Xuning Feng

Effects of surface stresses on contact problems at nanoscale

Based on the surface elasticity theory, we examined the effects of surface stresses on nanosized contact problems. The Fourier integral transform method is adopted to derive the general solution for the contact problem under pressure. As two examples, the deformations induced, respectively, by a uniform distributed pressure and a concentrated force are analyzed in detail. The results indicate some interesting characteristics in contact mechanics, which are distinctly different from those in classical elasticity theory. Both the contact normal stress and the deformation gradient on the deformed surface vary smoothly across the loading boundary as a result of surface stress. In addition, the indent depth and the maximum normal contact stress depend strongly on the surface stress for nanoindentation.

An approximate continuum theory for interaction between dislocation and inhomogeneity of any shape and properties

An approximate continuum theory is developed to effectively handle the problem of interaction between dislocations and inhomogeneity of any shape and properties. The inhomogeneity is, based on the Eshelby equivalent inclusion theory, equivalent to a homogenous one with a transformation strain. The interaction force between dislocation and the inhomogeneity can then be evaluated from the work done by the dislocation stress field during the transformation. The proposed continuum theory is applicable to a variety of inhomogeneities, such as pore, gas bubble, shear band and plastically deformed zone. It can be reduced to the classical continuum theory for some special cases.

Rule-based fault diagnosis of hall sensors and fault-tolerant control of PMSM

Hall sensor is widely used for estimating rotor phase of permanent magnet synchronous motor(PMSM). And rotor position is an essential parameter of PMSM control algorithm, hence it is very dangerous if Hall senor faults occur. But there is scarcely any research focusing on fault diagnosis and fault-tolerant control of Hall sensor used in PMSM. From this standpoint, the Hall sensor faults which may occur during the PMSM operating are theoretically analyzed. According to the analysis results, the fault diagnosis algorithm of Hall sensor, which is based on three rules, is proposed to classify the fault phenomena accurately. The rotor phase estimation algorithms, based on one or two Hall sensor(s), are initialized to engender the fault-tolerant control algorithm. The fault diagnosis algorithm can detect 60 Hall fault phenomena in total as well as all detections can be fulfilled in 1/138 rotor rotation period. The fault-tolerant control algorithm can achieve a smooth torque production which means the same control effect as normal control mode (with three Hall sensors). Finally, the PMSM bench test verifies the accuracy and rapidity of fault diagnosis and fault-tolerant control strategies. The fault diagnosis algorithm can detect all Hall sensor faults promptly and fault-tolerant control algorithm allows the PMSM to face failure conditions of one or two Hall sensor(s). In addition, the transitions between health-control and fault-tolerant control conditions are smooth without any additional noise and harshness. Proposed algorithms can deal with the Hall sensor faults of PMSM in real applications, and can be provided to realize the fault diagnosis and fault-tolerant control of PMSM.

Influence of thickness and number of dielectric layers on residual stresses in micromultilayer ceramic capacitors

The residual stresses due to high-temperature processing in micromultilayer ceramic capacitors (MLCCs) with various thicknesses and numbers of dielectric ceramic layers were investigated by using a three-dimensional elastoplastic finite element model with temperature-dependent material properties taken into account. For comparison, an explicit analytical solution for the in-plane residual stress in the dielectric ceramic layer was derived. Both the numerical results and the analytical model showed that the thickness ratio of the dielectric layer to electrode layer has a dominant impact on the residual stress states. There exists a critical thickness for the dielectric ceramic layer in MLCCs in the case of a given thickness of the electrode layer, below which both high tensile out-of-plane stresses and high compressive in-plane stresses could cause the cracking of the brittle dielectric layers near the electrode tips and/or the debonding of the electrode/dielectric interface.

Thermal Runaway Propagation Within Module Consists of Large Format Li-Ion Cells

Thermal runaway (TR) propagation within a large format lithium ion battery module includes two stages: the Initiation Stage and the Propagation Stage. Experiments were conducted to investigate the mechanisms of TR initiation at single cell and TR propagation in a battery module. A lumped TR propagation model was built based on heat transfer theory, and was calibrated by experiment data. The calibrated TR propagation model can analyze the heat transfer amount through different paths during TR propagation. Base on analysis on the heat transfer paths, methods were proposed to prevent TR propagation within battery module. TR propagation can be successfully prevented according to the method proposed, which is verified by experiment.

Research on simplification of simulating the heat conduction in the lithium-ion battery core

This paper discusses the model simplifing issue in battery thermal simulation. The paper verifies that for the large power battery simplifying the multilayer battery core as a lumped cuboid is reasonable. So when doing simulation, building a multilayer core is unnecessary. And the calculation cost can be reduced by the lumped model. Specific power battetry of 70Ah is dissembled to be modeld. Thermal models of are established, including models with a lumped core and with multilayer cores. For the lumped core, the anisotropic thermal conductivities are got by equations calculating series and parallel equivalent thermal conductivity. While for the multilayer core models, the core contains numbers of unit cells and the volume of which is equal to that of the lumped. In addition, under the boundary conditions of inner heat source and surface heating, steady state simulations are performed. Simulation results indicate that the temperature distributions of the lumped model and the multilayer model are almost the same. For one thing, large number of multilayers and low shell thermal conductivity contribute to a uniform temperature distribution within the core, so it is reasonable to simplify the multilayer core as a lumped cuboid. For another, due to the size of the battery and the shell property, it is difficult to find a simple curve to fit the simulation temperature on the battery surface. Although minor differences still exist, the lumped core can well subsitute the multilayer core in battery thermal simulation.

Online Weld Breakage Diagnosis for the Battery of Electric Vehicle: A Data-Driven Approach

A data-driven diagnostic approach is developed and proved successful to identify the weld breakage of the connector in battery pack according to the data-upload by the remote monitoring platform. Firstly, two modes of the weld breakage: complete breakage and loose contact, as well as their statistical patterns are illustrated. To further assure the weld breakage fault, the capacity of battery pack was estimated using probability density function approach, and the statistical patterns are further analyzed to identify the characteristics of weld breakage. The approach proposed in this paper provides inspirations for the development of diagnostic methods from a data- driven view.