Non-destructive Testing Measurements Research Articles

Pathways toward the Use of Non-Destructive Micromagnetic Analysis for Porosity Assessment and Process Parameter Optimization in Additive Manufacturing of 42CrMo4 (AISI 4140).

Laser-based powder bed fusion of metals (PBF-LB/M) is a widely applied additive manufacturing technique. Thus, PBF-LB/M represents a potential candidate for the processing of quenched and tempered (Q&T) steels such as 42CrMo4 (AISI 4140), as these steels are often considered as the material of choice for complex components, e.g., in the toolmaking industry. However, due to the presence of process-induced defects, achieving a high quality of the resulting parts remains challenging in PBF-LB/M. Therefore, an extensive quality inspection, e.g., using process monitoring systems or downstream by destructive or non-destructive testing (NDT) methods, is essential. Since conventionally used downstream methods, e.g., X-ray computed tomography, are time-consuming and cost-intensive, micromagnetic NDT measurements represent an alternative for ferromagnetic materials such as 42CrMo4. In this context, 42CrMo4 samples were manufactured by PBF-LB/M with different process parameters and analyzed using a widely established micromagnetic measurement system in order to investigate potential relations between micromagnetic properties and porosity. Using multiple regression modeling, relations between the PBF-LB/M process parameters and six selected micromagnetic variables and relations between the process parameters and the porosity were assessed. The results presented reveal first insights into the use of micromagnetic NDT measurements for porosity assessment and process parameter optimization in PBF-LB/M-processed components.

Formation Model for Acoustic Characteristics of Solid Media with Ordered Fracturing

Introduction. The development of new structural materials and improvement of existing technologies for the production of new products on their basis lead to the emergence of new types of medium discontinuities. Therefore, the development of new models of discontinuities that take the previously ignored parameters into account seems to be relevant for the purposes of nondestructive testing and structural measurements. This concerns, e.g., the roughness of adjacent surfaces of microcrack ordered sets.Aim. Theoretical substantiation for the processes of elastic waves propagation through an elastic medium containing an ordered lattice of microcracks with boundary conditions in the linear slip approximation, modified by taking into account the parameters of micro-convexities of microcrack rough boundaries. Database formation for experimental studies aimed at determining the physical and mechanical characteristics of structural materials.Materials and methods. The acoustic characteristics of materials were determined based on the derivation and solutions of dispersion equations describing the formation and propagation of effective longitudinal, transverse, and Rayleigh surface elastic waves in elastic media with ordered cracking. Their values were also used to determine the effective speed of Rayleigh surface waves.Results. The conducted simulation of elastic wave formation processes showed that an increase in the concentration of microcracks leads to a decrease in the phase velocities of effective longitudinal, transverse, and surface waves, as well as to an increase in the attenuation coefficients at given ultrasound frequencies and material parameters.Conclusion. The radius of the microsphere that replaces the surface micro-convexity and the roughness parameter Rz have a significant impact on the formation of physical and mechanical characteristics of materials, which are determined by the results of ultrasonic measurements. The developed model can be recommended as a basis for interpreting the results of ultrasonic measurements.

Plastic properties estimation of aluminum alloys using machine learning of ultrasonic and eddy current data

In this study, a nondestructive testing (NDT) technique was developed to estimate the plastic properties of aluminum (Al) alloys using machine learning (ML) based on ultrasonic and eddy-current data. To validate the performance of the proposed technique, hundreds of Al alloys with a wide spectrum of mechanical properties were fabricated under different compositional and heat treatment conditions. From these specimens, the NDT parameters were measured and used as the input features of the ML model. The outputs estimated from this ML model were yield strength, ultimate tensile strength, and elongation. The estimation results were compared with those obtained from destructive tensile testing, which was performed after the completion of the NDT measurements. The relative error between the estimated and ground-truth values was approximately 8%. In particular, among the various NDT parameters, the ultrasonic nonlinearity and electrical conductivity are sensitive to the plastic properties. The related scientific findings are also discussed.

High accuracy terahertz computed tomography using a 3D printed super-oscillatory lens

An illumination beam with a subwavelength waist and extended focal depth is ideal for terahertz computed tomography. In this paper, a binary terahertz super-oscillatory lens is proposed with a full width at half-maximum of 0.97λ, a focal length of 48λ, a focal depth of 25λ, and a numerical aperture of 0.24. It was designed using the simulated annealing algorithm, fabricated by three-dimensional printing, and applied in continuous-wave terahertz computed tomography operating at 278.6 GHz. When combined with the total variation minimisation algorithm, this setup was able to recognise a hollow cylinder with wall thickness 1.1λ and a bar of diameter 0.93λ inside a chamber, with mean errors of less than 5%. Our approach provides an effective way to enhance the resolution and reconstruction fidelity of terahertz computed tomography and to promote it as an effective tool for non-destructive testing and three-dimensional measurement.

