Magnetoacoustic Emission Research Articles

Effect of strain and excitation conditions on magneto acoustic emission signals in Q235 steel using maximal overlap discrete wavelet transform

ABSTRACT This study explores the effect of strain on Magneto Acoustic Emission (MAE) characteristics in Q235 steel plates under various excitation frequencies and voltages. Using Maximal Overlap Discrete Wavelet Transform (MODWT), we processed envelope energy signals derived from MAE signals generated from samples subjected to incremental tensile forces revealing critical variations in features extracted from AC and DC components such as RMS, mean bias and energy distribution. The results demonstrate the significant impact of strain on MAE signal characteristics, particularly under higher excitation frequencies and voltages, which enhances the detection of subtle plastic deformations. Our approach provides a refined methodology for enhancing MAE-based Non-Destructive Testing (NDT) practices, crucial for the reliable assessment of material integrity in engineering applications.

Magneto acoustic emission technique: A review of methodology, applications, and future prospects in non-destructive testing

The magneto acoustic emission (MAE) technique is an emerging non-destructive testing (NDT) method that has shown potential for defect detection in the bulk of material, proven vital for the safety and integrity of the material. The MAE technique has shown promising results among modern non-destructive testing techniques for ferromagnetic materials. Although MAE technique is a long-established NDT method, it has the potential for further development. This paper provides an in-depth review of MAE signals' physical origin and characteristics, compares them with their counterpart, Magneto Barkhausen Noise (MBN), and explores data acquisition methods and applications, including specific case studies in material defect detection. The research gaps in the MAE technique are discussed, and the paper explores potential developments, highlighting future perspectives and possible improvements.

Non-contact measurement of the dynamic magnetostriction parameters of ferromagnets

The magnitude of magnetostriction of a ferromagnetic material largely determines the efficiency of electromagnetic-acoustic transformation and the intensity of magnetoacoustic emission, which are based on the application of alternating magnetic fields. This study shows that laser interferometry allows dynamic magnetostrictive behavior to be measured in an alternating magnetic field. Experiments reveal that dynamic magnetostrictive sensitivity determined from the amplitude of the second harmonic of elastic vibrations in ferromagnetic materials correlates with the value of the maximum magnetostrictive elongation of the studied ferromagnetic materials.

Theoretical model of magnetoacoustic emission considering the microstructure of ferromagnetic material

Magnetoacoustic emission (MAE) holds great promise for evaluating the mechanical properties of ferromagnetic materials. To refine the problems of the current theoretical and numerical models of MAE, a theoretical MAE model that considers the microscopic dependence of the hysteresis properties is proposed in this paper. The microstructure (dislocation density and grain size) and the correlation of MAE jumps are considered and incorporated into the model. Then, the influences of magnetization parameters and microstructure parameters on the envelope of the MAE signal are analyzed by the proposed theoretical model. The proposed theoretical model is then fully evaluated by simulations and experiments. The MAE experiments are conducted on ferromagnetic specimens with different hardnesses, and the MAE signals with different hardnesses are simulated by inverting the basic parameters of the MAE model with the genetic algorithm. Further, the crucial hysteresis parameters of the specimens are calculated using the results of microscopic measurements and the calculated parameters agree well with inversion results from experimental signals. The results demonstrate that the proposed theoretical model is valid for the MAE signal simulation. The trends of different hardnesses can be predicted by the MAE simulation signals. Moreover, the model can be used for theoretical analysis of the microscopic dependence of the MAE signal.

Influence of occluded hydrogen on magnetoacoustic emission of low-carbon steels

The peculiarities of the interaction of hydrogen with low-carbon steels were studied by the magnetoacoustic emission method (MAE). It was established that the low concentration of hydrogen in the steel structure has an insignificant effect on their elastic characteristics. Hydrogen in the steel structure contributes to the increase of MAE by 16% under the induction of a magnetic field of 0.92 T, and for plastically deformed steel, the presence of hydrogen contributes to the increase of MAE by 23% compared to non-hydrogenated material. The less carbon in the steel, the greater the influence of hydrogen on MAE. The dualistic nature of the effect of low hydrogen concentration on the generation of MAE is illustrated: increase of MAE activity up to a certain concentration of hydrogen, and then its decrease. It is important to take this into account when developing methods for non-destructive control of the local concentration of hydrogen in metals.

