Nonlinear Ultrasonic Testing Research Articles

Profiling the thermal damage gradient in concrete using linear and non-linear ultrasonics

Processes such as carbonation and thermal damage result in a depth-dependent variation in concrete mechanical properties, which are typically characterized by invasive sampling and destructive testing. In this study, several ultrasonic testing methods are employed to nondestructively measure gradients in elastic properties within concrete and mortar slabs, induced by varying amount of exposure to elevated temperatures. The slabs are subjected to two distinct heat exposures, carefully chosen to create different gradients within the first few centimeters below the surface. The first exposure scenario following the ISO fire standard led to superficial damage. Deeper damage was achieved with radiant panels. We use linear and non-linear ultrasonic testing, with the aim of characterizing the resulting property gradients including refracted P-waves, analysis of surface wave dispersion and higher harmonic generation. Additionally, we employ NRUS (nonlinear resonant ultrasound spectroscopy) to test slices extracted from the different depths within the slabs. The ultrasonic test results are benchmarked and interpreted in relation to a suite of other multiphysical measurements (resistivity, capacity, temperature). This work represents a first crucial step towards the development of a new method for measuring gradients of nonlinear elastic properties within concrete through nondestructive ultrasonic testing.

Nonlinear ultrasonic test applied to discern factors controlling cracking of cement mortar affected by reinforcement corrosion

Intermodulation ultrasonic testing technique was used to detect corrosion- induced cracking in prismatic mortar samples. Three sets of five specimens were prepared and subjected to accelerated corrosion conditions. The different times of exposure allowed to attain unlike damage conditions in every sample of each set. The onset of damage was monitored through the evolution of the accumulated Intensity Modulation Ratio (R) and crack width measurements. The accumulated values of the Intensity Modulation Ratio were used to study the effect of different testing factors (cover depth, corrosion rate or amplitude of the input pump signal) and increased monotonically clearly discriminating the different damage levels. These observations point to the possibility of stablishing damage thresholds to detect cracking using nonlinear ultrasonic (NLU) techniques.

Study on ultrasonic lamb wave testing technology of honeycomb sandwich structures

Abstract Honeycomb sandwich composite panels have complex structures, large sizes, many types of defects, and significant sound attenuation, which lead to low efficiency and poor sensitivity of ultrasonic non-destructive testing. In the study, a non-linear ultrasonic lamb wave testing technique for honeycomb sandwich composite panels is proposed. Firstly, the anisotropic propagation characteristics and modal structure of lamb waves in honeycomb sandwich composite panels are analyzed, and the lamb wave modes with non-linear ultrasonic accumulation are excited. Secondly, the data extraction method and imaging algorithm of non-linear ultrasonic lamb wave imaging testing are proposed. Finally, an enhanced imaging algorithm is proposed to improve image quality based on the sliding window algorithm. Based on the comparative analysis of air-coupled ultrasonic testing images and metallographic tests, it can be seen that non-linear ultrasonic lamb wave testing signals can be used to characterize the damage distribution characteristics of honeycomb sandwich composite panels, display debonding and weak debonding defects, and have the advantages of being able to perform on the same side testing and high efficiency, which can be used for non-destructive testing of honeycomb sandwich composite panels.

Creep strain prediction in power plant material via ANN modelling of nonlinear ultrasonic test results

ABSTRACT Reliable and accurate prediction of the creep life of power plant components is crucial for both economic and safety reasons. Existing prediction models, based on creep test data, can be complex and time-consuming. Nonlinear ultrasonic (NLU) is a widely-accepted non-destructive testing (NDT) technique for evaluating damage progression in crept specimens. The information from NLU measurements alone is insufficient to forecast the life of any component. In real-time applications, intelligent NDT protocols are needed to enable fast and accurate life prediction of such components. A methodology for creep life prediction using artificial neural networks (ANN) has been introduced based on NLU test results of crept P92 steel specimens. The technique involved creep tests of P92 specimens exposed to a temperature of 625⁰C with applied stress ranging from 120MPa to 160MPa, NLU measurements at each step load, and prediction of creep life of the material with a ANN trained with creep strain and NLU test data. The technique involves prediction from previously generated historical data, thus saving both cost and time of conducting continuous experiments. This approach for ANN modeling of NLU data can be considered a reliable, time-saving, and effective technique for assessing creep damage progression in power plant components.

Nonlinear Ultrasonic C-Scan Imaging for Contact-Type Defects in Diffusion-Bonded Joints-A Case Study.

