Ultrasonic Reflection Coefficient Research Articles

An accurate measurement method for center oil film thickness in high-speed roller bearing using ultrasound

A multicycle focal spot mapping method is proposed to design the specific pulse emission frequency and the recorded pulse number. A great number of successive ultrasonic pulses with a specific emission frequency are utilized to examine the lubricant film in the roller bearing so that at least one ultrasonic pulse will interrogate the center of the contact region. Subsequently, the center oil film thickness is calculated by the selected minimum ultrasonic reflection coefficient amplitude. A statistical test analysis and an experimental analysis are performed to validate the proposed method. The results show that the proposed method can be used to accurately measure the center oil film thickness in high-speed roller bearings, which overcomes the speed limitation of the existing method.

Two-dimensional imaging of elastic properties of rock core samples from measurements of angle-dependent ultrasonic reflection coefficients

Laboratory and field measurements often fail to identify small-scale variations in rock elastic properties. Due to limited spatial resolution, conventional laboratory methods cannot properly describe rock formations exhibiting a high degree of heterogeneity, thereby masking differences between stiff and compliant layers. Continuous sample measurements can mitigate this problem but are not widely used by the industry. We build upon our previous work and apply laboratory angle-dependent ultrasonic reflection coefficient (ADURC) measurements to achieve detailed two-dimensional descriptions of the elastic properties of complex rock samples. This method successfully yields high-resolution information on P- and S-wave velocities, as well as bulk density, across the surface of rock samples. Elastic properties are estimated using a nonlinear inversion algorithm that matches laboratory measurements with numerical simulations. ADURC data acquired at various sample locations enable detailed rock descriptions, where the effective measurement area is determined by the size of the receiver, measurement frequency, and incidence angle. Consequently, the sampling area is smaller compared with triaxial loading and acoustic transmission tests, for which the resolution is controlled by sample size. Measurements conducted on samples exhibiting different levels of spatial complexity validate the capability of the ADURC method to identify small-scale heterogeneities. For the reported experiments, variations in angle-dependent reflectivity give rise to corresponding variations in the estimated P- and S-wave velocities and density, which can exceed 60%. These small-scale variations across heterogeneous rock samples often are overlooked by conventional laboratory methods.

Measurement of coating–substrate interface stiffness using a constructed ultrasonic echo phase derivative spectrum

Measurement of coating–substrate interface stiffness can indirectly characterize interface bonding quality. This paper proposes a noval quantitative inversion coating–substrate interface stiffness method based on the multi-resonance frequencies of a constructed ultrasonic echo phase derivative spectrum (UEPDS). The theoretical relationship between UEPDS resonance frequencies and interface stiffness is derived. The detection frequency and high-sensitivity interface stiffness range are optimized based on the sensitivity analyzed. Numerical simulation and experiment are implemented on a 0.48 mm aluminum layer/carbon steel substrate specimen to prove the validity of the proposed ultrasonic method. The simulation results show that the maximal relative error between the inversion and the preset interface stiffnesses is reduced from 23% to 8% compared with the traditional ultrasonic reflection coefficient amplitude spectrum-based (URCAS-based) method. The experiment results indicate that the UEPDS-based inversion interface stiffnesses have the same trend as the nominal contact pressures between the coating–substrate interface.

Calibration of Oil Film Thickness Acoustic Reflection Coefficient of Bearing under Multiple Temperature Conditions

Rolling mill bearings are prone to wear, erosion, and other damage characteristics due to prolonged exposure to rolling forces. Therefore, regular inspection of rolling mill bearings is necessary. Ultrasonic technology, due to its non-destructive nature, allows for measuring the oil film thickness distribution within the bearing during disassembly. However, during the process of using ultrasonic reflection coefficients to determine the oil film thickness and distribution state of rolling mill bearings, changes in bearing temperature due to prolonged operation can occur. Ultrasonic waves are susceptible to temperature variations, and different temperatures of the measured structure can lead to changes in measurement results, ultimately distorting the results. This paper proposes using density and sound speed compensation methods to address this issue. It simulates and analyzes the oil film reflection coefficients at different temperatures, ultimately confirming the feasibility and effectiveness of this approach. The paper establishes a functional relationship between bearing pressure and reflection coefficients, oil film thickness, and reflection coefficients. This allows for the compensation of reflection coefficients under any pressure conditions, enhancing the accuracy of oil film thickness detection. The proposed method provides technical support for the maintenance of plate rolling processes in the steel industry.

