Metal Magnetic Memory Testing Research Articles

Research on the force-magnetic relationship of bridge steel under tensile stress based on magnetic memory effect

It’s of great significance to conduct the nondestructive evaluation of steel bridges to extend their service life. The metal magnetic memory testing (MMMT) method can effectively evaluate the stress states of ferromagnetic components. To improve the accuracy and reliability of the stress evaluation on bridge steel structures based on MMMT technology, an improved force-magnetic coupling model considering loading history is proposed, which can reflect the impact of material mechanical properties on magnetization behavior. The MMMT is carried out on the Q345qD bridge steel plates under load-unload tensile stress considering the relative location between the specimen and the geomagnetic field, according to the rotation angle θr. It comprehensively analyzes the variation laws of representative tangential and normal components of the magnetic signal, i.e. Hm(y) and Hm(z), corresponding to different inspection parameters during the loading process. The mean value Ay of the Hm(y) curves and the linear fitting slope Kz of Hm(z) curves are applied to characterize the variation laws of magnetic signal with respect to the applied load Fa. According to the fitting curves of Ay and Kz with Fa, it quantitatively demonstrates the applied loads. It further puts forward the normalized magnetic characteristic parameters Ayn and Kzn to characterize the force-magnetic relationship of the specimen, which are less affected by the position of the specimen in geomagnetic field. Finally, the proposed force-magnetic coupling model is applied to calculate the variation of normalized magnetization ΔMn. The theoretical results are compared with the synthetic magnetic characteristic parameter AKn obtained by experiment. It shows an average error of 8.53% between ΔMn and AKn, which proves the feasibility and effectiveness of the force-magnetic coupling model proposed in this paper.

Influence of microstructure and geometric dimension on metal magnetic memory testing

Metal magnetic memory testing (MMMT) is a prominent NDT method for early damage diagnosis of ferromagnetic structures due to its significant advantages in stress concentration state evaluation. While it is still challengeable to apply the existing criteria from the laboratory to practical application, and some of the main reasons are the microstructure transformation and geometric dimensions for the ferromagnetic material itself. To explore the influence of microstructure and geometric dimension on MMMT, static tensile tests of specimens made of Optim 900QC steel with different microstructures and geometric dimensions have been carried out, and the MMMT signals of the specimens during the tests were collected and analyzed. It is found that the microstructure not only change the strength of the steel, but also affect the MMMT signal of the steel, and the bigger the grain is, the stronger the magnetic field is. Geometric dimension would also affect the MMMT signal, and thickness affects the MMMT signal the most, width less, and length the least. The results of the present work indicate that the microstructure and the geometric dimensions should be the same to fix the gap of damage determination criteria between the laboratory and the engineering application. When it is impossible to fabricate specimens with the same dimension with the engineering structure, set the same thickness would improve the accuracy of the criteria.

Research on the microphysical mechanism of metal magnetic memory testing through 45 # steel under compressive stress

To explore the microphysical mechanism of metal magnetic memory testing (MMMT) technique, the effect of compressive stress on the domain structure in 45# steel specimen and the pinning effect of stress-induced defects on domain walls (DWs) were investigated by in-situ Lorentz Transmission Electron Microscopy (LTEM). The changes in domain structure and defects are observed simultaneously. And the deformation and magnetic moment distribution of the specimen under compressive stress were measured and analyzed. The results show that, the rotation of magnetic moment corresponding to the deformation of the specimen can greatly reduce the magnetoelastic energy according to the calculation of magnetoelastic energy. When stress is removed, the domain structures do not restore, and DWs’ pinning effect of defects could be clearly observed. The results provide a vigorous support for the memory effect of ferromagnetic material on historical stress.

