Metal Magnetic Memory Testing Research Articles

Characterization of Fatigue Damage of Crankshaft Remanufacturing Core by Two-Dimensional Magnetic Memory Signal

Fatigue damage degree of crankshaft remanufacturing core was studied based on Metal Magnetic Memory Testing. Bending fatigue test of crankshaft remanufacturing core was conducted on the resonant fatigue test rig and variations of two-dimensional magnetic memory signal distribution in crankshaft pin fillets were studied at different bending fatigue cycle. Experimental research shows that distributions of Hp(x) signals, namely, tangential component of spontaneous stray field and Hp(y) signals, namely, normal component of spontaneous stray field in crankshaft pin fillets have no obvious change with loading cycle when no crack initiation and propagation occur in crankshaft pin fillets. Characteristics of Hp(x) and Hp(y) signal both show dynamic variations when crack in crankshaft pin fillets initiates and extends at medium rate or high rate. Metal Magnetic Memory Testing is a dynamic method for monitoring fatigue crack propagation in crankshaft.

Research on the Signal Feature Extraction Method in Steel-Cord Conveyor Belt with Metal Magnetic Memory Testing

Research on the Signal Feature Extraction Method in Steel-Cord Conveyor Belt with Metal Magnetic Memory Testing

Characteristics of metal magnetic memory signals of different steels in high cycle fatigue tests

ABSTRACTThe detection of crack initiation in steel Q235, 16MnR and 20 g was carried out by metal magnetic memory (MMM) technique. Fifty specimens of welded and base metal were tested. Both MMM testing and metallographic examination were done to them when unloaded at the different phase of high‐cycle fatigue testing, and hence MMM signals before and after crack initiation could be recorded. The values of magnetic intensity gradient were calculated, and whose critical value was determined and proposed for early defects detection. The results show that the magnetic intensity (Hp) curve became concave responding to the occurrence of stress concentration, and its gradient (dHp/dx) increased greatly; at the critical dHp/dx, no change occurred to the microstructure, but beyond the critical value, dHp/dx increased suddenly and a large number of intragranular slips were found in the microstructure. Three different kinds of materials have different critical values of magnetic intensity gradient.

Magnetic Memory Testing and Intensity Failure Analysis of Fractured Bolt of Cylinder Head on Hydrogen Gas Compressor

Along with the wide application of pressure energy, large scale reciprocating compressor unit is becoming one of the necessary key equipments in petrochemical industry. The reciprocating compressor has complicated structure and it is very difficult to carry out measurement & analysis to the operation status of various components. Above all, as the most important fastener of the compressor, once fracture of cylinder head bolt of the reciprocating compressor occurs, major disaster will occur. Metal magnetic memory testing technology is a nondestructive examination technology based on magneto-mechanical effect principle. Specific change of leakage magnetic field will occur in stress & deformation concentrated region under combined action of alternate work load and geomagnetic field, macroscopic cracking can be detected and stress concentration and early state damage can be evaluated by utilizing this specific change, We carried out on-site examination on the fractured bolt of cylinder head of hydrogen gas compressor unit in refinery of certain petrochemical corporation with latest metal magnetic memory testing technology. On the basis of intensity analysis and dynamic load calculation to cylinder head bolt of the reciprocating compressor, we analyzed the cause of bolt fracture by using metal magnetic memory testing technology and drew out the magnetic memory signal distribution characteristics of the bolt and its fracture. We verified the correctness of testing result of the metal magnetic memory technology on cylinder head bolt and its fracture with metallographic examination technology; furthermore, we studied the reliability of bolt fatigue crack & fracture analysis and investigation of accident cause by using magnetic memory characteristic distribution signal.

Analysis of Metal Magnetic Memory Testing Technology

The magnetic memory effect and the principle of magnetic memory testing are described; The phenomenon of the magnetostriction is discussed. An instance is used with detail to analysis of the effect and mechanism of metal magnetic memory testing technology. Some opinions about the further work needs to be done in this area are given finally.