Diffusion bonding technology is widely used in the connection of precision components, yet accurately and reliably detecting contact-type defects on the bond interface still remains a significant problem. Nonlinear ultrasonic methods have been proven to be sensitive to contact-type defects; however, the use of continuous wave or tone burst wave excitation limits its wider application. In this paper, dual-probe nonlinear ultrasonic testing with pulse wave excitation is proposed to detect contact-type defects in diffusion-bonded joints. A titanium alloy diffusion-bonded specimen with artificial defects was fabricated, and the corresponding detection device was designed based on the existing ultrasonic C-scan testing system. A C-scan imaging program based on nonlinear parameters was developed by extracting the fundamental and second harmonic waves of the reflection echo on the bond interface. The results demonstrated that the proposed detection scheme can obtain the nonlinear parameters of diffusion-bonded interfaces, and the nonlinear ultrasonic C-scan image of the bond interface is also obtained. The nonlinear parameter in the contact-type defects areas calculated from the bond interface echo is about 10 times (20 dB) higher than that in macro defects areas, whose gap is about 10 μm. The results indicate that the nonlinear ultrasonic methods seem to be more sensitive to contact-type defects and have a great potential to complement the insufficient detection capability of linear ultrasound for diffusion-bonded joints.

Research on nonlinear ultrasonic method for evaluating the mechanical properties of 3D printing aluminum alloy

Micro defects, such as pore and inclusions, inevitably appear in the forming process of three-dimensional (3D) printed materials, which would affect the mechanical properties of materials. Therefore, a nondestructive testing method is urgently needed to evaluate the effect of these micro defects on the mechanical properties of materials. In the present work, by using a nonlinear ultrasonic testing technology, mechanical test and characterization of material microstructure, the relationship between the relative acoustic nonlinearity parameter (RANP), tensile strength and material defect ratio of 3D printed aluminum alloy specimens under different scanning powers is investigated. The analysis results show that the greater the material defect ratio is, the smaller the tensile strength is and the greater the RANP is, and the RANP could be used to evaluate the strength of materials. Moreover, fatigue damage induced by high cycle fatigue loading test in the first stage of early performance degradation, the results of nonlinear ultrasonic testing show that the RANP presents an increasing trend as the fatigue load increases. By observing changes in material microstructure, it is found that the increasing acoustic nonlinearity parameter is due to the directional coarsening degree of the precipitated phase increasing, which shows that RANP is very sensitive to the change of material microstructure. The above results show that, the nonlinear ultrasonic testing technology can quantitatively evaluate and predict the mechanical performance and early performance degradation of 3D printing aluminum alloy.

A nonlinear ultrasonic nondestructive testing method for microdefects of medical magnesium alloy coatings

A nonlinear ultrasonic nondestructive testing method for microdefects of medical magnesium alloy coatings

Nitriding layer depth detection based on mixing frequency nonlinear ultrasonic parameters

Nitriding treatment can improve the surface properties of workpieces, thus increasing the service life of the workpiece. The depth of nitriding layer is not only one of the important indexes for evaluating the nitriding effect, but also an important factor affecting the end-use performance of the workpiece. While the existing hardness and metallographic methods cannot meet the needs for non-destructive testing of nitriding layer depth in shaft parts. Therefore, a method using non-linear ultrasonic testing technology is proposed for non-destructive evaluation of nitriding layer depth. In this study, 1045 steel shaft specimens with different nitriding layer depths were prepared by a liquid salt bath nitriding method. The total depth of the nitriding layer was measured using a microhardness tester, and metallographic microscopy was applied to observe microstructure changes before and after nitriding treatment. With the proposed non-destructive method, the longitudinal critically refracted (LCR) wave mixing detection model was established and the ultrasonic nonlinear coefficients were used for characterizing the nitrided layer depths. Experimental results show that the LCR wave sum frequency (LCRWSF) detection model better characterizes the nitriding layer depth of 1045 steel and has higher sensitivity. As a result, the LCRWSF model is more suitable to efficiently estimate the nitrided layer depth.

