Experimental study on magnetomechanical coupling effect of Q235 steel tubular member specimens

The magnetomechanical coupling tests were performed on Q235 steel tubular model specimens in NIM-2000HF magnetomechanical coupling equipment. The hysteresis loops were obtained in different magnetic fields and stresses. The magnetization curves were also achieved at different stresses. The influence of applied stresses on the hysteresis loops was investigated. The stress sensitive region and linear stress sensitive region of magnetic induction are determined for the model specimen according to the experimental data. The linear dependence relation of magnetic induction versus applied stresses is established, and the optimum magnetic field is determined in the stress sensitive range of magnetic induction, which builds a basis for nondestructive testing (NDT) of stress with the total magnetic flux for steel structure.

MAGNETOMECHANICAL BEHAVIORS OF GIANT MAGNETOSTRICTIVE MATERIALS

The Laves phase alloy Tb-Dy-Fe, commercially known as Terfenol-D, exhibits the giant room-temperature magnetostriction at moderate field strength of a few kOe due to its combination of high magnetostriction and low magnetocrystalline anisotropic energy. Thus, this pseudobinary rare earth iron compound has found quite a number of applications such as in magnetomechanical transducers, actuators and adaptive vibration control systems. The simultaneous measurements of magnetostriction and magnetization at various fixed compressive pre-stresses applied in the axial direction for Tb0.3Dy0.7Fe1.95 samples are presented. The results show that the magnetostriction increases with increasing compressive stress until it reaches 1742 ×10^6 under 25 MPa, so does the coercive magnetic field. And the hysteresis loop area for magnetization and magnetostriction also increases with the increment of applied compressive stresses. But the maximum magnetic susceptibility χ（dM/dH） is obtained under zero stress field and the strain derivative dλ/dH increases to the highest amplitude of 0.039×10^-6 A^-1m at a stress level of 5 MPa. In the strain versus magnetization intensity curve, the initial fiat stage mainly consisting of a 180° domain wall motion becomes shorter with increasing stress. It means more initial domains are driven to the transversal direction under the compressive stress before magnetization, which is consistent with the improvement of the magnetostriction.

Relationship between Magnetomechanical Damping Capacity and Vibration Modes

The mathematical expressions for magnetomechanical damping capacity are presented by applying Smith-Birchak's model in torsion pendulum and cantilever beam.The peak value ψ_p is found to be related to physical parameters and material constants in the form Kλ_s=αψ_pε_p.which can be used to estimate the magnetostrictive constant λ_s from the damping capacity-strain amplitude curve.A good agreement of experimental data and theoretical prediction was observed in HIDAMETS Cr15A13NiCu.

Modeling of the loading path dependent magnetomechanical behavior of Galfenol alloy

The magnetomechanical behavior of single-crystal Galfenol alloy was found to be strongly dependent on the loading paths. An energy-based anisotropic domain rotation model, assuming that the interaction between domains can be ignored and the probability of the magnetic moment pointing along a particular direction is related to the free energy along this direction, is used to simulate the magnetostriction versus magnetic field and stress curve and to track the magnetic domain motion trail. The main reason for loading path dependent effect is the rotation/flipping of the magnetic domains under different loading paths. The effect of loading and unloading paths on 90° magnetic domain motion was studied by choosing different loading and unloading state and paths. The results show that prior loading magnetic field can make the 90° magnetic domains flip to the directions of 45°domains because the magnetic field is the driving force to make the domains rotate, and the final loading state and the loading path both have great influence on the motion of 90° magnetic domains.

Internal Stress Distribution Model of the Magnetomechanical Hysteresis of Fe-Cr-Al Based Alloys

The damping capacities of Fe-13Cr-6AI, Fe-12Cr-1Mo-6AI and Fe-12Cr-1Mn-6Al （at.%） alloys as a function of strain-amplitude tested in a given static load are characterized in the 3-point bending deformation mode. After being modified, Smith-Birchak model is applied to describe the results. It is shown that the modified model agrees with the experimental data much better than the original one. Finally, the influences of stress factors on the damping capacity of the alloys are analyzed.

THE NONLINEAR MAGNETOELASTIC PROPERTIES OF <110> ORIENTED TB_(0.27)DY_(0.73)FE_(1.95) POLYCRYSTALLINE ALLOYS UNDER COUPLED MAGNETOMECHANICAL LOADING

In the paper, the nonlinear magnetoelastic properties of composition Tb0.27Dy0.73 Fel.95 〈 110 〉 oriented polycrystalline alloys are investigated under coupled loads of high mag- netic field and compressive stress. The magnetization and magnetostriction are measured simul- taneously under applied magnetic field from -800 to 800 kA/m and compressive stress from 0 to 25 MPa at room temperature. The strain coefficient and relative permeability are obtained by differential calculation from the experimental curves. The results show that the values of satura- tion magnetization （M~） under different compressive stresses remain invariably constant in the region of the high magnetic field. The saturation magnetostriction （As） increases with increasing compressive stress and reaches 1680 ~ 10-6 under 25 MPa. According to the increase of the com- pressive stress, the hysteretic loop area of magnetization and magnetostriction increases, while the maximum relative permeability and strain coefficient decrease. Additionally, the influence of the bias magnetic field on the mechanical property is taken into account. The stress-strain relation- ship is nonlinear and sensitive to the applied external magnetic fields along the axis of rod. The results obtained are a useful complement to the existing experiments for theoretical approaches and engineering applications.

