Ultrasonic Nondestructive Evaluation Research Articles

Microstructure quality assessment for hybrid additive manufactured Ti6Al4V components via ultrasonics

Metal components with functionally organized microstructures for specific applications are emerging thanks to hybrid additive manufacturing (AM). The customization of these high value components accentuates the need for nondestructive methods to characterize their microstructural functional patterns. Nondestructive evaluation (NDE) methods that are economical, fast, energy efficient, and easy to integrate into routine component inspections are preferred. Most importantly, NDE methods must be sensitive to changes in the microstructure such that regions that do not satisfy the design requirements (i.e. out-of-spec regions) can be detected. In this work, ultrasonic NDE methods grounded in diffuse backscatter modeling were used to detect and quantify spatial property variations resulting from a hybrid AM process. The manufacturing process coupled directed energy deposition (DED) with milling in a cyclical manner. These methods were successfully implemented to evaluate the microstructural uniformity of Ti6Al4V samples as well as to make comparisons across an ensemble of samples manufactured with identical parameters. Out-of-spec regions were mapped with respect to the sample geometry on a layer-by-layer basis. The results of this work are expected to inform future NDE strategies for both research and practitioner contexts, and limitations are discussed.

Imaging elastic waves in solids: how to use laser feedback interferometry to visualize them.

The use of ultrasonic elastic waves is a well established technique for non-destructive testing of materials and structures, in particular to exploit the interaction of waves with structural features to detect and characterize defects. Optical methods offer the advantage of visualising the distribution of elastic waves in a non-contact manner without disturbing the elastic wave. In this work we propose a laser feedback interferometry (LFI) based system as a cost effective, non-contact, alternative to a well established laser Doppler vibrometer technique. We demonstrate the visualization of the elastic waves, using an example of an elastic wave propagating through a prismatic acrylic rod. We show that the ultra-compact and simple implementation of LFI enables accurate visualization of the elastic waves in solids, and opens the pathway to a range of new opportunities in ultrasonic non-destructive testing and evaluation.

Approaches to Ultrasonic Non destructive Evaluation of Composites in Aircraft Components

Non-Destructive Evaluation (NDE) has played a pivotal role in the course of development of composites in airframe structural components at the Advanced Composites Division (ACD) of National Aerospace Laboratories (NAL), through novel co-curing, co-bonding fabrication routes. An account of Ultrasonic NDE through C-scan technique on advanced composites is given here.

Ultrasonic evaluation of ply and interleaf layer properties of interleaved composite laminates

An ultrasonic nondestructive evaluation procedure is presented for the ply and interleaf layer properties of carbon/epoxy composite laminates having interleaf resin layers at their interlaminar interfaces. It is shown that the material properties of plies (density, thickness, and transversely isotropic complex elastic moduli) and elastic interleaf layers (density, thickness, Young’s modulus, and Poisson’s ratio) can be identified by best fitting the theoretical energy transmission spectra of longitudinal waves through the laminate immersed in water to those obtained in ultrasonic measurement. It is also demonstrated that compared to the mass-less and null-thickness spring-type interlaminar interface model employed in the previous works, the present finite-thickness interleaf layer model can better reproduce the experimental transmission spectra of a unidirectional interleaved composite laminate containing ultrasonic bandgaps. Furthermore, the property characterization in the case where the plies and interleaf layers are assumed to be elastic and viscoelastic, respectively, is also examined. It is also shown that the ply and interleaf layer properties determined for the unidirectional laminate can be used to reproduce the transmission spectra measured for a quasi-isotropic laminate consisting of the same plies and interleaf layers.

Critical Examination of Distance-Gain-Size (DGS) Diagrams of Ultrasonic NDE with Sound Field Calculations.

Ultrasonic non-destructive evaluation, which has been used widely, can detect and size critical flaws in structures. Advances in sound field calculations can further improve its effectiveness. Two calculation methods were used to characterize the relevant sound fields of an ultrasonic transducer and the results were applied to construct and evaluate Distance-Gain-Size (DGS) diagrams, which are useful in flaw sizing. Two published DGS diagrams were found to be deficient because the backward diffraction path was overly simplified and the third one included an arbitrary procedure. Newly constructed DGS diagrams exhibited transducer size dependence, revealing another deficiency in the existing DGS diagrams. However, the extent of the present calculations must be expanded to provide a catalog of DGS diagrams to cover a wide range of practical needs. Details of the new construction method are presented, incorporating two-way diffraction procedures.