A PZT active sensing method for monitoring prestressing force based on the ultrasonic reflection coefficient

Prestress monitoring is key to ensuring the safety and longevity of post-tensioned prestressed structures. A new method of prestress monitoring, based on piezoceramic transducers, is proposed. Compared to traditional ultrasonic detection, we utilize piezoelectric (PZT) active sensing monitoring, eliminating the need for a specialized ultrasonic probe. First, a relationship model between the signal received energy and loading force is established based on the principle of ultrasonic reflection coefficient at the contact interface. On this basis, we overcome the low signal-to-noise ratio issue associated with the traditional method by employing the time reversal (TR) method. Next, the model parameters were fitted using experimental data. The values of the fitting evaluation metrics, SSE and RMSE, tend to be close to 0, while the R-squared value tends to be close to 1. This indicates the reliability of the model. Finally, the prestressing force validation tests are conducted through unloading tests. The average relative error between the measured and actual values across different paths ranges from 6.85% at the minimum to 15.61% at the maximum. Since the method is related to the proximity of the interface contact, it can be applied in other areas of civil engineering, such as assessing the adhesive strength of composite structures, crack development, and detecting axial stress.

Ultrasonic measurement for lubricant film thickness with consideration to the effect of the solid materials

An improved ultrasonic reflection coefficient phase model is proposed for lubricant film thickness measurement with consideration to the influence of the solid layers. In the model, the theoretical relation of the lubricant film thickness to ultrasonic reflection coefficient phase is established, which is used for effectively determining the lubricant film thickness. Furthermore, the proposed model is verified by both the finite element analysis and experiments. The results show that the lubricant film thickness ranges between 2 μm and 45 μm can be measured by using the proposed model, which covers both the spring model region and the blind region. In addition, at a small film thickness, the reflection coefficient phase is significantly affected by the acoustic impedances in both solid layers. However, the reflection coefficient phase is dominantly affected by the solid layer in the neighbourhood of the incidence source at a large film thickness.

Ultrasonic in-situ measurement method and error analysis of wear of PEEK water-lubricated bearing materials

Water-lubricated polymer bearing is the key component to guarantee the function of ship propulsion systems, nuclear main pumps, hydraulic turbines and other important equipment. Abnormal wear of the water-lubricated polymer thrust bearing is a common failure under harsh working conditions such as low speed, heavy load, and sediment. Accurate acquisition of bearing wear is of great value for revealing the bearing wear mechanism and evaluating the bearing service life. Therefore, this paper proposes an in-situ measurement method of bearing wear based on ultrasound and parameter inversion. The objective function is defined as the correlation coefficient of the ultrasonic reflection coefficient amplitude spectrum. Different parameters, such as thickness, acoustic velocity, density and attenuation factor, are inverted by the particle swarm algorithm. Simulations are performed to analyze the influence of single-parameter to multi-parameter inversions on the objective function and the inversion of thickness. Taking the PEEK material as the subject, the experiment shows that the parameter inversion of thickness, density and attenuation factor has the highest accuracy, with errors within 0.15%, 2% and 95%, and the maximum absolute error of wear is 20 μm. If the amplitude of the reflected signal is small, the intensity of the transmission signal will affect the identification result of thickness.

A wear monitoring method and influencing factors of water-lubricated polymer bearings based on improved ultrasonic reflection coefficient amplitude spectrum and ultrasonic reconfiguration calculation

