Ultrasonic Reflection Measurements Research Articles

Nondestructive Evaluation of Residual Stress in Shot Peened Inconel Using Ultrasonic Minimum Reflection Measurement.

Shot peening is a process wherein the surface of a material is impacted by small, spherical metal shots at high velocity to create residual stresses. Nickel-based superalloy is a material with high strength and hardness along with excellent corrosion and fatigue resistance, and it is therefore used in nuclear power plants and aerospace applications. The application of shot peening to INCONEL, a nickel-based superalloy, has been actively researched, and the measurement of residual stresses has been studied as well. Previous studies have used methods such as perforation strain gauge analysis and X-ray diffraction (XRD) to measure residual stress, which can be evaluated with high accuracy, but doing so damages the specimen and involves critical risks to operator safety due to radiation. On the other hand, ultrasonic testing (UT), which utilizes ultrasonic wave, has the advantage of relatively low unit cost and short test time. One UT method, minimum reflection measurement, uses Rayleigh waves to evaluate the properties of material surfaces. Therefore, the present study utilized ultrasonic minimum reflectivity measurements to evaluate the residual stresses in INCONEL specimens. Specifically, this study utilized ultrasonic minimum reflection measurements to evaluate the residual stress in INCONEL 718 specimens. Moreover, an estimation equation was assumed using exponential functions to estimate the residual stress with depth using the obtained data, and an optimization problem was solved to determine it. Finally, to evaluate the estimated residual stress graph, the residual stress of the specimen was measured and compared using the XRD method.

Estimating P- and S-Wave Velocities in Fluid Mud Using Seismic Interferometry

Fluid mud plays an important role in navigability in ports and waterways. Characterizing and monitoring the seismic properties of the fluid mud can help understand its geotechnical behavior. Estimation of the wave velocities in fluid mud with high accuracy and repeatability enables investigating the behavior of parameters like the yield stress in a nonintrusive and reliable way. We perform ultrasonic reflection measurements in a laboratory to investigate the wave propagation in a water/fluid-mud layered system. The component of wave propagation in the water layer inevitably brings kinematic dependence on the characteristics of that layer, making the estimation of exact velocities in the fluid mud more challenging. In order to extract the wave velocities only in the fluid-mud layer, we use a reflection geometry imitating field measurement to record the ultrasonic data from sources and receivers in the water layer. We then use seismic interferometry to retrieve ghost reflections from virtual sources and receivers placed directly at the water-mud interface. Using velocity analysis applied to the ghost reflections, we successfully obtain the P-wave and S-wave velocities only inside the fluid-mud layer, and investigate the velocity change during the self-weight consolidation of the fluid mud. Our results indicate that the S-wave velocities of the fluid mud increase with consolidation time, and show that reflection measurements and ghost reflections can be used to monitor the geotechnical behavior of fluid mud.

On the relation of setting and early-age strength development to porosity and hydration in cement-based materials

Previous research has demonstrated a linear relationship between compressive strength (mortar cubes and concrete cylinders) and cumulative heat release normalized per unit volume of (mixing) water for a wide variety of cement-based mixtures at ages of 1 d and beyond. This paper utilizes concurrent ultrasonic reflection and calorimetry measurements to further explore this relationship from the time of specimen casting to 3 d. The ultrasonic measurements permit a continuous evaluation of thickening, setting, and strength development during this time period for comparison with the ongoing chemical reactions, as characterized by isothermal calorimetry measurements. Initially, the ultrasonic strength-heat release relation depends strongly on water-to-cement ratio, as well as admixture additions, with no universal behavior. Still, each individual strength-heat release curve is consistent with a percolation-based view of the cement setting process. However, beyond about 8 h for the systems investigated in the present study, the various strength-heat release curves merge towards a single relationship that broadly characterizes the development of strength as a function of heat released (fractional space filled), demonstrating that mortar and/or concrete strength at early ages can be effectively monitored using either ultrasonic or calorimetry measurements on small paste or mortar specimens.

