Ultrasonic Attenuation Measurements Research Articles

Ultrasonic evaluation of additively manufactured components with embedded structures

In recent years, the use of ultrasonic nondestructive evaluation (NDE) for in situ and ex situ assessment of Additive Manufacturing (AM) parts has garnered interest due to its proficiency in defect detection and material characterization. This study focuses on evaluating the ability to resolve internal structures created by AM and hybrid AM using ultrasonic NDE as well as assessing the impact of microstructure heterogeneity. For this purpose, first the parameter space for laser powder bed fusion (LPBF) of SS316L is mapped in a Lumex Avance 25 system. Based on this parameter mapping, optimal process parameters are identified and sets of process parameters are selected to vary the thermal history of the samples, while minimizing the influence of porosity. Two groups of samples are printed with these parameter sets: a solid group of samples, and a group with internal structures, such that each internal structure sample has an equivalent solid sample. Measurements of ultrasonic velocity, attenuation, and backscatter amplitude are collected and compared against the intended geometry to assess the impact of non-optimal processing on the ability to resolve internal structures with ultrasound. The viability and limitations of using ultrasound to assess internal features created with AM are discussed.

Ultrasonic Attenuation of Carbon-Fiber Reinforced Composites

Ultrasonic attenuation measurements were conducted on cross-ply and quasi-isotropic lay-ups of eight types of carbon-fiber reinforced composites (CFRPs) using through-transmission methods with diffraction correction. Attenuation values were substantially higher than those of unidirectional composites and other structural materials. Wave modes, fiber distributions, matrix resins, and consolidation methods affected total attenuation. Transverse mode, quasi-isotropic lay-up, and polyimide and thermoplastic resins generally produced higher attenuation. No clear trends from the fiber distribution were revealed, indicating that it is not feasible presently to predict the attenuation of various lay-ups from the unidirectional values. That is, direct attenuation tests for different laminate lay-ups are needed. This work expanded the existing attenuation database by properly determining the attenuation coefficients of two additional layup types of CFRP laminates. Results showed the merit of ultrasonic attenuation measurements for quality control and structural health monitoring applications. A crucial benefit of the through-transmission methods is that they enable the prediction of Lamb wave attenuation in combination with software like Disperse (ver. 2.0.20a, Imperial College, London, UK, 2013).

Quantification of porosity in composite plates using planar X-ray phase contrast imaging

The application of planar Edge-Illumination X-ray Phase-Contrast imaging (EI-XPCi) for the non-destructive quantification of porosity in carbon fiber reinforced polymer (CFRP) specimens, a significant concern in aerospace applications, was investigated. The method enables fast, planar (2D) scans providing access to large samples. A set of woven CFRP plates with porosity content ranging from 0.7% to 10.7% was examined. In addition to standard X-ray attenuation, EI-XPCi provides differential phase and dark-field signals, sensitive to inhomogeneities and interfaces at scales above and below the system spatial resolution, respectively. The correlation with the porosity content from matrix digestion obtained from the dark-field signal was comparable to that from ultrasonic attenuation. The novel analysis of the standard deviation of differential phase (STDP), sensitive to inhomogeneities above the system resolution (approximately 12 μm), resulted in a very high correlation (R2 = 0.995) with the matrix digestion porosity content, outperforming ultrasonic attenuation measurements.

Assessment of flaws in cold sintered ZnO via longitudinal ultrasonic wave speed and attenuation measurements

