aim of this research is to prove the reliability of different diagnostic methodologies, the real extent of global and local damage and the extent of the residual stiffness of the macro elements of the structures (façade, tower, walls of nave, transept) that are subjected to different mechanism of failure.

Field Implementation of Wireless Vibration Sensing System for Monitoring of Harbor Caisson Breakwaters

A wireless sensing system for structural health monitoring (SHM) of harbor caisson structures is presented. To achieve the objective, the following approaches were implemented. First, a wave-induced vibration sensing system was designed for global structural health monitoring. Second, global SHM methods which are suitable for damage monitoring of caisson structures were selected to alarm the occurrence of unwanted behaviors. Third, an SHM scheme was designed for the target structure by implementing the selected SHM methods. Operation logics of the SHM methods were programmed based on the concept of the wireless sensor network. Finally, the performance of the proposed system was globally evaluated for a field harbor caisson structure for which a series of tasks were experimentally performed by the wireless sensing system.

Aircraft Wing Inspection Based on Anomalous Wave Propagation Imaging

Non-destructive evaluation (NDE) and structural health management (SHM) with the ability to evaluate the severity of a damage are important to ensure the reliability of a structure. We propose a local non-destructive evaluation (NDE) system based on Anomalous Wave Propagation Imaging (AWPI) method. When possible damage is flagged during the lifecycle of the structure, the proposed system will be launched for automatic damage evaluation. This technology was demonstrated on a CFRP skin-spar-stringers wingbox integrated with an AE sensor. 17 mm diameter impact damage was made between the stringers using hammer strike from outer surface of the skin. Based on the impact location determined by other global structural health monitoring system, the AWPI automatically inspects an area 400×400 mm2 with the impacted location enclosed. Anomalous Wave Propagation Movie (AWPM) was generated as inspection result. As contrast to its predecessor, the AWPM shows only the damage induced ultrasonic wave (anomalous wave), making the damage detection an intuitive decision making process. Precise damage localization was performed by identifying the location of area with anomalous wave propagation in the AWPM. Besides, the size of the area with anomalous wave agreed well with the size of impact damage, which demonstrated that damage size quantification is possible using the proposed system. Being sensitive only to anomalous wave, it is expected that this NDE system is exceptionally suitable not only for aircraft structures such as wingbox with stiffeners, but also for other complex engineering structures.

Recent Research in Nondestructive Evaluation of Civil Infrastructures

Assessing the condition of a structure is necessary to determine its safety and reliability. Ideally, structural health monitoring should be similar to medical health monitoring of the body. In medical health monitoring, the life signs such as pulse and blood pressure give an overall indication of the overall health of the body. This is analogous to global structural health monitoring, in which damage to the structure can be identified by measuring changes in the global properties of the structure. Once the body signs show an anomaly, we do a battery of tests to determine the cause of the anomaly. Analogously in structural health monitoring, nondestructive evaluation (NDE) can be used to determine the nature of the damage. NDE methods to determine local damage are also becoming more accepted in practice. This paper describes some of the recent and current National Science Foundation projects in this area of research. Promising areas for NDE are identified.