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The vibration isolator is a key part of many ultra-precision machines and measuring apparatus. Magnetic suspension vibration isolators (MSVIs) will have excellent application prospects in these instruments to restrain external oscillations. So this paper firstly proposes a new basic configuration of MSVI. Then, in order to study the mechanical characteristics of the MSVI, an analytical expression of the magnetic force is established. The effectiveness of which is demonstrated by the experiment and finite element analysis (FEA). The stiffness of the MSVI is obtained by the derivative of the established analytical magnetic force. Both the axial magnetic force and stiffness appear strong nonlinearity when the inner ring moves at both ends of the fixed outer ring. While the inner ring travels in the middle of the fixed outer one, the axial magnetic force and stiffness indicate approximate linearity with enough bearing capacity. Furthermore, parametric analysis, based on the created magnetic force and stiffness, is performed. The analytical results show that the axial magnetic stiffness may achieve a zero or even negative stiffness value in this range at some size dimensions. The MSVI appears to have a negative stiffness characteristic. More importantly, if a linear and nonlinear positive stiffness spring is combined with the MSVI, it can increase the load capacity of the MSVI. As an example study, the vibration isolation performance of the MSVI is analyzed. The vibration isolation calculation and experiment with the zero stiffness MSVI will be the further focus of the paper. [ABSTRACT FROM AUTHOR]

Abstract The response surface methodology in the design of experiments (DOE) wizard and Gurson-Tvergaard-Needleman (GTN) model were employed to estimate the optimum GTN damage parameters and to validate their significant effects respectively on the ductile fracture behavior of ECAP deformed AZ61 magnesium alloy. Hollomon's flow stress was applied to identify uniform deformation and non-uniform deformation regions to investigate the void nucleation and coalescence processes separately. The significance of statistical results was evaluated with the analysis of variance (ANOVA) based on P-values and coefficients of determination (R 2). Correspondingly, the contributions of ECAP plastic deformation and the corresponding local plasticity (damage progresses) on the progress of GTN ductile fracture damage parameters were studied. Desirability function was used to show the significance of individual and interaction effects of optimum initial damage parameters on the respective response variables. By using response surface methodology, the optimum GTN damage parameters were determined at the corresponding positions of each critical response variables. Results also showed that varying both stress triaxiality and damage variables simultaneously can greatly affect the curve fitting process of experimental, simulation and GTN model curves. However, at constant stress triaxiality condition, the GTN model curve was observed perfectly fitting with the tensile test curve. [ABSTRACT FROM AUTHOR]

Abstract The discrete-continue model (DCM) combining the three dimensional discrete dislocation dynamics (DDD) and finite element method (FEM) is employed to investigate the influence of interfacial dislocation networks (IDNs) and lattice mismatch on the dynamics evolution of dislocations in the matrix channel of the single crystalline Nickel-bases superalloys (SCNBSs). For a given slip plane, the matrix dislocations with all three possible Burgers vectors are considered. For comparison, the critical resolved shear stresses (CRSSs) for matrix dislocation entering and freely gliding in the channel are calculated for both cases with and without IDNs considered. It is found that the CRSS for free gliding is evidently larger than that for entering the matrix channel, although the latter only considering the Orowan mechanism is generally used to describe the hardening of SCNBSs in the literatures. More importantly, the IDNs not only increase the CRSS for free gliding evidently but also change the matrix dislocations dissociation to a certain extent. The IDNs and lattice mismatch can either promote the dislocation dissociation or has no evident influence on it. Which effect the IDNs take depends on the character of the matrix dislocation. By means of DDD simulations, new CRSS models considering the effects of IDNs, lattice mismatch, matrix dislocation character and dislocation dissociation are suggested. Further, a criterion is also developed to estimate whether the dislocation dissociation can happen or not in the matrix channel with or without IDNs. Highlights • The interfacial dislocation network (IDN) plays an important role in the dislocation evolution in Nickel-based superalloys. • The IDN increases the critical resolved shear stress (CRSS) for dislocation freely gliding in the channel evidently. • The IDN can change the dissociation of matrix dislocations. • New CRSS models including the influence of IDN, lattice mismatch, dislocation character and dissociation are developed. • A criterion for dislocation dissociation is suggested. [ABSTRACT FROM AUTHOR]

Magnetic flux leakage (MFL) response predicting is important for defect estimation. This paper first proposes a concept of basic signal by discovering the combination property of the MFL response. The basic signal can be used to predict the MFL response conveniently by a basic signal combination method (BSCM), which is also innovatively put forward in this paper. In this method, the basic signal is calculated in advance, and the MFL response can be calculated by several transformation and combination operations. Both the simulation and experimental results demonstrate the feasibility of BSCM. Compared with other traditional methods (magnetic dipole method and finite-element method), BSCM shows a good performance on both the computational speed and accuracy. [ABSTRACT FROM AUTHOR]