The cold sintering process (CSP) is a low temperature processing technique that utilizes a transient phase to synthesize dense ceramics. However, some CSP parts contain microflaws that arise due to pressure gradients and inhomogeneities in temperature and distribution of the transient phase. This work uses high frequency ultrasound (20 MHz) to verify the presence of defects larger than 15 μm in effective radius in CSP ZnO samples of varying densities (84–97%). The acoustic data were compared to X-ray Computed Tomography (XCT) images to validate the findings. Acoustic metrics used in this work include wave speed, which is affected by differences in the effective elastic properties of the medium, and attenuation, which is wave energy loss due to scattering from defects, including those smaller than the wavelength. Wave speed maps were inhomogeneous suggesting density gradients which were verified with SEM. Areas of high attenuation (> 300 Np/m) are present in all samples independent of relative density and correspond to defects identified in XCT ranging from 15 μm to 50 μm in effective radius. This suggests the presence of microflaws possibly due to the inhomogeneous removal of the transient phase. However, some high attenuation spots do not correspond to visible defects in XCT which suggests the presence of features such as texturing which are undetectable with XCT. These results show the viability of high frequency ultrasound for defect detection in cold sintered ZnO.

Experimental assessment of low-temperature martensite transformations in Ni-rich polycrystalline Ni–Ti alloys

Ultrasonic velocity and attenuation measurements of a commercially available Ni-rich polycrystalline Ni–Ti alloy were simultaneously obtained upon cooling from room temperature (RT) down to 130 K. The anelastic spectra show multiple anomalies in both velocity and attenuation curves, which evidence a complex nature of structural rearrangements exhibited by Ni–Ti alloy, associated with relaxations and phase transformations. In particular, some evident anomalies at 285 and 180 K, not previously exploited using ultrasonic measurements on Ni-rich polycrystalline Ni–Ti alloy, were associated with austenite to pre-martensitic (B2 → R) and pre-martensitic to martensitic (R → B19’) phase transitions, respectively. The peculiar temperature separation between these transformations was interpreted based on chemical composition and the Ni–Ti alloy microstructure evolution. X-ray diffraction (XRD), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) were also used to add complementary results about phase transformations and thermal events exhibited by Ni–Ti alloy at low temperatures. XRD, Rietveld refinement, SEM and transmission electron microscopy (TEM) analyses confirm the coexistence of the austenite B2, martensite B19’, and Ni4Ti3 phases at RT. DSC measurements indicated reversible two-stage martensitic transitions involving B2 ↔ R ↔ B19’ phase transformations at similar temperatures than the observed from ultrasonic anomalies. Besides that, several anelastic relaxation events identified around the phase transitions reveal the occurrence of complex physical mechanisms, such as accommodation of the twinned R-phase and martensite domain walls, twinning boundaries mobility, and the coupling between stress-induced dislocation motion and interstitial diffusion, not reported simultaneously in the literature. The ferroelastic nature of martensite and pre-martensite phase transformations was confirmed for a commercially available Ni-rich polycrystalline Ni–Ti alloy studied in this work.

Ultrasonic scattering in two-phase polycrystalline materials

Typically, many of the polycrystalline materials found in nature and those created using different manufacturing processes consist of multiple phases. Careful nondestructive characterization of these materials is of fundamental importance for quality assurance because microstructure is strongly correlated with mechanical performance. Ultrasonic scattering measurements have shown high sensitivity to material microstructure such that this approach is of interest for multi-phase materials. A fundamental understanding of scattering from idealized two-phase materials would provide essential information regarding the predictive nature of scattering measurements to quantify such microstructures. For this purpose, samples were created using spark plasma sintering (SPS) from mixtures with three different ratios (with respect to mass) of Cu and Fe powders. These elements do not alloy such that the resulting samples will not have any intermediate phases. Moreover, one pure Cu sample and one pure Fe sample were also sintered using SPS. The samples were imaged using electron backscatter diffraction (EBSD) to quantify the material organization. Ultrasonic backscatter and attenuation measurements were performed on the samples and the results were used for comparison with scattering models. Prospects for nondestructive evaluation of such materials are also discussed. [Work supported by Air Force Research Laboratory (AFRL) under prime contract FA8650-15-D-5231.]

