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Microbial induced calcium carbonate precipitation (MICCP) has applications in improving the quality of cementitious constructions by enhancing its compressive strength, reducing porosity, and increasing durability against environmental degradation. In this study, an attempt has been made to develop an in situ, online, and nondestructive ultrasonic monitoring tool to capture bacterial self-healing in cementitious materials using cheaper source of bacterial nutrition medium. Samples casted and cured in corn steep liquor (CSL) and nutrient broth (NB) demonstrated higher ultrasonic pulse transmitted signals at successive days of curing relative to water cured control (C) specimens. The rise in ultrasonic signal due to bacterial admixing and curing is due to calcite precipitation in bacterial admixed and cured specimens. The compressive strength of CSL specimens was 8.8%, 11.4%, and 11.1% higher, while in NB specimens was 13.5%, 14.6%, and 12.7% higher as compared to water casted and cured specimens at 7, 14, and 28 days, respectively. The water absorption in bacterial treated specimens was significantly reduced due to the filling of pores in the mortar matrix and a reduced sorptivity coefficient of 0.0027 and 0.0022 was observed in CSL and NB specimens respectively as compared to 0.0197 of water casted and cured C specimens. This suggests successful calcite precipitation in bacterial treated mortar specimens and ultrasonic pulse transmission monitoring technique can successfully pick up bacterial intrinsic healing and can serve as in situ and nondestructive monitoring technique in civil engineering applications. Bacterial intrinsic self-healing in cementitious materials is an inherent process and this paper highlights the successful implementation of nondestructive and in situ ultrasonic wave monitoring tool to pick the same. Commonly used nondestructive testing (NDT) techniques like ultrasonic pulse velocity (UPV), acoustic emission monitoring can capture crack initiation in cementitious structures but not its intrinsic healing. In present research, ultrasonic wave monitoring has been used to capture bacterial microstructural development in the initial curing period in MICCP. This innovative NDT technology would go a long way in developing an in situ ultrasonic monitoring technique to pick up efficacy of MICCP in concrete structures for on-site applications. [ABSTRACT FROM AUTHOR]

We develop decision support and automation for the task of ultrasonic non-destructive evaluation data analysis. First, we develop a probabilistic model for the task and then implement the model as a series of neural networks based on Conditional Score-Based Diffusion and Denoising Diffusion Probabilistic Model architectures. We use the neural networks to generate estimates for peak amplitude response time of flight and perform a series of tests probing their behavior, capacity, and characteristics in terms of the probabilistic model. We train the neural networks on a series of datasets constructed from ultrasonic non-destructive evaluation data acquired during an inspection at a nuclear power generation facility. We modulate the partition classifying nominal and anomalous data in the dataset and observe that the probabilistic model predicts trends in neural network model performance, thereby demonstrating a principled basis for explainability. We improve on previous related work as our methods are self-supervised and require no data annotation or pre-processing, and we train on a per-dataset basis, meaning we do not rely on out-of-distribution generalization. The capacity of the probabilistic model to predict trends in neural network performance, as well as the quality of the estimates sampled from the neural networks, support the development of a technical justification for usage of the method in safety-critical contexts such as nuclear applications. The method may provide a basis or template for extension into similar non-destructive evaluation tasks in other industrial contexts. [ABSTRACT FROM AUTHOR]

Multilayer printed circuit boards (PCBs) can be produced not only in the traditional way but also additively. Both traditional and additive manufacturing can lead to invisible defects in the internal structure of the electronic component, eventually leading to the spontaneous failure of the device. No matter what kind of technology is used for the production of PCBs, when they are used in important structures, quality control is important to ensure the reliability of the component. The nondestructive testing (NDT) of the structure of manufactured electronic components can help ensure the quality of devices. Investigations of possible changes in the structure of the product can help identify the causes of defects. Different types of manufacturing technologies can lead to diverse types of possible defects. Therefore, employing several nondestructive inspection techniques could be preferable for the inspection of electronic components. In this article, we present a comparison of various NDT techniques for the evaluation of the quality of PCBs produced using traditional and additive manufacturing technologies. The methodology for investigating the internal structure of PCBs is based on several of the most reliable and widely used technologies, namely, acoustic microscopy, active thermography, and radiography. All of the technologies investigated have their advantages and disadvantages, so if high-reliability products are to be produced, it would be advantageous to carry out tests using multiple technologies in order to detect the various types of defects and determine their parameters. [ABSTRACT FROM AUTHOR]

This article presents a concept, materials, and methods to devise a Bond Quality Index (BQI) for assessing composite bond quality, approximately correlating to the respective bond strength. Interface bonding is the common mechanism to join two composite structural components. Ensuring the health and quality of the bond line between two load-bearing composite structures is crucial. The article presents the classification and data-driven distinction between two types of bond lines between similar structural components. The interface bonds in composite plates were prepared using polyester peel ply and TX-1040 nylon peel ply. For all the plates, ultrasonic inspection through scanning acoustic microscopy (SAM) (>10 MHz) was performed before and after localized failure of the plate by impinging energy. Energy was impinged 0–10 J/cm2 of in the 16-ply plates, and 0–25 J/cm2 were impinged in 40-ply plates. Followed by bond failure and SAM, a new parameter called the Bond Quality Index (BQI) was formulated using ultrasonic scan data and energy data. The BQI was found to be 0.55 and 0.45, respectively, in plates with polyester peel ply and TX-1040 nylon peel ply bonds. Further, in 40-ply plates with polyester peel ply resulted in a BQI equivalent to 3.49 compared to 0.75 in plates with a TX-1040 nylon peel ply bond. Currently, the BQI is not normalized; however, this study could be used for AI-driven normalized BQIs for all types of bonds in the future. [ABSTRACT FROM AUTHOR]

