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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]

This study involves the investigation of the mechanical properties of the extruded tube products with reinforced silicon carbide particulates (SiCp). Finite element analyses are firstly conducted to analyze the plastic flow of the magnesium alloy AZ61 within the die and to investigate the effects of initial billet temperatures on the extrusion loads and final product temperatures. AZ61/SiCp composite ingots reinforced with different weight fractions of SiCp are fabricated by a melt stirring technique. A specially designed die set is used in the extrusion experiments to obtain tubes with uniform thickness distribution in the circumferential direction. The extruded tubes are also heat treated to obtain even better mechanical properties. Finally, tensile tests, Vickers microhardness, tests and microstructure observation are performed on the billets and extruded tubes of AZ61 monolithic alloys and AZ61/SiCp composites. A much smaller grain size and higher tensile strength and hardness are achieved for the extruded AZ61/SiCp composite tubes. [ABSTRACT FROM AUTHOR]

Abstract: The experiments of electronic speckle pattern interferometer (ESPI) successfully applied to sandwich plates with two inserts has been earliest presented in this paper. Proposed ESPI has advantages of full-field and non-destructive testing, which can measures microscopic out-of-plane displacement in the elastic region without wasting specimen. For validation purpose, the finite element method (FEM) analysis was conducted. By comparing the results of ESPI and FEM displacement fields around the inserts, a convincing agreements is revealed. The effect of insert spatial interval on the deformation of two-inserted sandwich plates was obtained by the ESPI and FEM: the wider the spatial interval of the two inserts is, the bigger the out-of-plane displacement at the insert center of sandwich loaded by the same force is. [Copyright &y& Elsevier]

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]

To study the principle of loss and heat at the end region of large 4-poles nuclear power turbine generator, 3D transient electromagnetic field and 3D steady temperature field finite element (FE) models of the end region are established respectively. Considering the factors such as rotor motion, core non-linearity and time-varying of electromagnetic field, the anisotropic heat conductivity and different heat dissipation conditions of stator end region, a 50 Hz, 1150 MW, 4-poles nuclear power turbine generator is investigated. The loss and heat at the generator end region are calculated respectively at no-load and rated-load, and the calculation results are compared with the test data. The result shows that the calculation model is accurate and the generator design is suitable. The method is valuable for the research of loss and heat at the end region of large 4-poles nuclear power turbine generator and the improvement of the generator's operation stability. The method has been applied successfully for the design of the larger nuclear power turbine generators [ABSTRACT FROM AUTHOR]