Development of Combined Methods Using Non-Destructive Test Methods to Determine the In-Place Strength of High-Strength Concretes

This study aims to develop combined methods with dual and triple use of different non-destructive test (NDT) methods and to examine the effectiveness of these methods. For this purpose, nine different high-strength concrete series were produced, and destructive and NDT methods were applied to these samples on the 3rd and 90th days. Surface hardness, ultrasonic pulse velocity, and penetration resistance were considered from NDT methods. Analyses were made on the response surface method using the NDT measurements and compressive strength values obtained, and four different mathematical models were developed. Models 1, 2, and 3 were designed with dual use of NDT methods, and model 4 was designed with triple use. The absolute relative deviation values for all the developed models’ early and final-age strengths were below 10%. It is of great importance to determine concrete quality with high accuracy and practicality, especially in places like Elazig, where there are thousands of newly constructed buildings since the Sivrice-Elazig earthquake, and rapid production is required. Therefore, it is thought that determining the strength values with high accuracy using the developed combined methods without damaging the building element will provide benefits in terms of time, labor, and cost.

Update on progress with NDT and CM apprenticeships

The author has previously reported on progress with NDT and CM apprenticeships1. This paper provides an update on progress since 2022. The UK has an ageing skills base and skills shortage particularly in the field of Non-Destructive Testing (NDT) and other Measurement related activities such as Machine Condition Monitoring (CM) and Structural Health Monitoring (SHM). These are vital skills (Often regulated) required across all Industry and Infrastructure. A portfolio of Apprenticeship Standards has been developed in the UK by the UK Institute for Apprenticeships and Technical Education (IfATE). BINDT has sponsored the development of three NDT Apprenticeship Standards. This paper gives an overview of the history, entry requirements, content, duration, funding and deliverables of these three apprenticeships plus an update on the results of Ofqual taking over quality assessment of the scheme.

Analysis of the accuracy of in-situ concrete characteristic compressive strength assessment in real structures using destructive and non-destructive testing methods

Estimation of in-situ concrete compressive strength in existing structures is considered as a crucial step in assessing structural capacity. Destructive testing (DT) by coring in conjunction with non-destructive testing (NDT) offers an interesting method for concrete strength assessment in existing constructions. The non-destructive assessment of in-situ strength requires a correlation between NDT measurements and the core compressive strengths. Therefore, the accurate quality of the in-situ strength assessment is a fundamental point. The NDT techniques such as Rebound Hammer (RH) and Ultrasonic Pulse Velocity (UPV) are widely used separately or in combination to estimate the in-situ strength. A series of on-site data (205 data triplets) of non-destructive testing (RH and UPV) and coring have been carried out on structural elements (columns and beams) in an existing building to assess the in-situ concrete strength according to the new standard version procedures (EN 13791-2019) with a comparison to its old version 2007. The analysis highlighted in a real on-site situation the positive effect of the new procedures in the recent version (2019) of EN 13791 on strength assessment, namely: the selection process of coring positions, the required number of cores, and the identification method of the conversion model. However, the statistical procedures proposed in the new version for calculating the in-situ characteristic strength appear to underestimate the results and seem to be excessively conservative as compared to the 2007 version.

Multi-objective optimization to evaluate the compressive strength of concrete by combining non-destructive techniques

The compressive strength of concrete is one of the most important mechanical parameters in the evaluation of the mechanical performance of reinforced concrete structures. The recent methodology for the evaluation of the mechanical strength of concrete of an existing structure combines non-destructive testing (NDT) measurements, such as rebound measurement and ultrasonic wave propagation velocity measurement, with destructive measurements (sampling) in order to develop a conversion model, between mechanical strength and non-destructive measurements. The conversion model is then used to estimate the local value of the resistance at each location of the non-destructive measurements and thus to represent the spatial variability. The goal of this study is to propose a new methodology based on multi-objective optimization to predict the compressive strength of concrete and its variability based on NDT measurements. To this end, a large experimental and synthetic database of destructive and non-destructive tests was used. The conclusions drawn from the synthetic data will be compared with the results obtained on the real database in order to test the potential of the proposed methodology. This study shows the principle of the methodology and the first results of its effectiveness in predicting compressive strength and its variability.