Investigation of Array Magnetic Memory Testing Technology on Extension of Metal Crack

Metal Magnetic Memory (MMM) testing method has its own effective and unique advantages on the research of extension of metal crack. The array magnetic memory testing sensor designed and assembled in accordance with specific conditions, could evidently enhance testing-efficiency, such as for components with complex shape or large surface area, and may simplify the test equipment correspondingly. A kind of array magnetic memory sensor with Hall elements as core components was designed and an experiment on metal magnetic memory testing on extension of metal crack was executed. The experiment results indicate that the magnetic memory testing technique could effectively monitor and qualitatively evaluate the progress of metal crack extension.

Metal Magnetic Memory Testing of X60 Pipeline Steel under Tension Load and Fatigue Load

To study the relation between stress and the Metal Magnetic Memory Testing (MMMT) signal Hp(y) of ferromagnetic structure, a material mechanics experiment using X60 pipeline steel specimens under tension load and fatigue load is performed. The results show: The value of MMMT signal in elastic stage is small under tension load, while the value of MMMT signal in plastic stage is large. In the process of static tension, the zero crossing point (ZCP) of initial MMMT signal curves shift to the fracture position, and there is only one ZCP of MMMT signal curve at the position of fracture area. In the process of low-load fatigue, the shape and distribution of MMMT signal curves are similar under different cycle numbers of fatigue load. The value of MMMT signal increases a little with the increase of cycle number of fatigue load, and then increases sharply when the specimen is to be fractured. There is only one ZCP of MMMT signal curve at the position of fracture area in the process of fatigue loading.

Fatigue damage assessment for ferromagnetic items based on the metal magnetic memory technique

Metal magnetic memory (MMM) testing is a novel magnetic method for inspecting the fatigue damage of ferromagnetic specimens. In order to promote further understanding of the relationship between the leakage magnetic field and the fatigue damage parameter, the distributions of the leakage magnetic field on different cycle numbers, N, were measured and analysed during the tensile stress fatigue experiment. The results indicate that using magnetic characteristics to evaluate the fatigue damage for specimens is effective. A new fatigue damage model was set up which can provide a good assessment method for the fatigue damage of ferromagnetic material. The stress intensity factor ΔK has a close relationship with the cycle number N and the distribution of the leakage magnetic field. It shows that the use of ΔK as a parameter to evaluate the degree of fatigue damage is feasible.

The State-of-the-Art Surveys for Application of Metal Magnetic Memory Testing in Remanufacturing

Metal magnetic memory（MMM） testing has been used in the residual life prediction of remanufacturing cores. The MMM testing is one of the most promising nondestructive testing methods for achieving early diagnosis on micro defects of remanufacturing cores. This method can not only detect the traditional macro-cracks, but also identify the micro-damage caused by stress concentration. The principle of MMM testing works in the conditions that without requiring of the external exciting magnetic field, the magnetic field distribution of the inspection surface is scanned and measured by means of magnetic mutation signals to find the possible existence of stress concentration and location of micro-cracks. This paper presents a state-of-art survey about MMM testing mechanism and application of MMM method in Russia, Britain, China and the other countries. It includes the applications of this method in power station turbine blade damage detection by Russia scholars, evaluating the gear creep damage by Polish scholars and detecting the stress concentration districts of the train wheels damaged parts by Chinese scholars. The paper also reports that Chinese scholars developed methods of using MMM testing to characterize initiating and growing of fatigue cracks, and applied this method for prediction of residual life of remanufacturing cores. Based on the comprehensive survey, this paper points out further trends of the research work in the area. The paper also points out that microscopic physical mechanism of the MMM phenomenon and application of MMM testing in defining the manufacturability of remanufacturing cores should be further studied. Introduction

Welded Joint Nonpenetration and Slag Inclusion Evaluation Based on MMM Signal Characteristic

The metal magnetic memory (MMM) technology, a new nondestructive testing (NDT), has potentials of quantitative evaluation on welded joint defects. This paper investigates MMM signal quantitative characteristic of welded joint defects. Steel Q235 welded joint specimens, prefabricated with nonpenetration and slag inclusion, have been scanned by MMM testing instrument at 0kN, 150kN and 230kN tension loads on tensile machinery. For the nonpenetration specimens, MMM peak amplitude ΔHp and the peak width D adds with the increasing of tensile load, but gradient K varies a little. As for the slag inclusion specimens, the ΔHp and K enhances along with tensile load increasing, but the D varies a little. The X-ray testing results at 0kN, 150kN and 230kN tension loads show the validity of MMM signal characteristic. This means the feasibility of the weld qualitative and quantitative evaluation based on MMM method.