The water-lubricated thrust bearings of the marine Rim-Driven Thruster (RDT) are usually composed of polymer composites, which are prone to serious wear under harsh working conditions. Ultrasonic is an excellent non-destructive monitoring technology, but polymer materials are characterized by viscoelasticity, heterogeneity, and large acoustic attenuation, making it challenging to extract ultrasonic echo signals. Therefore, this paper proposes a wear monitoring method based on an improved ultrasonic reflection coefficient amplitude spectrum, introducing an ultrasonic transfer function to mathematically resolve the attenuation coefficients in the propagation model, and using a differential evolutionary algorithm to invert the thickness, sound velocity, density, and attenuation coefficients of polymer bearings simultaneously. The effects of different influencing factors on the ultrasonic signal and identification results are explored, including probe contact pressure, surface roughness and surface inclination; In order to remove the influence of water film overlap on the identification of polymer bearing thickness, a water film separation method based on time-frequency domain ultrasonic reconfiguration is proposed to construct the ultrasonic theoretical time domain waveform of the bearing. An ultrasonic wear measurement system is built to record the ultrasonic echoes of PEEK test blocks with different pressures to the probe, surface roughness, and tilt angles. The experiment is carried out on the water film calibration test rig, using a high-precision spiral micrometer to simulate the mixing of water films of different thicknesses with polymer test block and collecting ultrasonic signals. The results show that the method has a thickness identification error of approximately 0.5% for PEEK specimens with different probe contact pressure, roughness, and tilt angle, and the reconfiguration thickness identification error is less than 1% for the full range of water film overlap.

Influence of viscoelasticity on ultrasonic propagation in poly(ethylene oxide) aqueous solution

Generally, ultrasonic propagation in ultrasonic non-destructive testing is regarded as a linear process, during which the interaction between ultrasonic and measured material is rarely considered. In this study, the mechanisms of ultrasonic propagation in viscoelastic poly(ethylene oxide) aqueous solution and the interaction between ultrasound and fluid are investigated. A theoretical model of ultrasonic propagation in a viscoelastic fluid is established, in which the body force from ultrasonic waves is added to the fluid momentum equation, and the viscoelasticity of the fluid is described by the Oldroyd-B model. The simulation results for the ultrasonic reflection coefficient at the solid–liquid boundary and the attenuation coefficient based on the multi-physics coupling method are experimentally verified. The results of this study show that the ultrasonic absorption coefficient at low frequencies from 2.25 to 7.5 MHz exhibits frequency dependence through ultrasonic relaxation spectroscopy. The simulation results of the velocity of disturbed flow during ultrasonic propagation show that the viscosity of the solution has a greater impact on the disturbance than the relaxation time, and the phase angle difference between the stress and strain also shows that the viscosity is the main factor affecting the ultrasonic propagation.

Wear monitoring method of water-lubricated polymer thrust bearing based on ultrasonic reflection coefficient amplitude spectrum

The water-lubricated thrust bearings of the marine rim-driven thruster (RDT) are usually composed of polymer composites, which are prone to serious wear under harsh working conditions. Ultrasonic is an excellent non-destructive monitoring technology, but polymer materials are characterized by viscoelasticity, heterogeneity, and large acoustic attenuation, making it challenging to extract ultrasonic echo signals. Therefore, this paper proposes a wear monitoring method based on the amplitude spectrum of the ultrasonic reflection coefficient. The effects of bearing parameters, objective function, and algorithm parameters on the identification results are simulated and analyzed. Taking the correlation coefficient and root mean square error as the matching parameters, the thickness, sound velocity, density, and attenuation factor of the bearing are inversed simultaneously by utilizing the differential evolution algorithm (DEA), and the wear measurement system is constructed. In order to verify the identification accuracy of this method, an accelerated wear test under heavy load was executed on a multi-functional vertical water lubrication test rig with poly-ether-ether-ketone (PEEK) fixed pad and stainless-steel thrust collar as the object. The thickness of pad was measured using the high-precision spiral micrometer and ultrasonic testing system, respectively. Ultimately, the results demonstrate that the thickness identification error of this method is approximately 1%, and in-situ monitoring ability will be realized in the future, which is of great significance to the life prediction of bearings.

Identification interface stiffness of coating/substrate structure based on ultrasonic pressure reflection coefficient amplitude spectrum

Due to the variation of interface stiffness, interface morphology, and testing frequency, coating/substrate interface stiffness identified through ultrasonic methods are usually non-unique and inaccuracy. This paper, a method for quantitative inversion interface stiffness of coating/substrate structure is proposed based on a constructed ultrasonic pressure reflection coefficient amplitude spectrum (URCAS). The URCAS of coupling medium/non-metallic coating/metal substrate structure is derived based on interfacial spring model. The high-sensitivity frequency and interface stiffness ranges are determined by analyzing the sensitivity of URCAS to testing frequency and interface stiffness in advance. The accurate inversion of interface stiffness is achieved through a least square objective function under the high-sensitivity frequency and interface stiffness ranges. The feasibility of proposed ultrasonic method was verified by numerical simulations and ultrasonic experiments implemented on epoxy resin coating/aluminum substrate specimens. Simulation results show that the inverted interface stiffnesses are in good agreement with the preset values, and the maximum relative error is less than 6% in the high-sensitivity interface stiffness range, while the inversion accuracy of interface stiffness significantly reduces, and the relative error exceeds 21% in the low-sensitivity range. Experimental results show that the tested tensile strength and interface stiffness have similar trends. The proposed ultrasonic method can quantitatively identify the interface stiffness and effectively characterize the bonding quality of coating/substrate interface.

