Suitable Non-destructive Testing Research Articles

The Influence of Microstructure Characteristics on Thickness Measurement of TBCs Using Terahertz Time-Domain Spectroscopy

Thermal barrier coatings (TBCs) exhibit excellent thermal insulation capabilities, proving crucial in enhancing the performance of turbine blades. Accurate measurement of TBC thickness is pivotal for the quality control and health monitoring of turbine blades. However, the absence of suitable non-destructive testing (NDT) methods poses a challenge in ensuring precise quality control and health assessment of TBCs. This study investigates the efficacy of terahertz time-domain spectroscopy (THz-TDS) in measuring TBCs thickness, specifically focusing on the microstructure characteristics of the top coat (TC), including grain morphology, internal porosity, surface roughness, and agglomerates. The findings emphasize the significance of grain morphology in determining thickness measurement due to the varied terahertz wave propagation modes. Moreover, the study involved polishing EB-PVD and APS samples to mitigate surface roughness. This process revealed a discernible linear correlation between reduced surface roughness and decreased measurement errors. The slopes of the error reduction curves ranged from 0.59 to 1.7 for EB-PVD and 2.17 to 5.79 for APS samples. Furthermore, the research observed THz light scattering within internal pores, resulting in diminished outgoing energies and subsequent increments in measurement errors.

Fatigue life evaluation of metastable austenitic stainless steel AISI 347 based on nondestructive testing methods for different environmental conditions

Due to aging nuclear power plants there is an increasing need for methods to evaluate the integrity of components and structures of nuclear engineering. During power plant operation, nuclear materials are exposed to the effects of temperature, corrosion and cyclic loading. These lead to microstructural changes resulting in material degradation, which can be detected by suitable nondestructive testing (NDT) methods. Fatigue testing setups for ambient temperature, distilled water and 300 °C were designed to represent relevant environmental conditions and instrumented with in-situ measurements of temperature, electric, micromagnetic and electrochemical NDT parameters. Constant amplitude and strain increase tests with specimens of metastable austenitic stainless steel AISI 347 (X6CrNiNb18-10, 1.4550) typically used for pipe components were conducted in total strain control. Data obtained were employed in short-time evaluation procedure StrainLife to generate fatigue life data. To establish an understanding between microstructure evolution and NDT data, scanning electron microscopic methods such as electron backscatter diffraction and energy dispersive X-ray spectroscopy were used. Electrochemical data yields fatigue life results as good as conventionally used parameters like stress and strain. These findings could enable usage of presented parameters for mobile or even online testing systems, since accessibility depending on application case can be much improved.

Online monitoring of manufacturing processes by acoustic emission

For many years, Cetim has been working on on-line control methodologies for manufacturing processes in order to reduce or even eliminate controls on finished parts. After the first works by conducted by the Acoustic Emission technique (AE) on the monitoring of sheet metal stamping process [1], the monitoring of new manufacturing processes such as metal cutting, wire drawing, spot welding, forging and especially are under study. In the present paper, the results of acoustic emission monitoring carried out on additive manufacturing production and also wire drawing are presented. For both processes on-line control during manufacturing is particularly important. Due to the geometric complexity of the parts produced by additive manufacturing, suitable nondestructive testing (NDT) means are limited. In addition, these are generally small series or even single parts with a long manufacturing time. For their part, wire drawing manufacturers currently have only visual inspection, unable to detect fine scratches on the wire at the output of production.

Feasibility of Using Shear Wave Ultrasonic Probes as Pump-Wave Sources in Concrete Microcrack Detection and Monitoring by Nonlinear Ultrasonic Coda Wave Interferometry.