This paper presents a comparative study of different methods for obtaining the dispersion curves of ultrasonic guided waves in anisotropic media. First, we present the classical algorithms used to find zeros and propose some improvements. Next, the spectral method is explained for modeling the guided waves in anisotropic materials while presenting a technique that can distinguish the modes present in the structure. The dispersion curves are plotted using a Matlab program and the results are compared with those of the DISPERSE software. In addition, a comparison with the results obtained by Nayfeh's works in the field of Nondestructive testing by ultrasonic guided waves is included. Then a discussion is developed to highlight the strengths of the spectral method. For proper non-destructive testing, we need reliable information about the modes that propagate in our waveguide. Both analytical and spectral approaches have limitations in obtaining the exact displacement and stress profiles in a plate media. To remedy this, normalization by the acoustic power is essential. Next, the displacement and stress fields obtained from the spectral method of the modes that can propagate in the plate are compared to those obtained analytically. A very good concordance is then noticed. Based on the results obtained, the spectral method presents a very good alternative for obtaining dispersion curves. It is a convergent method, stable, easy to implement with a very low calculation time. [ABSTRACT FROM AUTHOR]

Multilayer printed circuit boards (PCBs) can be produced not only in the traditional way but also additively. Both traditional and additive manufacturing can lead to invisible defects in the internal structure of the electronic component, eventually leading to the spontaneous failure of the device. No matter what kind of technology is used for the production of PCBs, when they are used in important structures, quality control is important to ensure the reliability of the component. The nondestructive testing (NDT) of the structure of manufactured electronic components can help ensure the quality of devices. Investigations of possible changes in the structure of the product can help identify the causes of defects. Different types of manufacturing technologies can lead to diverse types of possible defects. Therefore, employing several nondestructive inspection techniques could be preferable for the inspection of electronic components. In this article, we present a comparison of various NDT techniques for the evaluation of the quality of PCBs produced using traditional and additive manufacturing technologies. The methodology for investigating the internal structure of PCBs is based on several of the most reliable and widely used technologies, namely, acoustic microscopy, active thermography, and radiography. All of the technologies investigated have their advantages and disadvantages, so if high-reliability products are to be produced, it would be advantageous to carry out tests using multiple technologies in order to detect the various types of defects and determine their parameters.

Glass, carbon, and hybrid/glass/carbon-reinforced polymer composites are the most important materials used in defense, aerospace, automobile, and sports industry because of their excellent mechanical properties. End-milling process is the final and important machining process of composites to achieve the desired shape and dimensions. The main concern of this research is to minimize delamination and surface roughness in carbon/glass/epoxy hybrid composites after end milling. The effects of tool material, spindle speed, feed rate, and cut depth on delamination and surface quality were investigated. Taguchi design of experiment method was used to vary the machining parameters. Surface quality was examined by a surface roughness tester, and the delamination of milled surfaces was inspected by non-destructive technique using ultrasonic testing. The surface morphology of milled surfaces was studied by scanning electron microscopy. Results were verified by signal-to-noise ratio and analysis of variance technique. Carbon/glass/epoxy hybrid composite exhibited better surface finish with diamond flute end mill cutter, spindle speed of 1500 rpm, feed rate of 0.15 mm/min, and cut depth of 0.05 mm. After nondestructive testing, minimum delamination in carbon/glass/epoxy hybrid composite was found using diamond flute end mill cutter at a spindle speed of 1500 rpm, feed rate of 0.10 mm/min, and cut depth of 0.10 mm. [ABSTRACT FROM AUTHOR]

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Reference blocks are required for ultrasonic calibration and non-destructive testing (NDT). There are already in existence sets of reference blocks constructed according to American Society for Testing and Materials standards, but as the industry evolves, we need more reference blocks with varied designs. In this study, two reference blocks of steel and aluminum are constructed. These blocks have several sets of flat bottom holes (FBH) with different diameters (0.5, 1, 1.5, 2 and 2.5 mm), angles (45° and 90°) and placements. The novel constructed reference blocks are evaluated using the ultrasonic and a displacement measuring interferometer (DMI). They allow for detailed FBH characterization in terms of defining their location, diameter, depth and so on. The two techniques show consistency in the majority of the outcomes. The expanded uncertainty of readings is found to be ±1•4 μm, according to DMI data. The findings show that the newly constructed blocks could be ideal for evaluating a variety of calibration factors including transducer sensitivity, dead zone, defect size, and depth. Furthermore, they can be used in NDT in various industries such as petroleum pipe production, steel manufacturing and so on. [ABSTRACT FROM AUTHOR]

