Numerical Analysis on Magnetic-induced Shear Modulus of Magnetorheological Elastomers Based on Multi-chain Model

Based on the magnetic interaction energy, using derivative of the magnetic energy density, a model is proposed to compute the magnetic-induced shear modulus of magnetorheological elastomers. Taking into account the influences of particles in the same chain and the particles in all adjacent chains, the traditional magnetic dipole model of the magnetorheological elastomers is modified. The influence of the ratio of the distance etween adjacent chains to the distance between adjacent particles in a chain on the magnetic induced shear odulus is quantitatively studied. When the ratio is large, the multi-chain model is compatible with the single chain model, but when the ratio is small, the difference of the two models is significant and can not be neglected. Making certain the size of the columns and the distance between adjacent columns, after constructing the computational model of BCT structures, the mechanical property of the magnetorheological elastomers composed of columnar structures is analyzed. Results show that, conventional point dipole model has overrated the magnetic-induced shear modulus of the magnetorheological elastomers. From the point of increasing the magnetic-induced shear modulus, when the particle volume fraction is small, the chain-like structure exhibits better result than the columnar structure, but when the particle volume fraction is large,the columnar structure will be better.

3-D Magnetic Sensor Module for Locating and Tracking MEMS Swallowable Capsule Based on Scalar Form of Magnetic Dipole Model

MEMS swallowable capsule is a novel technology in the non-invasive surgery. This technology provides a way to diagnose directly into the deep intestinal where the traditional invasive technology implemented, such as X-Ray, endoscopy. It is a key for us to locate and track the position of a MEMS capsule in clinical applications. To solve this problem, we implemented a magnetic sensor module based on the scalar form of the magnetic dipole model,which was designed with very small size （5.2 ＊ 2. 1 ＊ 1.2 em） and easy to assemble to satisfy the system requirement. Here we discuss in detail the principle of magnetic dipole model, rules of selecting sensor and functions of the module. Some trials are established to test the characteristic of the module. The results of the Cm experiment demonstrates that the module follows the rules of the new magnetic dipole model form.

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.

Interaction forces between soft magnetic particles in uniform and non-uniform magnetic fields

The influence of the magnetization of a soft magnetic sphere on the surrounding magnetic field is measured and characterized.The interaction force between two soft magnetic particles is directly measured using an ultra precision load sensor in uniform and non-uniform magnetic fields. The interaction force largely follows an inverse fourth power law as a function of separation distance between particle centers. At small distances,the effect of magnetization of one particle on the magnetization of its adjacent particle causes the attractive（repulsive） force to be larger（smaller） than that predicted by the inverse fourth power law.The theoretical prediction based on a modified dipole model,that takes into account the coupling effect of the magnetization among soft magnetic particles,gives excellent agreement with the measured force in a uniform magnetic field.The interaction force under a non-uniform applied magnetic field can be reasonably predicted using the dipole-dipole interaction model when the local magnetic field is used to determine the magnetization.