Ultrasonic and acoustic pulse velocity methods for nondestructive detection of early decay in wood poles

Wood poles are widely used to support overhead distribution and transmission power lines in North America and the world. These poles are vulnerable to internal deterioration due to extreme weather conditions, requiring a large number of poles to be inspected every year. This paper presents a comparative study of four stress wave-based nondestructive testing (NDT) methods commonly used for condition assessment of wood poles. These include the traditional approaches of sounding, sonic pulse velocity, and ultrasonic pulse velocity tests; and a new approach that considers the orthotropic characteristics of wood, uncertainties in the elastic properties, ultrasonic wave velocity and attenuation. Two poles with an internal hole of 4% of the cross-section are evaluated and compared by each method. Ultrasonic measurements of wave velocity and attenuation considering orthotropic characteristics of wood and uncertainties in the elastic properties provide a reliable wave-based NDT method for the detection of early decay in wood poles.

In vivo pulse-echo measurement of apparent broadband attenuation and Q factor in cortical bone: a preliminary study

Quantitative ultrasound (QUS) methods have been introduced to assess cortical bone health at the radius and tibia through the assessment of cortical thickness (Ct.Th), cortical porosity and bulk wave velocities. Ultrasonic attenuation is another QUS parameter which is not currently used. We assessed the feasibility of in vivo measurement of ultrasonic attenuation in cortical bone with a broadband transducer with 3.5 MHz center frequency. Echoes from the periosteal and endosteal interfaces were fitted with Gaussian pulses using sparse signal processing. Then, the slope of the broadband ultrasonic attenuation (Ct.nBUA) in cortical bone and quality factor were calculated with a parametric approach based on the center-frequency shift. Five human subjects were measured at the one-third distal radius with pulse-echo ultrasound, and reference data was obtained with high-resolution x-ray peripheral computed tomography (Ct.Th and cortical volumetric bone mineral density (Ct.vBMD)). Ct.Th was used in the calculation of Ct.nBUA while is obtained solely from ultrasound data. The values of Ct.nBUA (6.7 ± 2.2 dB MHz−1 .cm−1) and (8.6 ± 3.1%) were consistent with the literature data and were correlated to Ct.vBMD (, , RMSE = 0.56 dB.MHz−1.cm−1, and , , RMSE = 0.76%). This preliminary study suggests that the attenuation of an ultrasound signal propagating in cortical bone can be measured in vivo at the one-third distal radius and that it provides an information on bone quality as attenuation values were correlated to Ct.vBMD. It remains to ascertain that Ct.nBUA and measured here exactly reflect the true (intrinsic) ultrasonic attenuation in cortical bone. Measurement of attenuation may be considered useful for assessing bone health combined with the measurement of Ct.Th, porosity and bulk wave velocities in multimodal cortical bone QUS methods.

Study of positional isomerism in N-propyl and Iso-propyl alcohol using ultrasonic technique

In the present work, positional Isomerism is studied in the binary mixtures of n-propyl alcohol and Iso-propyl alcohol in nitrobenzene as the common solvent. Ultrasonic velocity and attenuation measurements using pulse–echo technique operated at 10 MHz have been taken at various concentrations of both alcohols in nitrobenzene, from 283.15K - 293.15K. It is observed that both the systems exhibit critical nature and show non-linear variation both in ultrasonic velocity of propagation and attenuation. Ultrasonic attenuation at lower concentrations of n-propyl alcohol in nitrobenzene reveals the dominant structural relaxation as compared to that of Iso-propyl alcohol in nitrobenzene.