Non-destructive testing of the cracks on the in-service bolt's shank with size M18 is a challenging technical problem. Due to the weak echo energy of cracks with large buried depths, the conventional phased array ultrasonic sector scan imaging has a low signal-to-noise ratio, resulting in the effective defect echo submerged in the structural wave of bolts. This work proposes a method of phased array ultrasonic sector scan imaging based on vector coherence factors to detect the microcracks on the surface of the bolt shank. This is achieved by weighting the phased array sector scan imaging with the vector coherence factor to detect the microcracks of the in-service helicopter damper bolt. Experimental work is also carried out to contrast the SNR value of cracks at buried depths of 70 mm and 90 mm with traditional phased array ultrasonic sector scanning images. This demonstrates that the proposed phased array ultrasonic sector scan imaging based on vector coherence factors detected the cracks with a depth of 0.1 mm at the buried depth of 90 mm. The SNR value of the cracks at the buried depth 70 mm in DAS_VCF images is improved by 11.67 dB, compared with the traditional DAS images, in the case of the focus depth at 60 mm. [ABSTRACT FROM AUTHOR]

In recent years, the maximum span of concrete-filled steel tube (CFST) arch bridges has substantially increased to nearly 700 m, rendering it a preferred bridge type for traffic nodes located in mountainous regions and deep canyons owing to its robust earthquake resistance and adaptability to varying terrain. Construction defects, particularly debonding gaps, significantly diminish the structural bearing capacity of these bridges. This study aims to realize the accurate quantitative calculation of debonding gaps in CFSTs through ultrasonic non-destructive testing. The first wave's acoustic time and overall ultrasonic pulse velocity (UPV) were employed as the state variables of ultrasonic pulse propagation in CFSTs with debonding gaps. Ultrasonic non-destructive tests were conducted on CFST specimens produced in the Qinghai-Tibet Plateau and Guangxi. An approximate calculation path of ultrasonic propagation in CFSTs was proposed, and the differences in the UPVs of CFSTs produced at different air pressures were analyzed. A calculation model of the UPVs of CFSTs was formulated using different air pressure influence coefficients. Additionally, a numerical simulation of the ultrasonic energy transfer in CFSTs with diverse debonding gaps was performed, elucidating the propagation mechanism of ultrasonic energy across the three-phase steel-concrete-air interface in CFSTs. The propagation law of ultrasonic waves in CFSTs was verified through dynamic ultrasonic energy snapshots and the state variable calculation results. Based on the experimental and numerical findings, a quantitative analysis method and correlation model for CFST debonding gaps were proposed, based on their UPVs at different air pressures. The quantitative calculation model was modified by analyzing the values measured at an actual CFST bridge, enabling the accurate quantitative analysis and calculation of the degree and scope of debonding gaps in CFSTs. • The transmission mechanism of ultrasonic pulse in debonding gaps of CFSTs was studied. • The ultrasonic tests of CFSTs under different air pressure were carried out. • The rationality of the calculation path for ultrasonic pulse in CFSTs was validated. • Calculation model for the gaps with different characteristics in CFSTs was proposed. [ABSTRACT FROM AUTHOR]

Ultrasonic tomography is a non-destructive testing method that allows for the internal visualization of concrete structures without causing any damage. This technique is widely employed to detect reinforcement and various types of damage, including voids, cracks, rebar corrosion, and debonding, among others. To enhance the accuracy and clarity of concrete tomograms, numerous image generation techniques have been explored. With the ever-increasing volume of information, it can become challenging to grasp the overall landscape and identify areas for improvement. The present work offers a comprehensive systematic review of the diverse image reconstruction techniques employed and the innovative developments within this research field. The prevalent techniques for both transmission and reflection tomography have been analyzed, delineating their respective characteristics. Furthermore, enhancement techniques have been recorded, and their discussion is provided. This comprehensive overview provides the basis for outlining future developments in ultrasonic tomography for concrete elements. [Display omitted] • Review of image reconstruction (IR) methods for ultrasonic tomography of concrete. • Contextualization of concrete tomography scenario among other research fields. • Discussion of IR techniques for concrete transmission and reflection tomography. • New enhancement methods for improving image accuracy are presented and discussed. • Overview of future possibilities in concrete imaging with ultrasonic tomography. [ABSTRACT FROM AUTHOR]

The non-destructive testing (NDT) plays a crucial role in geotechnical engineering and geophysical applications, especially in the design of earthquake-resistant foundations, geotechnical field investigation, and material characterization and detection of underground anomaly. Currently, the existing signal interpretation methods in NDT measurements still predominantly rely on empirical relations or subjective judgements. In this paper, we present the GeoNDT software, which is developed to provide an advanced physics-based signal interpretation method for NDT characterization of multiphase geomaterials. GeoNDT is able to model the propagation of stress waves and dispersion relations in dry (elastodynamic), saturated (two-phase poroelastodynamic), and three-phase frozen (multiphase poroelastodynamic) geomaterials using the meshless spectral element method. GeoNDT is flexible, general-purpose, and can be used seamlessly for advanced signal interpretation in geophysical laboratory testing including the bender element and ultrasonic pulse velocity tests, characterization of complex multiphase geomaterials, and in situ shallow seismic geophysics including the falling weight deflectometer and multichannel analysis of surface waves tests. The advanced physics-based signal interpretation feature of GeoNDT allows the quantitative characterization of geophysical and geomechanical properties of geomaterials and multilayered geosystems independently without making any simplified assumptions as common in the current practice. [ABSTRACT FROM AUTHOR]

