Showing papers on "Ultrasonic testing published in 2020"

Residual stress analysis of additive manufacturing of metallic parts using ultrasonic waves: State of the art review

Abstract: Additive manufacturing has become a major growing field in materials engineering, following a new tendency for custom, high precision and on-demand fabrication. Residual stresses are prone to appear in any production technique, which remain a challenge to be measured. These stresses can lead to a reduction on mechanical performance and even cause premature failure. Thus, a wide understanding of residual stress is critical for greater part reliability. Among Non-destructive Testing (NDT) techniques, acoustic and ultrasonic waves remain widely used to determine stresses, voids and defects in a wide array of parts. In this contribution, Ultrasonic Testing (UT) is highlighted as an alternative for measuring residual stress both during and after fabrication.

A New Approach for Fault Detection, Location and Diagnosis by Ultrasonic Testing

Abstract: Wind turbine blades are constantly submitted to different types of particles such as dirt, ice, etc., as well as all the different environmental parameters that affect the behaviour and efficiency of the energy generation system. These parameters can cause faults to the wind turbine blades, modifying their behaviour due, for example, to the turbulence. A new method is presented in this paper based on cross-correlations to determine the presence of delamination in the blades. The experiments were conducted in two real wind turbine blades to analyse the fault and non-fault blades using ultrasonic guided waves. Finally, the energy analysis of the signal based on wavelet transforms allowed to determine energies abrupt changes in the correlation of the signals and to locate the faults.

Laser opto-ultrasonic dual detection for simultaneous compositional, structural, and stress analyses for wire + arc additive manufacturing

Abstract: The complex, nonequilibrium physical, chemical, and metallurgical nature of additive manufacturing (AM) tends to lead to uncontrollable and unpredictable material and structural properties. Therefore, real-time monitoring of AM is of great significance. However, current AM relies on separate postprocess analyses, which are usually destructive, costly, and time-consuming. In this study, we investigated a laser opto-ultrasonic dual (LOUD) detection approach for simultaneous and real-time detection of elemental compositions, structural defects, and residual stress in aluminium (Al) alloy components during wire + arc additive manufacturing (WAAM) processes. In this approach, a pulsed-laser beam was used to excite the surfaces of Al alloy samples to generate ultrasound and optical spectra. As a result, the compositional information can be obtained from the optical spectra, while the structural defects and residual stress distributions can be extracted from the ultrasonic signals. The silicon (Si) and copper (Cu) compositions obtained from optical spectral analyses are consistent with those obtained from the electron-probe microanalyses (EPMA). The 1 mm blowhole and the residual stress distribution of the sample were detected by the ultrasonic signals in the LOUD detection, which shows consistency with the conventional ultrasonic testing (UT). Both results indicate that the LOUD detection holds the promising of becoming an effective testing method for AM processes to ensure quality control and process feedback.

Conformal gradient-index phononic crystal lens for ultrasonic wave focusing in pipe-like structures

Abstract: We explore a conformal gradient-index phononic crystal lens integrated within a pipe to amplify guided wave modes toward improved ultrasonic inspection of pipelines. The proposed conformal lens is composed of an array of cylindrical steel stubs attached to the outer surface of a steel pipe, which are tailored according to the hyperbolic secant profile of refractive index in the circumferential direction of the pipe. Hence, the ultrasonic guided wave energy is focused in the axial direction of the pipe and amplified at the focal point of the lens. Refractive indices are calculated using dispersion curves obtained from the finite element simulations of the stubbed unit cells, and the curved lens is designed for the second longitudinal wave mode of the pipe, which is commonly used in guided wave testing. The proposed lens design is implemented on a steel pipe, which is typically used in the distribution networks utilized in cities, and simultaneous focusing of longitudinal wave modes in a broad frequency range is verified through both numerical models and experimental measurements.