Study of Acoustic Attenuation Trends in Permendur 49 Magnetostrictive Material

The mechanical properties of ferromagnetic materials change when the magnetization level of these materials changes. This phenomenon occurs due to magnetostriction. The change in direction of the magnetic domains is the reason for magnetostriction. In this paper, we hypothesize that the amount of acoustic attenuation in ferromagnetic materials depends on their magnetization level. To prove this hypothesis, a numerical approach is employed and the results compared to previous results in the literature. Permendur, an iron-cobalt alloy that exhibits a large magnetostriction effect, is used for the simulation. The results of the numerical study show that ultrasonic reflection and transmission coefficients in Permendur change in response to changes in the external magnetic field. A comparison between these numerical results and experimental results in the literature allows us to determine the changes in acoustic attenuation due to the magnetic field. The results show that there is an increasing trend at first, and then a decreasing trend, between acoustic absorption attenuation and increasing external magnetic field. This approach would be useful in ultrasonic testing of ferromagnetic materials when the reflected echoes are not detectable due to attenuation.The mechanical properties of ferromagnetic materials change when the magnetization level of these materials changes. This phenomenon occurs due to magnetostriction. The change in direction of the magnetic domains is the reason for magnetostriction. In this paper, we hypothesize that the amount of acoustic attenuation in ferromagnetic materials depends on their magnetization level. To prove this hypothesis, a numerical approach is employed and the results compared to previous results in the literature. Permendur, an iron-cobalt alloy that exhibits a large magnetostriction effect, is used for the simulation. The results of the numerical study show that ultrasonic reflection and transmission coefficients in Permendur change in response to changes in the external magnetic field. A comparison between these numerical results and experimental results in the literature allows us to determine the changes in acoustic attenuation due to the magnetic field. The results show that there is an increasing trend at first, and then a decreasing trend, between acoustic absorption attenuation and increasing external magnetic field. This approach would be useful in ultrasonic testing of ferromagnetic materials when the reflected echoes are not detectable due to attenuation.

Study of Acoustic Attenuation Trends in Permendur 49 Magnetostrictive Material

The mechanical properties of ferromagnetic materials change when the magnetization level of these materials changes. This phenomenon occurs due to magnetostriction. The change in direction of the magnetic domains is the reason for magnetostriction. In this paper, we hypothesize that the amount of acoustic attenuation in ferromagnetic materials depends on their magnetization level. To prove this hypothesis, a numerical approach is employed and the results compared to previous results in the literature. Permendur, an iron-cobalt alloy that exhibits a large magnetostriction effect, is used for the simulation. The results of the numerical study show that ultrasonic reflection and transmission coefficients in Permendur change in response to changes in the external magnetic field. A comparison between these numerical results and experimental results in the literature allows us to determine the changes in acoustic attenuation due to the magnetic field. The results show that there is an increasing trend at first, and then a decreasing trend, between acoustic absorption attenuation and increasing external magnetic field. This approach would be useful in ultrasonic testing of ferromagnetic materials when the reflected echoes are not detectable due to attenuation.

Investigation of ultrasonic soft tissue-bone reflection coefficients correlating with curve severity in children with adolescent idiopathic scoliosis.