Multi-scale ultrasonic imaging of sub-surface concrete defects

This paper introduces a new method for creating the ultrasonic image of concrete that utilizes both linear and nonlinear wave properties in a single measurement. Linear ultrasonic imaging relies on wave velocity. The resolution of linear ultrasonics for various inclusion sizes and inclusion-to-base material ratios is numerically and experimentally studied. The nonlinear ultrasonic testing (NLUT) image is based on the acoustic nonlinearity coefficient, calculated using inputs of the first and second harmonic amplitudes, wave number, and the distance between the transmitter and receiver. The ultrasonic waveform is decomposed into its harmonics using wavelet transform. Their wave velocities, wave numbers, and amplitudes are extracted to calculate the linear wave velocity and the acoustic nonlinearity coefficient. Four calibration samples with different inclusions are tested to evaluate the effectiveness of combining two imaging methods: pure concrete, concrete with small foam inserts simulating air inclusions, and two concrete samples with larger foam inclusions. The angle dependence of acoustic nonlinearity coefficient is shown. The results show that constructing both linear and nonlinear ultrasonic imaging is necessary when the defect’s properties are unknown.

Second Harmonic Modulation for Ultrasonic Signals Based on the Design of the Phononic Crystal Filter.

Nonlinear ultrasonic non-destructive testing (NDT) is a widely used method for detecting micro-damages in various materials and structures due to its high sensitivity and directional capability. However, the extraction and modulation of extremely weak nonlinear ultrasonic signals is quite a challenge in practical applications. Therefore, this paper focuses on the second harmonic modulation signal method in nonlinear ultrasonic NDT and proposes the design of the phononic crystal filter (PC filter) to achieve this filtering function. Through finite element simulations, it is demonstrated that the filtering frequency of the filter is influenced by the structural configuration, material wave speed, and geometric characteristics. Then, the design method for cubic PC filters is established. Furthermore, a time-domain finite element method is introduced to verify the filtering ability of the filter and further validate the rationality of this design approach.

Study on Characterizing for Corrosion Degrees of 1045 Steel with Nonlinear Ultrasonic Coefficients

Corrosion is a widespread issue that leads to the degradation of material properties. Their own limitations are present in the existing methods for detecting the degree of corrosion. The aim of this study is to characterize the corrosion degree using nonlinear ultrasonic technology. Specimens of 1045 steel with different corrosion degrees were produced in different experimental conditions. The degree of corrosion was determined using the mass loss method and the microstructures of specimens with different corrosion degrees, and no corrosion was observed with the metallographic microscope. A nonlinear ultrasonic testing model based on the critically refracted longitudinal (LCR) wave was designed. The results show that the nonlinear ultrasonic coefficients of the 1045 steel increase monotonically with increasing degrees of corrosion under the LCR wave testing model. The increased values of the nonlinear coefficient are linked to the transformation of the material structure caused by corrosion. It may be possible that the degree of corrosion of the materials will be characterized and detected nondestructively using the nonlinear ultrasonic coefficients of the LCR wave.

Nonlinear ultrasonic concrete crack identification with deep learning based on time-frequency image

ABSTRACT By combining time-frequency images and deep learning models, the nonlinear ultrasound signals can be classified, detected, and predicted, using the nonlinear coefficient as a fundamental label for training deep learning models. This integrated approach enables quantitative identification and real-time monitoring of concrete damage, promoting the widespread adoption of nonlinear ultrasonic techniques in engineering applications. As a basis, the relationship between damage variations and nonlinear coefficients is discussed by performing nonlinear ultrasonic damage testing on concrete specimens with different crack lengths and angles. The testing signals are converted into time-frequency images using the short-time Fourier transform and the continuous wavelet transform, and both types of images are combined for data augmentation and input into the deep learning model for training, with nonlinear coefficients serving as labels for the time-frequency images. The MobileNetV2, VGG16, and ResNet18 deep learning models are trained separately on time-frequency image datasets for the length specimens, the angle specimens, and the length-angle specimens, and the performance of the different models is evaluated and compared. The results show that all three models have accuracy rates above 94%, indicating good identification performance. Finally, with the example, the nonlinear coefficients of the testing signals are compared with the labels of the nonlinear coefficients in the time-frequency images identified by the deep learning model, which confirms the high accuracy of damage identification by the deep learning model.

Application of Odd Harmonic Resonances of a Single Crystal to Generation and Reception of Superharmonic Waves for Sensitive Monitoring of Heat-Treated Materials.

In nonlinear ultrasonic testing, the quadratic and more recently cubic nonlinearity parameters are frequently measured as a quantitative indicator of damaged material state. Application of higher-order harmonics can improve the sensitivity of detection and monitoring for damages and microstructures due to their higher values of nonlinearity parameters. The excitation and reception of higher-order harmonics, so-called superharmonics, which use the third to fifth harmonics arising from nonlinear wave propagation, is not sufficiently investigated and applied. The purpose of this communication is to develop a highly sensitive superharmonic nondestructive technique that efficiently generates and receives third- and fifth-order harmonics using the odd harmonic resonances of a single piezoelectric crystal. The method focuses on the measurement of fifth harmonic generation and reception, and the calculation of the relative quintic nonlinearity parameter (δ'). The method also addresses the issue of source nonlinearity that may be contained in the measured fifth harmonic amplitude. The measurement results of δ' for a series of precipitation heat-treated samples clearly show a much better sensitivity than the results of the cubic nonlinearity parameter (γ'). The proposed method enables a highly sensitive and true pulse-echo mode nonlinear ultrasound testing.