Ultrasonic attenuation of an agar, silicon dioxide, and evaporated milk gel phantom

Background:It has been demonstrated that agar-based gel phantoms can emulate the acoustic parameters of real tissues and are the most commonly used tissue-mimicking materials for high-intensity focused ultrasound applications. The following study presents ultrasonic attenuation measurements of agar-based phantoms with different concentrations of additives (percent of agar, silicon dioxide and evaporated milk) in an effort of matching the material's acoustic property as close as possible to human tissues.Methods:Nine different agar-based phantoms with various amounts of agar, silicon dioxide, and evaporated milk were prepared. Attenuation measurements of the samples were conducted using the through-transmission immersion techniques.Results:The ultrasonic attenuation coefficient of the agar-based phantoms varied in the range of 0.30–1.49 dB/cm-MHz. The attenuation was found to increase in proportion to the concentration of agar and evaporated milk. Silicon dioxide was found to significantly contribute to the attenuation coefficient up to 4% weight to volume (w/v) concentration.Conclusion:The acoustic attenuation coefficient of agar-based phantoms can be adjusted according to the tissue of interest in the range of animal and human tissues by the proper selection of agar, silicon dioxide, and evaporated milk.

Ultrasonic monitoring of variations in dust concentration in a powder classifier

Fine powders are generated in large volumes by industrial activities such as mining, metallurgical processing, energy generation and processing of waste. To meet specifications for further use, powder processing such as comminution and size classification are commonly applied. To optimise the design and operation of air-flow based classification processes, continuous on- line, monitoring of variations in dust particle concentration are an asset. This paper reports on the development of a novel ultrasonic measurement system suitable for robust monitoring of air-borne dust concentration variations during the operation of powder classification installations. The system was tested on a pilot-scale classifier designed for air-borne separation and recovery of ultrafine powders from coal combustion fly ashes. The monitoring method is based on a measurement of ultrasonic wave attenuation by particles suspended in the air-flow of the classifier.

Comparison of Experimental Measurements of Material Grain Size Using Ultrasound

Material grain size is related to metallic material properties and its elastic behaviour. Measuring and monitoring material grain size in material manufacturing and service is an important topic in measurement field. In this paper, three materials, i.e., aluminium 2014 T6, steel BS970 and copper EN1652, were chosen to represent materials with small, medium and large grain size, respectively. Various techniques of measuring material grain size were demonstrated and compared. These techniques include the measurements from material microstructure images, backscattered ultrasonic grain noise using a conventional transducer, longitudinal wave attenuation using ultrasonic arrays and shear wave attenuation using a lead zirconate titanate (PZT) plate. It is shown that the backscattered ultrasonic noise measurement and material attenuation measurement are complementary. The former is pretty good for weak scattering materials, e.g., aluminium, while the latter for materials with large grains, e.g., steel and copper. Consistent measured grain size from longitudinal and shear wave attenuations in steel and copper suggests that shear wave attenuation can be calculated from the measured longitudinal wave attenuation integrated with Stanke–Kino’s model or Weaver’s model, if there is a difficulty to either excite or capture shear waves in practice. The outcome of the paper expects to provide a further step towards the industrial uptake of these techniques.

Linear and Nonlinear Shock Attenuation of Aqueous Methylcellulose Solutions

Aqueous methylcellulose solutions are fascinating inverse-freezing materials, known to reversibly form gels upon heating. Recently, these materials have been found to undergo this endothermic solidification upon impact. The impact-induced solidification was shown to occur in the microseconds’ timescale, setting the path for examining their functionality for shock absorption purposes. This present work focuses on characterizing the ability of methylcellulose solutions to mitigate impact forces, and on quantifying their attenuation coefficients for weak ultrasonic pulses as well as violent impacts. Ultrasonic attenuation measurements at temperatures higher than the gelation temperature (solid gel), reveal unique behavior which is attributed to the thermogelation mechanism. Impact experiments on 2 cm thick solutions have shown unexpectedly strong force and impulse mitigation, along with a high attenuation coefficient that grows exponentially with frequency. This attenuation performance was even further improved by increasing the concentration of gel-forming material. Reducing the thickness of the sample to 1 cm does not apparently reduce the force and impulse mitigation characteristics from those measured for 2 cm thickness, which is a distinct "anomaly" of materials used for wave mitigation. These observations imply that in the materials investigated herein, the main mechanism of shockwave attenuation is the sol→gel phase-transition, in contrast to shockwave passage through the viscous material bulk. Thus, the common normalization of the attenuation coefficient to the thickness of the medium is not valid for these materials.