Characterizing the As-Fabricated State of Additively Fabricated IN718 Using Ultrasonic Nondestructive Evaluation

This article reports on the characterization of the “as-fabricated” state of Inconel 718 samples fabricated using laser directed energy deposition (DED). Laser-DED is known to produce complex metastable microstructures that can significantly influence the baseline ultrasonic response compared to conventional processing methods. The present work uses three parameters to characterize the samples: (a) ultrasonic velocity, (b) an attenuation coefficient, and (c) a backscatter coefficient. The baseline ultrasonic response from the DED sample was compared against the ultrasonic properties of conventional IN718 samples reported in the literature. The results suggest that strong grain boundary scattering from large macrograins can lead to attenuation and backscatter values that are significantly higher than conventional samples. Additionally, the results including velocities, attenuation and backscatter coefficients were found to be dependent on the fabrication direction, with the build direction being different from the transverse directions. Finally, destructive analysis was used to develop conjectures to explain the experimentally observed ultrasonic response.

Reliability and failure modelling of microelectronic packages based on ultrasonic nondestructive evaluation data

Reliability testing and failure modelling is crucial and very challenging for modern electronics, especially safety critical electronics-based systems working under harsh environmental conditions. In this paper, an approach based on ultrasonic Non-Destructive Evaluation (NDE) is proposed to establish a failure model for solder joints which is urgently needed for prognostic and health management of electronics. Printed Circuit Boards (PCB) containing flip-chip and Area Array packages were designed and aged using Accelerated Thermal Cycling (ATC) testing. During ATC testing solder joint degradation was regularly monitored by taking out the test boards from the temperature chamber at four thermal cycle intervals for ultrasonic micro-imaging. Data pre-processing techniques including dynamic range-based intensity normalization, gain compensation, and calibration for random transducer defocusing errors were developed to enhance the data consistency, integrity and accuracy. Furthermore, solder joint image labelling and segmentation methods were developed by exploiting the geometrical features of the solder joints to extract individual solder joints and Region of Interests (ROIs) from the sequential ultrasound images collected throughout the testing. The mean intensity of the ROIs was used as the precursor to degradation to build the solder joint failure model, from which cycles to failure for individual solder joints are finally derived for life prediction.

Study on ultrasonic nondestructive evaluation method for grain size of magnesium alloy components with complex profile

In order to solve the problems of difficult measurement, inaccurate results and serious interference of diffusion and attenuation in the nondestructive evaluation of grain size of magnesium alloy components with complex profile, the sound field models of plane, cylindrical and conical parts based on the multiple Gaussian sound beam method are studied, and the attenuation mechanism of ultrasonic propagation in the medium of complex components and the diffusion and attenuation components in curved test blocks are analyzed, An evaluation method of ultrasonic attenuation of grain size based on diffusion loss correction is proposed to eliminate the influence of complex components on the total amount of ultrasonic attenuation. The results show that the ultrasonic nondestructive evaluation method of grain size based on sound velocity diffusion correction can effectively reduce the system error and improve the accuracy of grain size evaluation of magnesium alloy components with complex profile.

Defect modes and localisation of quasi-Lamb waves along a sidewall of corrugated aluminium plates

This study presents an observation of quasi-Lamb wave (QLW) localisation in a periodically corrugated plate with defects. The QLWs are excited and detected on one side of aluminium plates that are periodically grooved on the upper and lower planes with a strip defect. The periodic grooves result in the frequency forbidden band, whereas the defect is responsible for the additional transmission in this band. The QLW-amplitude measurements along the aluminium plates exhibit the transmission spectra of the defect modes as well as the QLW localisation near the middle strip. The numerical and experimental results confirm the additional transmission of the QLW defect mode and its frequency shifting. As the defect length increases, the transmission peak moves from the upper to the lower edges of the forbidden band. Furthermore, the calculated dispersion curves of the QLWs break at the frequency of the forbidden bands, and a localised mode appears in the middle when the defect length is nonzero. The experimentally observed QLW defect modes in elastic plates not only enrich our knowledge on the interaction between elastic waves and structures but also significantly benefit related engineering applications, such as ultrasonic non-destructive evaluation, elastic-wave filtering, and undersea acoustic-signal enhancement.