An adaptive approach to non-destructive evaluation (NDE) of cast irons containing precipitated graphite particles with the help of magnetoacoustic emission

Physical properties of cast irons strongly depend on both their microstructure and the presence of casting defects. The paper analyses the possibility of application of magnetoacoustic emission (MAE) for nondestructive detection of flawed cast iron components. The investigated samples containing dross, chunky graphite and lamellar graphite were compared with the reference, flawless, spheroidal cast iron sample. The optimisation adaptive procedure was applied for sensitivity enhancement. Application of five different acoustic emission sensors and filtering band optimisation enabled finding the optimum sensor/band configuration allowing not only for flawed samples identification, but also for discerning various kinds of flaws.

Effect of operational factors on magnetoacoustic emission of low-carbon steels

The features of magnetoelastic acoustic emission (MAE) generation in the low-carbon (ferritic-pearlitic) steels during their magnetization by an external quasi-static magnetic field are investigated. The influence of elastic stresses, plastic deformations, volume damage of the material, heat treatment as well as the carbon content in iron alloys and the volume of remagnetization on the sum of the MAE signals amplitudes is established. An increase of the magnetization volume and heat treatment lead to an increase of the sum of the MAE signals amplitudes. The other factors cause its decrease compared to the state of supply of the ferromagnet. The obtained results are important for the construction of methods for assessing the local degradation of equipment materials of pipeline networks.

On the Application of Magnetoacoustic Emission for a Nondestructive Assessment of the Post Welding Heat Treatment of High Chromium Steel Weld Seams

The paper analyses the possibility of post weld heat treatment (PWHT) quality assessment with the help of magnetoacoustic emission (MAE) signal measurements. Two welded superheater tubes, made of high chromium VM12 steel, were analysed—as welded and heat treated one. The analysed sample in the as welded state exhibited significantly higher hardness, accompanied by a big difference in the MAE signal intensity (of order of about 50%). In order to explain that, the influence of tempering on the MAE signal intensity is demonstrated for the very similar X20CrMoV12.1 steel. It is shown that the observed increase of the MAE intensity as a function of annealing time is directly correlated with the change in hardness. The as described dependence allows to propose a method based on the MAE signal measurements as a new tool for the PWHT assessment.

Автоматизированная система комплексного неразрушающего контроля структуры и механических свойств материалов машиностроения

An automated system with two optimized modular devices is presented — MULTITEST-MC010 for research of ferromagnetic materials with the methods for measuring magnetic noise and magneto acoustic emission of Barkhausen and MULTITEST — CD010 for research of mechanical engineering materials with the methods of velocity measurement of longitudinal waves C and attenuation coefficient δof ultrasound. The main approaches and principles for the automated data processing of complex non-destructive testing are presented, as well as the setup of the modular devices of the automated system. For approbation of the system the influence of the heat treatment (hardness) in structural steel 40X on the non-destructive information parameters of the magnetic noise and the magneto acoustic emission — magnetic noise voltage EBN and voltage of the magneto acoustic emission EMAE was studied. The mechanical properties in foundry cast iron samples with complex measurement of the information parameters , C, by simultaneous use of the two modular devices of the system were also studied. The possibility for the complex application of these parameters for non-destructive testing of the mechanical properties after heat treatment in structural steel 40X and the tensile strength in cast iron specimens has been proven.

Application of Acoustic Emission and Thermal Imaging to Test Oil Power Transformers

In this paper, the research methodology and the results of the analysis carried out using the acoustic emission (AE) and thermal imaging for a selected oil power transformer are presented. The basis for the research, by means of the AE method, was the author’s patented research method. The AE descriptor maps on the side walls of the tested transformer along with the location of areas with increased AE activity and an analysis of the properties of AE signals recorded at the measurement points located in these areas have been performed. The results showed no partial discharges that could threaten further operation of the tested transformer as well as three areas where increased magnetoacoustic emission occurred. Thermal imaging studies were carried out in the 7.5 μm < λ < 13 μm band. Three areas were located on the calculated thermograms: the entire upper surface of the transformer tank and two areas on the side walls of the tested transformer in which increased IR radiation occurred. The results of the analysis of the research results for the two methods correspond with each other, having a common part, and complement each other giving a broader description of studied phenomena.

Study on the characteristics of magneto acoustic emission for mild steel fatigue.