Detection of Internal Holes in Additive Manufactured Ti-6Al-4V Part Using Laser Ultrasonic Testing

Abstract: For a non-contact, non-destructive quality evaluation, laser ultrasonic testing (LUT) has received increasing attention in complex manufacturing processes, such as additive manufacturing (AM). This work assessed the LUT method for the inspection of internal hole defects in additive manufactured Ti-6Al-4V part. A Q-switched pulsed laser was utilized to generate ultrasound waves on the top surface of a Ti-6Al-4V alloy part, and a laser Doppler vibrometer (LDV) was utilized to detect the ultrasound waves. Sub-millimeter (0.8 mm diameter) internal hole defect was successfully detected by using the established LUT system in pulse-echo mode. The method achieved a relatively high resolution, suggesting significant application prospects in the non-destructive evaluation of AM part. The relationship between the diameter of the hole defects and the amplitude of the laser-generated Rayleigh waves was studied. X-ray computed tomography (XCT) was conducted to validate the results obtained from the LUT system.

Impact Damage Evaluation in Composite Structures Based on Fusion of Results of Ultrasonic Testing and X-ray Computed Tomography.

Abstract: Barely visible impact damage (BVID) is one of the most dangerous types of structural damage in composites, since in most practical cases the application of advanced non-destructive testing (NDT) methods is required to detect and identify it. Due to its character of propagation, there are minor signs of structural damage on a surface, while the internal damage can be broad and complex both in the point of view of fracture mechanisms and resulting geometry of damage. The most common NDT method applied e.g., in aircraft inspections is ultrasonic testing (UT), which enables effective damage detection and localization in various environments. However, the results of such inspections are usually misestimated with respect to the true damage extent, and the quantitative analysis is biased by an error. In order to determine the estimation error a comparative analysis was performed on NDT results obtained for artificially damaged carbon fiber-reinforced composite structures using two UT methods and X-ray computed tomography (CT). The latter method was considered here as the reference one, since it gives the best spatial resolution and estimation accuracy of internal damage among the available NDT methods. Fusing the NDT results for a set of pre-damaged composite structures with various energy values of impact and various types of impactor tips applied for introducing damage, the evaluation of estimation accuracy of UT was possible. The performed analysis allowed for evaluation of relations between UT and X-ray CT NDT results and for proposal of a correcting factor for UT results for BVID in the analyzed composite structures.

In situ synchrotron ultrasonic fatigue testing device for 3D characterisation of internal crack initiation and growth

Abstract: This work presents a new ultrasonic fatigue testing device for studying the initiation and propagation mechanisms of internal microstructurally short fatigue cracks using in situ synchrotron tomography. Its principle is described as well as the method used for automatically detecting crack initiation and its subsequent growth. To promote internal crack initiation, specimens containing internal casting defects were tested between the high cycle and very high cycle fatigue regimes (107-109 cycles). Preliminary results show the ability of this new device to initiate an internal microstructurally short crack in a reasonable testing time and monitor its growth.

Fully noncontact measurement of inner cracks in thick specimen with fiber-phased-array laser ultrasonic technique

Abstract: To realize a fully noncontact ultrasonic testing method for inner cracks inspection in thick metal specimen, a phased array laser ultrasonic testing system with using a compact optic fiber array bundle and a laser interferometer is developed in this study. The focusing and steering of the shear wave and longitudinal wave generated with seven fiber-phased-array laser sources in thermoelastic regime is investigated by a numerical simulation and validated by the experiment. A non-contact measurement of the inner-surface cracks by both the angle-beam testing method and time-of-flight diffraction method with the fiber-phased-array laser ultrasonic technique have been studied.