Summary: Lithium (Li)‐ion battery is an important energy storage for electronic production and electric vehicles. Battery aging is accompanied by a state change in the active material. The method of active material status evaluation in a nondestructive way has become a major topic in battery research. In this study, a battery in situ testing with multiple noncontact ultrasonic excitation signal methodology is proposed, and for the first time to use acoustic energy to analysis signal transmittance and reflectance. Based on a 1/20C charging and discharging experiment of commercial NCM111 pouch battery, the deformation, density, wave speed, acoustic impedance, and other parameters of NCM111/graphite material under different Li stoichiometry are estimated. Acoustic property of active material has been used as a medium to explain the mechanism of ultrasonic signal changes. The experiment result shows that acoustic energy is highly correlated with the calculated acoustic impedance of the active material, and there is no accurate correspondence with battery voltage and capacity. Ultrasonic is an effective method to study the status of Li battery. [ABSTRACT FROM AUTHOR]

In this paper, we propose an acoustic block for widening the bandwidth and modulating center frequency of airborne transducers to improve the ultrasound imaging or metrology system. When acoustic block is attached, the characteristics of the ultrasonic transducer are changed by the squeeze film effect. Extra elastic and damping force are generated by squeeze film damping and can be changed according to parameters of acoustic block. For impedance matching, a CMUT vibrating in bending mode was used. The CMUT's FBW is 3.18 % and the center frequency is 103.5 kHz. We changed the area ratio of the acoustic block and attached it to the CMUT. The FBW was changed to 7.14 to 9.14 % and the center frequency to 108.7 to 112.1 kHz. With acoustic block, conventional transducers can be transformed into transducers with better performance in areas such as non-destructive testing and ultrasonic imaging. [ABSTRACT FROM AUTHOR]

Glass fiber-reinforced polymer (GFRP) ship structures have hull plate thicknesses of 10 mm or more and are fabricated using a higher proportion of resin matrix systems than E-glass fiber reinforcements. Therefore, GFRP is classified as a highly attenuative material, and this characteristic is a major cause of large errors in ultrasonic nondestructive testing for quality inspections. In this study, considering the aforementioned design and fabrication characteristics of GFRP ship structures, hull plate prototypes with various glass fiber weight fractions, glass contents (Gc), and laminate thicknesses were fabricated. Then, a pulse-echo ultrasonic test was performed with the fabricated prototypes, and the attenuation characteristics of the GFRP hull plates were investigated by conducting statistical analyses. These results demonstrated that with a variation of 30–50% in the Gc used for GFRP structure design, the plate thickness variation had a greater impact than the Gc variation on the attenuation characteristics. The increase in Gc naturally increased the scattering of ultrasonic waves but did not significantly affect the attenuation coefficient. The effects of the inner voids on the ultrasonic waves were also investigated, and the results confirmed that the laminates in this Gc region did not significantly affect attenuation. [ABSTRACT FROM AUTHOR]

Tensile strength (TS) is an important mechanical property of a material. The conventional mechanical measurement method destroys the object under investigation; hence, the non-destructive evaluation oftensile strength of materials has become a research hotspot in recent years. Currently, there are some accuracy problems associated with evaluating the tensile strength of materials on the basis of single non-destructive testing (NDT) methods such as ultrasonic or electromagnetic methods. In this study, 45 steel is used as an example to study various non-destructive testing methods. First, seven different heat treatment systems are used to prepare standard specimens with different tensile strengths, which are measured bytensiletests. Second, non-destructive testing signals for each specimen are obtained as ultrasonic signals, magnetic Barkhausen noise and magnetic hysteresis signals, and the characteristic parameters of the signals are extracted. Then, single-parameter non-destructive evaluation (SNE) models oftensile strength with three different non-destructive testing methods are developed. Furthermore, a multivariate non-destructive evaluation (MNE) method based on ultrasonic signals, magnetic Barkhausen noise and magnetic hysteresis is proposed to improve the accuracy of the tensile strength measurements obtained from non-destructive testing. A deep residual network (ResNet) is used to combine the features of the three non-destructive testing parameters and an MNE model of tensile strength is developed. Moreover, a data pretreatment method based on the fuzzy mapping relationship is applied to train the MNE model successfully and enhance the stability, accuracy and reliability of the obtained results. Finally, the accuracies of the above fourtensile strength evaluation models are confirmed by verification using the specimens. The results show that the MNE model has higher accuracy than the SNE models. [ABSTRACT FROM AUTHOR]

Ultrasound is considered as an effective nondestructive testing method. This review paper discusses the potential of ultrasonic techniques for defect detection and fractures in construction and building materials, which explains the basic principles of ultrasonic approaches and their widespread application in non-destructive testing (NDT). The paper also summarizes the benefits of ultrasonic computerized tomography (UCT), highlighting its high resolution, stability, and low radiation compared to other techniques. Additionally, it introduces an enhanced usage of UCT that involves the flexible arrangement of transmitting and receiving probes in ultrasonic apparatus to improve the accuracy of UCT signals. [ABSTRACT FROM AUTHOR]

The time-of-flight diffraction (TOFD) technique is used as an important non-destructive testing method in weld integrity evaluation and failure analysis. However, an accurate measurement of the time-of-flight (TOF) has proven to be difficult due to the low time resolution of the measured signal. Conventional deconvolution techniques have been used to improve the time resolution of the signal but are not effective for ultrasonic TOFD signals because the frequency contents of the signals are non-static in space-frequency distribution. To overcome this problem, a method is proposed in this paper that estimates the TOF in two steps. In the first step, the measured signal is decomposed into a series of narrowband signals using a wavelet transform and an atom dictionary is adaptively established according to the characteristics of a selected narrowband signal. In the second step, matching pursuit (MP) is used to derive a sparse representation of the selected narrowband signal. A steel specimen with artificial defects is prepared, experiments are carried out and the results confirm the efficacy of the proposed algorithm. [ABSTRACT FROM AUTHOR]

