Magnetoacoustic Emission Research Articles

Magneto-acoustic emission for the characterisation of ferritic stainless steel microstructural state

The role of residual stresses in the failure of metallic components and the need to determine such stresses is well recognised. Magneto-acoustic emission (MAE) is a relatively new non-destructive detection technique and its working principle is based on Barkhausen discontinuities or noise and magnetostriction when a ferromagnetic material is subjected to a varying magnetic field. MAE is being used to characterise the stress state of a ferritic stainless steel (AISI 430). Other stress measurement techniques; X-ray diffraction (XRD), magnetic Barkhausen noise (MBN) have also been used to support the results achieved using MAE. A new measurement parameter has been developed for microstructural characterisation called MAE absolute energy and has proved to be a useful quantitative method in MAE waveform measurement.

Investigation of magnetic and magnetomechanical hysteresis properties of Fe–Si alloys with classical and mechanical Barkhausen effects and magnetoacoustic emission

Grain oriented Fe 3.5% Si sheet samples with a Goss (GO) microstructure and Fe 3.5% samples with nonoriented (NO) grains were tested using two Barkhausen effects, the classical Barkhausen effect (HBE) and the mechanical Barkhausen effect (MBE), as well as the magnetoacoustic emission (MAE). The aim of the work was to present further evidence that the B(H) hysteresis with effects like HBE and MAE, and magnetomechanical hysteresis with MBE are correlated via internal stress barriers pinning domain walls (DWs). In the case of a GO alloy, the long axis of the sample was parallel to the [100], [110], and [111] directions with respect to the rolling direction. The HBE and MAE were measured using a C-core electromagnet supplied with a triangular wave form of current intensity. The MBE intensity was recorded during a monotonous increase of shear stress using a torque machine. The maxima of MBE intensity for the “first load” mode for a NO sample and for three GO samples indicate an internal stress distribution pinning 90° DWs. The MAE plots reveal at least two maxima which are well correlated with H strength values where creation and annihilation of magnetic domains appears. Since the MBE and MAE are associated with abrupt jumps of 90° DW, the existence of MBE and MAE reinforces the fact that such DWs are present in the tested samples. These walls belong mainly to the secondary closure domains at GO alloys and to closure domains at NO alloy.

Designing a magnetoacoustic emission measurement configuration for measurement of creep damage in power plant boiler tubes

We discuss design features that are needed for magnetoacoustic emission (MAE) measurement of creep damage in the outer walls of boiler tubes. MAE is used because it decreases monotonically with increasing creep damage. Features of magnet design for boiler tube inspection are presented. Relationship of total MAE to Barkhausen noise path integrals is discussed. Also, dependence of MAE on frequency and tube wall thickness is delineated. Finally, measurements are discussed which show how azimuthal asymmetry in creep damage is echoed in azimuthal asymmetry in MAE. All tests were performed on 2Cr–1Mo Polish steel tube specimens.

Finite element modeling of magnetoacoustic emission and of stress-induced magnetic effects at seam welds in steel pipes

Prior finite element modeling (FEM) has shown how creep damage reduces the voltage signal in a secondary coil wrapped around a C-core electromagnet positioned above a seam weld in a steel pipe. Prior hysteresis modeling has also demonstrated the reduction of magnetoacoustic emission (MAE) due to uniform creep damage in a steel specimen. In this article, it is shown how to evaluate the MAE due to a nonuniform distribution of creep damage at a seam weld using FEM. Also, FEM is used to evaluate the C-core secondary emf due to a nonuniform stress distribution, which is developed at a seam weld due to the internal pressure of hot steam passing through the pipe. In this latter case, use is made of the stress distribution computed at the seam weld by Stevick. It is found that nonuniform creep damage also reduces the MAE signal, as is found experimentally. The stresses due to internal pressure in the pipe are shown by FEM to increase the C-core secondary emf, which is opposite to the effect of creep damage. A comparison is made between stressed and unstressed cases, with and without creep damage.

NDE OF CREEP DAMAGE AT SEAM WELDS VIA MAE

This paper presents magnetoacoustic emission measurements taken on creep-damaged seamwelded pipe. Measurements were made with portable field-usable equipment on a special pipe that was strongly creep-damaged on one end but essentially undamaged on the other end. The MAE voltage decreased as the C-core magnetizing magnet was moved from the undamagedend to the damaged end of the pipe. The results suggest that magnetoacoustic emission isreduced as a result of the presence of creep damage at and near the seam weld. This agrees with recent modeling predictions,

Magnetoacoustic emission and Barkhausen noise of cobalt nickel oriented silicon steel and permalloy

The profiles of MAE and BN for Co, Ni, oriented Fe–3.5% Si, and permalloy between − H max to + H max were investigated under 0.5 and 1 Hz triangle applied magnetic field. The profiles of Co (contained 180° domain walls only) under different H max and different frequency show that the peak to peak voltage of MAE increase when the H max and frequency are increasing, and the shape of the profiles of MAE is similar to that of BN under the same condition. But for Ni the shapes of profiles of MAE and BN are not similar to each other. It means that the sources of MAE and BN for Co are the same i.e. 180° domain wall motion. Not only the motion of non-180° domain wall but also 180° domain wall motion are the source of MAE. Besides that, domain wall nucleation and annihilation are also the sources of MAE.

