Nondestructive Evaluation Techniques Research Articles

On the Long-Term Performance of Solitary Wave-Based Transducers for Nondestructive Evaluation Applications

Abstract A nondestructive evaluation (NDE) technique based on highly nonlinear solitary waves (HNSWs) has been developed recently by a few groups worldwide. The technique is based on the propagation and detection of these waves along a one-dimensional monoperiodic array of spherical particles in which one end of the array is in contact with the material/structure to be inspected, and the particle at the opposite end induces the waves by means of a mechanical impact. Several studies have demonstrated that the dynamic interaction between the waves and the element to be evaluated is dependent on the geometric and mechanical properties of the structure, and such dependency can be monitored by sensing the waves reflected at the interface between the array and the structure. This NDE technique is typically performed by using the so-called HNSW transducer. The term transducer indicates a portable device that consists of a monoperiodic array of particles, a device to trigger the waves, and a sensing element to detect the waves. In the study presented in this article, the long-term performance of three transducers was investigated by placing them above a test object whose mechanical and geometric properties were left constant for a week while the transducers triggered and detected thousands of waves. Any variability of the waves was quantified by extracting simple features such as amplitude, time of flight, and cross-correlation. To investigate the cause of variabilities, 16 measurements were captured with short videos at ∼1000 fps. The results of the study demonstrate that the traveling time of the solitary waves is the most reliable parameter for long-term monitoring with the lowest variability and the least susceptibility to physical changes within the array. In addition, the findings of this study allow the framing of a valid strategy to improve the design of the transducers in order to make the HNSW-based technique suitable for long-term monitoring.

Pulse-Modulation Eddy Current Evaluation of Interlaminar Corrosion in Stratified Conductors: Semi-Analytical Modeling and Experiments.

Interlaminar corrosion (ILC) poses a severe threat to stratified conductors which are broadly employed in engineering fields including aerospace, energy, etc. Therefore, for the pressing concern regarding the safety and integrity of stratified conductors, it is imperative to non-intrusively and quantitatively interrogate ILC via non-destructive evaluation techniques. In this paper, pulse-modulation eddy current (PMEC) for imaging and assessment of ILC is intensively investigated through theoretical simulations and experiments. A semi-analytical model of PMEC evaluation of ILC occurring at the interlayer of two conductor layers is established based on the extended truncated region eigenfunction expansion (ETREE) along with the efficient algorithm for the numerical computation of eigenvalues for reflection coefficients of the stratified conductor under inspection. Based on theoretical investigation, PMEC evaluation of ILC in testing samples are further scrutinized by using the PMEC imaging system built up for the experimental study. The theoretical and experimental results have revealed the feasibility of PMEC for imaging and evaluation of ILC in stratified conductors.

FIB-DIC Residual Stress Evaluation in Shot Peened VT6 Alloy Validated by X-ray Diffraction and Laser Speckle Interferometry.

Ga-ion micro-ring-core FIB-DIC evaluation of residual stresses in shot peened VT6 (Ti-6Al-4V) alloy was carried out and cross-validated against other non-destructive and semi-destructive residual stresses evaluation techniques, namely, the conventional X-ray diffraction and mechanical hole drilling. The Korsunsky FIB-DIC method of Ga-ion beam micro-ring-core milling within FIB-SEM with Digital Image Correlation (DIC) deformation analysis delivered spatial resolution down to a few micrometers, while the mechanical drilling of circular holes of ~2 mm diameter with laser speckle interferometry monitoring of strains gave a rough spatial resolution of a few millimeters. Good agreement was also found with the X-ray diffraction estimates of residual stress variation profiles as a function of depth. These results demonstrate that FIB-DIC provides rich information down to the micron scale, it also allows reliable estimation of macro-scale residual stresses.

