Ultrasonic Wave Speed Measurements Research Articles

Ultrasonic measurement of milk heat coagulation time (HCT)

The dairy industry relies on heat coagulation tests (HCTs) to determine high-quality milk heat stability for typical thermal processes. For the HCT, an oil bath heats 1–2 ml of milk to 140 °C. The test lasts 20–30 min and finishes with visual confirmation of milk coagulation. This time for coagulation is recorded as the HCT time. While standard in the industry, this test is time-consuming and prone to operator-dependent bias. Thus, an automated alternative for measuring HCT time is desirable. This work proposed the use of ultrasonic monitoring and employed 10 MHz contact and immersion ultrasonic transducers in combination with conventional pH and rheological sensors. Room-temperature skim milk was coagulated in standard containers with a Glucono-Delta-Lactone acid concentration of 3% while simultaneously being monitored by the ultrasound, rheological, and pH sensors, at testing rates of 1 s, ca. 6 s, and 2 min, respectively. The resulting ultrasonic wave speed measurements revealed an increasing trend throughout the coagulation process. Additionally, an inflection point within the increasing wave speed corresponded to rheological and pH parameters indicating coagulation. This work demonstrates the potential for ultrasonics to be used as sensors for coagulation within the dairy industry.

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.

Thermomechanical model for monotonic and cyclic loading of PEEK

An internal state variable (ISV) model for polyether ether ketone (PEEK) is developed to capture experimental measurements conducted below its glass transition temperature. The model is based on the response of two relaxing components put in parallel, one having a back stress response that softens with plastic flow. This softening allows reproducing both monotonic and cyclic loading, and is possibly associated with detangling, melting of network junctions, and/or change in crystallinity. The resulting model, which is thermodynamic and multidimensional, was used to capture the response of PEEK 450G using thermal expansion (23 °C to 120 °C), heat capacity (−40 °C to 140 °C), monotonic extension and compression (−85 °C to 150 °C; 0.0001 s−1 to 3000 s−1; strains up to 40–80%), equilibrium stress measurements in compression (23 °C to 120 °C; strains up to 60%), and ultrasonic longitudinal and shear wave speed measurements along and transverse to the directions of compression (23 °C to 120 °C; up to 50% plastic compression). The model is compared to the response under monotonic and cyclic shear and internal dissipation is assessed using the equivalent adiabatic temperature rise.

A generalized spherical harmonic deconvolution to obtain texture of cubic materials from ultrasonic wave speed

In this paper, the spherical harmonic convolution approach for HCP materials (Lan et al., 2015) is extended into a generalised form for the principal purpose of bulk texture determination in cubic polycrystals from ultrasonic wave speed measurements. It is demonstrated that the wave speed function of a general single crystal convolves with the polycrystal Orientation Distribution Function (ODF) to make the resultant polycrystal wave speed function such that when the three functions are expressed in harmonic expansions, the coefficients of any one function may be determined from the coefficients of the other two. All three Euler angles are taken into account in the description of the ODF such that the theorem applies for all general crystal systems.The forward problem of predicting polycrystal wave speed with knowledge of single crystal properties and the ODF is solved for all general cases, with validation carried out on cubic textures showing strong sensitivity to texture and excellent quantitative accuracy in predicted wave speed amplitudes. Importantly, it is also revealed by the theorem that the cubic structure is one of only two crystal systems (the other being HCP) whose orientation distributions can be inversely determined from polycrystal wave velocities by virtue of their respective crystal symmetries. Proof of principle is then established by recovering the ODFs of representative cubic textures solely from the wave velocities generated from a computational model using these texture inputs, and excellent accuracies are achieved in the recovered ODF coefficients as well as the resultant pole figures. Hence the methodology is argued to provide a powerful technique for wave propagation studies and bulk texture measurement in cubic polycrystals and beyond.

A spherical harmonic approach for the determination of HCP texture from ultrasound: A solution to the inverse problem

A new spherical convolution approach has been presented which couples HCP single crystal wave speed (the kernel function) with polycrystal c-axis pole distribution function to give the resultant polycrystal wave speed response. The three functions have been expressed as spherical harmonic expansions thus enabling application of the de-convolution technique to enable any one of the three to be determined from knowledge of the other two. Hence, the forward problem of determination of polycrystal wave speed from knowledge of single crystal wave speed response and the polycrystal pole distribution has been solved for a broad range of experimentally representative HCP polycrystal textures. The technique provides near-perfect representation of the sensitivity of wave speed to polycrystal texture as well as quantitative prediction of polycrystal wave speed. More importantly, a solution to the inverse problem is presented in which texture, as a c-axis distribution function, is determined from knowledge of the kernel function and the polycrystal wave speed response. It has also been explained why it has been widely reported in the literature that only texture coefficients up to 4th degree may be obtained from ultrasonic measurements. Finally, the de-convolution approach presented provides the potential for the measurement of polycrystal texture from ultrasonic wave speed measurements.

Compressive evaluation of homogeneous and graded epoxy-glass particulate composites.