Experimental Study on Fatigue Damage of Drilling Tool Materials Based on Magnetic Memory Detection

In drilling engineering, the cost of drilling tool fracture is enormous, and studying the fatigue failure process of drilling tools has practical significance. This paper uses metal magnetic memory detection technology to design and conduct fatigue damage tests on typical drilling tool material 42CrMo specimens under tensile, torsional, compressive, tensile, compressive, and torsional dynamic loading conditions. By analyzing the changes in the tangential component Hp(x) and gradient value K of the magnetic memory signal under different load conditions with the number of loading times, the process of fatigue failure of the specimens and the trend of changes in the magnetic memory signal in local stress concentration areas are explored. The characteristic parameters of fatigue damage based on magnetic memory detection were extracted and the critical point at which fatigue damage leads to crack initiation was inferred. This confirms that metal magnetic memory testing technology is an effective means of analyzing the fatigue damage process of drilling tools and provides a certain reference for formulating judgment standards for drilling tool maintenance on site.

Quantitative Evaluation of Corrosion Defects on Structural Steel Plates via Metal Magnetic Memory Method

ABSTRACT The detection and evaluation of corrosion defects take on a critical significance to ensure the service safety of steel structures in civil engineering. The quantitative evaluation of corrosion defects has not been well addressed though metal magnetic memory (MMM) testing technology has been investigated in steel corrosion problems. In this study, the Q345qD steel plates were taken as the specimens of MMM testing. Specimens with different corrosion degrees were developed through electrochemical corrosion, and the change laws of the MMM signals and the characteristics of different corrosion specimens were analyzed. A three-dimensional (3D) magnetic charge model of the corrosion area was built based on the magnetic charge theory, such that the change laws of the MMM signal in the corrosion area from the mechanism were explained. The finite element simulation results of the corrosion specimens were well consistent with the experimental and theoretical results. A quantitative evaluation method for corrosion defect depth was proposed in combination with finite element simulation and experimental data. Comparing the experimental data and the inversion data, the relative errors of the determined defect depth h were within 20%, suggesting that the proposed evaluation method is feasible for the quantitative evaluation of steel corrosion depth.

Relationship between stress and magnetic signal of steel box girder based on magnetic memory method

Metal magnetic memory testing (MMMT) is a nondestructive testing technique that can detect early signs of damage in components. Many scholars have studied the effect of uniform stress on the self-leakage magnetic field (SLMF) strength of ferromagnetic materials. However, there is still insufficient research on the stress concentration caused by uneven stress, under the combined action of bending and shear. In this study, we studied the law of distribution of the magnetic signal, HP(y) and magnetic gradient, K, on a part of the surface of a steel box girder damaged by buckling, using a four-point bending pattern. The results showed that combining the three peak positions, namely, the magnetic signal, its newly added comparing initial magnetic signal, and magnetic gradient distribution curves, could accurately determine all stress concentration positions on the flange of the steel box girder, and reduce the interference of the initial complex residual magnetic field. Furthermore, we studied the quantitative relationship between normal stress, shear stress, and a magnetic signal. It was found that the stress-magnetic relationship conformed to the Jiles–Atherton model. The peak value of HP(y) – 𝜎, |HP(y)|a – 𝜎, and Kmax – 𝜎 relationship curves could be used as the characteristic point of the critical yield stress at the action of normal and shear stress. The degree of stress concentration of the flange and web could be quantitatively evaluated by fitting the Kmax – 𝜎 relationship. This study can provide an experimental reference for the application of MMMT in the evaluation and early warning of the state of damage to a steel box girder.

Signal Processing Methods of Enhanced Magnetic Memory Testing

As a particular kind of detection technology under weak magnetization, metal magnetic memory testing is very likely to be affected by external factors in the detecting process, which may lead to incorrect results. In order to minimize the negative influence of interrupting signals and improve the detection accuracy, this paper adopted the enhanced metal magnetic memory testing method to preliminarily increase the signal-to-noise ratio (SNR) of the detection signal and then compares the denoising effects of wavelet threshold denoising method, empirical mode decomposition (EMD) denoising method, EMD-wavelet threshold denoising method, ensemble EMD (EEMD), complementary EEMD (CEEMD), variational mode decomposition (VMD), local mean decomposition (LMD) and empirical wavelet transform (EWT) on the detection signal and the gradient signal respectively. The results show that the enhanced metal magnetic memory testing method can significantly increase the SNR of the obtained signal and cannot improve the SNR of a gradient signal which is generated from the obtained signal. The different denoising methods can further boost the SNR and improve the detection accuracy of the obtained signal and the gradient signal. Among the eight signal processing methods, wavelet threshold, EMD and its improved methods are more applicable in the denoising of enhanced metal magnetic memory testing signals. The Wavelet threshold denoising, EMD-wavelet threshold denoising and EEMD denoising all have good denoising effects, and the denoising results to the same signal are analogous.