Remaining Useful Life Prediction of Aerial Bundled Cables in Coastal Areas Using Thermal and Corrosion Degradation Models

Insulated aerial bundled cables (ABCs) are preferred over conventional bare conductor cables in electrical distribution system as ABCs are more safe, less prone to electricity pilferage and offers higher reliability. However, the degradation phenomenon of ABCs is sudden as compared to conventional cables especially in coastal areas. Sudden failures of ABCs in coastal areas make the maintenance planning challenging. Hence, accurate reliability estimation is required which can enable timely maintenance planning and in turn reducing the chances of failures. A novel reliability model is reported in this work which is derived from historical failure data of particular type of ABCs coupled with the degradation models. The models are based upon the actual environmental conditions experienced by the cables under study. The actual loading data as well as environmental data of two sites of varying distance from Seashore are used to develop the respective reliability models. The reliability prediction from proposed reliability model is then validated using time to failure computation through comparison of historical infrared thermography based Non-destructive testing (NDT) data, acquired at the sites under study, with reference to NDT measurements acquired from the ruptured/failed cable. The validation indicates the efficacy of the proposed reliability model.

Nondestructive Monitoring Hydration of Belite Calcium Sulfoaluminate Cement by EIS Measurement.

In this study, the impact of water-to-cement (w/c) ratios of belite calcium sulfoaluminate cement (BCSA) on the hydration kinetics and the electrochemical impedance spectroscopy (EIS) parameters is studied. According to the analysis of classic hydration measurements, such as calorimetry tests, chemical shrinkage content, and chemically bound water content, it can be concluded that a higher w/c ratio clearly accelerates the hydration of BCSA cement paste. The electrical resistivity of BCSA0.35 cement paste is more than 4.5 times that of BCSA0.45 and BCSA0.5, due to the gradually densified micropore structure blocking the electrical signal transmission rather than the free charged-ion content. The porosity of BCSA0.5 is 27.5% higher than that of BCSA0.35 and 7.8% higher than that of BCSA0.45, which proves the resistivity is clearly related to the variation in microstructure, especially for the porosity and pore size distribution. The novelty of this study is the linear regression with logarithm terms of electrical resistivity and classic hydration parameters such as chemical shrinkage, cumulative hydration heat, and chemically bound water is established to extend the classical expression of cement hydration degree. It indicates that the electrochemical impedance spectroscopy can be taken as a nondestructive testing measurement to real-time monitor the cement hydration process of cement-based materials.

Blind comparison of saturation ratio profiles on large RC structures by means of NDT and SFE—Application to the VeRCoRs mock-up

The prediction of large concrete structures behaviour such as bridges, dams and nuclear containment buildings (NCB) is a vital issue regarding the evaluation of the durability, safety and effect on the surrounding environment. In this work, experimental and numerical estimations of the saturation ratio profiles in the VeRCoRs NCB mock-up structure are presented, and their blind comparison is discussed. Non-destructive testing (NDT) based capacitive measurements are processed to quantify the saturation ratio experimentally. Then, a weakly coupled thermo-hydric (TH) finite element model is presented within the serviceability state of VeRCoRs for the numerical counterpart. The uncertainty in the capacitive measurements and the constitutive parameters of the numerical model are highlighted as coming from the following three sources: (a) the natural randomness of the material properties and physical processes, (b) the limited knowledge of some input parameters in the mathematical model either obtained experimentally at the specimen scale and (c) empirically derived in the exploitation of the physical process. The influence of the uncertainty in the saturation ratio estimations is presented by error bars experimentally and is addressed by a stochastic finite element (SFE) study in the numerical work. Accounting for uncertainties in NDT and SFE measurements, the mean values of saturation ratio (reported in %) profile are forecasted up to 40% and 34% respectively, with standard deviation for both in the range of 3.5–4.5% in magnitude.

Electron Beam Welding Process of Port Stub of CFETR Vacuum Vessel Sector Mockup

Port structures are important parts of vacuum vessel (VV) in China Fusion Engineer Test Reactor (CFETR), which consists of port stubs and port extensions, mainly provides channels for the installation and maintenance of internal components, such as divertor and blanket, and provides interface for auxiliary heating system, diagnostic system, and vacuum pumping. A 1/8 VV sector mockup with port structures is used to explore the key manufacturing technology of CFETR VV. Electron beam welding (EBW) process development of port structures of 1/8 VV sector mockup is introduced in this article taking the inner shell of upper port stub as an example. Through EBW test and process optimization, the surface formation, microstructure, and mechanical properties of the weld are obtained. On this basis, the EBW of the inner shell of the upper port stub is carried out. After phased array ultrasonic nondestructive testing and laser tracker measurement, the weld quality is excellent, and contour accuracy has reached the technical requirements. This study provides important support for the engineering design and construction of the CFETR.