Ultrasound interferometry for the evaluation of thickness and adhesion of thin layers

A simulation work has been carried out to characterise thin layers by a technique called ultrasound interferometry, which is based on the resonance and anti-resonance of ultrasound waves verified in the presence of some interfaces having different acoustical impedances. Normal incidence ultrasonic reflection measurements have been considered. The reflection coefficients were calculated against frequency, velocity and thickness. A graphical user interface (GUI), developed in Matlab environment was used to simulate the calculation of several coating thicknesses (velocities) over different substrates, like iron and aluminium. The results are based on the representation of reflection or transmission coefficients against frequency, thickness and velocity in the coatings. The developed GUI is a very important tool to predict the behaviour of thin layers embedded between two thicker media, like mechanical properties providing the calculation of its thickness and ultrasonic velocity, in fast and easy way.

An investigation of microstructure evolution in cement paste through setting using ultrasonic and rheological measurements

The response of hydrating cement paste through setting are monitored using rheological measurements and ultrasonic reflection measurements. Increases in the elastic modulus and yield stress of cement paste with time are obtained from the rheological measurements. Ultrasonic measurements are performed using horizontally polarized shear waves (SH) reflected off of the hydrating cement paste. Changes in the ultrasonic signal through setting are related with changes in the porosity and stiffness of an equivalent water-filled poroelastic material, which provides identical acoustic impedance. The measured changes in the shear modulus obtained from ultrasonic measurement are shown to correlate well with increase in elastic modulus obtained from rheological measurements. The increase in the shear modulus of the porous material obtained from the ultrasonic measurements is shown to correspond well with the observed increase in the yield stress of the cement paste. By combining the information from rheological and ultrasonic measurements, it is found that even in the fluid stage there is sufficient structural integrity in the arrangement of cement grains to support low-amplitude shear stress and the evolution of a continuously connected network of cement particles within the paste is coincident with a rapid increase in the shear modulus of the porous skeleton.

Ultrasonic measurements on poroelastic slabs: Determination of reflection and transmission coefficients and processing for Biot input parameters

Ultrasonic reflection and transmission measurements on saturated, plane-parallel, poroelastic slabs are presented. A data processing technique is proposed to obtain poroelastic parameters from transmission measurements. A special experimental data acquisition and processing technique is applied to minimize the finite beam effects of the transducers. This technique yields results which can be compared with poroelastic plane-wave theory. Results of normal- and oblique-incidence measurements are presented, and transmission data are processed to yield wave speeds, sample thickness, angle of incidence, tortuosity, and permeability. The results show good agreement with independent measurements, and they are subsequently used as input for a forward modeling of the complete transmitted and reflected waveforms utilizing Biot theory. The agreement between recorded and modeled signals is good, both in time and frequency domain.

Crystallization and shear modulus of a forming biopolymer film determined by in situ x-ray diffraction and ultrasound reflection methods

The structure and the rigidity of a forming biopolymer film were determined using concurrent x-ray diffraction and ultrasonic reflection measurements. Film formation of a xylan solution (de-ionized water, 10g∕l xylan, 4g∕l glycerol) was studied during water evaporation at 24(±2)°C, 37(±5)%RH. X-ray diffraction (XRD) data showed the crystallization and ultrasonic data the increase of the shear modulus (G) during water evaporation. Xylan crystallized into small xylan dihydrate crystallites, the number of which increased as water evaporated. Crystallization began earlier than the increase in G during film formation. The increase in G also continued after the crystallites were fully formed, indicating still ongoing structural changes in the amorphous parts. The maximum value of G was 0.1–0.5GPa. XRD measurements performed ex situ showed a crystallinity of 16%–19% (±5%) and a fairly isotropic crystallite orientation in the surface plane of the films.