Non-Destructive In-Process Quality Evaluation Of Plant-Sourced Food During Drying

Plant-sourced food has a crucial role in the human food supply as the source of calories and many valuable micronutrient compounds that enhance a balanced and healthy lifestyle. However, a portion of food intended for human consumption produced globally become wastage per year because of a lack of proper processing and preservation technologies. Drying is one of the broadly utilised preservation technologies in plant-sourced food. Most drying studies focused on post-process evaluation on product quality; meanwhile, monitoring and controlling amid the drying process (in-process) is essential because these activities can improve the drying condition and optimise the end product’s quality. Furthermore, the non-destructive inspection method is essential in developing smart food processing units and can be more efficient, rapid, reduced sample waste, and environmentally friendly than traditional inspection methods. The authors also discuss the overview of quality parameters investigated during plant-sourced food drying with in-process and non-destructive quality evaluation techniques. Finally, the authors also discuss the prospects and challenges of the real-time and non-destructive quality evaluation application.

A Perspective of The Needs and Opportunities for Coupling Materials Science and Nondestructive Evaluation for Metals-Based Additive Manufacturing

This paper presents a perspective of the needs and opportunities associated with the multidisciplinary problem of nondestructive evaluation (NDE) of additive manufacturing (AM). Recognizing the multidisciplinary nature of the problem, as well as the need to bridge knowledge between the different communities, the paper is structured to provide brief backgrounds and details relevant to both communities, as well as present an assessment of the state of the art. This paper, in some respects, is meant to be a primer of the different landscapes, as well as a catalyst for making future connections. At the end, it will be clear that there is much more work to be done, but that the work that is ongoing is exciting, and the potential to exploit NDE techniques for metals-based AM is very high.

Progressive fracturing of concrete under biaxial confinement and repetitive dynamic loadings: From damage to catastrophic failure

Concrete materials are frequently exposed to extreme environments, such as high confining pressures (e.g., deep underground support), dynamic loadings (e.g., natural phenomena and human-induced events), and coupled confinement and dynamic loadings. The behaviours of concrete materials under such conditions result in challenges for the diagnosis and prognosis of structural changes from local damage to catastrophic failure, which is critical to the safety and sustainability of civil infrastructures. This paper aims to explore mechanical properties and progressive fracturing of concrete materials subjected to biaxial confinement and repetitive dynamic loadings. A triaxial Hopkinson bar (Tri-HB) system is used to apply the coupled loading conditions, and obtain the dynamic stress-strain information by interpreting recorded stress-wave signals. Non-destructive evaluation (NDE) techniques, including ultrasonic measurement and synchrotron-based micro-computed tomography (micro-CT), are utilised to quantify progressively damage evolution and fracture characteristics. The digital volume correlation (DVC) and imaging processing techniques are further applied to compute volume deformation fields and to classify microcrack types (i.e., matrix crack, interfacial crack and transgranular cracks). Results show that, with increasing the number of impacts, dynamic peak stress decreases along the impact direction but increases along the lateral direction while the peak strain values increase in both directions. The microcracks firstly initiate at the middle of rear-end of the specimen, continuously propagate along the impact direction, then develop at the top and bottom of the specimen, and eventually coalesce with the occurrence of shear sliding. The observation of microcracks are well validated by ultrasonic measurement. The formation of shear bands was highly dependent on the propagation and coalescence of interfacial and matrix cracks, while transgranular cracks induced by compressive strain localization as displayed in DVC deformation fields play an essential role in the fracture energy under repetitive dynamic loadings.

Arch Stone Bridges: Procedures for Evaluation of Structural Integrity

ABSTRACT In the Balkan Peninsula, the single-arched stone masonry bridge has served for centuries as an essential part of transportation infrastructure. Being exposed to the natural elements and to aging, several of these structures are in a state of disrepair that is accelerated by neglect. Nevertheless, these are important samples of the built heritage encapsulating historical materials, methods of construction and ancient craftsmanship. Still standing for over half a millennium, such bridges testify the wisdom by which the masons chose the location and form of the arch to span over torrents minimizing the wear from water scouring and floods. Preservation of the bridges that are still standing is a priority. With increasing number of bridge collapses reported in the past years under extreme flood, an immediate need emerges for methods of evaluation of the structural vulnerability and measures to enhance their resilience. Using as a case study a bridge built in fifteenth century in Greece, this paper unfolds the essential attributes of a comprehensive assessment framework that combines non-destructive evaluation techniques to reveal information about technologies and details, with a numerical investigation of the resilience of the structure to floods and seismic hazards in order to identify risks of bridge integrity.