Multiparameter magnetomechanical NDE

We present a new approach to microstructural magnetic nondestructive evaluation (NDE) based on multiparameter measurements of magnetomechanical properties. A steel specimen was magnetized with a C-core using a triangular waveform of order 1 Hz in frequency. Hysteresis loops were obtained for five quantities: magnetoacoustic emission (MAE) and Barkhausen effect (BE) intensities, magnetic flux derivative, external magnetic field strength, and magnetostriction. The ability to extract the magnetic flux second derivative and the derivative of the magnetostriction permitted the investigation of several new interrelationships between MAE and other magnetic properties. Approximate coincidences were observed between MAE peak field position and peaks in magnetic flux second derivative and derivative of the magnetostriction. These effects are discussed and reproduced using existing magnetic modeling of MAE and corresponding modeling of flux density and magnetostriction.

Correlation between acoustic emission and magnetic and mechanical Barkhausen effects

The Barkhausen effect and magneto-acoustic emission as well as the mechanical Barkhausen and mechanically induced magneto-acoustic emission were measured for the XC10 steel. Mechanical load was performed for different levels of magnetic field. A close correlation between Barkhausen noise and acoustic emission was observed for mechanical load. It was argued that magneto-acoustic emission is due to non-180° DW irreversible motion.

Nondestructive evaluation of irradiation effects in RPV steel using Barkhausen noise and magnetoacoustic emission signals

The hysteresis loop, Barkhausen noise (BN), magnetoacoustic emission (MAE) and microhardness of the reactor pressure vessel steel have been measured. The configuration of hysteresis loop showed no change up to 10 18 n/cm 2, however, the BN and MAE energy showed characteristic transition according to the neutron dose. The BN depended more strongly on the density of defect clusters than the MAE in the early stage of irradiation. The results are explained in terms of the interaction between magnetic domain wall and irradiation-induced defect clusters.

Study of magnetization processes and the generation of magnetoacoustic and Barkhausen emissions in ferritic/pearlitic steel

Magnetoacoustic emission (MAE), Barkhausen emission (BE), and hysteresis loop measurements have been made on steel specimens heat treated to produce ferritic/pearlitic structures with various volume fractions of ferrite Vα. It was found that in the low-field region the BE activity decreases whereas the MAE signal increases with Vα. Increasing Vα also results in a decrease in the initial peak height of MAE profiles and the formation of outer peaks in BE profiles. It was observed by Lorentz microscopy that in ferrite non-180° domain wall motion occurs readily in the low-field region, while in pearlite significant 180° domain wall motion takes place only when a reversed field was applied. These results can account for the variations in the MAE and BE profiles with Vα. The sensitivity of the MAE and BE profiles to Vα enables both techniques to be exploited for monitoring the ferrite content of steel components.

Stress Effect on Magnetoacoustic Emission of Nickel.

Acoustic emission (AE) is stress pulses generated during dynamic processes in solids. AE is reflected by structural change of the material such as dislocation and crack growth and it is utilized as nondestructive evaluation technique for fracture or fatigue. On the other hand. AE is also observed during dynamic magnetization process of ferromagnetic materials. The phenomenon is called Magnetoacoustic Emission (MAE), and it is caused by abrupt and discontinuous displacement of magnetic domain walls pinned by inclusions, voids, dislocations, grain boundaries etc. Moreover, the characteristics of MAE change with the applied stress since the stress influences the structure of the magnetic domains and the pinning effects. This paper reports that the total event count of MAE for nickel decreases with the tensile stress and increases with compressive stress in the case when the stress is parallel to the magnetic field.

Magnetostriction and its contribution to noise in a PWM inverter fed induction machine

PWM inverter fed induction machines generate significant noise. The noise comes not only from radial air gap forces but also from magnetostriction. It turns out that magnetostrictive and radial air gap forces have about the same magnitude in medium sized induction machines. A FEM model, based on actual magnetostrictive data for electric steel sheet, has been derived for calculation of magnetostrictive deformation of the stator. The FEM model has been verified on a test machine in which the radial air gap force is eliminated. Measurements with the test machine connected to a PWM inverter reveal the same spectrum as from standard PWM inverter fed machines. Thus there is reason to believe that noise comes from magnetostrictive deformation and not from magneto acoustic emission (MAE).

The effect of stresses approaching and exceeding the yield point on the magnetic properties of high strength pearlitic steels

The results of a study of the effects of stresses that approach and exceed the yield point on the magnetic properties of a sample of 50D pearlitic steel are reported. Unlike previous work which has only examined residual stress behaviour, measurements were made in-situ while sample remained under stress. Hysteresis loops, permeability curves and magnetostriction loops are presented and a variety of magnetic parameters analysed. The implications of this analysis for the application of non-destructive evaluation techniques such as magnetic flux leakage, magnetic Barkhausen noise and magnetoacoustic emission are discussed. Key changes in magnetic behaviour occur well before yield and this raises the possibility of developing magnetic NDE methods of predicting when a sample is approaching the yield point.