In this paper, a method combining ultrasonic travel time measurement with inversion is proposed to reconstruct the solid temperature field. Based on the measured transient ultrasonic propagation time, the inverse problem of acoustic thermal coupling is solved directly, and the unknown equivalent heat flow is estimated. Then, the time and space distribution of the internal temperature field can be reconstructed accurately by calculating the corresponding heat conduction problems. Through the estimation of two typical heat flow function forms, the accuracy and influencing factors are simulated and analyzed. The feasibility and error of this method are analyzed through a transient verification experiment of a steel plate heated first and then cooled and a steady-state experiment in the literature. The results show that, compared with the previous methods, this method can predict the distribution of non-uniform temperature field more accurately and effectively. This method is expected to be an effective method for nondestructive testing of temperature distribution of solid structures. [ABSTRACT FROM AUTHOR]

Key message: Considering anisotropy in image reconstruction algorithm for ultrasound computed tomography of trees resulted in a more accurate detection of defects compared to common approaches used. Context: Ultrasound computed tomography is a suitable tool for nondestructive evaluation of standing trees. Until now, to simplify the image reconstruction process, the transverse cross-section of trees has been considered as quasi-isotropic and therefore limiting the defect identification capability. Aims: An approach to solve the inverse problem for tree imaging is presented, using an ultrasound-based method (travel-time computed tomography) suited to the anisotropy of wood material and validated experimentally. Methods: The proposed iterative method focused on finding a polynomial approximation of the slowness in each pixel of the image depending on the angle of propagation, modifying the curved trajectories by means of a raytracing method. This method allowed a mapping of specific elastic constants using nonlinear regression. Experimental validation was performed using sections of green wood from a pine tree (Pinus pinea L.), with configurations that include a healthy case, a centered, and an off-centered defect. Results: Images obtained using the proposed method led to a more accurate location of the defects compared to the filtered backprojection algorithm (isotropic hypothesis), considered as reference. Conclusion: The performed experiments demonstrated that considering the wood anisotropy in the imaging process led to a better defect detection compared to the use of a common imaging technique. [ABSTRACT FROM AUTHOR]

In this study, near-surface cracks in a railhead are inspected thoroughly using phased array ultrasonic testing (PAUT). This research finds an alternative technique to inspect for near-surface cracks because the conventional non-destructive testing method for rail inspection lacks the capacity to inspect the near-surface crack profile. This study shows that PAUT can determine not only the crack depth but also the near-surface crack profile, so that the inspector can estimate the stage of crack growth and how the crack propagates. This information is valuable to the rail maintainer as one of the considerations for deciding the thickness of metal to remove when grinding the rail. In this study, after the measurement, the inspected region of the cracked railhead is sliced into thin pieces so that crack network information can be extracted. A 3D image reconstruction of the surface cracks based on the crack marks from all of the sliced rail pieces is performed. This image is then used as a reference to confirm the PAUT results. The results show that PAUT can clearly deliver crack profile estimation and provide an accurate estimation of a 3.51 mm crack-tip depth with an absolute error range of 8%-18%. The results also suggest that PAUT is a potential method for installation in a measurement train for near-surface crack inspection. [ABSTRACT FROM AUTHOR]

The possibility to use ultrasonic nondestructive testing for the diagnosis and characterization of decay in building materials due to salts crystallization is here investigated. Salts crystallization is one of the main sources of decay for stone materials, especially for cultural heritage items underwater or exposed to water, and its early detection as well as a continuous monitoring is highly desirable. Currently, this often requires the use of destructive methods and the sampling of the items under inspection. This work shows promises to the successful use for this purpose of ultrasonic nondestructive testing. [ABSTRACT FROM AUTHOR]

Scrutinizing delaminated composites is extensively conducted based on measurements of various types of nondestructive sensing apparatus, classified herein as systems of thermographic inspection, piezoelectric inspection, optical interferometric inspection, electromagnetic testing, ultrasonic testing, and visual testing. The development of the subject has been reviewed during 2000-2017. Not only does the substantial corresponding literature strongly indicates numerous increasing industrial demand for composites, including carbon fiber-reinforced polymer, glass fiber-reinforced polymer, and fiber-reinforced metal laminate, but also the significant potential of composites to delaminate when subjected particularly to impact, machining operation or manufacturing imperfections. Conducting a study on the corresponding literature, the subject of delamination inspection within composites is found to be a dynamic, mature field, while lacking a thorough literature review. Therefore, the present study addresses the mentioned gap regarding various sensation systems utilized so as to detect internal anomalies in composites for the review arrangement. To that end, the literature inclusion in terms of citation times is electronically adopted associated with an appropriate combination of keywords. The study may be considered as a comprehensive, up-to-date review covering all delamination inspection techniques founded on sensation systems, thus benefiting the readers with information in an organized configuration. [ABSTRACT FROM AUTHOR]