Research on Magnetomechanical Coupling Effect of Q235 Steel Member Specimens

In this study,magnetomechanical coupling tests were performed on Q235 solid round steel model specimens in NIM-200HF magnetomechanical coupling equipment.Hysteresis loops were obtained in different magnetic fields and stresses.Magnetization curves were also achieved at different stresses.Influence of the applied stresses on the hysteresis loops was investigated.The stress sensitive region and linear stress sensitive region of magnetic induction were determined for the model specimen according to the experimental data.The dependence relation of magnetic induction versus applied stresses was established,and the optimum magnetic field was determined in the stress sensitive range of magnetic induction,which builds a basis for nondestructive testing(NDT) of stress with the total magnetic flux for steel structure.Based on modified Jiles-Atherton's model of magnetic hysteresis,the hysteresis loop for Q235 steel 4-mm diameter model specimen was numerically simulated,which was well consistent with the experimental results.

Metal magnetic memory field characterization at early fatigue damage based on modified Jiles-Atherton model

In order to propel the development of metal magnetic memory （MMM） technique in fatigue damage detection, the Jiles-Atherton model （J-A model） was modified to describe MMM mechanism in elastic stress stage. A series of rotating bending fatigue experiments were conducted to study the stress-magnetization relationship and verify the correctness of modified J-A model. In MMM detection, the magnetization of material irreversibly approaches to the local equilibrium state Mo instead of global equilibrium state M^n under cyclic stress, and the M0-a curves are loops around the Mar,-a curve. The modified J-A model is constructed by replacing M~ in J-A model with M0, and it can describe the magnetomechanical effect well at low external magnetic field. In the rotating bending fatigue experiments, the MMM field distribution in normal direction around cylinder specimen is similar to the stress distribution, and the calculation result of model coincides with experiment result after some necessary modifications. The MMM field variation with time at a certain point in fatigue process is divided into three stages with the variation of stable stress-stain hysteresis loop, and the calculation results of model can explain not only the three stages of MMM field changes, but also the different change laws when the applied magnetic field and initial magnetic field are different. The MMM field distribution in normal direction along specimen axis reflects stress concentration effect at artificial defect, and the magnetic signal fluctuates around the defect at late fatigue stage. The calculation results coincide with the initial MMM principle and can explain signal fluctuates around the defect. The modified J-A model can explain experiment results well, and it is fit for MMM field characterization.

Characterization of the Elastic-plastic Region Based on Magnetic Memory Effect

Detecting stress concentration, especially critical stress state leading to structure damage or failure, is one of the most important tasks of equipment diagnosis. Metal magnetic memory technique needs further research to evaluate stress concentration quantitatively due to ambiguous physical mechanism, though it has potential to detect early defects in ferromagnetic materials. Mild Q235 steel defective specimens in demagnetization state were loaded in tension up to visible necking, with magnetic memory signals measurement made at increasing stress levels. Magnetic signals varied greatly under first several loadings and subsequently tended to stability in the elastic region, which showed that the magnetization always approaches the anhysteretic magnetization curve and was explained by the theory of magnetomechanical effect. In the plastic stage, an abnormal wave occurred in the stress concentration zone and its height value was sensitive to plastic deformation levels and dependent on the distance between the probe and defect, in accordance with the simulation results based on the magnetic dipole model. Different magnetic signal characteristics in the elastic-plastic region indicate that the magnetic memory technique can identify macroyielding and early damage, which is of profound significance for ensuring safe operation of equipment in service.

Modified magnetomechancial model in the constant and low intensity magnetic field based on J-A theory

The existing magnetomechancial models cannot explain the different experimental phenomena when the ferromagnetic specimen is respectively subjected to tension and compression stress in the constant and low intensity magnetic field,especially in the compression case. To promote the development of magnetomechancial theory, the energy conservation equation, effective magnetic field equation, and anhysteretic magnetization equation of the original Jiles-Atherton（J-A）theory are elucidated and modified, an equation of the local equilibrium status is employed and the differential expression of the modified magnetomechancial model based on the modified J-A theory is established finally. The effect of stress and plastic deformation on the magnetic parameters is analyzed. An excellent agreement is achieved between the theoretic predictions by the present modified model and the previous experimental results. Comparing with the calculation results given by the existing models and experimental results, it is seen indeed that the modified magnetomechanical model can describe the different magnetization features during tension-release and compression-release processes much better, and is the only one which can accurately reflect the experimental observation that the magnetic induction intensity reverses to negative value with the increase of the compressive stress and applied field.