Study on the influence of ultrasonic impact treatment (UIT) on stress evaluation of laser cladding coating by using metal magnetic memory technology

The effect of ultrasonic impact treatment (UIT) on stress of laser cladding coating evaluated with metal magnetic memory technology (MMMT) was discussed, so a stress control method was proposed. In this paper, a metal magnetic memory testing device of EMS-2003, a two-channel pen metal magnetic memory probe and a non-ferromagnetic three-dimensional electronically controlled displacement plat form were employed to collect Hp(y) signal defined as the normal component of MMM signal, and tensile test was carried out on LC-50 testing machine. To prove the theoretical analysis, the microstructure and three dimensional surface topography of coating under different repetition rates of UIT were observed by using optical microscope and laser scanning confocal microscopy. The results show that the influence of detection line on Hp(y) signal can be ignored, and the distribution of Hp(y) signals under different tensile loads are all approximately an oblique line, which can be explained by the magnetic dipole model. As tensile load increases, the magnetic field intensity gradient of Hp(y) signal (K) becomes higher, and after coating is in the plastic deformation state, the value of K becomes lower gradually as tensile load increases further. When tensile loads are the same, the value of K becomes higher gradually as the repetition rate of UIT increases. But as repetition rate of UIT increases, the slope of K becomes lower gradually, and the changes on microstructure and deformation caused by UIT are seen as main reasons. At last, the experimental results were theoretically discussed based on the magnetostriction effect, and it was thought that the change on orientation of magnetic domain was the main reason.

Magnetic Signal Characteristics in Critical Yield State of Steel Box Girder Based on Metal Magnetic Memory Inspection

Metal magnetic memory testing (MMMT) is a nondestructive testing technique that can detect early signs of damage in components. Many scholars have studied the effect of uniaxial stress on the self-magnetic-leakage field (SMLF)’s strength. Nevertheless, there is still insufficient research on the combined action of bending and shear. We studied the law of distribution of the magnetic signal, ΔHSF(y), at different stress parts of a steel box girder and the quantitative relationship between the magnetic characteristic parameters and the external load. The results showed that the MMMT could accurately detect the early stress concentration zone (SCZ) and predict the final buckling zone of steel box girders. It could be judged that the corresponding parts of the steel box girder had entered the elastic-plastic working stage by the reverse change of the ΔHSF(y)-F and |HSF(y)|a -F curve trends, this feature could be used as an early warning sign before the steel box girder was deformed or destroyed. The fitted |HSF(y)|ave -F linear expression could be used as the expression between the magnetic signal and the shear capacity. All the evaluation methods were expected to provide a basis for effectively evaluating the stress state of steel box girders with the MMMT method.

Influence of tensile stress on magnetic flux leakage signal of ferromagnetic steel after overcoming initial magnetization disturbance

By locally enhancing the intensity of external excitation magnetic field (H0), a relatively stable local flux loop is formed at the test site, which can effectively overcome the problems of random and variable initial magnetization state, small test data base and low signal-to-noise ratio of ferromagnetic specimens in metal magnetic memory testing (MMMT). The results of magneto-mechanical coupling theory and experiment study show that under tensile stress (σt), the ascending part of the magnetization curve is stably constrained within 40 MPa, which is far less than the normal working load, and the descending part of the magnetization curve changes almost linear with the increase of σt. The gradient value of normal component (dHp(z5)/dx) increases by about 105% and the relative gradient value (Δ[dHp(z5)/dx]) increases by about 76% in the range of 0 MPa ≤ σt ≤ 180 MPa with the increase of σt. When H0 reaches 943.4 A/m and 1415.1 A/m, the characteristic parameter namely peak-to-peak amplitude, S(z)p-p, can stably describe σt linearly.

