A THEORETICAL MODEL OF MAGNETOELASTIC BUCKLING FOR SOFT FERROMAGNETIC THIN PLATES

As an essential model of magnetoelastic interaction between magnetic field and mechanical deformation, the study on magnetoelastic buckling phenomenon of soft ferromagnetic plates in a magnetic environment has been conducted. One of the key steps for the theoretical prediction of the critical magnetic field is how to formulate magnetic force exerted on the magnetized medium. Till today, the theoretical predictions, from theoretical models in publications, of the magnetoelastic buckling of ferromagnetic cantilevered beam-plate in transverse magnetic field are all higher than their experimental data. Sometimes, the discrepancy between them is as high as 100%. In this paper, the macroscope formulation of the magnetic forces is strictly obtained from the microscope Amperion current model. After that, a new theoretical model is established to describe the magnetoelastic buckling phenomenon of ferromagnetic thin plates with geometrically nonlinear deformation in a nonuniform transverse magnetic field. The numerical method for quantitative analysis is employed by combining the finite elemental method for magnetic fields and the finite difference method for deformation of plates. The numerical results obtained from this new theoretical model show that the theoretical predictions of critical values of the buckling magnetic field for the ferromagnetic cantilevered beam-plate are in excellent agreement with their experimental data. By the way, the region of applicability to the Moon-Pao's model, or the couple model, is checked by quantitative results.

Mechanical properties of lattice grid composites

An equivalent continuum method only considering the stretching deformation of struts was used to study the in-plane stiffness and strength of planar lattice grid com- posite materials. The initial yield equations of lattices were deduced. Initial yield surfaces were depicted separately in different 3D and 2D stress spaces. The failure envelope is a polyhedron in 3D spaces and a polygon in 2D spaces. Each plane or line of the failure envelope is corresponding to the yield or buckling of a typical bar row. For lattices with more than three bar rows, subsequent yield of the other bar row after initial yield made the lattice achieve greater limit strength. The importance of the buckling strength of the grids was strengthened while the grids were relative sparse. The integration model of the method was used to study the nonlinear mechanical properties of strain hardening grids. It was shown that the integration equation could accurately model the complete stress-strain curves of the grids within small deformations.

Buckle Propagation in Steel Pipes of Ultra-high Strength:Experiments,Theories and Numerical Simulations

In this paper,experimental,theoretical and numerical approaches were employed to scrutinize the buckle propagation events occurring in pipes subjected to external pressure.Two groups of samples with different radius-to-thickness ratios were fabricated using steel pipes of ultra-high strength and were subjected to compression of external pressure in a sealed pressure vessel specially designed and customized for the experiment.Experimental results were recorded through a data acquisition system.For facilitating the theoretical calculations,uniaxial tensile tests were performed on tensile pieces cut from the same pipes to obtain the material properties.It was found from the experimental results that once a buckle is initiated in a pipe,the external pressure dropped to a specific value called buckle propagation pressure and kept at this level until the whole pipe is flattened into a dog-bone shape.Based on the measured material properties and geometric parameters,theoretical solutions were computed using established ring models and shell model,and finite element predictions were also obtained from ABAQUS software.The efficiency and accuracy of the shell model and finite element model were expounded by comparing various theoretical solutions and numerical predictions with the experimental results.With the authenticated shell model and finite element model,a deep insight into the phenomenon of buckle propagation of pressurized long pipes was provided by performing a series of parametric study.