This paper represents a first attempt to study the feasibility of using shear wave (SW) ultrasonic probes as pump-wave sources in concrete microcrack detection and monitoring by Nonlinear Ultrasonic Coda Wave Interferometry (NCWI). The premise behind our study is that the nonlinear elastic hysteretic behavior at microcracks may depend on their orientation with respect to the stationary wave-field induced by the pump-wave source. In this context, the use of a SW probe as a pump-wave source may induce the nonlinear elastic behavior of microcracks oriented in directions not typically detected by a conventional longitudinal pump-wave source. To date, this premise is hard to address by current experimental and numerical methods, however, the feasibility of using SW probes as a pump-wave source can be experimentally tested. This idea is the main focus of the present work. Under laboratory conditions, we exploit the high sensitivity of the CWI technique to capture the transient weakening behaviour induced by the SW pump-wave source in concrete samples subjected to loading and unloading cycles. Our results show that after reaching a load level of of the ultimate stress, the material weakening increases as a consequence of microcrack proliferation, which is consistent with previous studies. Despite the lack of exhaustive experimental studies, we believe that our work is the first step in the formulation of strategies that involve an appropriate selection and placement of pump-wave sources to improve the NCWI technique. These improvements may be relevant to convert the NCWI technique into a more suitable non-destructive testing technique for the inspection of microcracking evolution in concrete structures and the assessment of their structural integrity.

Phased array ultrasonic test signal enhancement and classification using Empirical Wavelet Transform and Deep Convolution Neural Network

In the recent past, Non-Destructive Testing (NDT) has become the most popular technique due to its efficiency and accuracy without destroying the object and maintaining its original structure and gathering while examining external and internal welding defects. Generally, the NDT environment is harmful which is distinguished by huge volatile fields of electromagnetic, elevated radiation emission instability, and elevated heat. Therefore, a suitable NDT approach could be recognized and practiced. In this paper, a novel algorithm is proposed based on a Phased array ultrasonic test (PAUT) for NDT to attain the proper test attributes. In the proposed methodology, the carbon steel welding section is synthetically produced with various defects and tested using the PAUT method. The signals which are acquired from the PAUT device are having noise. The Adaptive Least Mean Square (ALMS) filter is proposed to filter PAUT signal to eliminate random noise and Gaussian noise. The ALMS filter is the combination of low pass filter (LPF), high pass filter (HPF), and bandpass filter (BPF). The time-domain PAUT signal is converted into a frequency-domain signal to extract more features by applying the Empirical Wavelet Transform (EWT) algorithm. In the frequency domain signal, first order and second order features extraction techniques are applied to extract various features for further classification. The Deep Learning methodology is proposed for the classification of PAUT signals. Based on the PAUT signal features, the Deep Convolution Neural Network (DCNN) is applied for further classification. The DCNN will classify the welding signal as to whether it is defective or non-defective. The Confusion Matrix (CM) is used for the estimation of measurement of performance of classification as calculating accuracy, sensitivity, and specificity. The experiments prove that the proposed methodology for PAUT testing for welding defect classification is obtained more accurately and efficiently across existing methodologies by providing numerical and graphical results.

Low-Frequency Magnetic Fields in Diagnostics of Low-Speed Electrical and Mechanical Systems

The magnetic field created by technical devices is a source of information. This information could be used in contactless diagnostics and predictive maintenance or for resolving problems along with standard NDT (nondestructive testing) methods, especially if we consider large, slow-speed devices, such as electromotors, transmissions, or generators. Identification of causalities of device failure processes with near magnetic field is one of the suitable NDT methods improving sustainability of systems. The measurements presented in the article were performed with the VEMA 04 fluxgate vector magnetometer with the DC-250 Hz bandwidth and 2 nT sensitivity. Postprocessing of the results was performed in the means of standard methods of discrete Fourier Transform, spectrogram creation and Wavelet Transform. The article presents data gathered during the measurement of a pair of extraction fans with power of 140 kW each and maximum revolutions up to 740 rev/min controlled by frequency converters and a single semi-Kaplan water power plant with 400 kW peak power at 1005 rev/min maximum generator speed. The measurements were performed before and after repairs of one of the ventilators in the ventilation system at 60% and 100% of maximal output power. The rotating magnetic fields of the fan electromotor stator, fan rotor revolutions, rotor slip frequency and ball-bearing frequencies were identified in frequency spectrums in the distance of 700 mm from fan electromotor axis in both cases. During the measurements on the semi-Kaplan turbine, the changes in states of mechanical and electrical components of the machine were monitored in the magnetic fields with increase of the power in the range of 0–95%, before and after phasing to the electrical grid. Standard processing methods, Discrete Fourier Transform, spectrograms and Discrete Wavelet Transform were used. In the spectrograms of the measured magnetic fields, the 1st–4th harmonics of the turbine shaft, generator shaft and also their side frequencies were identified. Significant changes of magnetic fields in time were identified in the area of 60–95% power. With the help of the Wavelet, transform intervals were identified where it is desirable to operate the turbine. The analyses of magnetic fields measurements performed on the power plant were compared with vibro-diagnostic principles.