Interpretable & Explainable Machine Learning for Ultrasonic Defect Sizing.

Despite its popularity in literature, there are few examples of machine learning (ML) being used for industrial nondestructive evaluation (NDE) applications. A significant barrier is the 'black box' nature of most ML algorithms. This paper aims to improve the interpretability and explainability of ML for ultrasonic NDE by presenting a novel dimensionality reduction method: Gaussian feature approximation (GFA). GFA involves fitting a 2D elliptical Gaussian function an ultrasonic image and storing the seven parameters that describe each Gaussian. These seven parameters can then be used as inputs to data analysis methods such as the defect sizing neural network presented in this paper. GFA is applied to ultrasonic defect sizing for inline pipe inspection as an example application. This approach is compared to sizing with the same neural network, and two other dimensionality reduction methods (the parameters of 6 dB drop boxes and principal component analysis), as well as a convolutional neural network applied to raw ultrasonic images. Of the dimensionality reduction methods tested, GFA features produce the closest sizing accuracy to sizing from the raw images, with only a 23% increase in RMSE, despite a 96.5% reduction in the dimensionality of the input data. Implementing ML with GFA is implicitly more interpretable than doing so with principal component analysis or raw images as inputs, and gives significantly more sizing accuracy than 6 dB drop boxes. Shapley additive explanations (SHAP) are used to calculate how each feature contributes to the prediction of an individual defect's length. Analysis of SHAP values demonstrates that the GFA-based neural network proposed displays many of the same relationships between defect indications and their predicted size as occur in traditional NDE sizing methods.

Nondestructive Ultrasonic Evaluation of Ferritic CrW Steel upon Long-term Aging

The microstructural evolution of heat-resistant ferritic CrW steel during long-term aging was characterized by ultrasonic wave velocity measurement. Long-term aging was conducted at 700°C for 4000 h. The ultrasonic wave velocity increased monotonically upon long-term aging. The ultrasonic wave velocity increased rapidly during the initial 1000 h of aging and moderately thereafter. The MSUB23/SUBCSUB6/SUB carbide and Fe2W Laves phases underwent coarsening through the Ostwald ripening mechanism, causing a decrease in Cr and W solute atom concentration of the iron matrix during 4000-h aging. The dislocation density also decreased because of the heat treatment. The width of martensite lath increased owing to dislocation recovery at the lath boundaries. The ultrasonic wave velocity depends on the Young’s modulus of the material, which may influence microstructural features such as dislocation substructure, precipitates, solute atom concentration, and martensite lath boundaries. This study utilizes ultrasonic wave velocity to quantify the damage level and microstructural changes during the long-term aging of ferritic CrW steel.br/

Apex-shifted Radon transform for baseline-subtraction-free (BSF) damage scattered wave extraction

In ultrasonic structural health monitoring (SHM) and nondestructive evaluation (NDE), the scattered waves caused by damage sites and defects are the key to damage diagnosis. However, structural components and boundaries also interact with traveling waves, creating events that can bury damage scattered waves. The baseline subtraction method, which directly subtracts the waveform of a damage signal from that of a pristine baseline signal, is a common processing technique to separate these damage scattered waves. However, baseline subtraction is less effective when a component is measured in different environmental/loading conditions from when its baseline was recorded. For instance, baseline subtraction can be ineffective in aerospace structural parts because such parts expect significant and routine changes in ambient temperature, pressure, and humidity. To overcome the limitations of baseline subtraction, this paper proposes to develop an spex-shifted Radon transform (ASRT)-based damage scattered event extraction technique without baseline subtraction. Our proposed ASRT method converts the original time-space domain signals to a time delay–curvature–apex offset domain, which targets specific geometries of scattered/reflected waves in the domain and compresses them into a single point-like region in the new domain. In this domain, identifying and isolating targeted events becomes significantly easier. To benchmark the performance of this baseline-subtraction-free (BSF) method, ASRT is applied for signals acquired from (1) spectral finite element-based simulations to scan a water-immersed steel specimen (2) 3-D wave simulations in a bent aluminum plate, and (3) a full matrix capture for experimentally scanning a high-density polyethylene (HDPE) with multiple holes. The goal in each case is to target and separate events of interest from the original signals using the proposed algorithm. The results suggest the ASRT method is effective as a damage scattered wave extraction tool for ultrasonic SHM and NDE.

