Minqiang Xu

Discuss on using Jiles-Atherton theory for charactering magnetic memory effect

The characterization of magnetic memory effect is the primary task of the metal magnetic memory (MMM) technique used in quantitative evaluation, and it has been characterized by the Jiles-Atherton (J-A) model in recent papers. The feasibility of using the MMM field to characterize magnetization intensity M and the feasibility of using the J-A model in MMM detection are discussed in this paper to clarify the magnetic memory effect in the elastic stage. According to analysis with the J-A model and the results of a rotating bending fatigue experiment, the MMM field follows the law that the state approaches equilibrium under the action of cyclic stress. This is similar to what the J-A model shows, only with replacement of the global equilibrium state Man in the J-A model with the local equilibrium state M0. The expression of M0 is obtained by considering the energy balance in the process of magnetization. M0 changes with the pinning resistance, external field, and type of stress cycle. Additionally, the M0−σ ...

Modeling plastic deformation effect on magnetization in ferromagnetic materials

Based on the Sablik-Landgraf model, an integrated model has been developed which provides a description of the effect of plastic deformation on magnetization. The modeling approach is to incorporate the effect of plastic deformation on the effective field and that on the model parameters. The effective field incorporates the contributions of residual stress, stress demagnetization term, and the plastic deformation. We also consider the effect of plastic deformation on the model parameters: pinning coefficient, the scaling constant and the interdomain coupling coefficient. The computed magnetization exhibits sharp change in the preliminary stage of plastic deformation, and then decreases slowly with the increase of plastic strain, in agreement with experimental results.

Using Modified J–A model in MMM detection at elastic stress stage

In order to propel the development of metal magnetic memory (MMM) technique in fatigue damage detection, a modified Jiles–Atherton (J–A) model is constructed to describe MMM mechanism in elastic stress stage. The MMM phenomenon is discussed from the view of energy minimum theory and equivalent magnetic field theory, the modified J–A model is constructed based on the energy balance in the process of magnetisation and the idea of J–A model, and the new model is used to simulate magnetomechanical effect by Matlab and compare with experimental results. It is shown that the forming process of MMM field is cyclic magnetisation in the range of equivalent magnetic field and the MMM field moves irreversibly towards a local equilibrium state . is the intermediate state with some pinning before M reaches the anhysteretic magnetisation state . The curve is a loop around the curve, and it changes with , H and the type of stress cycle. The modified J–A model that is suited for MMM detection is constructed by replacing in J–A model with and changing some parameters, and it can describe magnetisation features in tension, release processes better and explain the changes in the sign of that have been observed in experiments more reasonably. The modified J–A model can simulate the process of MMM field to become steady and the MMM field variation at fatigue process theoretically by changing model parameters, which is confirmed by experimental results. The results of theoretical research, simulation analysis and experiment verification all indicate that the modified J–A model can be used to describe MMM mechanism in elastic stress stage and analyse MMM field changes at fatigue process.

Fatigue Damage Evaluation on Ferromagnetic Materials Using Magnetic Memory Method

Measuring magnetic parameters nondestructively is important for understanding fatigue phenomena of ferromagnetic materials. In this study, metal magnetic memory method is used as a new diagnostic tool to evaluate fatigue process. Both normal and tangential components of residual magnetic field have been studied on medium carbon steel specimens subjected to rotary bending fatigue. The results indicate that the normal component is related to different stress states while the variation trend of the tangential component with number of cycles shows a good agreement with the fatigue stages. This approach seems to be able to predicate fatigue lifetime.

Application of empirical mode decomposition in early diagnosis of magnetic memory signal

In order to eliminate noise interference of metal magnetic memory signal in early diagnosis of stress concentration zones and metal defects, the empirical mode decomposition method combined with the magnetic field gradient characteristic was proposed. A compressive force periodically acting upon a casing pipe led to appreciable deformation, and magnetic signals were measured by a magnetic indicator TSC-1M-4. The raw magnetic memory signal was first decomposed into different intrinsic mode functions and a residue, and the magnetic field gradient distribution of the subsequent reconstructed signal was obtained. The experimental results show that the gradient around 350 mm represents the maximum value ignoring the marginal effect, and there is a good correlation between the real maximum field gradient and the stress concentration zone. The wavelet transform associated with envelop analysis also exhibits this gradient characteristic, indicating that the proposed method is effective for early identifying critical zones.

Stress State Detection Based on Metal Magnetic Memory Theory

The metal magnetic memory (MMM) technology, a new nondestructive evaluation (NDE) method, is an effective means for early damage prediction. However, there is so much work to do, such as the relationship between the magnetic field density and stress state. This paper aims at finding out MMM signal characteristics of critical damage stress state by tension experiments. Comparisons between MMM testing and traditional NDE method are presented. The principle of MMM testing is investigated. Different materials, low carbon steal X70 and medium carbon Q235B, are detected on-line and off-line respectively. It is found that MMM signal rules are gradually increasing up to fluctuating on the verge of yield and sharp changing of magnetic polarity on the verge of fracture. With the increase in material strength, magnetic field density of low carbon steel X70 is lower than that of medium carbon steel Q235B. This offers fundamental study for the quantitative MMM testing of critical damage stress state.Copyright