A shape factor based ultrasonic measurement method for determination of bolt preload

Abstract: The existing ultrasonic testing models cannot accurately measure bolt preload due to the non-uniform distribution of axial stress in the effective stressed region of bolt and cannot rapidly complete the calibration of detection coefficients due to the difficulty to determine the key parameters such as effective stressed length. In order to eliminate the impact of non-uniform distribution of axial stress on the measurement, realize rapid and accurate calibration of detection coefficients and further improve the measurement accuracy of bolt preload, the concept and determination method of shape factor are proposed. Based on the shape factor, a combination of longitudinal and transverse waves is adopted to establish a mathematical model for measuring the preload applied to a bolt during assembly, avoiding the need to measure ambient temperature. The calculation method of shape factor is obtained by statics simulation of a bolted joint. Through the combination of finite element simulation and experimental calibration, the material factors and temperature factors of 45# steel as well as the shape factors of M20 and M16 bolts are obtained. The experiments show that the relative error of this method is within 5%, which meets the requirements of engineering applications.

Development of an omni-directional magnetic-concentrator-type electromagnetic acoustic transducer

Abstract: As an important branch of non-destructive testing, electromagnetic ultrasonic testing is widely used in various industries because of its high detection efficiency and the lack of a need for the test sample to have a coupling agent or a surface pretreatment. As a core component of electromagnetic ultrasonic testing, electromagnetic acoustic transducers (EMATs) have received extensive attention in recent years. However, the mode selectivity of EMATs is reduced because of the non-uniformity of the magnetic field of traditional permanent magnets and the multimode phenomenon of guided waves. To solve this problem, an omni-directional magnetic-concentrator-type electromagnetic acoustic transducer (OD-MC-EMAT) is proposed herein. Which was added to the magnetic concentrator on a traditional EMAT to guide and concentrate the magnetic field of traditional permanent magnets, thereby improving the defect inspection ability of the EMAT. The proposed OD-MC-EMAT consisted of a cylindrical permanent magnet, an omni-directional magnetic concentrator, and a multi-cluster of circular meander coils, and it exhibited better mode selectivity than a traditional EMAT. A finite element simulation and an experiment proved that the mode selectivity of the transducer improved after adding the magnetic concentrator, and experiments to study the transducer characteristics and defect detection were also carried out. Finally, the configuration of the OD-MC-EMAT was optimized through an orthogonal experiment. The influence of each parameter on the transducing efficiency of the proposed OD-MC-EMAT was studied, and the optimal parameter combination was confirmed.

Multi-resolution non-contact damage detection in complex-shaped composite laminates using ultrasound

Abstract: Numerous nondestructive testing (NDT) methods have been developed to perform inspections of engineered structures. Frequently, increased precision of a given method is associated with longer inspection time. The trade-off between precision and inspection time is especially apparent in ultrasonic testing (UT). The imaging resolution is directly related to the applied frequency of the ultrasound. As an example, guided waves propagating in plate-like structures, provide the means for fast inspection of large areas due to their long propagation distances. Damage characterization accuracy is, however, limited in this case due to relatively large wavelengths. On the other hand, local inspection with high-frequency bulk waves provides much more accurate damage characterization thanks to shorter wavelengths. The drawback of local inspection is the long scanning time necessary for large components. In order to optimize the inspection time and accuracy, we propose a two-step damage evaluation framework. In the first step, a global full-field screening with the use of guided waves is performed to determine the possible damage locations. In the second step, the identified hot spots are further evaluated with a high-frequency bulk wave system. Both testing modalities are implemented using non-contact laser vibration sensors. A piezoceramic exciter is used for the guided wave setup, while a pulsed laser excitation source is used in the bulk wave setup. The proposed approach minimizes sample preparation time and is completely non-intrusive. The feasibility of the proposed framework is demonstrated in a complex shape, thin-walled composite structure with multiple defects.

Ultrasonic Assessment of the Concrete Residual Strength after a Real Fire Exposure

Abstract: After a fire, the assessment of concrete residual strength can be a challenge. Since the strength reduction depends on the distance from the heated surface examination based on destructive test, i.e., core samples, is not precise enough. Therefore, more detailed methods can establish the influence of the high temperature in the zone, which no longer has visible cracks. That method can be used to assess layer thickness to remove due to the fire damage. The Ultrasound Pulse Velocity (UPV) method with point heads was used in the paper to examine samples taken from a structure after the real fire. Moreover, to make the analysis more precise, an effect associated with the porosity in concrete was also considered to separate pure fire effect.