Ultrasonic nondestructive evaluation of the bonding strength of polyurethane coatings based on feedforward comb filtering effect

Because of the ability to protect and decorate materials, polyurethane coatings (PU) are being applied more and more extensively in the transportation, furniture, automotive, and electronic industries. However, it is difficult to effectively evaluate the bonding quality of coatings by conventional destructive methods for high-volume products in industrial applications. In this work, an ultrasonic nondestructive method based on the feedforward comb filtering effect was proposed to assess the bonding strength of the PU coatings. The coating and substrate interface can be modeled as a distributed spring system. The phase of the reflected ultrasonic wave is highly related to the interfacial stiffness. The superimposed signals can be well analyzed based on the comb filtering effect, and an index called the ratio of notch frequencies to interval frequencies (NIR) was constructed to represent the phase difference. Finite element simulations were conducted to show the index’s construction method and variation with different interfacial stiffnesses. Immersed ultrasonic testing experiments with a transducer of 39.43 MHz were then conducted on PU coatings on two kinds of substrates made of aluminum and magnesium alloys. Each specimen was scanned as a grid to mimic the procedure of the well-known cross-cut test. The notch frequencies of the scanned received signals were applied to obtain the NIR index. To avoid the interference of the thickness of coatings, the decimal part of NIR was further proposed to link with the bonding strength obtained by the cross-cut test. This index changes accordingly with aluminum- and magnesium-based coatings’ bonding strength. The results prove that the proposed ultrasonic method based on the feedforward comb filter effect is high potential to assess the bonding strength of coatings nondestructively.

Interaction effects from the elastodynamic scattering by two symmetric spherical cavities

The scattering of harmonic waves has been studied extensively for problems in quantum mechanics, acoustics, electromagnetics, and elasticity. Solutions to elastodynamic problems are the basis for ultrasonic non-destructive evaluation measurement models. Therefore, in this study, we investigate the use of the boundary element method (BEM) in the frequency domain using an off-boundary technique in which the observation points are taken inside the scattering object. This methodology removes both non-integrable singularities from the domain of integration along with avoiding ill-conditioning effects that occur at fictitious eigenfrequencies of which both require using special computationally demanding procedures to obtain solutions. Additionally, we employ both free and half-space fundamental solutions (Green’s displacement tensors) to investigate the elastodynamic scattering of an incident, plane, time-harmonic longitudinal wave in the frequency domain of a homogeneous, isotropic, and linear elastic solid with one or two spherical cavities. The half-space fundamental solution reduces the number of required boundary elements in half, which significantly reduces computational resource requirements. We only consider spherical cavities in this paper to illustrate the full and half-space off-boundary BEM and analyze the interaction effects associated with the elastodynamic scattering by two symmetric spherical cavities. To verify the validity of the free and half-space off-boundary BEM formulations, surface displacement results are compared with existing surface displacement results and show good agreement. Finally, the half-space off-boundary BEM is used to illustrate the interaction effects of the back and forward scattered displacement fields as a function of the distance from the spherical cavities.

The design of one-dimensional elastic diffusers

The paper presents a stochastic approach to generate randomly rough surfaces with a prescribed mean angular intensity distribution for elastic wave scattering. The analytical and numerical technique is implemented for a linearly elastic medium-vacuum interface, to generate band-limited uniform diffusers which may have applications for wave manipulation and ultrasonic non-destructive evaluation. Longitudinal incidence is assumed, and the theory allows for bulk wave mode conversions, with the surfaces designed to produce prescribed intensity distributions for both reflected compression wave modes, as well as the mode-converted vertically polarized shear wave modes. The angular distribution of these two cases is shown to be significantly different; additional, more exotic intensity distributions are also demonstrated to highlight the versatility of the model.