Examining Ferromagnetic Materials Subjected to a Static Stress Load Using the Magnetic Method

This paper discusses the experimental examination of anisotropic steel-made samples subjected to a static stress load. A nondestructive testing (NDT) measurement system with a transducer, which enables observation of local hysteresis loops and detection of samples’ inhomogeneity, is proposed. Local hysteresis loops are measured on two perpendicular axes, including one parallel to the rolling direction of the samples. The results confirm that the selected features of the local hysteresis loops provide important information about the conditions of ferromagnetic materials. Furthermore, it is shown that the selected parameters of the statistical analysis of the achieved measurements are beneficial for evaluating stress and fatigue changes induced in the material.

Genetic Parameters of Stem and Wood Traits in Full-Sib Silver Birch Families

This study investigated heritability of stem and wood traits to improve Swedish silver birch (Betula pendula Roth.) through breeding. Birch is 12% of Sweden’s forest area but mainly used for low value pulp or firewood. This paper applied non-destructive test (NDT) methods, and estimated traits’ heritability (h2), to help breed birch for high value solid wood products. Two trials of 22 families were assessed at age 19 for stem diameter (DBH), stem straightness, rough brown bark height (BH), grain angle (GA), Pilodyn penetration depth (Pilo) and acoustic velocity (AV). X-ray densitometry was performed on a subsample of radial cores taken at 1.3 m from the ground to get an average benchmark density. The h2 values were moderate for GA (0.20 and 0.21) and Pilo (0.53 and 0.48) at the two sites, but the h2 values for AV were low (0.05 and 0.30). There were moderate genotypic correlations between BH and DBH (0.51–0.54). There were low genotypic and phenotypic correlations between NDT measurements and other traits so including NDT in birch breeding efforts should not inadvertently reduce size, stem or wood quality. The high genetic correlations between sites suggest that GA, Pilo and AV values were determined more by genotype than by environment.

К ТЕОРИИ ЛАЗЕРНОЙ ГЕНЕРАЦИИ УПРУГИХ ВОЛН В ФЕРРОМАГНИТНЫХ МЕТАЛЛАХ ПРИ ТЕМПЕРАТУРЕ МАГНИТНОГО ФАЗОВОГО ПЕРЕХОДА

Laser generation of ultrasound has found wide application in modern technologies: to control the quality of composite materials, to detect layer separation in adhesive-bonded joints, subsurface and surface defects, as well as the quality of a product's surface in the process of manufacture. For excitation of waves in metals, pulse laser is normally used. In metallurgy, as well as in promising 3D technologies, it is necessary to control products at high temperatures (800°С and higher). To design ultrasound equipment with a pulsed laser radiation generator as the ultrasound source, it is required to conduct theoretical research of the process of laser generation of ultrasound in ferromagnetic metals at the temperature of magnetic phase transition, since the hot metal conversion for ferrum and ferrum-based alloys is, as a rule, performed namely at this temperature of 768 °С. The results of the experimental works allow to conclude that the temperature dependence of normalized amplitude of acoustic pulse in ferrum is of extreme character in the range of magnetic phase transition, i.e., in the range of Curie point. In this work a goal has been set to study the process of laser generation of ultrasound in ferromagnetic metal in the condition of non-linear dependence of the volume-expansion coefficient on the temperature. The task of thermoelastic excitation of longitudinal and transverse waves in ferromagnetic metal by a laser pulse at the temperature of magnetic phase transition has been solved. Diagrams of longitudinal and transverse wave patterns when ferromagnetic metal is exposed to laser pulses of various diameters have been obtained. Recommendations for effective use of laser generation of ultrasound in non-destructive testing and thickness measurement have been given.

Spatial variability assessment of structures from adaptive NDT measurements

Inspection by non-destructive testing (NDT) techniques is an effective way for assessing structures’ condition state, their pathologies and locating potential critical areas. However, establishing accurate diagnoses requires numerous measurements while available budget is limited. Nevertheless, determining the spatial variability of the material properties leads fewer of the required measurements, as it characterizes zones with almost identical properties and helps identify weak areas. But assessing this spatial variability still requires numerous measurements. It should be limited by a rational criterion that could be expressed in terms of accuracy and cost minimization. In the present work, we develop an adaptive approach to characterize spatial variability of structures’ material properties modelled by transformed Gaussian random fields. The methodology is performed in two steps. Firstly, the correlation length of the Gaussian random field is computed for a given accuracy. Secondly, the number of measurements is refined to estimate the first two moments of the random field with a given accuracy too. These two steps result in a minimization of the number of measurements (i.e the cost) for a target accuracy. The proposed methodology and theoretical results are illustrated using synthetic and real data.