Recurrence quantitative analysis for porosity characterization of CFRP with complex void morphology

The porosity characterization of Carbon Fibre Reinforced Plastics (CFRP) by ultrasonic attenuation measurement is restricted when the back-wall echoes are weak or absent at high porosity, and the estimation accuracy is decreased with increment of porosity due to complex void morphology. In this paper, Real Morphology Void Models (RMVMs) with different porosity were established to simulate the interaction between ultrasonic waves and voids with complex morphology. Subsequently, Recurrence Quantification Analysis (RQA) was introduced to process ultrasonic backscattered signals generated by voids so as to present Recurrence Plots (RPs) for porosity characterization. Recurrence Rate (RR) was selected as RQA variable to quantitatively analyze RPs, avoiding the determination of additional parameters. The correlation between porosity P and RR was revealed by simulation for the first time, and verified by experiments with CFRP laminates having porosity of 0.8%–4.2%. The complex and random void morphology induced the non-mapping relationship between P and RR, influencing estimation accuracy of porosity. The normalized results indicated that porosity characterization with RR was less affected by void morphology for P > 1.97% in comparison with ultrasonic attenuation measurement. It is concluded that RQA is valuable for porosity characterization of CFRP with high porosity and strong attenuation.

Laboratory observations of frequency-dependent ultrasonic P-wave velocity and attenuation during methane hydrate formation in Berea sandstone

SUMMARYKnowledge of the effect of methane hydrate saturation and morphology on elastic wave attenuation could help reduce ambiguity in seafloor hydrate content estimates. These are needed for seafloor resource and geohazard assessment, as well as to improve predictions of greenhouse gas fluxes into the water column. At low hydrate saturations, measuring attenuation can be particularly useful as the seismic velocity of hydrate-bearing sediments is relatively insensitive to hydrate content. Here, we present laboratory ultrasonic (448–782 kHz) measurements of P-wave velocity and attenuation for successive cycles of methane hydrate formation (maximum hydrate saturation of 26 per cent) in Berea sandstone. We observed systematic and repeatable changes in the velocity and attenuation frequency spectra with hydrate saturation. Attenuation generally increases with hydrate saturation, and with measurement frequency at hydrate saturations below 6 per cent. For hydrate saturations greater than 6 per cent, attenuation decreases with frequency. The results support earlier experimental observations of frequency-dependent attenuation peaks at specific hydrate saturations. We used an effective medium rock-physics model which considers attenuation from gas bubble resonance, inertial fluid flow and squirt flow from both fluid inclusions in hydrate and different aspect ratio pores created during hydrate formation. Using this model, we linked the measured attenuation spectral changes to a decrease in coexisting methane gas bubble radius, and creation of different aspect ratio pores during hydrate formation.

Improved ultrasonic interferometer technique for propagation velocity and attenuation measurement in liquids.

Propagation velocity and attenuation are the two basic parameters used for the ultrasonic investigations of liquids. An ultrasonic interferometer is a widely used tool as a cost effective solution for propagation velocity measurement. The ultrasonic attenuation measurements are not possible using the existing interferometers commercially available in the market. Ultrasonic attenuation can be measured using the pulse echo method, which is relatively complex and expensive. Generally, in interferometers, a radio frequency voltage of more than 100 V is used to excite the piezoelectric transducer. In this article, an improved design of the ultrasonic interferometer with low (5 V) rf voltage excitation is discussed. The proposed design has several advantages over existing systems. The low voltage excitation reduces heating of the sample under study. Detection of the received signal is done directly at the transducer. The critical effects of a coaxial cable in rf detection are minimized by dc detection at the transducer node. The impedance response of the transducer is used for the detection of nodes and antinodes for attenuation and velocity measurements. The use of an instrumentation amplifier enables one to amplify the extremely small voltage changes across the transducer due to interference. The developed method has the capability to measure attenuation due to high receiver sensitivity. The technique has been validated for the propagation velocity and attenuation measurement in standard samples of water and other liquids. The results thus obtained have been compared with the literature and the conventional pulse echo technique which shows close agreement.