Ultrasonic Attenuation of Ceramic and Inorganic Materials Using the Through-Transmission Method

Ultrasonic attenuation coefficients of ceramic and inorganic materials were determined for the longitudinal and transverse wave modes. Sample materials included hard and soft ceramics, common ceramics, ceramic-matrix composites, mortars, silicate glasses, rocks, minerals and crystals. For ceramic attenuation measurements, a standardized method has existed, but this method based on a buffer-rod arrangement was found to be inconsistent, producing vastly different results. Resonant ultrasound spectroscopy was also found to be unworkable from its sample preparation requirements. Experimental reevaluation of the buffer-rod method showed its impracticality due to unpredictable reflectivity parameters, yielding mostly negative attenuation coefficients. In this work, attenuation tests relied on a through-transmission method, which incorporated a correction procedure for diffraction losses. Attenuation exhibited four types of frequency (f) dependence, i.e., linear, linear plus f4 (called Mason-McSkimin relation), f2 and f3. The first two types were the most often observed. Elastic constants of tested materials were also tabulated, including additional samples too small for attenuation tests. Observed levels of attenuation coefficients will be useful for designing test methods for ultrasonic nondestructive evaluation and trends on ultrasonic attenuation are discussed in terms of available theories. However, many aspects of experimental findings remain unexplained and require future theoretical developments and detailed microstructural characterization. This study discovered a wide range of attenuation behaviors, indicating that the attenuation parameter can aid in characterizing the condition of intergranular boundaries in combination with imaging studies.

Ultrasonic non-destructive evaluation of composites: A review

Ultrasonics is an NDT (Non-Destructive Testing) technique used to detect faults in structural components by applying a set of techniques and classifying them accordingly. This paper aims to bring together the most relevant published work on different types of techniques for Non-Destructive Evaluation (NDE) of various defects using Ultrasonic. The Ultrasonic testing techniques are relatively simple, highly sensitive and less time-consuming hence have been approved for use on various domains like composite testing, aerospace, automotive and transport. The fundamentals, their applications and constraints of various techniques are covered, along with motions to assess the performance of the techniques. Ultrasonic testing became popular, and with the progress made, new methods were discovered and corrected which resulted in defect detection and improving various material properties.

Non-Destructive Evaluation of the Quality of Adhesive Joints Using Ultrasound, X-ray, and Feature-Based Data Fusion

The aim of this work is to achieve reliable nondestructive evaluation (NDE) of adhesively bonded aerospace components by developing novel multidimensional data fusion techniques, which would combine the information obtained by ultrasonic and X-ray NDE methods. Separately, both NDE techniques have their advantages and limitations. The integration of data obtained from pulse echo immersion ultrasound testing and radiography holds immense potential to help improve the reliability of non-destructive evaluation. In this study, distinctive features obtained from single techniques, traditional ultrasonic pulse echo testing, and radiography, as well as fused images, were investigated and the suitability of these distinctive features and fusion techniques for improving the probability of defect detection was evaluated. For this purpose, aluminum single lap joints with brass inclusions were analyzed using ultrasound pulse echo and radiography techniques. The distinctive features were extracted from the data obtained, and images of features obtained by both techniques were fused together. Different combinations of features and fusion algorithms were investigated, considering the desire to automate data evaluation in the future.

An Ultrasonic Non-Destructive Evaluation of Contents of Silica Powder and Carbon Black in Nitrile Rubbers

An Ultrasonic Non-Destructive Evaluation of Contents of Silica Powder and Carbon Black in Nitrile Rubbers

A modified sideband peak count based nonlinear ultrasonic technique for material characterization

The ultrasonic Non-Destructive Testing and Evaluation (NDT&E) has been widely used for Structural Health Monitoring (SHM). The conventional linear ultrasonic technique which is suitable for detecting macro-scale defects is routinely used in industry; however, it often fails to detect the micro-scale defects. Generally, micro-defects in a material appear first due to dislocations at grain boundaries. These micro-defects then grow and coalesce to form macro-defects. The crack growth rate is much faster for macro-defects than micro-defects. Therefore, monitoring micro-defects is important to avoid catastrophic failures of structures. Nonlinear ultrasonic techniques help to detect micro-defects. A recently developed nonlinear ultrasonic technique called Sideband Peak Count - Index (SPC-I) technique has some inherent advantages over other nonlinear techniques for monitoring progression of micro-defects. In this research, the SPC-I technique is further modified. This modified technique, Sideband Peak Intensity (SPI) technique, is shown to be more robust and easier to implement. Both SPC-I and SPI techniques are used to monitor the damage progression in impact induced damages in metals. Similarities and dissimilarities between these two techniques are investigated. Then it is concluded that the SPI technique is good as a general-purpose robust damage monitoring tool that can be used by less skilled users while the SPC-I technique although requires more skills has more sensitivity and has the flexibility for an in-depth damage analysis in materials.