Linear and Nonlinear Ultrasonic Techniques for Monitoring Stress-Induced Damages in Concrete

Abstract When stress in concrete exceeds certain threshold value, microcracks are nucleated, these microcracks can propagate and coalesce forming macrocracks, resulting in the gradual decay of the mechanical properties of concrete and eventual failure of the concrete structures. For safety concerns, one needs to develop suitable nondestructive testing methods capable of detecting past overloads of concrete structures during its service life. In this work, the stress-induced damage in concrete is monitored using ultrasonic techniques, exploiting the coupling between the stress level experienced by concrete and its wave propagation parameters. Cyclic compression tests with increasing maximum load level have been performed on specimens made of concrete with coarse-grained (CG) aggregates. Experimental results have been analyzed by two different ultrasonic methods—the linear and the nonlinear ultrasonic techniques. In linear ultrasonic technique, the stress level experienced by the specimens is related to the variations in signal amplitude and velocity of ultrasonic waves. In nonlinear ultrasonic method, the sideband peak count (SPC) technique is used for revealing the stress-induced damage corresponding to each load step. In comparison to linear ultrasonic parameters, the nonlinear ultrasonic parameter SPC-I appears to be more sensitive to the variations of the internal material structures during both loading and unloading phases. Moreover, the SPC technique has shown to be capable of identifying both the initial damage due to the evolution and nucleation of microcracks at the microscopic scale, and the subsequent damages induced by high overload, resulting in an irreversible degradation of the mechanical properties.

Sensitization of Austenitic Stainless Steels: Current Developments, Trends, and Future Directions

In this manuscript, the latest developments pertaining to sensitization are discussed. Sensitization leads to intergranular corrosion and intergranular stress corrosion cracking. The advantages and disadvantages of conventional methods to combat sensitization are elaborated. Emerging/newer techniques such as grain boundary engineering, creation of orientation gradients, and high density of twinning to improve resistance to sensitization are also covered. Detection and monitoring of deleterious phase precipitation such as carbides, nitrides, and other intermetallic phases during operation necessitate making use of nondestructive testing (NDT) methods. Possible information that we get from NDT is for material characterization includes the size, shape, and location of a defect. Herein, the significant developments for monitoring and detection of phases concerning sensitization by NDT are discussed. These range from magnetic methods to ultrasonic techniques. The multi-physics approach is essential to fully utilize NDT to ensure/predict the lifetime of the components used in the industry. Further, proper selection of suitable NDT for defect detection can avert accidents, catastrophic failures, and economic losses due to corrosion degradation. For this, the corrosion engineer/corrosionist properly apply the suitable techniques (prevention, monitoring, and assessment) to address the issues of sensitization among the wide choice available.

Research of On-Site Screening and Non-Destructive Testing for Damaged Wooden Components of the Long Corridor in Temple of Heaven

Take the Long Corridor in Temple of Heaven as an example, some screening and testing process for its wooden components which have damaged was recommended. By pre-knocking survey, the wooden components which probably have damaged were screened out and as the important focus. Then, some non-destructive testing methods such as stress-wave testing and micro-drilling resistance testing were utilized. By the comparison, analysis and interaction correction for the testing images, the internal damaged situation of wooden components were obtained. Three typical types of wooden components were selected in this study, and some specific and suitable non-destructive testing methods which adapt to their position characteristic were discussed. Thus, it can give some useful suggestions and data supporting for the later repairing and management works.