A 3D electromagnetic model of the end region of a 1550 MW nuclear generator is set up. The electromagnetic forces on the involute and nose parts of the end winding under a rated operation are obtained through the 3D time-step finite element method. The electromagnetic forces on different coils in the same phase are analyzed. By changing the rotor’s relative length and stator coil’s linear length in the 3D electromagnetic model, the electromagnetic force distributions on the end winding are obtained. The influence of each structure change on the electromagnetic force in different directions is studied in detail. Conclusions that can be helpful in decreasing the electromagnetic forces on the end winding through optimizing the end region design are presented. [ABSTRACT FROM AUTHOR]

A new efficient framework coupling the two dimensional (2D) discrete dislocation dynamics (DDD) and the extended finite element method (XFEM) is developed for modeling the dynamic evolution of multiple dislocations in crystalline materials with abundant interfaces/surfaces. By a specially introduced stress calculation scheme with cut-off radius and virtual elements, the present algorithm can capture interaction between neighboring dislocations accurately although no time-consuming dislocation-core enrichment is employed. Since it is not sensitive to the FE mesh size and large XFEM time step can be used, its efficiency is evidently improved compared with other DDD frameworks. Due to the merits of XFEM itself, the present DDD-XFEM scheme can treat intractable surface/interface problems conveniently, with no additional image stress calculation as in the DDD-FEM superposition framework and special plastic-strain distribution near the surfaces/interfaces as in the discrete-continuous method (DCM) needed. For these, it can be used to model plastic behaviors of crystals with abundant interfaces/surfaces (i.e. grain/phase boundaries and crack/void surfaces). To show the ability of present DDD-XFEM scheme, it is used to simulate the mechanical responses of polycrystalline aluminum with assumed rigid and penetrable grain boundaries. A three-stage model for dislocation penetrating through grain boundary (DPTGB) is suggested. The results show that the present DDD-XFEM scheme can capture the formation of dislocation pile-ups and thus the Hall-Petch effect successfully. The DPTGB can decrease the flow stress and hardening rate evidently; moreover, it can weaken the grain size effect and may enhance the cyclic stress relaxation of polycrystals greatly. Image 1 • A more efficient and accurate XFEM-DDD framework for simulating the micro-plasticity of materials is developed. • The newly developed XFEM-DDD framework can well deal with various complex discontinuities in materials. • The present XFEM-DDD framework can simulate efficiently the problems on much longer/larger temporal/spatial scale. • A three-stage model for dislocation penetrating through GB (DPTGB) is suggested. • The grain size effect on strength and the cyclic stress relaxation are captured efficiently by the present scheme. [ABSTRACT FROM AUTHOR]

This paper aims to investigate the temperature field evolution of the single track clad in wide-beam laser cladding. By using the birth and death element technique, a 3D transient finite element (FE) model was established to study the temperature field evolution, temperature gradient (G), cooling rate (ε), and solidifying rate (R) of the molten pool. The temperature field results of the molten pool were also validated by the temperature measurement and characteristics of the clad. Meanwhile, the effect of main parameters namely as laser power, scanning speed, laser absorptivity, laser power efficiency, and preheat temperature on the peak temperature of the molten pool and temperature variation rate were discussed in detail. Then, the effect of laser power and scanning speed on G, ε, R, and G/R were also investigated and the corresponding microstructure was analyzed. The results show that from the top surface of the clad to the interface between the clad and substrate, G/R decreases slightly at first and then increases sharply while the cooling rate continues to decrease. Moreover, the peak temperature of the molten pool increases with an increase of laser power, laser absorptivity, laser power efficiency, and preheat temperature, while with the increasing of scanning speed, the peak temperature decreases. [ABSTRACT FROM AUTHOR]

A three-dimensional (3-D) electromagnetic model of the end region of a 600 MW turbogenerator is set up. The variations of electromagnetic force densities of the stator end winding under rated load and three-phase short circuit from full load are obtained by numerical simulation. Then, the electromagnetic forces varying with time and space on the end winding are applied to the 3-D fine finite-element model established in ABAQUS/CAE for structural analysis, and the deformation and stress distributions of the stator end winding during rated load and three-phase short circuit are numerically analyzed by means of the ABAQUS software. Furthermore, the influences of structural and material parameters of the end winding on its dynamic responses under rated load are numerically investigated. Based on the numerical results, an optimal scheme for the design of the turbogenerator stator end winding is proposed. [ABSTRACT FROM PUBLISHER]