Fatigue life of materials or structures can be classified into three stages: fatigue hardening or softening, crack initiation and crack propagation, which includes two stages. Current mature non-destructive testing (NDT) methods can only detect macro or visible cracks in stage II crack propagation. In order to detect and evaluate the fatigue damage occurring before stage II crack propagation quickly and effectively, magneto acoustic emission (MAE) measurement was carried out on laboratory specimens with different numbers of fatigue cycles. With the accumulation of fatigue damage, the RMS of MAE decrease steadily on the whole, making MAE a promising non-destructive method for evaluating fatigue damage. To make MAE applicable in noisy environments, square waveform voltage were selected to excite magnetic fields, and 'T' type MAE signals with higher amplitude were produced. The variation of MAE with number of fatigue cycles at different excitation intensity indicated that the defects associated with fatigue damage have greater effects on the creation and annihilation of domain walls. The point where the MAE amplitude begins to increase instead of decrease with fatigue can be an indicator for the onset of stage II crack propagation. This article is part of the theme issue 'Advanced electromagnetic non-destructive evaluation and smart monitoring'.

Influence of the two-stage plastic deformation on the complex of the magnetoacoustic characteristics of low-carbon steel and diagnostics of its structural state

Magnetic, ultrasound and magnetoacoustic properties of low-carbon steel subjected to cold plastic deformation by rolling with different compression and subsequent flat pressing have been investigated. The hardness and coercive force are changing non-monotonically with deformation degree increase determined by cross-section change. Change of shape during flat pressing leads to the partial softening of the samples that lost flatness during rolling. The coercive force increases at low deformation degrees and has a maximum at 6% deformation degree and monotonously decreases with increasing of the deformation degree up to 20%. Peculiarities of hardness and magnetoacoustic properties are related to the change of dislocation structure and relaxation of longitudinal compressive stresses.The softening of the material can be detected by the amplitude of the parameter interrelated with the shape of the major hysteresis loop. The parameter proportional to the field of the maximum of magnetoacoustic emission can be a diagnostic parameter of the resulting hardening of steel under study as a result of two-stage plastic deformation.

Complex application of magnetic and magnetoacoustic parameters in the structuroscopy of ferromagnetic materials

The set of magnetic parameters and amplitude-frequency spectral characteristics of magnetoacoustic emission (MAE) of a large group of metal ferromagnetic materials differing in their physical properties and size are investigated. It is shown that the change in critical fields determined by the shape of the magnetization curve and the hysteresis loop of bulk samples with an increase in the annealing temperature of cold-deformed steel 20G is 1.5–3 times greater than the change in such well-known parameters for estimating the stress-strain state, such as coercive force and residual magnetic induction. It has been established that the amplitude of magnetoacoustic emission correlates with the residual magnetic induction, which makes it possible to recommend the complex application of these testing parameters in scanning systems of structuroscopy of ferromagnetic materials.

Analysis of the possibility of creep damage detection in T24 heat resistant steel with the help of magnetic nondestestructive testing methods

The paper presents the result of an analysis of applicability of various electromagnetic methods of nondestructive evaluation for creep damage detection in a novel heat resistant steel - T24 grade. Two sample sets, cut out from membrane wall tubes, were investigated – the as-delivered one and another exploited for 36,000 h in a power plant. There are described results of magnetic hysteresis loops B(H), Barkhausen noise (BN) and magnetoacoustic emission (MAE) signals measurements. Changes of the B(H) loops shape are observed mainly in the “knee” regions. The BN signal is practically unaffected by exploitation. The most strongly changing signal is the MAE signal, yet the change is not very easy to quantify as it concerns signal envelopes shape not overall intensity. The paper describes various possible signal parameters that can be used. The best one seems to be the ratio of the total pulse count for a quarter of magnetisation (demagnetisation) to the one for the magnetisation half-period. The important issue is in that case a proper choice of the threshold level in order to obtain good sensitivity to creep damage level and reasonably low stochastic pulse count scatter.

On the application of magnetoelastic properties measurements for plastic level determination in martensitic steels

Abstract The change in the dislocation density, induced by plastic deformation, influences strongly the magnetic domain structure inside the material. Being so, classic parameters, like the coercivity or magnetic permeability, can be a good measure of the deformation level, yet their reliable determination in a non-destructive way in industrial environment is problematic. The magnetoacoustic emission (MAE) which results from the non-180° domain walls (DW) movement in materials with non-zero magnetostriction can be used as an alternative. The intensity of the MAE signal changes strongly as a result of plastic deformation for both tensile and compressive deformation. It is however possible to discern those cases by analysing the changes in the shape of the MAE signal envelopes. The set of the martensitic steel samples (P91) deformed up to 10% (for both tension and compression) was investigated. Due to geometrical limitations imposed by the special mounting system, enabling compression without buckling, the sample had the shape resulting in low signal to noise (S/N) ratio. Being so the optimization of FFT filtering and wavelet analysis was performed in order to improve sensitivity of the proposed method of deformation level determination.