Metal magnetic memory testing of welded joints of ferritic and austenitic steels

The method of the metal magnetic memory testing is a passive method of non-destructive testing based on the residual magnetic field (RMF) of a component. It allows the localization of stress concentration zones in the objects under examination. The defects in welded joints are places of stress concentration. Also, due to the geometric notch effect and thermal deformations after welding, the welded joint is a stress concentrator. Therefore, not all indications obtained in the method of the MMM testing are defects in the common, standard meaning. Additionally, in the weld seams of austenitic steels, the non-uniformity of delta ferrite in the joint results in changes in the RMF distribution and gives rise to indications. The paper presents the ways of examination and assessment of welded joints by means of the method of the MMM testing. The presented research methodology is the outcome of a synthesis of own experience and the provisions of standards ISO 24497-1, 2, 3: 2007. The results obtained in the MMM testing were compared to the results of the radiographic testing (RT). It was found that the MMM testing allowed the detection of imperfections, including defects, in welded joints at the production stage. Knowing the potential of the method of the MMM testing it seems well justified that it should be used in the examination of welded joints at the operation stage. These joints, after non-destructive testing at the production stage, are not free from defects. The defects, together with imperfections at the micro-level, concentrate stresses from working loads. Wear processes and the development of micro- and macro-cracks proceed in them the fastest. By finding the stress concentration zones, the areas of potential cracks can be found. The development of reliable procedures of examination and assessment of welded joints with the use of the method of the metal magnetic memory testing still needs a lot of research.

Characterizing stress concentration by metal magnetic memory signal of H_{p} (x)

A novel method for quantitative characterization of stress concentration based on the tangential component of metal magnetic memory (MMM) signal, Hp(x), was studied via fatigue testing and MMM testing of notched plate samples. In this research, the changing regularity of Hp(x) signals is found out. A method to calculate stress concentration factor from Hp(x) signals is established, and a new conception of magnetic stress concentration factor KH , Hp(x)max/Hp(x)ave, is put forward to quantitatively characterize stress concentration in mechanical components. The research provides the potential possibility of quantitative inspection for metal magnetic memory testing.

Investigation on metal magnetic memory signal during loading

The dynamic variation of amplitude and gratitude of metal magnetic memory (MMM) signals for a crack on a crane crossbeam was investigated during loading from 0 to 80KN. The result shows that the amplitude and gratitude of MMMT signals slowly increase from 0 to 50KN, quickly increase from 50 to 70KN and rapidly decrease from 70 to 80KN. The crack emerged result in the peak to peak value rapidly increasing and the shape of MMM signals change to sharp. The stress released results in decreasing of the peak to peak of the amplitude and gratitude of MMM signals. MMM testing method can be used to monitor the activity of surface crack or damage in steel structure.

Steam Turbine Blade MMM Testing and Failure Analysis

Metal magnetic memory (MMM) method, based on the magneto-elasticity and mechanical effect theory, is a new nondestructive testing technology. This paper aims at the material property and failure analysis for steam turbine blade with MMM method. The failure blade and its fracture face are tested with MMM technology at workshop. It has been found that the MMM signal variation gradient of the crack transition zone in the fracture face is minimal, that of the crack initiation zone is in the middle, and that of the tear fracture zone is maximal. MMM testing results reflect material behavior degradation of the failure blade. In order to proof the MMM results, the dynamic stress of the steam turbine blade under the operation loading is calculated by WESTHOMES software and analyzed theoretically. It has proved the validity of the MMM method applied on material property evaluation and failure analysis for steam turbine blade.