Evaluation of Defect Detection in Aluminium, CFRP and Epoxy Resin Plates Using Non-contact Air-Coupled Ultrasonic Waves

Abstract: In the field of aerospace materials and structures, water coupled ultrasonic testing was not desirable due to changes in properties and contamination reason. Therefore, in the present study non-contact air coupled ultrasonic transducers were proposed as an alternative examination for such applications. This present study describes our practical knowledge of using piezoelectric air-coupled transducers for visualization and defect identification of aluminium, CFRP and epoxy-resin specimens. Further, the effectiveness of the system is verified by experiments conducted in the inspection of artificial defects and 2D images was reconstructed through scanning of specific specimen surface. Results show that, all the created defects were identified successfully using C-scan technique. The measured defect values were compared with experimental defect values and shows good agreement. The 1 MHz piezoelectric transducer was the best for all the three specimens which is used in the present study because of the material structure being evaluated. The bulk wave piezoelectric transducer was identified as extensive pulse attenuation by the structure of the aluminium, CFRP and epoxy resin.

Neural Learning Based Blind Source Separation for Detection of Material Defects in Pulsed Thermography Images

Abstract: In this paper, we introduce a neural learning-based approach to blind source separation for detection of material flaws in pulsed thermography (PT) images. This approach can be used to detect internal defects (pores) in metallic Additively Manufactured (AM) materials. Such defects occur in high-strength alloys produced with direct laser sintering AM method for nuclear energy applications. Pulsed thermal imaging system utilizes a high intensity flash lamp to rapidly heat surface of sample, a high sensitivity infrared camera to capture data of surface temperature variations. The data cube obtained with PT (stack of surface temperature images at different times) can be analyzed with image processing algorithms to detect material defects. Compared with conventional nondestructive evaluation (NDE) methods, such as digital radiography and ultrasonic testing, the PT pulsed infrared thermal detection technique has advantages of one-sided noncontact measurements, fast processing of large sample areas captured in one image. Detection of small material defects requires finding features in thermal images, which have signal contrast levels approaching sensitivity limit of IR camera. In this study, an optimized Neural Learning based Blind Source Separation (NLBSS) algorithm, including Principal Component Analysis (PCA), and Independent Component Analysis (ICA) is demonstrated to automatically extract principal temporal and spatial features of thermography frames to enhance flaw detection. By using the NLBSS algorithm, material internal defects can be automatically detected. Furthermore, this processing approach compensates for experimental thermal imaging artifacts, such as noise and uneven heating. By merging artificial intelligence with the photothermic, the NDE system detects internal calibrated defects of various sizes and depths in AM nuclear-grade metallic alloys.

Local Ultrasonic Resonance Spectroscopy: A Demonstration on Plate Inspection

Abstract: Local ultrasonic resonance spectroscopy (LURS) is a new approach to ultrasound signal analysis, which was necessitated by a novel inspection method capable of the contact-free, localized, broadband generation and detection of ultrasound. By performing a LURS scan, it is possible to detect local mechanical resonances of various features and of the specimen itself. They are highly sensitive to local mechanical properties. By observing different parameters in the frequency spectrum (e.g., resonance amplitude and resonance peak frequency), geometrical, material and condition properties can be visualized for all of the scanning positions. We demonstrate LURS for inspection of a carbon fiber reinforced polymer plate. Local defect resonances of delaminations and a flat-bottom hole were detected in the frequency range from 25 to 110 kHz. Analyzing the higher frequency range (0.3 MHz to 1.5 MHz) of the same scan, the shift of the thickness resonance frequency of the plate and its higher-order resonance frequencies carry the information about the aluminum inclusions. LURS shows an advantage in characterizing the localized features of the specimens via contact-free ultrasonic inspection.