Comparison of ultrasonic wave transmission and reflection measurements with P- and S-waves on early age mortar and concrete

This paper reports on results of round robin tests comparing two nondestructive, ultrasonic techniques: the wave transmission method using P-waves and the wave reflection method using S-waves. The experiments were conducted within the activities of the RILEM Technical Committee TC ATC-185 with the objective to evaluate the ability of these methods to continuously monitor the setting and hardening process of cementitious materials. In total, eight different mortar and concrete mixtures were subjected to the ultrasonic tests. Additionally, experiments were conducted to determine the penetration resistance (ASTM C 403), the in-situ temperature rise, the adiabatic heat release, and the chemical shrinkage (of the cement paste phase) of the investigated materials. The results revealed that, originating from the different wave types, the two ultrasonic methods monitor the setting process of mortar and concrete in significantly different ways. Despite these differences, the comparison of the ultrasonic test results with the development of the adiabatic heat and the chemical shrinkage has proven that P-wave velocity and reflection loss, as the parameters measured by the two methods, have a consistent and direct relationship to the cement hydration process.

Comparison of ultrasonic wave transmission and reflection measurements with P- and S-waves on early age mortar and concrete

Comparison of ultrasonic wave transmission and reflection measurements with P- and S-waves on early age mortar and concrete

Temperature Effects on Strength Evaluation of Cement-Based Materials with Ultrasonic Wave Reflection Technique

Among the various factors that influence the strength gain of cementitious materials at early age, curing temperature can be regarded as an important parameter due to its great effect on the hydration kinetics of portlandcement. The temperature effects on the relationship between the compressive strength of paste, mortar, or concrete and the reflection loss obtained with ultrasonic shear-wave reflection measurements were observed. In the study, three different constant curing temperatures (15, 25, and 35 °C) were used for a given paste or mortar. The temperature effects were observed by comparing the established relationship between reflection loss and compressive strength for portland cement mortar under different isothermal curing conditions. Additionally, the established correlations between the two studied parameters were verified by applying alternating curing temperatures to the mortar. As a third step, the temperature dependence of the relationship between the two studied parameters was further verified by observing concrete cured under various conditions. The study shows that for a given material, the relationship between the reflection loss and the compressive strength is independent of curing temperature.

Nondestructive Characterization of Adhesive Joint Durability Using Ultrasonic Reflection Measurements

The present work investigates the durability of two commercial epoxy adhesives nondestructively using ultrasonic reflection measurements from the interfacial region between the adhesive and the adherend. This method, which is primarily sensitive to the interfacial properties, employs a new specimen geometry that overcomes the drawbacks of the conventional closed adhesive sandwich. The interfacial region was modeled using the spring boundary conditions. The normal and tangential spring constants were determined, as a function of degradation, from normal-incidence longitudinal and shear-wave measurements. Obliquely incident shear-wave measurements were also performed using a newly developed dual-element PVDF transducer. An efficient angular spectrum approach was developed to model the oblique-incidence measurement system, and the predictions of the model were compared with measurements for various levels of degradation.

Nondestructive Characterization of Adhesive Joint Durability Using Ultrasonic Reflection Measurements

The present work investigates the durability of two commercial epoxy adhesives nondestructively using ultrasonic reflection measurements from the interfacial region between the adhesive and the adherend. This method, which is primarily sensitive to the interfacial properties, employs a new specimen geometry that overcomes the drawbacks of the conventional closed adhesive sandwich. The interfacial region was modeled using the spring boundary conditions. The normal and tangential spring constants were determined, as a function of degradation, from normal-incidence longitudinal and shear-wave measurements. Obliquely incident shear-wave measurements were also performed using a newly developed dual-element PVDF transducer. An efficient angular spectrum approach was developed to model the oblique-incidence measurement system, and the predictions of the model were compared with measurements for various levels of degradation.