• Tomograms can be improved by the ray tracing technique. • Detail explanation about Dijkstra algorithm. • Experimental program endorse the advantages. The ultrasonic tomography is an important tool in nondestructive evaluation of concrete structures. It is usual to consider in ultrasonic reconstruction that the mechanical waves only propagate in straight-lines between the transmitter and the receiver transducers, corresponding to the behavior in a homogenous material. In a concrete specimen, however, mechanical waves may deviate from an internal flaw, which affects the resulting tomograms. In this study, the ray tracing technique based on the Network Theory, which allows to consider waves not travelling in a straight-line, was incorporated into the tomography processing. Experimental tests were carried out on concrete specimens with different internal flaws. The results indicated the importance of using the ray tracing technique to properly detect the size and the shape of internal flaws, improving the obtained tomograms. All the necessary algorithms for the application of the Network Theory were presented. [ABSTRACT FROM AUTHOR]

Abstract In this paper, an ultrasonic non-destructive measurement technique is proposed to detect and size cracks in engineering materials. This measurement technique is based on Time of Flight Diffraction (TOFD) permitting the detection and location of cracks employing the compression waves diffraction phenomena. Then, the cracks are sized by the estimation of Time of Flight (TOF) of the diffracted waves. In the simulation and experimental investigations, the TOFs are estimated in two steps, the first step is the envelope extraction by Hilbert Transform (HT). The second step is the envelope estimation using a Matching Pursuit (MP) approach optimized by Differential Evolution (DE) in order to reach fast and accurate results. Consequently, the estimation results confirm the efficiency of the proposed measurement technique, which can be considered as an encouraging method for crack sizing in industrial materials. [ABSTRACT FROM AUTHOR]

Ultrasonic non-destructive testing signal can be decomposed into a set of chirplet signals, which makes the chirplet transform a fitting ultrasonic signal analysis and processing method. Moreover, compared to wavelet transform, short-time Fourier transform and Gabor transform, chirplet transform is a comprehensive signal approximation method, nevertheless, the former methods gained more popularity in the ultrasonic signal processing research. In this paper, the principles of the chirplet transform are explained with a simplified presentation and the studies that used the transform in ultrasonic non-destructive testing and in structural health monitoring are reviewed to expose the existing applications and motivate the research in the potential ones. [ABSTRACT FROM AUTHOR]

The experimental results of a novel ultrasonic monitoring method to identify different types of flaws in reinforced concrete are presented. The authors' previous work has demonstrated the ability to use the proposed ultrasonic guided wave leakage (UGWL) to identify the onset of mechanical delamination. This paper presents the results from using the UGWL method to identify chemical delamination (corrosion) and cracking in concrete (other than delamination at the steel-concrete interface) in reinforced concrete. The proposed UGWL method monitors the change in amplitude of ultrasonic waves leaked from a guided wave transmitted through an embedded steel reinforcing bar. The energy of UGWL is influenced by the conditions between the steel reinforcing bar, acting as the waveguide, and the surrounding concrete. This experimental study demonstrated that the UGWL monitoring method is sensitive not only to the onset of delaminations, but also to the development of corrosion activity and cracks. [ABSTRACT FROM AUTHOR]

Highlights • Non-destructive testing was carried out on coral aggregate seawater concrete (CAC). • Rebound hammer, ultrasonic pulse velocity and combined method were employed. • Various mathematical models of strength prediction of CAC by various methods have been achieved. • The applicability of testing strength curves of OPC and LAC to CAC were also discussed. Abstract Coral aggregate concrete (CAC) is a material that is becoming increasingly popular in reef concrete structural applications. In the present work, CAC was cast in a wide range of compressive strength varying from 30 to 75 MPa. The ultrasonic pulse velocity (UPV), the rebound hammer (RH) and the compressive strength (f cu) test were conducted at 28 and 90 days. The influence of sisal and age on the relationship between f cu - UPV and f cu - RH were discussed. Additionally, the mathematical model of strength prediction by UPV, RH and the combined method were established (testing strength curve, TSC). Finally, the applicability of TSC of Portland concrete (OPC) and lightweight aggregate concrete (LAC) to CAC were also discussed. The results show that the curing ages have a certain influence on the TSC. Therefore, the 28 d and 90 d strength test curves for special engineering by UPV, RH and combined methods were established. For ease of use, the TSC for regional engineering by various methods were also established. The relative standard error (e r) of the TSC can meet the requirements of the specification for special and regional. In addition, the TSC of OPC and LAC does not apply to the strength prediction of CAC through the error analysis. [ABSTRACT FROM AUTHOR]

The present paper deals with the measurement of coat thickness on wood using an ultrasonic measurement method. Exterior wood coatings (waterborne acrylate dispersions) with coating film thickness between 80 - 115 μm were examined. The non-destructive film thickness measurement used a Sursonic ultrasound measuring device, enabling measurement of the thickness of thin films on nonferromagnetic and simultaneously non-conductive materials. The device also enables measurement of very thin layers of coating films, where the transit time of an ultrasound pulse through the film is shorter than the time width of the pulse. The accuracy of measurement using this measuring device was determined; destructive measurement using a light microscope was chosen as a reference measurement method. Differences in the results measured using the destructive and non-destructive methods were recorded; nevertheless, in most cases, these differences are smaller than the uncertainty of measurement using the light microscope. It can be concluded, therefore, that the results of the two compared methods match over the entire range of thickness of 80 - 115 μm. The largest differences in the measurement readings from the destructive and non-destructive methods were identified in the range of 97 - 103 μm. [ABSTRACT FROM AUTHOR]

