PERTURBATION ANALYSIS FOR MAGNETO-PLASTIC INSTABILITY OF FERROMAGNETIC BEAM-PLATES WITH GEOMETRIC IMPERFECTION

The magneto-plastic instability of a ferromagnetic beam-type plate with simple supports and small initial imperfection is analytically investigated in this paper for that the plastic deformation of the plate with a linear-strain hardening relation is considered when the plate is located in a strong uniformly distributed magnetic ?eld. After the distribution of magnetic ?elds related to the de?ected con?guration of plate is imaginably divided into two parts, i.e., one is related to the ?at plate and the other dependent on the perturbation of magnetic ?elds for which the plate con?guration changes from the ?at into the deformed state, the perturbation technique is employed to analyze the distribution of the perturbation magnetic ?elds in and out-of the magnetic medium of the ferromagnetic structure in a transverse magnetic ?eld, which leads to some analytical formulae/solutions for the magnetic ?elds and the resulting magnetic force exerted on the plate. Based on them, the magneto-plastic buckling and snapping of the plate in a transverse magnetic ?eld is discussed, and the critical magnetic ?eld is analytically formulated in terms of the parameters of geometry and material of the plate employed by solving the governing equation of the magneto-plastic plate in the applied magnetic ?eld. Further, the sensitivity of the initial imperfection on the magneto-plastic instability, expressed by an ampli?cation function, is obtained by solving the dynamic equation of de?ection of the plate after the inertial force in the transverse direction is taken into account. The results obtained show that the critical magnetic ?eld is sensitive to the plastic characteristic, e.g., hardening coe?cient, and the instability mode and de?ection of the plate are dependent on the geometrical imperfection as well.

Influence of high pulsed magnetic field on tensile properties of TC4 alloy

The tensile tests of TC4 alloy are carried on electronic universal testing machine in the synchronous presence of high pulsed magnetic field（HPMF） parallel to the axial direction.The effects of magnetic induction intensity（5 = 0,1 T,3 T,and 5 T） on elongation（5） of TC4 alloy are investigated.At 3 T,the elongation arrives at a maximum value of12.41%,which is enhanced by 23.98%in comparison with that of initial sample.The elongation curve shows that 3 T is a critical point.With B increasing,the volume fraction of α phase is enhanced from 49.7%to 55.9%,which demonstrates that the HPMF can induce the phase transformation from β phase to α phase.Furthermore,the magnetic field not only promotes the orientation preference of crystal plane along the slipping direction,but also has the effect on increasing the dislocation density.The dislocation density increases with the enhancement of magnetic induction intensity and the 3-T parameter is ascertained as a turning point from increase to decrease tendency.When B is larger than 3 T,the dislocation density decreases with the enhancement of B.The influence of magnetic field is analyzed on the basis of magneto-plasticity effect.The high magnetic field will enhance the dislocation strain energy and promote the state conversion of radical pair generated between the dislocation and obstacles from singlet into triplet state,in which is analyzed the phenomenon that the dislocation density is at an utmost with B = 3 T.Finally,the inevitability of optimized 3-T parameter is further discussed on a quantum scale.

Magnetic Control of the Earthquakes

Many observations reliably exhibit correlations between the magnetic perturbations and seismic responses, convincing that the magneto-seismicity is not a myth. Magnetic control of the earthquakes is based on physics of magneto-plasticity, the remarkable phenomenon, which implies generation of the electron spin pairs on the trapped dislocations, in which Coulomb interaction is switched off. Microwave irradiation at Zeeman frequencies in these pairs stimulates the motion of dislocations, inducing release of elastic energy into the safe plastic deformation. Magneto-seismic correlations unambiguously demonstrate that the earthquakes are indeed suppressed by low-frequency (wide and continuous spectrum from Hz to MHz) microwaves The detailed mechanism of this phenomenon is discussed and experimental proofs are given in terms of magneto-plasticity as a feasible means to control earthquakes.

Self-Excitation of the Earthquakes

Numerous correlations between magnetic and seismic events unambiguously indicate that the magnetic control of the earthquakes is a fundamental phenomenon. It proceeds from the remarkable physics of magneto-plasticity of solids, which implies acceleration of dislocations by microwaves. The motion of dislocations provides release of dangerous elastic energy of the earthquake focus and transforms elastic energy into the safe energy of plastic deformation. Magneto-plasticity seems to be the most important mechanism of the magnetic control because the piezoelectric effect as a suggested mechanism of magnetic control should be excluded (Chelidze et al.). Magnetic control certifies earthquake focus as a receiver of microwaves;on the other side, numerous observations exhibit emission of microwaves generated by earthquake focus, so that it can be considered as a permanent generator of microwaves. The idea of this paper is to offer a mechanism of self-excitation of the focus: self-triggering is suggested to be induced by microwaves generated by earthquake focus itself. The more intensive is the crack formation, the higher is the density of microwaves, which accelerate dislocations and intensify crack formation: it is a feedback breeding, avalanche-like process. Both functions of earthquake focus, to be simultaneously generator and receiver of microwaves, are integrated into the same space and time. It excludes such limitation of the magnetic control as the penetrability of the rocks for microwaves.

Effect of a weak magnetic field on ductile-brittle transition in micro-cutting of single-crystal calcium fluoride

Magneto-plasticity occurs when a weak magnetic field alters material plasticity and offers a viable solution to enhance ductile-mode cutting of brittle materials.This study demonstrates the susceptibility of non-magnetic single-crystal calcium fluoride(CaF_(2))to the magneto-plastic effect.The influence of magneto-plasticity on CaF_(2) was confirmed in micro-deformation tests under a weak magnetic field of 20 mT.The surface pile-up effect was weakened by 10-15 nm along with an enlarged plastic zone and suppressed crack propagation under the influence of the magnetic field.Micro-cutting tests along different crystal orientations on the(111)plane of CaF_(2) revealed an increase in the ductile-brittle transition of the machined surface with the aid of magneto-plasticity where the largest increase in ductile-brittle transition occurred along the[112]orientation from 512 nm to a range of 664-806 nm.Meanwhile,the subsurface damage layer was concurrently thinner under magnetic influence.An anisotropic influence of the magnetic field relative to the single-crystal orientation and the cutting direction was also observed.An analytical model was derived to determine an orientation factor M that successfully describes the anisotropy while considering the single-crystal dislocation behaviour,material fracture toughness,and the orientation of the magnetic field.Previously suggested theoretical mechanism of magneto-plasticity via formation of non-singlet electronic states in defected configurations was confirmed with density functional theory calculations.The successful findings on the influence of a weak magnetic field on plasticity present an opportunity for the adoption of magnetic-assisted micro-cutting of non-magnetic materials.

Mechanism of Residual Stress Reduction in Low Alloy Steel by a Low Frequency Alternating Magnetic Treatment

Residual stress reduction in low alloy steel by a low frequency alternating magnetic treatment and its mechanism were investigated. Experimental results revealed that average stress reductions of 20%-24% were obtained in the welded samples. Moreover, compared with the zones with lower initial stress levels, more remarkable stress reductions were obtained in the stress concentration zones. The microstructures and magnetic domains were observed by scanning electron microscopy （SEM） and atomic force microscopy （AFM）. Based on the analysis of the microstructure and magnetic domain changes, the mechanism of stress reduction by the magnetic treatment has been concluded： （1） the magneto-plastic deformations mainly due to the more uniform redistribution of dislocations are the fundamental cause of stress relaxation; and （2） surface topography is also proved to affect the magnetic treatment results to some degree by influencing magnetic domains.