Monitoring the microstructure of pearlitic steels by magnetoacoustic emission

Magnetoacoustic emission (MAE) and Barkhausen emission (BE) measurements have been made on hypereutectoid steel samples heat treated to produce completely pearlitic microstructures with various interlamellar spacings. Both the peak height ratio of the MAE profile and the amplitude of the BE profile were found to increase with increasing interlamellar spacing. These results can be explained in the context of the domain structure and the domain wall processes observed by Lorentz microscopy. The correlation of the spacing with the shape of the MAE and BE profiles shows that both techniques are useful for monitoring the pearlite interlamellar spacing.

Effect of sweep and bias field amplitudes on the magnetoacoustic emission: Dhar, A.; Clapham, L.; Atherton, D.L. IEEE Transactions on Magnetics, Vol. 27, No. 6, pp. 5364–5366 (Nov. 1991)

Effect of sweep and bias field amplitudes on the magnetoacoustic emission: Dhar, A.; Clapham, L.; Atherton, D.L. IEEE Transactions on Magnetics, Vol. 27, No. 6, pp. 5364–5366 (Nov. 1991)

Magnetizing frequency dependence of magneto-acoustic emission in pipeline steel: Dhar, A.; Atherton, D.L. IEEE Transactions on Magnetics, Vol. 28, No. 2, pp. 1003–1007 (Mar. 1992)

Magnetizing frequency dependence of magneto-acoustic emission in pipeline steel: Dhar, A.; Atherton, D.L. IEEE Transactions on Magnetics, Vol. 28, No. 2, pp. 1003–1007 (Mar. 1992)

Non-destructive evaluation of spheroidized steel using magnetoacoustic and Barkhausen emission

Magnetoacoustic emission (MAE) and Barkhausen emission (BE) measurements have been made on pearlitic steel samples annealed to produce spheroidized microstructures with various sizes and distributions of carbides. It was found that spheroidization of the pearlitic structure and coarsening of carbide particles result in a decrease in the peak height ratio of the MAE profile and the formation of a second peak in the BE profile. These results can be interpreted from observations of the domain structure by Lorentz microscopy. The sensitivity of the MAE and BE profiles to the carbide size and morphology makes both techniques useful for monitoring the microstructure of spheroidized steels.

Detection of irradiation effects of reactor vessel steels by magneto-acoustic emission : 47722 Kwon, O.-Y.; Ono, K. Journal of Acoustic Emission, Vol. 9, No. 4, pp. 227–236 (Oct. – Dec. 1991)

Abstract : The irradiation effects of reactor vessel steels were studied by magneto-acoustic emission (MAE). MAE is a new method of non-destructive evaluation. It is generated primarily by domain wall motions during magnetization of ferromagnetic materials in the alternating magnetic field. Since MAE activity is sensitive to the microstructural changes, it is applied to determine the status of steel samples exposed to neutron irradiation. Two commercial steels, A302B plate and A533B weld, and two model alloys were irradiated at four different conditions; high and low flux, two fluence levels and three temperatures. For each material/condition and unirradiated control samples, MAE intensity in rms voltage with increasing magnetic field was measured. Direct and envelope-detected MAE waveforms were also recorded. Measurements were also made for the samples unirradiated but aged at 288 C up to 278 hours in order to separate the effects of thermal aging from irradiation effects. Barkhausen effects were also investigated using a surface probe. The results presented here show that MAE waveform analysis can be a promising non-destructive evaluation technique for monitoring the microscopic changes in the steel components subjected to neutron irradiation.

The measurement of residual stresses in structural components by magnetoacoustic emission : 48242 Scruby, C.b.; Dalzell, W.; Buttle, D.J. Proceedings of the 10th International Conference on NDE in the Nuclear and Pressure Vessel Industries, Glasgow (Scotland), 11–14 Jun. 1990. pp. 649–656. Edited by M.J. Whittle, J.E. Doherty and K. Iida. ASM International, (1990)

The measurement of residual stresses in structural components by magnetoacoustic emission : 48242 Scruby, C.b.; Dalzell, W.; Buttle, D.J. Proceedings of the 10th International Conference on NDE in the Nuclear and Pressure Vessel Industries, Glasgow (Scotland), 11–14 Jun. 1990. pp. 649–656. Edited by M.J. Whittle, J.E. Doherty and K. Iida. ASM International, (1990)

The monitoring of stress and microstructure by magnetoacoustic emission : 37933 Scruby, C.B.; Buttle, D.J.; Briggs, G.A.D.; Jakubovics, J.P. United Kingdom Atomic Energy Authority, Harwell, AERE-R-12782, 16 pp. (Oct. 1987)

The monitoring of stress and microstructure by magnetoacoustic emission : 37933 Scruby, C.B.; Buttle, D.J.; Briggs, G.A.D.; Jakubovics, J.P. United Kingdom Atomic Energy Authority, Harwell, AERE-R-12782, 16 pp. (Oct. 1987)