Assessment of the Length and Depth of Delamination-Type Defects Using Ultrasonic Guided Waves

Abstract: Fiber-reinforced composite laminates are being increasingly used in various engineering components in the sectors of aerospace and green energy. Due to impacts throughout the service life of the structure, matrix breakage and delaminations significantly altering the structural integrity of the laminate can occur. Hence, robust guided wave structural health monitoring systems are required to ensure continuous safety of engineering structures. In this paper, the ultrasonic method based on the analysis of A0 mode reflecting within the defected area has been proposed to extract the length and the depth of the delamination-type defect. The technique proposed in this study extracts the depth of the damage by analyzing the magnitude variations of direct A0 mode which are caused by the difference of wave velocities in the upper and lower sub-laminates. This results in an altering and frequency-dependent forward-scattered amplitude of direct A0 mode. Furthermore, the proposed approach uses previously obtained information about the depth of the defect, which allows for the determination of the phase velocities of A0 and S0 modes in the upper and lower sub-laminates. As a result, the accuracy of the damage length estimation is increased. The performance of the proposed method was proven with 2D and 3D numerical simulations and experiments on samples with artificial defects. The method validation results showed that the proposed method with some limitations is capable of extracting the length of delamination with an approximate error below 6%.

High Precision Detection Method for Delamination Defects in Carbon Fiber Composite Laminates Based on Ultrasonic Technique and Signal Correlation Algorithm.

Abstract: This paper presents a method based on signal correlation to detect delamination defects of widely used carbon fiber reinforced plastic with high precision and a convenient process. The objective of it consists in distinguishing defect and non-defect signals and presenting the depth and size of defects by image. A necessary reference signal is generated from the non-defect area by using autocorrelation theory firstly. Through the correlation calculation results, the defect signal and non-defect signal are distinguished by using Euclidean distance. In order to get more accurate time-of-flight, cubic spline interpolation is introduced. In practical automatic ultrasonic A-scan signal processing, signal correlation provide a new way to avoid problems such as signal peak tracking and complex gate setting. Finally, the detection results of a carbon fiber laminate with artificial delamination through ultrasonic phased array C-scan acquired from Olympus OmniScan MX2 and this proposed algorithm are compared, which showing that this proposed algorithm performs well in defect shape presentation and location calculation. The experiment shows that the defect size error is less than 4%, the depth error less than 3%. Compared with ultrasonic C-scan method, this proposed method needs less inspector’s prior-knowledge, which can lead to advantages in automatic ultrasonic testing.

Identification of Stress States in Compressed Masonry Walls Using a Non-Destructive Technique (NDT).

Abstract: The structure safety can be assessed, but only indirectly, by identifying material properties, geometry of structures, and values of loads. The complete and comprehensive assessment can be done only after determining internal forces acting inside structures. Ultrasonic extensometry using an acoustoelastic effect (AE) is among the most common non-destructive techniques (NDT) of determining true stresses in structures. Theoretical bases of the method were described in the mid 20th century. They were founded on the correlation between ultrasonic waves and the value and direction of stresses. This method is commonly used to determine stresses mainly in homogeneous materials without any inherent internal defects. This method is rarely applied to porous or composite materials, such as concrete or rock due to a high dispersion of results. Autoclaved aerated concrete (AAC), characterized by high homogeneity and porosity, is the popular material in the construction sector, used to produce masonry units. The discussed tests involved the acoustoelastic effect to determine stresses in the masonry wall made of AAC. This paper presents a widely theoretical background for the AE method, and then describes the author’s own research on AAC divided into two stages. At first, the empirical relationships between compressive stress and velocity of longitudinal ultrasonic wave, including humidity, were determined. In stage II, nine masonry walls were tested in axial compression. Mean compressive stresses in the masonry wall determined with the proposed method were found to produce a satisfactory confidence level up to ca. 50% of failure stresses. Results were significantly understated for stresses of the order of 75% of failure stresses.