Study of Deformation Behavior of AISI 1025 Carbon Steel with Different Microstructures Using Metal Magnetic Memory and Acoustic Emission Testing

Studies are carried out to investigate the tensile deformation behavior of AISI-type 1025 carbon steel with different microstructures using metal magnetic memory and acoustic emission testing (AE) techniques. Seven AISI 1025 carbon steel specimens were heat treated for different microstructures and then subjected to tensile deformation until fracture. AE was conducted during tensile deformation and the deformation-induced self-magnetic leakage fields (SMLFs) were measured using a giant magneto-resistive sensor after unloading. Results reveal that SMLF signal values are influenced by microstructure and residual stress aroused due to plastic deformation. Among different specimens, SMLF signal peak amplitude is highest in the brine-quenched specimen followed by the tempered specimen, while hardness is highest in the brine-quenched specimen. SMLF signal peak amplitude and hardness are the lowest in the annealed specimen. SMLF signal is higher in tempered specimens compared to the untempered specimens. From AE measurements, it is observed that martensitic steel emits higher acoustic emissions during deformation but decreases when tempered. The acoustic emissions generated in the martensitic steel are also of higher amplitude. The results are correlated with optical micrographs and hardness measurements.

Stress Evaluation of Welded Joints with Metal Magnetic Memory Testing Based on Tension-Compression Fatigue Test.

Metal magnetic memory testing (MMMT) is an effective nondestructive technique for fatigue damage monitoring of weldments because of its capacity for stress evaluation. An experimental investigation of the effect of the applied fatigue stress on MMMT signals, including the tangential component Bx and the normal component Bz, during tension–compression fatigue tests in welded joints was carried out systematically. The Bx and Bz signals at different fatigue cycles and fatigue stresses were collected and analyzed, and the results showed that there was a peak of Bx and abnormal peaks of Bz that existed at the welded joint before loading. After loading, the peak of Bx and the abnormal peaks of Bz reversed, and the Bx signals moved upward and the Bz signals rotated anticlockwise dramatically in the first few fatigue cycles. After the fatigue cycle number was larger than 1000, Bx and Bz were stable, with very little fluctuation. In addition, the characteristics of Bx signals, the mean value, and the peak value of the average of Bx had an extremely significant linear relationship with the applied fatigue stress during the stable stage of the fatigue test, which indicates that MMMT is a feasible method for fatigue stress evaluation and even residual fatigue life estimation for weldments in service.

Forward model of metal magnetic memory testing based on equivalent surface magnetic charge theory

The magnetic dipole theory has been widely and successfully used to qualitatively analyze the testing signals of metal magnetic memory (MMM) testing. However, the magnetic charge density of the existing models is always an assumed value distributed uniformly or linearly along the defect section or in a stress concentration area, as a result the existing models are unsuitable for quantitatively analyzing the metal magnetic memory signal. In this work, a new forward model of MMM testing is established by considering the influence of uneven stress on magnetic charge density distribution, discretizing the specimen into numbers of micro elements firstly, assuming that the magnetic characteristic parameters of each element are evenly distributed and the magnetic charge density changes with stress in each element which can be determined by combining the modified magneto-mechanical model and the classical theory of magnetic charges. Compared with the experimental results of hole defect and crack defect specimen, the theoretical results calculated by the proposed model prove to be in good agreement with the testing results both qualitatively and quantitatively. Consequently, the proposed model is a new theoretical and quantitative model for analyzing the experimental change rule of metal magnetic memory testing. Then, the effects of stress concentration and macroscopic defects on the distribution of magnetic field are analyzed, showing that when there is only a stress concentration in the specimen, the horizontal component is negative valley, and the normal component changes from negative to positive valley peak in the stress concentration area; when there is a crack defect in the specimen, the distribution of magnetic field is just opposite to that when there is only a stress concentration. The distribution characteristics of the magnetic field can be used to judge the damage type in the specimen. Moreover, taking crack defect for example, the horizontal and normal component of magnetic field and their characteristic parameters changing with the size parameters of crack defect, such as width, length, depth and buried depth of crack defect, are analyzed in detail. The results show that the <inline-formula><tex-math id="M1">\begin{document}${W_{\Delta {H_x}}}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20220176_M1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20220176_M1.png"/></alternatives></inline-formula> and <inline-formula><tex-math id="M2">\begin{document}${W_{\Delta {H_z}}}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20220176_M2.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20220176_M2.png"/></alternatives></inline-formula> increase lineally with the increase of the width of crack, <inline-formula><tex-math id="M3">\begin{document}$\Delta {H_x}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20220176_M3.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20220176_M3.png"/></alternatives></inline-formula> and <inline-formula><tex-math id="M4">\begin{document}$\Delta {H_z}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20220176_M4.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20220176_M4.png"/></alternatives></inline-formula>increase with the increase of the length and depth of crack, but gradually decrease with the increase of defect buried depth.