Viscoelastic Behavior of Alkyl Ether Sulfate Systems Containing Nanosized Colloidal Silica

AbstractSurfactant systems incorporating wormlike micelles (WLM) are utilized in both industrial and consumer products. While the viscoelastic behavior of such systems provides for many desired end‐use properties, there is often a need to further modify the rheological properties of such systems. These WLM systems behave much like polymer systems. Furthermore, incorporation of nanosized particles results in interaction of nanoparticles with the large WLM structures altering the rheological behavior. While there are a number of studies that have focused on the effect of particles on the rheological behavior in cationic surfactant systems, fewer studies have been done on systems containing anionic surfactants. In this study, relaxation behaviors in systems containing sodium alkyl ether sulfate and sodium carbonate were studied. The anionic surfactant was an alkyl ether sulfate with an average chain length of 12 carbons and one ethoxy group. WLM behavior was achieved through the addition of sodium carbonate. Ludox TMA, a nanosized colloidal silica, was employed at different concentrations in the WLM systems. Temperature was varied between 5 and 45°C. While characterization of relaxation in terms of the Maxwell model adequately described data below the threshold of ωτ ~1, the model failed to adequately describe behavior at higher frequencies. A modified expression with an additional relaxation mode adequately described relaxation throughout the frequency range studied. It was also found that zero‐shear viscosities generally increased with an increase in silica concentration, and relaxation times decreased. Measurements of relaxation due to a compressive stress via ultrasonic attenuation measurements in the surfactant/particle systems are also discussed.

Fourier Spectrum Pulse-Echo for Acoustic Characterization

Ultrasonic wave attenuation (α) measurement by pulse-echo method exhibits pronounced dependence on experimental conditions. It is shown to be an inherent characteristic of the method itself. Estimation of α from the component wave amplitudes in the frequency scale gives more accurate and consistent value. This technique, viz., the Fourier spectrum pulse-echo (FSPE) is demonstrated to determine the ultrasonic velocity (v) and attenuation constant (α) in ultrapure de-ionized water at room temperature (25 °C) at 1 and 2 MHz wave frequency.

Ultrasonic wave propagation in powders

Powder clumps (cakes) has a significant effect on the flowability and stability of powders. Powder caking is mainly caused by moisture migration due to wetting and environmental (temperature and humidity) changes. The process of moisture migration caking involves creating liquid bridges between the particles during condensation which subsequently harden to form solid bridges. Therefore, an effective and reliable technique is required to quantitatively and non-invasively monitor caking kinetics and effective stiffness. This paper describes two ultrasonic instruments (ultrasonic velocity pulse and airborne ultrasound systems) that have been used to monitor the caking phenomenon. Also, it discusses the relationship between the ultrasonic velocity and attenuation measurements and tracking caking kinetics and the effective stiffness of powders.

High-resolution ultrasonic spectroscopy

Abstract. High-resolution ultrasonic spectroscopy (HR-US) is an analytical technique for direct and non-destructive monitoring of molecular and micro-structural transformations in liquids and semi-solid materials. It is based on precision measurements of ultrasonic velocity and attenuation in analysed samples. The application areas of HR-US in research, product development, and quality and process control include analysis of conformational transitions of polymers, ligand binding, molecular self-assembly and aggregation, crystallisation, gelation, characterisation of phase transitions and phase diagrams, and monitoring of chemical and biochemical reactions. The technique does not require optical markers or optical transparency. The HR-US measurements can be performed in small sample volumes (down to droplet size), over broad temperature range, at ambient and elevated pressures, and in various measuring regimes such as automatic temperature ramps, titrations and measurements in flow.