Advanced Materials Research Vols. 79-82

Abstract: In the current paper, the hysteretic dynamics of magnetorheological dampers is modeled by a differential model. The differential model is constructed on the basis of a phenomenological phase transition theory. The model is expressed as a second order nonlinear ordinary differential equation with bifurcations embedded in. Due to the differential nature of the model, the hysteretic dynamics of the MR dampers can be linearized and controlled by introducing a feedback linearization strategy.

Abstract: Based on experimental results reported in the reference, Liang-Rogers’ constitutive model for SMA is used to simulate the stress-strain curves of NiTi shape memory alloy films under uniaxial tension with isothermal conditions. The effects of film compositions and temperature on the tensile behavior of NiTi shape memory alloy films are discussed. By comparing the simulation results with the experimental results, it is found that the simulation curves agree basically with the experimental curves except that the phase-transformation regions are wider in the simulation curves. This demonstrates that the Liang-Rogers’ model can be used to predict the thermomechanical behavior of shape memory alloy films roughly. This study provides some theoretical foundation for the quantitative description and prediction of the actuation mechanism when shape memory alloy films are used as micro-actuators.

Abstract: The main raw material of solar energy is multi-crystalline silicon. Directional solidification technique is one important technological process of metallurgy purification technology for multi-crystalline silicon. It can purify metallurgical grade silicon by removing metal impurities and control crystal growth at the same time. In experiment, metallurgical grade silicon by acid leaching pre-treatment, was purified by our self-assembled directional solidification furnace. The sample was analyzed by electron-prode micro analysis (EPMA). According to the results, the removal efficiency of Fe and Al is 96.3% and 96.7%, respectively. The removing mechanism of metal impurities and the difference between theory value and experiment value were also discussed. The segregation effect in directional solidification is the reason of removing Fe, but analgesic effects of the segregation effect combined with vacuum volatilization are that of removing Al. When the silicon ingot was cooled down, lengthways section of silicon ingot was cut and etched, crystal growth was studied. The results indicate that columnar crystal growth shows diverging tendency from the bottom to the top of silicon ingots, and solidification interface shape is convex. The reasons may be the nucleation of new crystals on crucible sidewall is very serious and the pulling rate is too high.

Abstract: A “sandwich-style” composite target with a 45 steel surface plate, polyethylene rubber sandwich plate, and 45 steel back plate is studied for jet penetration resistance. The effects of varying layer thickness are analyzed using AUTODYN software and energy-thickness (E-T) curves in Matlab. The influence of the scale effect on each of these composite layers is analyzed. Results from the E-T curves confirm that varying the thickness of the 45 steel back plate has an obvious influence on jet penetration resistance. Moreover, varying the thickness of the front plate and the sandwich plate has a large effect on jet fracture after penetration of the composite target. Experiments prove that the results of the simulation are correct, and that the scale effect is present for these composite targets under jet penetration.

Abstract: Since a fine ceramic is possessed of creditable physical and chemical material properties: high thermal resistance, chemical inertness and frictional wear resistance, its applications have been increasing in various industrial fields. Yttria(Y2O3) ceramic, which is formed of cubic crystal structure, has been considered as a light-transmitting material for an optical application and suitable buffer layer in the electronic industry. And its other applications have been increasing recently. For the effective applications of Yttria ceramic, it needs to improve a surface characteristic such as the waviness and surface roughness. The lapping process with in-process electrolytic dressing(IED) method has been performed in the surface machining of high hard-brittle material. IED method is able to overcome the surface machining defects caused by worn grains and unstable chip discharge during conventional lapping process. However, the machining control should be carefully conducted and investigated about each material because its material properties are different each other and exceedingly sensitive. Taguchi method, called robust design, is a useful method for engineering productivity elevation. It is able to search a powerful factor, which influences optimal process design, in accordance with considering noise factors reduction. When diverse factors influence a result according to complex actions each other, it needs to search optimal condition of factors. Response surface design has been widely used in various industrial fields. It helps to solve process design problems in accordance with robust design of process condition.

Abstract: In this paper, the finite element software——ABAQUS Computing Platform is used to build two-dimension unit cell of the composite one-way slab model. Compute it by two ways: 1)supposing that the fiber and matrix are elasticity, but they are different for material parameters, and this assumption is generally used. It can be computed directly in the ABAQUS software; 2)supposing that the fiber is elasticity, but the matrix is the viscoelasticity. For the matrix, its viscoelastic character can be simulated by the solid constitutive model with three parameters. The maximum stress (MS) judgment criterion is used to determine whether the matrix is destroyed. If the matrix is destroyed, the stiffness of the whole matrix would be degraded by means of the degradation factor, which determined by the Camanho parameter degradation pattern. Compare the stress and strain curves got through the numerical simulation and through the experiments, and find that the second situation is similar to the experiment’s result.