Adolescent idiopathic scoliosis (AIS) is a three-dimensional curvature of spine. Children with AIS and low bone quality have higher chance to get curve progression leading to bigger spinal curvature. In addition, bone quality affects acoustic impedance of bone, thus influencing the reflection coefficient of ultrasound signal from the soft tissue–bone interface. This study aimed to estimate the bone quality of AIS patients based on the reflection coefficients to determine the correlation of the bone quality with curve severity. A simple bone model was used to develop an equation to calculate the reflection coefficient value. Experiments were conducted on five different phantoms. Acrylic was used to design a vertebral shape to study the effect of surface roughness and inclination, including: smooth flat surface (SFS), smooth curved surface (SCS), rough curved surface (RCS), and the rough curved inclined surface (RCIS). A clinical study with 37 AIS patients were recruited. The estimated reflection coefficient values of plate phantoms agreed well with the predicted values and the maximum error was 6.7%. The reflection coefficients measured from the acrylic-water interface for the SFS, SCS, RCS, RCIS (3° and 5°) were 0.37, 0.33, 0.28, (0.23 and 0.12), respectively. The surface roughness and inclination increased the reflection loss. From the clinical data, the average reflection coefficients for children with AIS were 0.11 and 0.07 for the mild curve group and the moderate curve group, respectively. A moderate linear correlation was found between the reflection coefficients and curve severity ( = 0.3). Patients with lower bone quality have observed to have larger spinal curvature.

Simultaneous measurement of thickness and sound velocity of porous coatings based on the ultrasonic complex reflection coefficient

The ultrasonic pulse-echo method is widely adopted in measuring coating thickness via parameter inversion of the reflection coefficient. However, the ultrasonic application to thermal barrier coatings (TBCs, as typically applied on aero-engine blades) remains a challenge, as the porous structure significantly attenuates sonic propagation, which is also difficult to characterize. In this article, a method that effectively addresses this issue without the need of the wave attenuation coefficient is presented. Specifically, the complex ultrasonic reflection coefficient can help calculate the coating-induced phase shift, which is found to linearly vary against the ultrasonic wave frequency. The slope of this linear function, depending on the structural porosity, enables simultaneous measurements of both the sound velocity and the thickness of the coating. Moreover, the effectiveness of the proposed method is verified by acoustic finite element simulations and experimental measurements of 8YSZ thermal barrier coatings.

Simultaneous measurement of layer thicknesses in thin layered materials using the phase of ultrasonic reflection coefficient spectrum

The wide application of layered materials proposes more requests for their mechanical performance. The measurement of layer thicknesses is an important part of performance evaluation for the layered materials. Ultrasonic testing is an effective method for thickness measurement. However, in thin layered materials, the layer thicknesses are immeasurable due to the overlap of ultrasonic echoes from interlayer interfaces. This work presented an ultrasonic method for simultaneous measurement of layer thicknesses in thin layered materials using the phase of ultrasonic reflection coefficient spectrum (PRCS) at normal incidence, and the other method using the magnitude of ultrasonic reflection coefficient spectrum (MRCS) was also investigated for comparison. The inversion algorithm based on the particle swarm optimization (PSO) was used to avoid convergence to local minima. Both the sensitivities to the thickness parameters and effects of frequency bandwidth of the transducer were studied for PRCS and MRCS. The results indicate that PRCS is sensitive to the layer thicknesses and larger frequency bandwidth is favorable for convergence zones to be produced. Compared with MRCS, the narrower convergence zones can be obtained using PRCS. The experimental measurement results of the thin Al-Ti bi-layered material confirm that the measurement of layer thicknesses using PRCS is more accurate than MRCS. The relative errors of the Al layer and the Ti layer between the PSO estimated values and the real values are −3.77% and +1.91% using PRCS, respectively.

Ultrasonic detection of white etching defect based on convolution neural network

<sec>Unlike classical defects formed by rolling contact fatigue, white etching defect (WED) including white etching area and white etching crack will cause surface to spall in the early stage and the service life to shorten seriously. Located in the subsurface of bearings, the tiny size WED is difficult to detect by conventional ultrasonic methods. The root cause of WED generation remains unclear. It is time consuming and expensive to prepare samples during the evolution of such defects. For characterizing the WED at early stage, five evolving states concerning the existing microscopic information are established in this paper. The immersion ultrasonic inspection process is simulated based on <i>k</i>-space pseudo spectrum method.</sec><sec>For the later evolutionary stage with crack, the bearing can be simplified into a homogeneous three-layer model by ignoring the internal grain structure. The crack depth is obtained by using the ultrasonic reflection coefficient amplitude spectrum (URCAS), with an error of 1.5%. For other states without crack, the spectrum characteristic is no longer evident with slight acoustic impedance difference between layers. The polycrystalline structure on a microscale is thus realized based on Voronoi diagram, from which the grain induced backscattering can be used to amplify the microstructure variations at different stages. The backscattering signal is influenced by the grain size and detection frequency from the simulation. Since a direct comparison of backscattering information among evolutionary stages is difficult, the five different evolutionary stages of WED are recognized with the help of deep learning. The received waveform is transformed into a time-frequency map by short-time Fourier transform. Based on RESNET network structure, the results show that the train accuracy and validation accuracy reach 92% and 97% respectively. This study provides a sound way to characterize WED, which is conducive to early failure prediction and residual life evaluation.</sec>