Quantitative characterization of machining-induced white layers in Ti–6Al–4V

Machining-induced white layers can affect the functional performance of engineered components, due to the resulting mechanical and microstructural properties. Destructive inspection methods such as cross-sectional microscopy are typically used to identify white layers, however, these methods are inherently costly and time-consuming. It is, therefore, desirable to detect this anomalous surface feature using non-destructive methods which requires improved knowledge around the characteristics of white layers. The present paper reports on the characterization of white layers formed during machining of Ti–6Al–4V, to aid future development of a reliable non-destructive assessment method. The microstructure of the material in the white layer was found to have a basal (0002) α-hexagonal close packed texture and there was no evidence of an α→β phase transformation during white layer formation. The white layer has a highly refined grain structure with an increased nanohardness of up to 15% compared with the bulk material. It is proposed that white layers in Ti–6Al–4V are formed by continuous dynamic recrystallization driven by severe plastic deformation during machining. According to the measured micro-mechanical properties of the white layer, suitable non-destructive testing methods are suggested for the detection of this surface feature.

Capability of non-destructive techniques in evaluating damage to composite sandwich structures

PurposeDefects can be caused by a number of factors, such as maintenance damage, ground handling and foreign objects thrown up from runways during an in-service use of composite aerospace structures. Sandwich structures are capable of absorbing large amounts of energy under impact loads, resulting in high structural crashworthiness. This situation is one of the many reasons why sandwich structures are extensively used in many aerospace applications nowadays. Their non-destructive inspection is often more complex. Hence, the choice of a suitable non-destructive testing (NDT) method can play a key role in successful damage detection. The paper aims to discuss these issues.Design/methodology/approachA comparison of detection capabilities of selected C-scan NDT methods applicable for inspections of sandwich structures was performed using water-squirt, air-coupled and pitch-catch (PC) ultrasonic techniques, supplemented by laser shearography (LS).FindingsTest results showed that the water-squirt and PC techniques are the most suitable methods for core damage evaluation. Meanwhile, the air-coupled method showed lower sensitivity for the detection of several artificial defects and impact damage in honeycomb sandwiches when unfocussed transducers were used. LS can detect most of the defects in the panels, but it has lower sensitivity and resolution for honeycomb core-type sandwiches.Originality/valueThis study quantitatively compared the damage size indication capabilities of sandwich structures by using various NDT techniques. Results of the realised tests can be used for successful selection of a suitable NDT method. Combinations of the presented methods revealed most defects.

Evaluation of 3D-printed parts by means of high-performance computer tomography

Conventional tactile and optical testing methods are not capable to detect complex inner geometries or complex surface shapes. Detecting porosities in parts is also not possible with those nondestructive methods. Among other material parameters, geometrical accuracy is essential to determine part's quality. Additive manufacturing processes also have to be optimized regarding geometry deviations caused by distortion or unfavorable orientation in the build chamber. For additive manufactured parts that incorporate previously mentioned features, high-performance computer tomography is the more suitable nondestructive testing method. Components of different materials such as plastics, ceramics, composites, or metals can be completely characterized. This nondestructive testing method was used for porosity analysis regarding the shape and local distribution of pores in an additive manufactured part to find correlations concerning the most suitable process conditions. The measured part data were also compared to original CAD files to determine zones of deviation and apply specific process strategies to avoid distortion. This paper discusses the results of integrating high-performance computer tomography (power: 500 W, max. part size: Ø 300 mm, 300 × 430 mm2) in a productionlike environment of additively manufactured parts for a wide range of technologies (i.e., electron beam melting and selective laser melting).

Online monitoring of delamination mechanisms in drilling of Mwcnts reinforced Gfrp nanocomposites by acoustic emission