The propagation of stress waves in epoxy-glass particulate composites and graded materials was studied experimentally. Materials tested in this study consisted of an epoxy matrix with various concentrations of spherical glass particles having a mean diameter of 42μm. Plate impact experiments were performed using a gas gun. Embedded within the specimens were manganin stress gauges used to record propagating compressive longitudinal stress waves through the material. High strain rate experiments using a Split Hopkinson Pressure Bar (SHPB) apparatus were also performed to evaluate the dynamic strength of the specimens, while quasi-static compression tests were undertaken to characterize their quasi-static behavior. Ultrasonic wave speed measurements were carried-out in order to obtain additional material properties and characterize the gradation in functionally graded materials (FGM). It was found that low volume fractions of particles are detrimental to the performance of the material under impact loading, while concentrations in the range of about 30 to 45% by volume exhibit characteristics of higher degrees of scattering. This suggests that materials in this latter range would be more effective in the thwarting of destructive shock waves than the homogeneous matrix material. Impact testing of FGM specimens suggests that impact loading on the stiff (high volume fraction) face results in much higher levels of scattering. Therefore, such materials would be effective for use in light weight armor or as shielding materials due to their effective attenuation of mechanical impulses.

Anisotropic loss of toughness with physical aging of work toughened polycarbonate

We have studied the response of mechanically toughened and physically aged polycarbonate primarily using Charpy impact and ultrasonic wave speed measurements. The toughening was conducted through plastic compression on as‐received PC. The Charpy impact tests showed anisotropic toughening, both in the absorbed energy and in the mode of fracture. The amount of toughening with plastic compression, even though anisotropic, is centered around the response of annealed and quenched samples, which represent the response of an unaged PC. There was an anisotropic drop in the toughness of some samples with aging. The time of this drop was uncorrelated in the different directions and disappeared for the highly toughened samples. This transition was bimodal and statistically distributed between either a fully ductile or a fully brittle failure. As the samples were prepared in a manner to remove induced residual stresses, this drop in toughening may be associated with an intrinsic anisotropic thermal aging of the deformed material. POLYM. ENG. SCI., 54:794–804, 2014. © 2013 Society of Plastics Engineers

Stress-dependent changes in the diffuse ultrasonic backscatter coefficient in steel: Experimental results

In this article, the effects of uniaxial compressive loading on the ultrasonic scattering from polycrystalline grains are shown for 10 MHz ultrasound in annealed, 1018 steel. The results show a decreasing value of the stress-dependent backscatter coefficient for normal incident ultrasound when the compression loading is perpendicular to the scattering direction. The change due to scattering is about 2 orders of magnitude greater than changes observed by others using ultrasonic wavespeed measurements. It is anticipated that this research can serve as the basis for many methods associated with nondestructive determination of stress in structural materials.

Experimentally based strategy for damage analysis of textile-reinforced composites under static loading

For a reliable design of components made of textile composites, a deep knowledge of their failure behaviour and of realistic damage models is necessary. Such models require the onset of damage and the evolution of different damage phenomena to be determined experimentally. In this context, an experimental damage analysis strategy is proposed here that combines crack density measurements, acoustic emission analysis and optical microscopy with the recording of stiffness degradation by ultrasonic wave speed measurements. The correlation between the results of quasi-static tests is discussed for two selected examples of textile composites: multi-layered flat bed weft-knitted glass fibre–epoxy composites and woven glass fibre–polypropylene composites made of hybrid fabrics.

Modeling the development of elastic anisotropy as a result of plastic flow for glassy polycarbonate

AbstractThe development of anisotropy as a result of plastic deformation below the glass‐transition temperature is investigated and modeled for amorphous polycarbonate. Initially, isotropic polycarbonate was subjected to different extents of plastic flow in compression, and the development of its anisotropic wave speed moduli were studied using ultrasonic wave speed measurements. Longitudinal and shear wave speed measurements were performed both in the axial and transverse directions, with respect to the axis of compression. The moduli clearly indicated the development of a transversely elastic response as a result of the uniaxial compression. The measured moduli were used to model the elastic response of polycarbonate using a model for stress that depends both on the elastic and plastic parts of the deformation. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers

An In Situ Ultrasonic Technique for Simultaneous Measurement of Longitudinal and Shear Wave Speeds in Solids

Ultrasonic wave speed measurements are widely used to infer the elastic properties of solids. In the standard method, longitudinal and shear transducers are used separately to measure the corresponding wave speeds in a material. A new experimental method is introduced for simultaneously measuring the longitudinal and the shear wave speeds using a single set of longitudinal or shear transducers. The method can also be used to measure the wave speeds in situ during deformation by placing the transducers along the loading axis. The transducers are housed in a specially designed fixture such that they are not subjected to loading. The technique is demonstrated by performing uniaxial compression experiments on fully dense isotropic solids (where the wave speeds are not expected to change during deformation) and in polymeric foams (where the wave speeds are affected by damage).