Estimate residual strength of degraded bonded joints by combining analytical models with non-Destructive evaluations

ABSTRACT Durability issues associated with adhesive degradation have hindered widespread use of bonding in aircraft applications and contributed to several bond-related in-service accidents, fostering extensive related research. While the non-destructive evaluation (NDE) of bondline quality remains elusive, some authors suggested that NDE could establish bond strength thresholds, supporting the theoretical concept of a residual effective bond overlap (REBO). These authors related strength thresholds to NDE of specimens with artificial weak bonds only phenomenologically. This work proposes two physical-based approaches, combining NDE with analytical models for stress analysis, to estimate the residual strength of environmentally degraded metallic bonded joints considering an approximated REBO. These approches incorporate fundamental characteristics of two physically distinct NDE techniques and a water-related aging mechanism. Statistically treated experimental data for verification was obtained from aluminum-epoxy bonded joints typical of aeronautic application. Two sets of these joints were exposed in a hot/wet controlled environment – to induce representative degradations – for different periods, non-destructively inspected, and mechanically tested. Each set of specimens differed only in the surface preparation to prompt dissimilar failure modes – adhesion and cohesion failures. Estimated residual strengths for different levels of degradation and failure modes were in agreement with quasi-static loads in a conservative fashion.

Acoustic Emission Source Location Using Finite Element Generated Delta-T Mapping.

One of the most significant benefits of Acoustic Emission (AE) testing over other Non-Destructive Evaluation (NDE) techniques lies in its damage location capability over a wide area. The delta-T mapping technique developed by researchers has been shown to enable AE source location to a high level of accuracy in complex structures. However, the time-consuming and laborious data training process of the delta-T mapping technique has prevented this technique from large-scale application on large complex structures. In order to solve this problem, a Finite Element (FE) method was applied to model training data for localization of experimental AE events on a complex plate. Firstly, the FE model was validated through demonstrating consistency between simulated data and the experimental data in the study of Hsu-Nielsen (H-N) sources on a simple plate. Then, the FE model with the same parameters was applied to a planar location problem on a complex plate. It has been demonstrated that FE generated delta-T mapping data can achieve a reasonable degree of source location accuracy with an average error of 3.88 mm whilst decreasing the time and effort required for manually collecting and processing the training data.

Detection of delaminations in AS4/PEEK composite plates using highly nonlinear solitary waves

We experimentally investigate a non-destructive evaluation (NDE) technique to detect defects in an AS4/PEEK fiber-reinforced thermoplastic composite using highly nonlinear solitary waves (HNSWs). HNSWs are generated using an experimental setup of a granular crystal sensor composed of a one-dimensional chain of steel beads. The granular chain is vertically aligned and placed in contact with the surface of the laminated composites containing a defect through the depth of their thickness. The influence of the defect and the defect location in AS4/PEEK is examined by analysing the characteristics (i.e., delay and amplitude) of the reflected HNSWs. Experimental results demonstrate the capability of the proposed HNSW-based NDE scheme in identifying defects in AS4/PEEK laminated composites, offering a low-cost and robust alternative to existing NDE methods.