Determination of acoustic nonlinearity parameters using thermal modulation of ultrasonic waves

Abstract: This study presents a test method and its theoretical framework to determine the acoustic nonlinearity parameters ( α , β , δ) of material using thermal modulation of ultrasonic waves. Temperature change-induced thermal strain excites the nonlinear response of the material and modulates the ultrasonic wave propagating in it. Experimental results showed a strong correlation between the relative wave velocity change and the temperature change. With a quadratic polynomial model, the acoustic nonlinearity parameters were obtained from the polynomial coefficients by curve fitting the experimental data. Their effects on thermal-induced velocity change were discussed. The parameters α , β , and δ govern the hysteretic gap, average slope, and curvature of the correlation curve, respectively. The proposed theory was validated on aluminum, steel, intact and damaged concrete samples. The obtained nonlinear parameters show reasonable agreement with values reported in the literature. Compared to other nonlinear acoustic methods using vibration or acoustic excitation, the thermal modulation method generates more uniform, slow changing, and larger strain field in the test sample. Employing the thermal effect as the driving force for nonlinearity instead of an undesired influencing factor, this method can measure the absolute values of α , β , and δ with good accuracy using a simple ultrasonic test setup.

Application of Ultrasonic Guided Waves for Inspection of High Density Polyethylene Pipe Systems.

Abstract: The structural integrity assessment of thermoplastic pipes has become an interesting area of research due to its elevated usage in the liquid/gas transportation industry. Ultrasonic guided wave testing has gained higher attention from industry for the inspection of elongated structures due to the reduced inspection time and cost associated with conventional non-destructive testing techniques, e.g., ultrasonic testing, radiography, and visual inspection. Current research addresses the inspection of thermoplastic pipes using ultrasonic guided waves as a low cost and permanently installed structural health-monitoring tool. Laboratory and numerical investigations were conducted to study the potential of using ultrasonic guided waves to assess the structural health of thermoplastic pipe structures in order to define optimum frequency range for inspection, array design, and length of inspection. In order to achieve a better surface contact, flexible Macro-Fiber Composite transducers were used in this investigation, and the Teletest® Focus+ system was used as the pulser/receiver. Optimum frequency range of inspection was at 15−25 kHz due to the level of attenuation at higher frequencies and the larger dead zone at lower frequencies due to the pulse length. A minimum of 14 transducers around the circumference of a 3 inch pipe were required to suppress higher order flexural modes at 16 kHz. According to the studied condition, 1.84 m of inspection coverage could be achieved at a single direction for pulse-echo, which could be improved by using a higher number of transducers for excitation and using pitch-catch configuration.

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

Abstract: 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.

Numerical and Experimental Modeling of Spot Welding Defects by Ultrasonic Testing on Similar Sheets and Dissimilar Sheets

Abstract: This paper investigates the impact of defects on similar sheets and dissimilar sheets used in the automotive industry. Spot welding is one of the types of resistance welding used in this experiment for sheet welding. The thickness of sheets welded by the spot welding method can be between 0.5 and 3 mm. In this paper, the simulation is performed by finite element method for non-destructive tests on spot welding. This study investigated the propagation of ultrasonic waves in two similar layers of stainless steel and galvanized stainless steel sheets and two dissimilar layers of stainless steel sheets and galvanized stainless steel sheets in different thicknesses. This test was performed by ultrasonic immersion method and the intensity and amplitude of the reaction of the resulting defect waves and its effect on the results were also investigated. Due to the performance of finite element method softwares, Comsol Multiphysics software because of its high accuracy used. It has been studied various factors and conditions including excitation frequency, boundary conditions, the most suitable position for the probr Fto stimulate the waves, focused or unfocused waves in the simulation, sensitivity analysis of mesh size and appropriate mesh size for simulation. In this paper, the joint of similar sheets and dissimilar sheets is investigated. For this performance, the average relative error that can meet the industrial requirement is mentioned. The results of the simulation with the results of the experimental test They were compared and investigated And with the amount of error tests, have acceptable results and it can be used with the error specified and can meet the needs of the automotive industry.