Research on temperature-magnetic properties based on metal magnetic memory testing technology

during the running of high-speed railway, the vibration and friction between wheel set and track will cause the temperature rise between wheel set and track. The metal magnetic memory detection technology is used to detect the small fault of wheel set, and the temperature will have a certain impact on the magnetic memory signal. In order to study the quantitative relationship between temperature and magnetic memory signal, the temperature magnetic property of 25CrMo4 material is proposed in this paper. Through the temperature magnetic experiment and simulation analysis of the material specimen, it is concluded that when the temperature is lower than Curie point, the magnetic flux leakage of the sheet is basically stable. The value in tangential direction is 130A/m, and the value in normal direction is 0A/m. When the temperature reaches Curie point, the value of the tangential direction changes to 169.9 A/m, and the normal direction is still 0A/m; And the temperature magnetic numerical simulation curve is constructed, which provides the basis for carrying out magnetic signal to material small fault under coupling load, and provides the basis for non-destructive testing.

Application of Metal Magnetic Memory Testing for Quantitative Evaluation of Stress Concentration in Ferromagnetic Steels

The objective of this research is to develop a quantitative algorithm between the magnetic parameter bm and the stress concentration factor in ferromagnetic steels. Specimens of U71Mn steel were machined into smooth plates with artificial defects (circular holes and rectangular holes) to represent various stress concentration degrees. Variations of the magnetic parameter bm with the stress concentration factor and the defect area were studied, respectively. The magnetic parameter bm of the U71Mn steel specimen was compared with that of the X80 steel specimen. Quantitative correlations of the magnetic parameter bm with the stress concentration factor and the defect area were investigated. The results show that the magnetic parameter bm is exponentially varied to the stress concentration factor and the defect area. The quantitative algorithm between the magnetic parameter bm and the stress concentration factor is influenced by the defect shape and the material type. An equation was proposed to evaluate the defect area based on the magnetic parameter bm.

Effect of tensile stress on metal magnetic memory signals during on-line measurement in ferromagnetic steel

Metal magnetic memory testing (MMMT) is a promising nondestructive technique for early damage evaluation of ferromagnetic materials due to its high sensitivity to the stress state. An experimental investigation of the effect of axial applied stress on MMMT signals, both the normal component Bz and the tangential component Bx, under on-line loaded and unloaded measurement condition has been carried out during the whole tensile test in 0.45%C steel. In the elastic deformation stage, Bz signal kept rotating counterclockwise while Bx signal kept moving upward under on-line measurement both when loaded and unloaded, but the MMMT signals measured unloaded tended to resume the initial state compared those measured loaded. In the plastic deformation stage, Bz signal rotated clockwise while Bx signal moved downward under on-line loaded measurement with the increase of tensile stress, while the MMMT signals measured unloaded reversed compared those measured loaded. The results of the present work indicate that MMMT is a feasible solution for stress state on-line monitoring of ferromagnetic components.