Detection of mode frequencies for spherical cavity embedded within a mild steel plate

The modern era of structures has observed a vast increase in non-destructive evaluation techniques in order to detect unwanted damages or porosities within the structure. Detection of defect frequencies will play a vital role in local defect resonance–based defect imaging in the future. In this paper, a technique for porosity and cavity detection in metals is discussed. A numerical investigation is carried out first on a square mild steel plate with a spherical cavity and a square mild steel block with multiple cavities. Different resonance frequencies and corresponding mode shapes in the case of the single cavity are calculated using steady state dynamic analysis. Six fundamental mode shapes are identified as Rocking (R), Torsional (T), Bouncing (B), 4-noded (4 N), 6-noded (6 N) and 8-noded (8 N) modes. Moreover, an explicit dynamic analysis is performed by exciting the model with a chirp signal for both cases of single and multiple cavities. The numerical study is supported by experimental results, performed on a mild steel plate embedded with a single spherical cavity and previously published literature. It is observed that the analytical, numerical as well as the experimental results obtained for all the modes are in close agreement with each other. The bouncing mode is found to be the promising one for pore imaging due to its uniform displacement across all the directions.

Improving Electromechanical Impedance Damage Detection Under Varying Temperature

The field of structural health monitoring has seen a fundamental shift in recent years, as researchers strive to replace conventional non-destructive evaluation techniques with smart material-based techniques. Perhaps the most promising of smart material techniques for developing structural health monitoring (SHM) systems is electromechanical impedance (EMI) which can be used for real-time structural damage assessment. In EMI, mechanical resonances of structure can be seen in electrical characteristics of piezoelectric transducers due to electromechanical coupling of transducer with the structure. Existence of damage will cause a structural stiffness change and therefore the resonant characteristics of the structure will be altered. This article presents an experimental and numerical study to investigate the effects of notch damage with temperature on the electrical impedance of the piezoelectric sensor used in the EMI technique. The practical implementation of the compact EMI method utilizes as its main apparatus an impedance analyser (Model Agilent 4294A) that reads the in-situ EMI of piezoelectric wafer active sensors (PWAS) attached to the monitored structure. The finite element modelling used ANSYS software three-dimensional (3D) capability to simulate an aluminium beam at varying temperatures. Real-time monitoring of the structure is achieved based on harmonic measurements. The results conclusively showed that the proposed temperature compensation technique eliminates the results ambiguity and enabled the EMI system to detect small damages that were otherwise indiscernible.

Nondestructive Evaluation of Stress Corrosion Cracking in a Welded Steel Plate Using Guided Ultrasonic Waves

Abstract Stress corrosion cracking (SCC) had occurred in early-generation high-level nuclear waste tanks constructed by welding carbon steel. This paper describes an ultrasonic inspection system and its fundamental ability to detect and quantify the length of SCC on thick welded steel plates. The finite element method (FEM) was applied to simulate the welding process to estimate the welding residual stress field. Growth of stress corrosion cracks is driven by crack stress intensities exceeding the subcritical cracking threshold intensity. The subject plate was experimentally inspected with ultrasonic nondestructive evaluation (NDE) techniques to characterize the extent of SCC. The NDE system uses a piezoelectric transducer to generate guided waves in the thick steel plate, and a scanning laser Doppler vibrometer (SLDV) to measure multidimensional time–space wavefield data over a user-defined scanning area in the plate surface. The measured wavefield data can show wave interactions in a localized area in the plate due to the presence of the discontinuities of the SCC. To generate an inspection image that can precisely show the crack’s location and/or the dimension, the wavefield data are further processed to generate inspection image that maps the entire sample plate so the crack can be clearly identified in the plate while its length can be readily estimated. The ultrasonic test results for crack length agree well with the visually estimated length and are close to that predicted by the FEM for cracks in the weld residual stress field.