Application of Wavelet Transforms for the Analysis of Acoustic-Emission Signals Accompanying Fracture Processes in Materials (A Survey)

We analyze the results of application of wavelet transforms to the analysis of acoustic-emission signals accompanying fracture processes in structural materials and the data of engineering diagnostics of various industrial objects. The methods used for the identification of the types of fracture processes in materials (steels, alloys, polymers, etc.) with the help of wavelet transforms are characterized. We consider the possibilities of wavelet transformations of acoustic-emission signals for the determination of the mechanisms of fracture in composites and processing of the signals of magnetoacoustic emission. Examples of the tests performed in the Physicomechanical Institute of the Ukrainian National Academy of Sciences and demonstrating the efficiency of wavelet analysis of signals are also presented.

Dynamic properties of micro-magnetic noise in soft ferromagnetic materials

Dynamic response of magnetic hysteresis, magnetic Barkhausen noise and magneto-acoustic emission in a soft ribbon and electrical steels was studied comprehensively. The measurements were performed under controllable magnetization conditions: sinusoidal/triangular waveforms of the magnetic induction and a triangular waveform of the magnetic field. Magnetizing frequency was varied in a wide range: fmag=0.5–500 and 0.5–100 Hz for the ribbon and the electrical steels, respectively. Magnetization amplitude was fixed on a near-saturation level Hmax≃100 A/m. Barkhausen noise signal was detected by a sample-wrapping/surface-mounted coil and differently filtered. It was found that intensity of the Barkhausen noise rises approximately as a square root function of the magnetizing frequency. Whereas, level of the magneto-acoustic emission follows the hysteresis loss trend with an additional linear term (classical loss component).

Estimation of effect of hydrogen on the parameters of magnetoacoustic emission signals

The features of the magnetoacoustic emission (MAE) signals during magnetization of structural steels with the different degree of hydrogenating were investigated by the wavelet transform. The dominant frequency ranges of MAE signals for the different magnetic field strength were determined using Discrete Wavelet Transform (DWT), and the energy and spectral parameters of MAE signals were determined using Continuous Wavelet Transform (CWT). The characteristic differences of the local maximums of signals according to energy, bandwidth, duration and frequency were found. The methodology of estimation of state of local degradation of materials by parameters of wavelet transform of MAE signals was proposed. This methodology was approbated for investigate of state of long-time exploitations structural steels of oil and gas pipelines.

The interrelationships of magnetic and magneto acoustic-emission characteristics of heat-treated steels of various chemical composition

The relationship between the amplitude of magnetoacoustic emission and the residual magnetic induction of the materials is shown. The dependence of magnetoacoustic emission (MAE) on the frequency of magnetization reversal of a group of steels of different chemical composition was investigated. In all the investigated cases, the MAE amplitude maximum corresponds to a field frequency of 3-5 Hz. The magnetic properties of two groups of steels subjected to various thermal treatments have been studied. It is shown that the residual magnetic induction of steels is a sufficiently universal parameter for controlling softening thermal treatments and that the amplitude of magnetoacoustic emission can be used as a testing parameter in scanning systems of structurescopy of ferromagnetic steels.

Evaluation of a Nitrided Case Depth by the Magnetic Barkhausen Noise

Applicability of magnetic methods for non-destructive evaluation of plasma nitrided cases was investigated comprehensively. Nitrided layers of 60–800 $$~\upmu \hbox {m}$$ thicknesses were produced on a 16MnCr5 steel surface varying the plasma temperature, the nitriding time and atmosphere. Low-frequency Barkhausen noise was measured by a unique laboratory system to obtain physically grounded data. The laboratory measurements were performed at the triangular waveforms of the magnetizing voltage and the surface magnetic field. A typical rms envelope with a single peak positioned near the hysteresis coercive field was obtained for the unnitrided homogeneous sample. All nitrided samples with the hardened surface layer demonstrated an additional envelope peak at higher fields. Deeper nitridation suppressed both envelope peaks equally making the classical rms parameter sensitive to variation of the nitrided case depth. An industrial method of detection of the Barkhausen noise was tested for comparison using a commercial Rollscan device. The industrial measurements gave a single-peak envelope for all studied samples and a lower depth sensitivity of the rms parameter. Bulk testing methods, the magnetic hysteresis and the magneto-acoustic emission, were not able to detect the nitrided cases.