Abstract: Severe Plastic Deformation (SPD) methods are currently hot research techniques of preparation of bulk ultrafine-grained materials.Among the various SPD methods, ECAP (Equal Channel Angular Pressing) and TE (Twist Extrusion) have respective advantages and disadvantages and there have many questions in this research area at home and abroad although they are representative and rapidly developing and the promising ones.ECAPT, ECAP organic integrated with TE, was introduced for the frist time and the process principle and features were set forth in this study. The numerical simulation of the process was further analyzed with DEFORM-3D software.The results show that there have two main deformation zones in forming process of ECAPT during a single pass, and vertical and horizontal shear deformation have been taken place in workpiece and the value of effective strain is equivalent to accumulated deformation of ECAP and TE after one pass; And the peak and average value of effective strain when ECAPT are far greater than those of effective strain during the process of ECAP or TE. It is confirmed that there have more effective strain rate and more stronger severe plastic deformation during the process of ECAPT,and it improves the ability of material’s plastic deformation.

Abstract: Maxwell 2D software is introduced in this paper to calculate the magnetic shielding effectiveness (MSE) properties of iron plate. The three-dimensional magnetic shield is thought isotropic and simplified as two-dimensional model to study its MSE properties by the finite element method. In this method, a uniform magnetic field is generated by two huge magnets and the MSE properties of iron plate, which is in the centre of the uniform magnetic field, is then calculated by the ratio of magnetic field intensity after and before magnetic shielding. All the results indicate that shape of shield materials affects the MSE properties much and the MSE properties of shield with square and circular shape with 3mm in depth are 39.3 and 53.5 dB, respectively. That means the shield shape with fewer bending is favorable to the conductivity of magnetic energy. It also shows that the MSE value decreased linearly with the distance between the magnetic shield and the centre of the magnetic field. That is, the increase of side length of magnetic shield will lead to the decrease of MSE properties of iron plate, which is agreement with the theoretical prediction of Lu H.M. model. Furthermore, the MSE properties of double layers shielding (iron plate with 2mm in depth and 3mm iron plate with 81% porosity) are also studied in this paper. The effect of places of iron plate with 2mm in depth is presented to play important role in double layers shielding and the MSE value increases with the distance between the two magnetic shields. Compared to that of shield with circular shape, the MSE properties are similar to each other when the distance of the two shields is 8mm. In addition, it also indicates that the MSE value is higher when the iron plate with 2mm in depth is inside of the other than that when it is outside.

Abstract: This paper investigated the mechanical properties and the relationships between fiber architecture and the composites properties of three-dimensional multidirectional braided composites made of Toray@T700 carbon fiber impregnated with TDE 86# epoxy resin using RTM. The strength and stiffness properties measured here include tension, compression, flexure and short beam shear, all of these in both the longitudinal and transverse directions. It is found that the 3D six-directional braided composites with 55 % fiber volume fraction and 25°surface braiding angle represent quasi-isotropic in-plane elastic behaviors due to their symmetric, intertwined architecture and unidirectional reinforcements in both the longitudinal and transverse directions. Compared with the tension strength and modulus, those for compressions in the same directions descend near 40% and 10% respectively. The cut-edge on the width destroys the integrity of microstructure and inevitably cuts down the carrying capacity of composites under the longitudinal tension.

Abstract: In present work, the critical buckling load of metallic foam composite sandwich panels is calculated by experimental, finite element methods (FEM) and theoretical analysis. The experimentally investigated is based on an edgewise compression test program to examine buckling failure and compressive properties. The metallic foam sandwich panels under edgewise compression tend to collapse in overall buckling mode. The most important factor that determines the overall buckling load of a sandwich panel under edgewise compression is the shear properties the metallic foam core. The sandwich beam theory and the FE model are developed for prediction of the buckling load of metallic foam sandwich structure. In despite of some differences existed among experimental data, FE and theoretical results, considering the existence of initial defects in sandwich structures which can’t be calculated in FE model and theory anlysis, the differences are in the reasonable range. The FE program developed in this paper can effectively be used to simulation of edgewise compression response for metallic foam composite sandwich structures. Theoretical and FE model results are in agreement with experimental result.