Characterization of Wall-Loss Defects in Curved GFRP Composites Using Pulsed Thermography

Curved glass fiber–reinforced polymer (GFRP) composites are superior to alloy-steel pipes due to their excellent corrosive resistance properties, finding wide applications in the transportation of petrochemicals, chemical storage tanks, and power and water-treatment plants. Among the defects found in GFRP pipes, internal pitting or wall loss is one of the most severe, caused by material deterioration and the friction of small particles in the transfer fluid. This study investigates these in-service discontinuities using a pulsed thermal nondestructive evaluation technique. The paper focuses on the quantification of defect depth using the temperature peak contrast derivative and defect sizing using the full width at half maximum method. Further, the paper investigates the ability of pulsed thermography to estimate pitting or wall-loss defects at various depths and sizes through simulation and experimentation. Thermographic signal reconstruction images are used for quantification of defects at a deeper depth. The results of the present study are then compared with well-established ultrasonic C-scan results.

Testing the Dispersion of Nanoparticles in a Nanocomposite with an Ultra-Low Fill Content Using a Novel Non-Destructive Evaluation Technique.

A non-destructive evaluation (NDE) technique capable of testing the dispersion of nanoparticles in a nanocomposite would be of great use to the industry to check the quality of the products made and to ensure compliance with their specifications. Very few NDE techniques found in the literature can evaluate the level of dispersion of the nanoparticles in the whole nanocomposite. Here, a recently developed NDE technique based on pulsed phase thermography (PPT) in transmission mode was used to assess the particle dispersion in ultra-low, less than 0.05 wt%, Ag enriched polymeric based nanocomposite manufactured with an innovative nano-coating fragmentation technique. The phasegrams obtained with the presented technique clearly showed clusters or bundles of Ag nanoparticles when present, down to the size of 6 µm. Therefore, the new NDE approach can be applied to verify that the expected levels of dispersion are met in the production process.

A State-of-the-Art Review of Bridge Inspection Planning: Current Situation and Future Needs

Inspections are important to ensuring adequate safety and performance of a bridge throughout its service life. Bridge inspections are highly connected with maintenance decisions and can help in managing maintenance activities while maintaining a reliable bridge network. Routine inspections are the most common type of highway bridge inspections in the United States. The National Bridge Inspection Standards (NBIS) requires that, for almost all bridges, a routine inspection should be conducted at least every 24 months. However, limitations of current bridge inspection practices impact the quality of information provided about bridge conditions and the subsequent decisions made based on that information. Much research in the field of bridge inspection planning has been conducted to assist bridge inspectors in the inspection planning process and improving routine inspections. Accordingly, the goal of this study is to provide an overview on current bridge inspection practices in the United States and conduct a systematic literature review on innovations in the field bridge inspections planning while investigating research gaps and future needs. This paper provides a background on the history of bridge inspection in the United States, including current bridge inspection practices and their limitations and analyzes the connections between nondestructive evaluation techniques, deterioration models, and bridge inspection management. The primary emphasis of the paper is a thorough analysis of research proposing and investigating different methodologies for inspection planning and scheduling. Studies were analyzed and categorized into three main types of inspection planning approaches, based on: reliability, risk-analysis, and optimization approaches. The study revealed gaps and limitations in the current proposed techniques for inspection planning. The findings of this review will help in characterizing the current state of bridge inspection programs and future research needs to enhance inspection programs and reduce the gap between inspection practice and research.

Predicting local material thickness from steady-state ultrasonic wavefield measurements using a convolutional neural network

Acoustic steady-state excitation spatial spectroscopy (ASSESS) is a full-field, ultrasonic non-destructive evaluation (NDE) technique used to locate and characterize defects in plate-like structures. ASSESS generates a steady-state, single-tone ultrasonic excitation in a structure and a scanning laser Doppler Vibrometer (LDV) measures the resulting full-field surface velocity response. Traditional processing techniques for ASSESS data rely on wavenumber domain analysis. This paper presents the alternative use of a convolutional neural network (CNN), trained using simulated ASSESS data, to predict the local plate thickness at every pixel in the wavefield measurement directly. The defect detection accuracy of CNN-based thickness predictions are shown to improve for defects of greater size, and for defects with higher thickness reductions. The CNN demonstrates the ability to predict thickness accurately in regions where Lamb wave dispersion relations are complex or unknown, such as near the boundaries of a test specimen, so long as the CNN is trained on data that accounts for these regions. The CNN also shows generalizability to ASSESS experimental data, despite an entirely simulated training dataset.