The development of cost effective and reliable bonded structures ideally requires an NDT method to detect the presence of poor quality, weak bonds or kissing bonds. If these bonds are more compliant in tension than in compression stress-strain nonlinearities provide a possible route to detection with the use of nonlinear ultrasonic techniques. This paper focuses on the kissing bond case and the resulting contact acoustic nonlinearity of the interface. A kissing bond is created by compression loading of two aluminium blocks. Non-collinear mixing of two shear waves producing a sum frequency longitudinal wave is the method of stimulation of contact acoustic nonlinearity in this research. The parametric space of the nonlinear mixing is measured in terms of interaction angle of the input beams and the ratio of their frequencies creating a ‘fingerprint’ of the sample's bulk and interface properties in the region where the beams overlap. The scattering fingerprint of a classically nonlinear solid is modelled analytically and a kissing interface is modelled numerically; these results are compared with experimentally measured values. The experimental interface is tested with varied interfacial loading, resulting in an increase in scattering amplitude as load is increased. Secondary peaks in the parameter space also appeared as loading increased, as well as other changes in the fingerprint pattern. [ABSTRACT FROM AUTHOR]

Inspection reliability of small-scale defects, targeting dimensions below 100 µm, is crucial for structural safety of critical components in high-value applications. Early defects are often possible to repair, contributing for the circular economy and sustainability by allowing extended life and reuse of components. During in-service operation, the small-scale defects are typically originated from creep, fatigue, thermal cycles, and environmental damage, or any combination of these multiphysical loading conditions. What are thresholds in Non-Destructive Testing (NDT) techniques to detect and reliably characterise small-scale defects? What is the state of the art of NDT-based solutions, in terms of small-scale defects located at surface, and interior of materials? Examples of small-scale defects in engineering materials are established, and a holistic review is composed on the detectability in terms of sensitivity and resolution. Distinguishable high detection accuracy and resolution is provided by computed tomography paired with computer laminography, scanning thermal microscopy paired with Raman spectroscopy, and NDT techniques paired with machine learning and advanced post-processing signal algorithms. Other promising techniques are time-of-flight diffraction, thermoreflectance thermal imaging, advanced eddy currents probes, like the IOnic probe, micro magnetic bridge probe used in magnetic flux leakage, driven-bacterial cells, Quantum dots and hydrogen-as-a-probe. [ABSTRACT FROM AUTHOR]

Several types of discontinuities and defects may be present on a weld, thus leading to a considerable reduction of its resistance. Therefore, ensuring a high welding quality and reliability has become a matter of key importance for many construction and industrial activities. Among the non-destructive weld testing and inspection techniques, the time-of-flight diffraction (TOFD) arises as a very safe (no ionising radiation), precise, reliable and versatile practice. However, this technique presents a relevant drawback, associated to the appearance of speckle noise that should be addressed. In this regard, this paper presents a new, intelligent and automatic method for weld inspection and analysis, based on TOFD, image processing and neural networks. The developed system is capable of detecting weld defects and imperfections with accuracy, and classify them into different categories. [ABSTRACT FROM AUTHOR]

There is a growing need for nondestructively evaluate the integrity of trees and wooden structural elements. Such an investigation can be performed with the use of different test methods. Nevertheless, in order to yield acceptable results, the test methods should consider the anisotropic nature of the wood, which includes the shape of the annual rings, and also the pith location in the cross-section. This paper presents a new method to determine the pith location of a tree or structural element made of timber or lumber based on ultrasonic tomography readings. [ABSTRACT FROM AUTHOR]

A pulse compression technique has been developed for the non-destructive testing of concrete samples. Scattering of signals from aggregate has historically been a problem in such measurements. Here, it is shown that a combination of piezocomposite transducers, pulse compression and post processing can lead to good images of a reinforcement bar at a cover depth of 55 mm. This has been achieved using a combination of wide bandwidth operation over the 150–450 kHz range, and processing based on measuring the cumulative energy scattered back to the receiver. Results are presented in the form of images of a 20 mm rebar embedded within a sample containing 10 mm aggregate. [ABSTRACT FROM AUTHOR]

Till quite recently, in-service defect monitoring of Industrial Equipments is being accomplished by tedious manual methodologies for utilizing the conventional or Non-Destructive techniques for defects monitoring. There have been efforts in the recent past to make use of mini mobile robots with NDE techniques for defect monitoring in the inspection of pipes with reasonable success. In this context, this paper proposes a new development methodology of conceptual Internet of Things (IoT) sensors based Non-Destructive Evaluation Technique (NDE) based on Ultrasonic for in-service defect monitoring of Industrial Equipments. The underlying philosophy chosen is 'integrating an ultrasonic Non-Destructive Evaluation sensor packaged with IoT based sensor'. During the run time, the integrity of material will be done. Non-Destructive testing allows measurement of material properties without inflicting any damage to the material in process. An IoT with wireless network coupled with NDE facilitates the mutual effort to monitor a certain aspect without the use of valuable fixed wired circuits. A typical system architecture of a 'paired module' comprising of IoT sensor and NDE sensor packaged to monitor the defect status conditions of the pipelines is envisaged. A specific study is elaborated to monitor the thickness of a in-service pipeline used in Industrial Equipment. This concept methodology aims to work as an alternate to the existing technologies in similar context while providing enormous advantages over the existing methods. [ABSTRACT FROM AUTHOR]