USING LABVIEW UNDER WINDOWS IN ADVANCED ULTRASONIC TESTING

Abstract Ultrasonic testing is used in a variety of applications. One application, the measurement of residual stress, utilizes acoustoelastic testing. In acoustoelastic testing, very small changes in ultrasonic wave speed are measured as a function of applied load. In this study, a testing setup has been implemented which utilizes National Instruments' LabVIEW software on a digital computer to control and analyze the acoustoelastic responses of various engineering materials. The high quality acoustoelastic results are indicative of the high resolution in ultrasonic wave speed measurements that is attained using this setup.

An Experimental Investigation of Damage Evolution in a Ceramic Matrix Composite

The mechanical behavior of a glass-ceramic matrix composite, SiC/CAS (calcium aluminosilicate reinforced with unidirectional SiC fibers), is studied. Results based on uniaxial tension experiments are presented for specimens with fibers aligned in the loading direction. Axial and transverse strain gages on all four gage section surfaces and in situ acoustic emission and ultrasonic wave speed measurements were used to monitor the evolution of damage. All measurements were made with high-resolution, continuous data acquisition. Post-test optical and scanning electron microscopy was also used to identify the various micromechanisms of damage. The experimental results demonstrate the existence of “zones of deformation” which are associated with the onset of different damage mechanisms. It is shown that the observed stress-strain behavior can be explained in terms of the material properties of the matrix and the fiber, the material processing, and the postulated zones of deformation.

Evaluation of tortuosity in acoustic porous materials saturated by air

Tortuosity is an important parameter for the prediction of the acoustical properties of porous sound absorbing materials. The evaluation of tortuosity by resistivity measurements is now used in several laboratories, although this method presents several drawbacks. In particular, the complete saturation by a conducting fluid of a porous foam having a high flow resistivity is difficult to obtain without partially damaging the structure of the cells. A simple technique based on ultrasonic wavespeed measurements in a material saturated by air is described. This method has been used previously only for water or superfluid helium saturated materials.

43874 Optimal determination of the elastic constants of composite materials from ultrasonic wave-speed measurements : Castagnede, B.; Jenkins, J.T.; Sachse, W.; Baste, S. Journal of Applied Physics, vol. 67, no. 6, pp. 2753–2761 (15 Mar. 1990)

43874 Optimal determination of the elastic constants of composite materials from ultrasonic wave-speed measurements : Castagnede, B.; Jenkins, J.T.; Sachse, W.; Baste, S. Journal of Applied Physics, vol. 67, no. 6, pp. 2753–2761 (15 Mar. 1990)

Phase and group velocity considerations for dynamic modulus measurement in anisotropic media

In anisotropic media, the direction of energy propagation does not necessarily coincide with the wave normal, i.e. the energy flux vector does not coincide with the wave normal. Since, experimentally, one measures group velocity not phase velocity, one must therefore be careful in interpreting ultrasonic wave speed measurements in anisotropic media. This is of particular importance in elastic property reconstruction where acoustic velocity measurements are used as the basis for determining anisotropic material properties. In this work, the consequences of energy flux deviation from the wave normal are considered for typical experimental geometries. Particular attention is devoted to developing appropriate relationships between the phase velocity and ultrasonic transit time measurements, as these relations are most useful for elastic property reconstruction. In all the cases considered, it is shown that the phase velocity can be directly calculated from appropriate time delay measurements.

Optimal determination of the elastic constants of composite materials from ultrasonic wave-speed measurements

A method is described to optimally determine the elastic constants of anisotropic solids from wave-speeds measurements in arbitrary nonprincipal planes. For such a problem, the characteristic equation is a degree-three polynomial which generally does not factorize. By developing and rearranging this polynomial, a nonlinear system of equations is obtained. The elastic constants are then recovered by minimizing a functional derived from this overdetermined system of equations. Calculations of the functional are given for two specific cases, i.e., the orthorhombic and the hexagonal symmetries. Some numerical results showing the efficiency of the algorithm are presented. A numerical method is also described for the recovery of the orientation of the principal acoustical axes. This problem is solved through a double-iterative numerical scheme. Numerical as well as experimental results are presented for a unidirectional composite material.

Determination of the elastic constants of anisotropic composite materials via laser photoacoustics

This paper presents the solution of the inverse anisotropic medium problem in which the elastic constants of an anisotropic composite material are determined from ultrasonic wave speed measurements made in nonprincipal directions of a specimen. The ultrasonic waves were generated via the point-source/point-receiver technique using a 2-ns pulsed Nd:Yag laser as a source and a 2.5-mm-diam capacitive or a 1.3-mm piezoelectric transducer as a receiver. Data were acquired during an isoangular scan of the source relative to one of the principal acoustic axes of symmetry. In each waveform, the arrivals of the quasilongitudinal and the two quasishear bulk modes were measured. The elastic constants of the material were then recovered using an optimization algorithm. Experimental results are presented for a transversely isotropic composite material. It was found that the nonlinear fit between the experimental and the recovered slowness values is excellent. Some discrepancies are observed for the two shear modes. These are shown to be related to the complexity of the detected signals.