Nondestructive Characterization of Adhesive Joint Durability Using Ultrasonic Reflection Measurements

Nondestructive Characterization of Adhesive Joint Durability Using Ultrasonic Reflection Measurements

Transducer misalignment effects in beam reflection from elastic structures

In two-transducer, fluid-coupled ultrasonic reflection measurements phase matched to guided modes of elastic solid structures, the effects of misalignment (i.e., differences) between the receiver angle and the incident beam angle on the receiver voltage have been studied. The received voltage is typically due to contributions from the specular reflection and any of the several possible guided wave modes excited by the incident wave field. It is found that misalignment leads to changes in the relative amplitudes of the various contributions. Further, the more highly collimated the beam (or the contributor), the more pronounced are the effects. It is shown that the signal maximum is not a reliable indicator of receiver alignment. These conclusions are based on measurements and on calculations that have been performed at incident angles selected both close to, or far from, phase-matching angles to guided wave modes on plates, curved surfaces, and cylindrical shells. Receiver voltage coordinate scans have been performed with receiver angles misaligned from the incident beam axis by 1 to 4 degrees. The receiver voltage versus scan parameter in planar and curved structures is calculated by employing complex transducer points to synthesize two-dimensional, sheet-beam transducer fields with Gaussian apertures, spectral analysis to formulate the beam-structure interaction problem, and asymptotic methods to evaluate the resulting spectral integrals. The model predictions are generally in good agreement with the experiments.

Characterization of suspensions by ultrasonic reflection measurements

The ultrasonic attenuation and the ultrasonic backscatter coefficient from suspensions are known to be correlated with the concentration of particles and the particle size distribution. However, for suspensions with a very low particle concentration (< 500 ppm) the effect of the particles on the attenuation or backscatter coefficient is in general not significant. In this paper a new ultrasonic technique is presented, which can be applied to characterize suspensions with a very low concentration of particles. The method is based on ultrasonic reflection from individual particles passing through a small measurement volume. Such a small volume is achieved by applying a focused transducer and windowing of the time signal. The amplitude of a received reflection depends on the position of the reflecting particle in the measurement volume and on the dimensions and shape of the particle. A forward analytical model describes the relations between the suspension properties (particle size distribution and particle concentration) and the measured histogram of amplitudes. The particle size distribution and concentration are obtained from the measurements via numerical inversion of the forward model. Results of measurements on a well-controlled suspension demonstrate the feasibility of this technique.

The characterization of oxide layers in adhesive joints using ultrasonic reflection measurements

The use of ultrasonic reflection coefficient measurements at both normal and oblique incidence for the detection and characterization of oxide layers at the adhesive-adherend interface in adhesive joints has been investigated. Tests have been carried out on aluminium alloy-oxide-epoxy specimens with a minimal (< 0.1 $\mu $m) thickness oxide layer, 43 and 15 $\mu $m thick sulphuric acid anodized oxide oxide layers and an industry standard, 3.5 $\mu $m thick chromic acid anodized oxide layer. A superpure aluminium-90 $\mu $m thick oxalic acid anodized layer-water system has also been investigated. The results indicate that the cell wall density of the sulphuric acid anodized oxide layer is only 1990 kg m$^{-3}$, compared to 2850 kg m$^{-3}$ for the oxalic acid anodized layer. The cell wall density and Young's modulus are obtained from normal incidence measurements. Predictions of the oblique incidence reflection coefficients using the effective elastic constants of the oxide layer obtained from a standard porosity model assuming these cell wall properties and the porosity measured from TEM images showed good agreement with the measurements made on both the sulphuric acid anodized and oxalic acid anodized specimens, only small adjustments to the properties being required to obtain a very good fit. The frequency range over which it is necessary to take measurements increases as the thickness of the oxide layer decreases. Maximum frequencies of 15 MHz for the oblique incidence measurements and 70 MHz for the normal incidence measurement were adequate to obtain values of $\rho $, C$\_{11}$ and C$\_{33}$ for a 43 $\mu $m thick sulphuric acid anodized layer to an estimated accuracy of $\pm $10% and to set a lower bound on C$_{55}$. In order for a 3.5$\mu $m thick oxide layer with similar properties to be detectable at normal incidence, the frequency would have to be increased to over 200 MHz, while the frequency of the oblique incidence measurements would have to be raised to about 25 MHz if a 5% change could reliably be detected, or 50 MHz if a 10% change is necessary in order to ensure detection.