A Novel Pulsed Eddy Current Criterion for Non-Ferromagnetic Metal Thickness Quantifications under Large Liftoff.

The pulsed eddy current (PEC) inspection is considered a versatile non-destructive evaluation technique, and it is widely used in metal thickness quantifications for structural health monitoring and target recognition. However, for non-ferromagnetic conductors covered with non-uniform thick insulating layers, there are still deficiencies in the current schemes. The main purpose of this study is to find an effective feature, to measure wall thinning under the large lift-off variations, and further expand application of the PEC technology. Therefore, a novel method named the dynamic apparent time constant (D-ATC) is proposed based on the coil-coupling model. It associates the dynamic behavior of the induced eddy current with the geometric dimensions of the non-ferromagnetic metallic component by the time and amplitude features of the D-ATC curve. Numeral calculations and experiments show that the time signature is immune to large lift-off variations.

Assessing the challenges of condition assessment of steel-concrete (SC) composite elements using NDE

Steel-concrete (SC) is a structural typology and construction method in which continuous steel plates are used on the surfaces of concrete walls or slabs, having dual role of formwork and longitudinal reinforcement. The continuous steel-plates on both sides of the concrete element improve economy by prefabrication, but hinder the use of traditional non-destructive evaluation (NDE) to assess the condition of the concrete. In this research, conventional NDE techniques were investigated with regards to their suitability for SC elements, with focus on detection of mechanical damage. Tests were performed on large-scale, mechanically damaged, SC elements. The deployed NDE methods were based on ultrasonic measurements using: the pulse echo technique; radiographic inspection; ultrasound 3D tomographer; impact-echo (IE); impulse-response (IR) and ground penetrating radar (GPR). It was assessed whether cracks of different sizes in the SC beams could be detected through the steel-plated surface. Perpendicular and oblique cracks of 0.1–2.5 mm width were studied. Resultsshow that ultrasonic testing and GPR were not suitable for testing through the steel surface, due to loss of the transmitted energy in the steel plates. Mechanical impact-based testing systems revealed promising results to detect cracks and de-bonding. Radiographic testing was successful in detecting the presence of cracks in cases when these had sufficient opening and length.

Comparative study on structural evaluation of flexible pavement using BBD and FWD

Flexible pavements undergo deterioration with increase in heavy traffic. Thus, there is a need to evaluate the existing pavement condition and undertake appropriate maintenance measure for safe and efficient flow of traffic. Benkelman Beam Deflectometer (BBD) and Falling Weight Deflectometer (FWD) are the most widely used non-destructive techniques for evaluation and strengthening of flexible pavements in India. There is a need for rational approach of pavement evaluation because of high cost associated with new road construction and limited financial resources for maintenance of roads. Benkelman beam deflectometer involves static loading whereas falling weight deflectometer involves dynamic loading which simulates moving traffic. The main objective of this study is to develop a correlation between FWD and BBD. This paper presents a typical case study on a 5 km length of National Highway from chainage 34+006 to 39+003 in Bangalore, Karnataka. Pavement structural evaluation is conducted using FWD and BBD. The tests were conducted on the same road stretch at the same point of loading. The results are analyzed as per Indian Road Congress (IRC) guidelines and overlay thickness is designed using KGP-BACK and IIT-PAVE. Linear correlation between BBD and FWD is developed using central deflection values and the co-efficient of correlation (R2) is found to be 0.8994. The developed correlation is then validated for present study data and available literature data. The root mean square error is found to be 6.77 and 7.67 respectively. Based on the observations, it is concluded that FWD serves as one of the more reliable method for the structural evaluation of pavements and this method proves to be cost effective by reducing the desired overlay thickness.