Development of a truncation artifact reduction method in stationary inverse-geometry X-ray laminography for non-destructive testing

In an industrial field, non-destructive testing (NDT) is commonly used to inspect industrial products. Among NDT methods using radiation sources, X-ray laminography has several advantages, such as high depth resolution and low computational costs. Moreover, an X-ray laminography system with stationary source array and compact detector is able to reduce mechanical motion artifacts and improve inspection efficiency. However, this system, called stationary inverse-geometry X-ray laminography (s-IGXL), causes truncation artifacts in reconstructed images due to limited fields-of-view (FOVs). In this study, we proposed a projection data correction (PDC) method to reduce the truncation artifacts arisen in s-IGXL images, and the performance of the proposed method was evaluated with the different number of focal spots in terms of quantitative accuracy. Comparing with conventional techniques, the PDC method showed superior performance in reducing truncation artifacts and improved the quantitative accuracy of s-IGXL images for all the number of focal spots. In conclusion, the PDC method can improve the accuracy of s-IGXL images and allow precise NDT measurements.

Comparison of Sandstone Damage Measurements Based on Non-Destructive Testing.

Non-destructive testing (NDT) methods are an important means to detect and assess rock damage. To better understand the accuracy of NDT methods for measuring damage in sandstone, this study compared three NDT methods, including ultrasonic testing, electrical impedance spectroscopy (EIS) testing, computed tomography (CT) scan testing, and a destructive test method, elastic modulus testing. Sandstone specimens were subjected to different levels of damage through cyclic loading and different damage variables derived from five different measured parameters—longitudinal wave (P-wave) velocity, first wave amplitude attenuation, resistivity, effective bearing area and the elastic modulus—were compared. The results show that the NDT methods all reflect the damage levels for sandstone accurately. The damage variable derived from the P-wave velocity is more consistent with the other damage variables, and the amplitude attenuation is more sensitive to damage. The damage variable derived from the effective bearing area is smaller than that derived from the other NDT measurement parameters. Resistivity provides a more stable measure of damage, and damage derived from the acoustic parameters is less stable. By developing P-wave velocity-to-resistivity models based on theoretical and empirical relationships, it was found that differences between these two damage parameters can be explained by differences between the mechanisms through which they respond to porosity, since the resistivity reflect pore structure, while the P-wave velocity reflects the extent of the continuous medium within the sandstone.

Acoustic wave velocity in long pieces of Salzmann pine for in-situ structural assessment

In-situ assessment of timber members by acoustic measurement usually requires specific procedures (indirect and semidirect measurement) compared with those used in the laboratory (direct) and over longer distances. This research aims to determine which procedure is the most suitable. Acoustic Non-Destructive Testing measurements were taken in 21 150 × 200 mm2 nominal cross-section Salzmann pine structural timber pieces from 9.5 to 11.0 m long from a 1768 structure. Wave velocity was obtained from ToF measured with different sensor arrangements (direct, indirect and semidirect) in different lengths using stress wave and ultrasound. The direct velocity value was very close to non-direct measurements (0.4% higher), while previous research works with shorter pieces (3–4 m) showed larger differences (3.3–5.4%). There were no significant differences between indirect and semidirect measurements when using the same device or between devices, although a steady ratio was observed in the last case. The most predictive velocity procedure was determined by the correlation between static and dynamic modulus of elasticity. The most reliable stiffness prediction was obtained with the global velocity method, taking ToF measurements at distances from 1 to 10 m. A second method was proposed, consisting of taking only 2 measurements, and it achieved practically the same predictive capacity.

Hybrid resampling scheme for particle filter‐based inversion

A novel online hybrid resampling (HR) scheme based on the combination of residual and multinomial resampling schemes is proposed. It can be implemented within the framework of the sequential Monte Carlo-based inversion algorithm, also known as particle filter (PF). Based upon the degeneracy of each particle, the choice of best resampling scheme among both candidates is made at each instant iteratively. Consequently, the inversion performance of PF improves by reducing the computational complexity of the resampling scheme. The proposed online HR scheme is incorporated here within the framework of the PF-based inversion scheme once applied on nuclear power plant steam generator non-destructive testing measurement data. The promising results showcase the efficacy of the technique.