Application of Metal Magnetic Memory Testing Technology to the Detection of Stress Corrosion Defect

The damage of equipment manufactured with ferromagnetic materials in service can be effectively detected by Metal Magnetic Memory Testing (MMMT) technology, which has received extensive attention in various industry fields. The effect of stress or strain on Magnetic Flux Leakage (MFL) signals of ferromagnetic materials has been researched by many scholars for assessing stress concentration and fatigue damage. However, there is still a lack of research on the detection of stress corrosion damage of ferromagnetic materials by MMMT technology. In this paper, the electrochemical corrosion system was designed for corrosion experiments, and three different experiments were performed to study the effect of corrosion on MFL signals. The distribution of MFL signals on the surface of the specimen was investigated. The results indicated that both the normal component Hn and tangential component Ht of MFL signals presented different signal characteristics when the specimen was subjected to different working conditions. Finally, two characterization parameters, Sn and St, were defined to evaluate the corrosion degree of the specimen, and St is better. The direct dependence of corrosion depth on the parameter was developed and the average error rates between the predicted and measured values are 8.94% under the same working condition. Therefore, the expression can be used to evaluate the corrosion degree of the specimen quantitatively. The results are significant for detecting and assessing the corrosion defect of ferromagnetic materials.

Quantitative research of defects for pipelines based on metal magnetic memory testing

Pipelines are widely used in the oil & gas industry but defects seriously affect their safe operation. Therefore, it is necessary to perform non-destructive testing (NDT) to quantify the defects. In this study, a magnetic dipole model was established to characterise the defects and magnetic flux leakage (MFL) of defects was simulated using the finite element method (FEM) to reveal the spatial distribution of the magnetic vector. Magnetic signals were measured using a tunnel magnetoresistance (TMR) sensor array and the results showed that defects with different sizes could be quantified using the metal magnetic memory (MMM) method. Three-dimensional distribution of the magnetic signal and its gradient reflected the defect profile well and the gradient of the magnetic signal was found to reduce the effect of non-uniform magnetisation. Furthermore, experimental results were verified by comparison with the simulation results and the comparison results showed a consistent variation trend. Quantitative analysis was conducted and the characteristic parameters of the gradients could be used to quantify the defects.

Magnetic crawler climbing detection robot basing on metal magnetic memory testing technology

Failure detection of high facilities always presents a tremendous challenge. Climbing-wall robot with detection capacity has become a main approach. But owing to their limitations in overcoming obstacles and complicated wall situation, reliable wall-climbing property and precise detection abilities are the most basic demand for achieving this function. Hence, further research is required to enhance robot capabilities in overcoming obstacles and accurate detection signal. The paper presents a new climbing-wall detection robot mechanism. The wall-climbing robot consists of two climbing modules. The two climbing modules are connected by anti-overturning mechanism to provide a capacity of anti-overturning during overcoming obstacle. The detection mechanism is installed at the bottom of the robot. Detailed design issues are presented with analyses of the design parameters. Transition displacement of anti-overturning mechanism and force transfer equation are derived, and stable operating conditions are verified. The abilities of flat surface locomotion, anti-overturning, preload and detection capacity are validated by using experiments. Experiment results show that the prototype achieves 10kg payload capacity on vertical surfaces and can overcome 10mm obstacle. 1mm×1mm circular groove can be found.

Relationship between applied force and magnetic field in a pseudo-static test of a portal frame

Metal magnetic memory (MMM) testing is a nondestructive approach for evaluating the stress concentration and early damage of ferromagnetic components. However, research on the MMM testing of large steel structures has been limited. Thus, this study investigates the suitability of MMM technology for monitoring the damage in steel structures exposed to complex stresses. The normal components of magnetic signals Hp(y) on the beams and columns of a portal frame are obtained through pseudo-static testing. The signal increment ΔHp(y) and its absolute value |ΔHp(y)| under different loads are analyzed. The relationship between the equivalent stress and magnetic signal is investigated through numerical simulation. The results show that the ΔHp(y) curves are similar during the elastic stage but change abruptly during the plastic phase. Moreover, the differences in the magnetic signal directions caused by the varying detection directions cannot be ignored. In the elastic stage, with the increase in the load, |ΔHp(y)| curves initially increase and then decrease. The formation of the ΔHp(y) curve is similar to the distribution of the equivalent stress. The mutation of ΔHp(y) can determine whether a specimen is entering the plastic phase, and can warn against structural failure. The magnetic signal distribution qualitatively reflects the stress distribution.