Among various unconventional Non-Destructive testing (NDT) methods, Acoustic Emission (AE) referred as the most suitable NDT method for detection and characterization of material defects during machining on nanocomposites. AE technique can also be applied for dynamic machining operation called drilling for better understanding of different drilling events from start to the end of the process. The present paper mainly focuses on on-line monitoring of drilling-induced delamination of multi-walled carbon nanotubes (MWCNTs) reinforced glass fiber reinforced plastic (GFRP) nanocomposites laminates through AE technique. A 4 mm thickness of 0.3wt% MWCNTs reinforced GFRP laminates were fabricated by 16 layers of glass fabric cloth with modified epoxy resins for drilling experimentation and trails were conducted on these laminates with uncoated, TiCN and TiAlN coated 6mm diameter carbide twist drills. Design of experiments were planned based on Taguchi L9 orthogonal array and speed, feed were considered as input process parameters. The AE output response parameters such as Root Mean Square (RMS) voltage, AE rise, energy, peak amplitude, hits, AE count, duration and counts to peak were helped to analyse the delamination mechanisms as well as cutting force generation during drilling on nanocomposites. From the experimental results, it was concluded that low feed rate (0.02 mm/rev) and high spindle speed (1500 RPM) with TiCN coated carbide drill gives the reduced delamination factor and thrust force values. Additionally, AE parameters were also highly influenced by the cutting parameters as well as delamination mechanisms. Out of all AE parameters AE-RMS voltage designated as the important parameter to analyse the delamination factor and increased RMS voltage observed with higher feed rate and cutting forces. The other AE parameters were very closely associated to the RMS voltage. Finally, it was confirmed that AE is most suitable NDT technique for on-line monitoring of drilling induced delamination for production of defect free holes on GFRP-MWCNTs composites laminates.

Condition Assessment of Existing Concrete Building Using Non-Destructive Testing Methods for Effective Repair and Restoration-A Case Study

Buildings constructed during early 70’s & late 80’s of the last century in India are found to be in distressed conditions due to inadequate specifications and poor construction practices. The continuous monitoring of concrete structures using suitable NDT (Non Destructive Testing) methods and use of possible restoration methods help in a considerable reduction of the rate of deterioration of concrete structures thereby increasing the life span of structures. NDT methods have greater advantage in evaluating the uniformity, homogeneity, approximate compressive strength, durability, the extent of corrosion of rebars in concrete etc. of damaged structures. The objective of the present study is to enhance the life of 50 year old existing hospital building (Partly RC and Brick masonry) in Kurnool, Andhra Pradesh. Condition assessments are carried out through a visual, field and laboratory evaluation of samples collected from the structure and results are presented in this paper. The paper also highlights the assessment of strength and durability of concrete to evaluate the extent of distress and damage in the building. Besides visual inspection, the Non Destructive Evaluation covering UPV & Rebound Hammer values and Half Cell Potential with respect to the status of corrosion of reinforcing bars and chemical tests on selected un-distressed RC columns, beams, and slabs are also presented and discussed. The repair and strengthening techniques using the latest materials and possible restoration works such as column jacketing, shotcreting, anticorrosive coatings, etc. have been suggested to enhance the life of the structure.

Selection of suitable NDT methods for building inspection

Construction of modern structures requires good quality concrete with adequate strength and durability. Several accidents occurred in the civil constructions and were reported in the media. Such accidents were due to poor workmanship and lack of systematic monitoring during the constructions. In addition, water leaking and cracking in residential houses was commonly reported too. Based on these facts, monitoring the quality of concrete in structures is becoming more and more important subject. This paper describes major Non-destructive Testing (NDT) methods for evaluating structural integrity of concrete building. Some interesting findings during actual NDT inspections on site are presented. The NDT methods used are explained, compared and discussed. The suitable methods are suggested as minimum NDT methods to cover parameters required in the inspection.

A comparison between finite element modeling and various thermographic non-destructive testing techniques for the quantification of the thermal integrity of macro-brush plasma facing components used in a tokamak.

The plasma facing components (PFCs) inside a tokamak are typically exposed to extremely high heat flux of the order of MW/m(2). The brazing quality between the plasma facing materials (PFMs) and the heat sink will determine the structural integrity and hence the effective service life of these PFCs. Suitable non-destructive testing (NDT) techniques for the pre-qualification of these components are thus essential to evaluate their structural integrity at various stages of their service life. Macro-brush type mockups of prototype PFCs with graphite as PFM have been inspected for their brazing quality using different active Infrared (IR)-thermographic NDT techniques. The results obtained from these techniques are compared and discussed. The brazing quality was quantified by establishing a comparison between the experimental results and the results from Finite Element Analysis (FEA). The percentage of contact between the PFM and the substrate was varied in FEA. FEA results when compared with experiments shows that tiles have different amounts of contact with the substrate ranging between 10% and 80%.