Guided plate waves in piezoelectrics immersed in a dielectric fluid. II. Experiments

Detailed ultrasonic reflection measurements in piezoelectric LiNbO3 are reported which are compared to the results of the theoretical analysis of the previous paper, part I. Differences in mode coupling and behavior are illustrated in several calculated examples. The calculated numerical results are demonstrated in a full image format. It is shown how dielectric fluid loading influences the reflection behavior and how strong piezoelectric coupling can lead to unexpected dispersion in the fundamental symmetric mode. The data confirms in each case the predictions of an exact partial-wave analysis of the problem, including the dielectric influence of the fluid. These phenomena play a role in the design and performance of piezoelectric sensing devices.

The detection of thin embedded layers using normal incidence ultrasound

A theoretical investigation of the use of normal incidence ultrasonic reflection measurements for the detection and characterization of thin layers embedded between two much thicker media has been carried out. It has been shown that the form of the relationship between the normal incidence longitudinal reflection coefficient and frequency is defined by the reflection coefficients at zero frequency and at half the resonance frequency of the layer. The reflection coefficient at zero frequency is solely a function of the impedances of the media on either side of the layer, while that at half the resonance frequency of the layer is a function of the impedances of all three media. In general, the sensitivity of the reflection coefficient to the presence of the layer increases as the product of frequency and layer thickness increases, the maximum sensitivity being at half the resonance frequency of the layer. Unfortunately, with thin layers, it is generally not practical to test at this frequency. However, the reflection coefficient curve can, in principle, be reconstructed from data measured at lower frequencies and the sensitivity of the reflection coefficient at lower frequencies to the characteristics of the layer can be predicted from the sensitivity at half the resonance frequency. The sensitivity is also critically dependent on the relative impedances of the three media and is generally greatest when the half spaces on either side of the layer have the same impedance. With favourable impedances, it is possible to detect layers whose thickness is a small fraction of the wavelength of the ultrasonic waves employed. However, with other combinations of impedances, the detection of much thicker layers is not possible.

Ultrasonic classification of imperfect interfaces

Ultrasonic reflection measurements from material interfaces are commonly used to detect and quantitatively characterize boundary imperfections of different kinds. Either shear or longitudinal waves can be used to assess the degree of the interface imperfection in acoustical terms. On the other hand, the evaluation of this data in terms of strength-related mechanical properties requiresa priori knowledge of the physical nature of the imperfection. It is shown in this paper that the ratio between the normal and transverse interfacial stiffnesses can be used to classify the interface imperfection. This ratio is readily measured, e.g., by comparing the longitudinal and shear reflection coefficients at normal incidence. Both theoretical and experimental results indicate that different types of imperfections, such as kissing, partial, and slip bonds, can be distinguished by this simple technique.

Ultrasonic reflection and guided wave propagation in biaxially laminated composite plates

This paper presents the results of numerous ultrasonic reflection measurements on plates of laminated composites in which the angle of incidence of a finite-aperture acoustic wave and its frequency have been varied. These experiments have been carried out on biaxially laminated graphite–epoxy specimens utilizing water as a fluid-coupling medium. The stacking sequence of the individual laminae is restricted such that in each layer a principal material axis lies in the incident plane of the acoustic wave. The data are compared to the results of a recent theoretical analysis based on an analytical treatment of wave propagation in orthotropic media in conjunction with a transfer matrix approach. Reflection and transmission coefficients are derived from which the characteristic behavior of the system is identified. Results are presented both as reflection spectra and dispersion curves. In general, very good agreement is found between prediction and experiment. Moreover, significant changes in the reflection spectra are observed, depending on the layer ordering in the composite plates.