Inverse identification of geometric and acoustic parameters of inhomogeneous coatings through URCAS-based least-squares coupled cross-correlation algorithm

Aiming to determine the geometric and acoustic parameters of inhomogeneous multi-layer coatings, an ultrasonic pressure reflection coefficient amplitude spectrum (URCAS) is derived using a material-oriented regularization scheme, when wave propagates perpendicularly to the coating surface. Based on the derived theoretical URCAS, a new objective function combining least-squares and cross-correlation algorithm is developed to simultaneously identify the thickness, sound velocity, density, attenuation coefficient amplitude, and attenuation coefficient power-law of the multi-layer coating. Genetic algorithm with the constraint of total multi-layer coating thickness being known is presented to optimize the nonlinear objective function for obtaining global optimal solution. Ultrasonic experiments were implemented on a dual-layer coating specimen with coating1/coating2/substrate structure using a flat immersion transducer with a central frequency of 15 MHz. The inversed thicknesses, sound velocities, and densities of the dual-layer coating were in good agreement with those measured through other methods, with less than 8.1% errors. The inversed attenuation coefficients of the coating 1 and coating 2 were α(f) = 1.02e-2 × f1.93 and α(f) = 4.62e-3 × f1.97, respectively. The upper bounds of the relative errors +r of inverted parameters were all less than 0.061. The proposed ultrasonic inversion method could be used to quantitatively characterize the surface integrity of inhomogeneous multi-layer coatings.

Porosity Characterization of Thermal Barrier Coatings by Ultrasound with Genetic Algorithm Backpropagation Neural Network

Porosity is considered as one of the most important indicators for the characterization of the comprehensive performance of thermal barrier coatings (TBCs). In this study, the ultrasonic technique and the artificial neural network optimized with the genetic algorithm (GA_BPNN) are combined to develop an intelligent method for automatic detection and accurate prediction of TBCs’s porosity. A series of physical models of plasma-sprayed ZrO2 coating are established with a thickness of 288 μm and porosity varying from 5.71% to 26.59%, and the ultrasonic reflection coefficient amplitude spectrum (URCAS) is constructed based on the time-domain numerical simulation signal. The characteristic features f 1 , f 2 , A max , Δ A of the URCAS, which are highly dependent on porosity, are extracted as input data to train the GA_BPNN model for predicting the unknown porosity. The average error of the prediction results is 1.45%, which suggests that the proposed method can achieve accurate detection and quantitative characterization of the porosity of TBCs with complex pore morphology.

Exact analytical solution to ultrasonic interfacial reflection enabling optimal oil film thickness measurement

The ultrasonic reflection from a lubricated interface has been widely analyzed to measure fluid film thickness, with different algorithms being applied to overcome measurement accuracy and resolution issues. Existing algorithms use either the amplitude or the phase angle of the ultrasonic interfacial reflection. In this paper, a new algorithm (named the “exact model – complex”) that simultaneously utilizes both the amplitude and the phase of the complex ultrasonic reflection coefficient is proposed and mathematically derived. General procedures for theoretical analysis in terms of measurement accuracy and uncertainty are proposed and applied to the new algorithm, the beneficial features of which (as compared to other existing algorithms) can be summarized as: 1) a direct calculation, instead of an iterative approximation, 2) guaranteed maximum measurement accuracy, and 3) acceptable measurement uncertainty. None of the existing methods have showed this combination of benefits. Moreover, two groups of raw data from previous experimental studies are utilized to further validate the practical feasibility of the new algorithm. Overall, the proposed “exact model – complex” algorithm fully exploits the potential of ultrasonic reflection for oil film thickness measurement, with an accurate and a convenient calculation suited to practical implementation.