To perform a non-destructive evaluation of wood, the Christoffel equation is frequently used to describe the relationship between the ultrasonic wave velocity and the mechanical parameters. In the context of acoustical tomography imaging of standing trees, the key contribution of this numerical study is to determine the influence of mechanical parameters of the wood radial-tangential plane on the wave velocity computation using the Christoffel equation. Mechanical parameters from six species were selected. A sensitivity analysis was carried out by increasing and decreasing every parameter by a given percentage, and then by computing the variation of velocity for a set of wave direction of propagations. The evolution of the wave velocity, according to the direction of propagation, depended on the considered species; there was a difference between the softwoods and the hardwoods. The sensitivity analysis showed a bigger influence of the Young's moduli, followed by the Poisson's ratio, and finally by the shear modulus. However, these last two parameters cannot be neglected when using the Christoffel equation to solve the inverse problem of standing tree tomography. A proposed solution involves determining the propagation paths using the Young's moduli as variables and then inversing the set of equations in accordance with the overall parameters. [ABSTRACT FROM AUTHOR]

Material state awareness of composites using conventional Nondestructive Evaluation (NDE) method is limited by finding the size and the locations of the cracks and the delamination in a composite structure. To aid the progressive failure models using the slow growth criteria, the awareness of the precursor damage state and quantification of the degraded material properties is necessary, which is challenging using the current NDE methods. To quantify the material state, a new offline NDE method is reported herein. The new method named Quantitative Ultrasonic Image Correlation (QUIC) is devised, where the concept of microcontinuum mechanics is hybrid with the experimentally measured Ultrasonic wave parameters. This unique combination resulted in a parameter called Nonlocal Damage Entropy for the precursor awareness. High frequency (more than 25 MHz) scanning acoustic microscopy is employed for the proposed QUIC. Eight woven carbon-fiber-reinforced-plastic composite specimens were tested under fatigue up to 70% of their remaining useful life. During the first 30% of the life, the proposed nonlocal damage entropy is plotted to demonstrate the degradation of the material properties via awareness of the precursor damage state. Visual proofs for the precursor damage states are provided with the digital images obtained from the micro-optical microscopy, the scanning acoustic microscopy and the scanning electron microscopy. [ABSTRACT FROM AUTHOR]

This work proposes a novel hybrid signal processing technique to extract information on disbond-type defects from a single B-scan in the process of non-destructive testing (NDT) of glass fiber reinforced plastic (GFRP) material using ultrasonic guided waves (GW). The selected GFRP sample has been a segment of wind turbine blade, which possessed an aerodynamic shape. Two disbond type defects having diameters of 15 mm and 25 mm were artificially constructed on its trailing edge. The experiment has been performed using the low-frequency ultrasonic system developed at the Ultrasound Institute of Kaunas University of Technology and only one side of the sample was accessed. A special configuration of the transmitting and receiving transducers fixed on a movable panel with a separation distance of 50 mm was proposed for recording the ultrasonic guided wave signals at each one-millimeter step along the scanning distance up to 500 mm. Finally, the hybrid signal processing technique comprising the valuable features of the three most promising signal processing techniques: cross-correlation, wavelet transform, and Hilbert-Huang transform has been applied to the received signals for the extraction of defects information from a single B-scan image. The wavelet transform and cross-correlation techniques have been combined in order to extract the approximated size and location of the defects and measurements of time delays. Thereafter, Hilbert-Huang transform has been applied to the wavelet transformed signal to compare the variation of instantaneous frequencies and instantaneous amplitudes of the defect-free and defective signals. [ABSTRACT FROM AUTHOR]

The reflection technique of ultrasonic waves was used for monitoring and nondestructively characterization of a mortar during its evolution. Using Argand Diagram to measure the resonant ultrasonic wave frequency and its width shows that they follow the rapidly changing in mechanical properties of the material at the young age. Both parameters increase during the time of hardening and also prove the effect of the sand particle size and temperature of the mortar properties. Moreover, measuring the width of the ultrasonic wave resonance allows distinguishing the different hydration phases of material. [ABSTRACT FROM AUTHOR]

Ultra-High Performance Fibre Reinforced Concrete is a material which is becoming increasingly popular in structural applications, mainly due to its superior mechanical characteristics. The mechanical properties of this material are of high importance and the development of non-destructive techniques is vital for the evaluation of the mechanical characteristics of existing structures. In the current study, Ultra-High Performance Fibre Reinforced Concrete with different amounts of steel fibres has been examined. Compressive and tensile tests have been conducted alongside with Ultrasonic Pulse Velocity and Rebound Hammer measurements and the development of appropriate empirical non-destructive models has been examined. [ABSTRACT FROM AUTHOR]

Multi-layered composites are frequently used in many applications as constructional materials. Such materials represent a difficult inspection task for some traditional techniques of non-destructive testing (NDT). Typical defects of composite materials are delaminations, lack of adhesion and crumpling, just to name a few. IR thermography and ultrasonics are typically considered as candidate techniques to detect different types of defects. In order to assess the potential usefulness of both methods, a composite laminate with a polytetrafluoroethylene disk inserted between two layers to simulate a delamination is investigated. Experimental evidences resulting from the two technologies are discussed. [ABSTRACT FROM AUTHOR]