Characterisation of stress concentration of ferromagnetic materials by metal magnetic memory testing

The relationship between the degree of stress concentration and the H p(y) signals of metal magnetic memory was investigated by tension–tension fatigue tests. Sheet specimens of 45CrNiMoVA steel were machined and two types of notches were cut into them to obtain two stress concentration factors. During the testing process, H p(y) signals were collected from three measured lines on the specimen surface. In the absence of a precut notch, the H p(y) signal curve of a measured line at the central position was linear. However, the H p(y) signal curves of measured lines near a precut notch or across a notch showed a distribution of abnormal magnetic peaks. The magnetic gradient K of the abnormal magnetic peaks was found to increase as the stress concentration factor increased. This feature could potentially be used to characterise the degree of stress concentration of ferromagnetic materials.

Stress measurement using magnetic Barkhausen noise and metal magnetic memory testing

This paper introduces a comparison of the magnetic Barkhausen noise (BN) and metal magnetic memory (MMM) testing techniques for stress measurement. BN has become an important non-destructive technique due to its exceptional material and stress characterization capabilities. MMM is a recently developed technique with special ability for stress detection and stress history. In the applied tensile experiment, BN and MMM signals were acquired via a BN measurement system and EMS-2003 MMM instrument. Relationships between magnetic signals and applied tensile stresses were derived from experiment results. The difference and correlation of the two methods are investigated. Conclusions were derived based on the experiment results.

Influences of environmental magnetic field on stress-magnetism effect for 20 steel ferromagnetic specimen

The stress-magnetism effect is a fundamental principle in metal magnetic memory testing technology, which is also a key issue in the life assessment of ferromagnetic materials. Curves of magnetising status versus stress in different environmental magnetic fields were studied for 20 # steel ferromagnetic specimens. It was found that influences of the environmental magnetic field on the stress-magnetism effect were very obvious. It shows that testing and estimating of metal magnetic memory testing technology is related to the geomagnetic field.

Metal magnetic memory effect caused by static tension load in a case-hardened steel

For investigating the magnetic abnormality influenced by stress in ferromagnetic materials, static tension tests on a case-hardened steel were carried out. Different loads, which covered tensile elastic loads up to plastic deformation and break, were applied. Meanwhile, the normal component of magnetic flux leakage, H p( y), was measured by metal magnetic memory testing. The results indicate that H p( y) values change with the tensile loads and positions. There exists a relationship between k, which is the inclination of the linear amplitude-locus magnetic flux leakage curve, and static tension load. A simple model is derived. Additionally, the mechanism of the magnetic memory effect can be explained by the theory of the interaction between dislocations and domains. The research provides the potential possibility of quantitative inspection for metal magnetic memory testing.

Experiment on relationship between the magnetic gradient of low-carbon steel and its stress

In geomagnetic field, a series of tensile experiments on the low-carbon steel sticks were carried out. A special homemade detector was used to measure the magnetic gradient on the material surface. The results showed that the relationship between the magnetic gradient and the stress varied with different conditions of measurement. There was no obvious correlation between the magnetic gradient and the tensile stress if the sample remained on the material test machine. If the sample was taken off from the machine, the measured magnetic gradient was linear with the prior maximum stress. In Nanjing, PR China, a place of 32°N latitude, the slope of the linear relationship was about 67(uT/m)/MPa. This offered a new method of non-destructive stress testing by measuring the magnetic gradient on the ferromagnetic component surface. The prior maximum applied stress of the sample could be tested by measuring the present surface magnetic gradient. Actually this phenomenon was the metal magnetic memory (MMM). The magnetic gradient near the stress concentration zone of the sample, the necking point, was much larger than other area. Thus, the hidden damage in the ferromagnetic component could be detected early by measuring the magnetic gradient distribution on its surface. In addition, the magnetic memory signal gradually weakened as the sample was taken off and laid aside. Therefore, it was effective for a given period of time to detect the stress or stress concentration based on the MMM testing.

Modeling and analysis of magnetic dipoles in weak magnetic field

The magnetic leakage field distribution resulting from linear defects of a tube sample in the geomagnetic field is modeled according to the magnetic dipole theory. The formula to compute the normal component of the weak magnetic field is deduced based on the spatial distribution of the magnetic dipole. The shape and characteristics of the zero line (an important criterion for magnetic memory testing) of the normal field is analyzed under different longitudinal magnetizations. Results show that the characteristics of the zero line should be considered when the metal magnetic memory testing method is used to find and locate the defect.