On the utility of linear and nonlinear ultrasound for evaluating microstructure-property relationships in laser powder bed fusion 316 L stainless steel

Given the complexity and potential for variability in components fabricated with metal additive manufacturing, the need for efficient, reliable, and nondestructive quality assurance is imperative for advancing its utilization in industry. Here, linear and nonlinear ultrasonic testing is used to nondestructively link microscale features and mechanical properties of 21 distinctly-printed AISI 316 L stainless steel samples manufactured by laser powder bed fusion. Groups of samples were heat-treated to induce microstructural changes under as-built, 600 ℃, 900 ℃, and 1100 ℃ conditions. While a linear ultrasonic parameter, wave speed, could not completely differentiate the evolution of microstructure and mechanical properties during heat treatment, the relative acoustic nonlinearity parameter β′ measured with second harmonic generation demonstrated sensitivity to incremental changes in heat treatment temperature, ultimate tensile strength, yield strength, dislocation density, and presence of oxide inclusions. Precise resonance frequency measurements were obtained using a fully noncontact configuration, and shifts in resonance frequency with heat treatment were connected to changes in average grain area and partial recrystallization. The large number of samples and high volume of ultrasonic testing in this study provides insight into part and measurement variability, which is key in demonstrating the feasibility of ultrasonic evaluation as the nondestructive solution for additively manufactured parts qualification.

Synthetic generation of vibroacoustic modulation signals for structural health monitoring

The vibroacoustic modulation (VAM) is a nonlinear ultrasonic testing method that utilizes the modulation of a high-frequency/low-amplitude probe wave with a low-frequency/high-amplitude pumping vibration, resulting in high sensitivities to damages in the structure. However, applying the method outside of the laboratory as a structural health monitoring system for actual structures is challenging, since the amplitude and frequency of the ambient vibrations – which is ideally utilized as pumping vibration – fluctuates over time. To circumvent this, we present a synthetic generation of the VAM signal using only the probe measurements , acquired at two (or more) stress levels of the structure when a steady state is reached. We could show that only 16 values (8 measured values of only two stress levels with a sampling frequency of 1/20 of the Nyquist frequency) are required to generate the often calculated Modulation Index with a mean deviation of 0.97% to the expected dynamic measured values for glass fiber reinforced composites and 1.86% for the aluminum specimens, which is negligible compared to a typical increase of the Modulation Index of 10–30 dB in case of severe damage. Even undersampled measurements at each stress level can be used without sacrificing accuracy, which reduces the sensing requirements for the sensor nodes. Moreover, this method decouples VAM from the actual need for a constant recurrent frequency and amplitude of the natural vibration in order to reliably compare measurements throughout the lifetime. Hence, this work aims to open the possibility of ultimately applying VAM to assess the structural health of complex structures.

Non-linear ultrasonic testing of the long-period stacking ordered phase volume fraction in magnesium alloys

The content of the long-period stacking ordered (LPSO) structure strengthening phase has an important influence on the tensile strength, compressive strength, ductility and other mechanical properties of magnesium (Mg) alloys. Therefore, effective detection of the volume fraction of the LPSO phase plays an important role in understanding the properties of the alloy. Focused on the problem that the accuracy of the non-destructive testing method for the LPSO phase precipitates with micron or nanometer scale is not sufficient, this paper studies the non-linear ultrasonic testing of the Mg alloy LPSO phase volume fraction. Based on the non-linear ultrasonic testing theory, the non-linear ultrasonic simulation of the simulation models with different LPSO phase contents was carried out using finite element simulation. The relationship between the volume fraction of the LPSO phase and the non-linear coefficient of ultrasonic simulation was studied and a non-linear ultrasonic testing system was established to test the Mg alloy specimens with different LPSO phase volume fractions. The results show that the non-linear ultrasonic testing method is sensitive to changes in the LPSO phase volume fraction. Thus, this method is an effective way to detect the LPSO phase volume fraction.