Fatigue assessment of old design axles: Service simulation and life extension

This paper proposes a damage-tolerant approach for ensuring the safe operation of railway axles with an old, non-EN-compliant design, until completion of their life cycle. The approach consists in defining a suitable non-destructive testing (NDT) inspection programme, which is based on the precise evaluation of service loads using multi-body simulation and on validated crack propagation models. The application of the proposed approach is presented for two different test cases, both representing old design axles for urban railway vehicles. It is demonstrated that NDT inspection intervals are highly dependent on the specific axle design and service scenarios, particularly with regard to the effects of braking.

Realization of Al/Mg-Hybrid-Joints by Ultrasound Supported Friction Stir Welding - Mechanical Properties, Microstructure and Corrosion Behavior

Fusion welding of dissimilar metals is in the most cases difficult or even impossible as a result of different melting points and the development of undesirable brittle intermetallic phases. This often leads to joint strengths considerable below the tensile strength of the base materials. By using Friction Stir Welding (FSW) it is possible to reduce the development of the intermetallic phases of Al/Mg-joints significantly but not to avoid them completely. Hence a hybrid welding system at the WKK of the University of Kaiserslautern was developed called “Ultrasound Supported Friction Stir Welding (US-FSW)” with the aim to shatter the brittle interlayer lines and to scatter fragments in the welding area during the FSW process. Pre-investigations have shown that for Al/Mg-US-FSW-joints the strength can be increased up to 30% in comparison to conventional FSW. Moreover for the reliable detection of nonconformities in the weld during a post-process inspection by suitable non-destructive testing (NDT) methods is necessary. Also there is a strong need for better process monitoring and control by in-process NDT methods. Furthermore the corrosion behavior of the basic materials and hybrid-joints was investigated by electrochemical methods indicating an increased corrosion of the Mg alloy in the area of the Al/Mg-butt weld.

Barkhausen Noise Emission of Surfaces Produced by Hard Milling Process

This paper deals with influence of tool wear on surface integrity after hard turning expressed mainly through the Barkhausen noise responses. Grinding operations can be sometimes replaced by hard machining (hard turning and milling). Chip separation in hard turning differs from mechanism of chip separation during grinding. For this reason surface integrity expressed in variable terms differs. Surface integrity can be expressed in such term as surface roughness, shape deviations as well as characteristics such as residual stresses, structure transformations, and microhardness alteration. Being so, it can be beneficial to apply the suitable nondestructive surface testing techniques to obtain information about surface integrity expressed in complexity of this term. Nowadays, Barkhausen noise technique is widely used in a variety of industrial applications. This technique is sensitive to stress state as well as microstructure features. For this reason, Barkhausen noise emission is used in this study to reveal magnetic and stress anisotropy developed in a certain stage of tool wear. The paper also discusses very high BN responses associated with the specific aspects of produced surfaces.

Advanced ultrasonic non-destructive testing for damage detection on thick and curved composite elements for constructions

In this work, the problem of non-destructive testing on composite components with complex shapes for civil constructions and transport infrastructures is analyzed. In such applications at the state of the art main challenges are related with the inspection of thick sandwiches with low density cores (below 80 kg/m3) and curved panels. After a review of suitable non-destructive testing techniques, an original set-up for low frequency (100 kHz) ultrasonic inspection is proposed, which combines different solutions in through-transmission mode. The set-up is based on a hybrid configuration coupling a contact emitting probe with a non-contact air-coupled receiver. The use of a contact probe in emission is necessary to have enough energy to analyze thick components with low density core. The contact between probe and surface is made small (spot of 1 mm) and smooth using a spherical cap to increase lateral resolution at low frequency and to allow scan on irregular surfaces sometimes present in curved parts. To improve understanding this cap has been tested here also with a single probe in pulse echo mode. The non-contact probe in reception allows a better inspection flexibility on curved and thick components, where pulse echo is not feasible at all. The system is mainly developed for inspection after production in an industrialized production process, where through-transmission testing is possible. The analysis of results on two different samples (one thick sandwich with low density 40 kg/m3, 50 mm thick PUR core and one curved laminate panel) shows that the proposed methods can efficiently inspect construction composites of complex shape with satisfactory signal-to-noise ratio (usually SNR > 15 dB) and lateral resolution (2–3 mm).