An Interface Pressure Detection Method of Cable Silicone Rubber-XLPE Based on Nonlinear Ultrasound

The interface pressure between the cable attachment and the body is crucial for the stable long-term operation of the cable. To solve the issue of interface insulation characteristics’ damage caused by the pressure transducer measurement method, a non-destructive testing method of silicone rubber interface pressure using nonlinear ultrasound is presented. Initially, the study analyzes the propagation characteristics of ultrasonic waves at the interface of cross-linked polyethylene and silicone rubber. The study also establishes the relationship between the nonlinear coefficient and the interface pressure. Subsequently, a nonlinear ultrasonic test platform is constructed using the pulse reflection method to measure the interface pressure of flat silicone rubber and cross-linked polyethylene through nonlinear ultrasonic testing. Theoretical and experimental results indicate that the fundamental amplitude of the frequency domain of the interface reflection wave decreases, and the second harmonic amplitude and nonlinear coefficient both increase as pressure increases. These results demonstrate that the nonlinear ultrasound, non-destructive testing method can accurately evaluate the interfacial pressure state of the cable accessories.

A Novel Method for Early Fatigue Damage Diagnosis in 316L Stainless Steel Formed by Selective Laser Melting Technology.

Early fatigue damage is an important factor affecting the service safety of 316L stainless steel parts formed by selective laser melting (SLM) technology. Nonlinear ultrasonic testing for early fatigue damage in SLM 316L stainless steel specimens was carried out. A new method for evaluation of early fatigue damage based on nonlinear ultrasonic testing was proposed. Empirical mode decomposition (EMD) was applied to the unsteady ultrasonic testing signal, and the signal was decomposed into multiple intrinsic mode functions (IMFs) that meet certain conditions; then, the specific IMF (ESI) containing the effective fatigue damage information was extracted. Lastly, fast Fourier transform (FFT) was applied to the specific IMF signal to obtain the required information to evaluate the damage in the measured part caused by fatigue. The results of nonlinear ultrasonic testing agreed well with transmission electron microscope experimental analysis and theoretical model of acoustic nonlinearity caused by dislocations. The change in nonlinear ultrasonic testing results reflected the generation and evolution of dislocation structure during the low-cycle fatigue regime of the SLM 316L stainless steel specimen and revealed the early fatigue damage mechanism of this metal part. Compared with the classical FFT method, the EMD-ESI-FFT method is more sensitive in identifying the early damage in SLM 316L stainless parts induced by fatigue loading, which is equivalent to improving the early fatigue damage identification and diagnosis ability and can better ensure the service safety of important metal parts.

Energy Transfer Efficiency Based Nonlinear Ultrasonic Testing Technique for Debonding Defects of Aluminum Alloy Foam Sandwich Panels

In order to improve the accuracy of detection results of debonding defects of aluminum alloy thin plate, the nonlinear ultrasonic technology is used to detect the simulated defect samples, aiming at problems such as near surface blind region caused by the interaction of incident wave, reflected wave and even second harmonic wave in a short time due to the small thickness of thin plates. An integral method based on energy transfer efficiency is proposed to calculate the nonlinear ultrasonic coefficient to characterize the debonding defects of thin plates. A series of simulated debonding defects of different sizes were made using aluminum alloy plates with four thicknesses of 1 mm, 2 mm, 3 mm and 10 mm. By comparing the traditional nonlinear coefficient with the integral nonlinear coefficient proposed in this paper, it is verified that both methods can quantitatively characterize the size of debonding defects. The nonlinear ultrasonic testing technology based on energy transfer efficiency has higher testing accuracy for thin plates.

Research Progress in Nonlinear Ultrasonic Testing for Early Damage in Metal Materials

There are some limitations when conventional ultrasonic testing methods are used for testing early damage in metal parts. With the continuous development of acoustics and materials science, nonlinear ultrasonic nondestructive testing technology has been used for testing of early damage in metal materials. In order to better understand the basic theory and research progress of the nonlinear ultrasonic testing technology, the classical nonlinear ultrasonic theoretical models, including the dislocation monopole model, dislocation dipole model, precipitate-dislocation pinning model, and contact nonlinear ultrasonic theory-microcrack model, are analyzed in depth. This paper introduces the application and research progress of nonlinear ultrasonic detection technology, which is derived from different acoustic nonlinear effects, such as higher harmonic, wave mixing and modulation, sub-harmonic, resonance frequency spectrum analysis, and non-linear ultrasonic phased array imaging. The key technologies and problems are summarized to provide a reference for the further development and promotion of nonlinear ultrasonic non-destructive testing technology.