Yanan Wang

Application of a Model for Quenching and Partitioning in Hot Stamping of High-Strength Steel

Application of quenching and partitioning process in hot stamping has proven to be an effective method to improve the plasticity of advanced high-strength steels (AHSSs). In this study, the hot stamping and partitioning process of advanced high-strength steel 30CrMnSi2Nb is investigated with a hot stamping mold. Given the specific partitioning time and temperature, the influence of quenching temperature on the volume fraction of microstructure evolution and mechanical properties of the above steel are studied in detail. In addition, a model for quenching and partitioning process is applied to predict the carbon diffusion and interface migration during partitioning, which determines the retained austenite volume fraction and final properties of the part. The predicted trends of the retained austenite volume fraction agree with the experimental results. In both cases, the volume fraction of retained austenite increases first and then decreases with the increasing quenching temperature. The optimal quenching temperature is approximately 290xa0°C for 30CrMnSi2Nb with the partition conditions of 425xa0°C and 20xa0seconds. It is suggested that the model can be used to help determine the process parameters to obtain retained austenite as much as possible.

Ice crystal growth of living onion epidermal cells as affected by freezing rates

ABSTRACT The entire crystallization process and the effect of freezing rates on the temperature of spontaneous freezing (TSF) of living onion epidermal cells were analysed in this study. The cells, stained with iodine at a concentration of 1%, were frozen at three different freezing rates, i.e. 2, 1.2, and 0.5°C/min, and were thawed at 5°C/min. The higher freezing rate caused a higher TSF. Moreover, this article presents a method for determining whether a cell is inactivated by a plasmolysis experiment. The results of plasmolysis showed that the formation of ice crystals did not cause fatal mechanical damages to the cells, even when the freezing rate was as slow as 0.1°C/min. Finally, this article also demonstrated the grey-scale changes that occurred in the cells, as evidenced by an image processing technique. This further highlighted the ice crystal growth process and showed the ice crystal content at different locations inside the cells.

Thermal–structural coupling analysis of brake friction pair based on the displacement gradient circulation method

In view of the braking process for the megawatt wind turbine brakes, considering the geometric and motion characteristics of brake pads and brake discs, a displacement gradient circulation method is put forward in this article, to resolve the deviation of coupling results caused by the difference of friction effect along the radial/circumferential direction of brake disc, and the thermal–structural coupling analysis of friction pair during the braking process is carried out. A three-dimensional model of transient heat transfer for brake friction pair is built based on the Abaqus software. The heat flow density is loaded by the displacement gradient circulation method, which is used to calculate the frictional heat flow during the braking process. The analysis results show that along the circumferential direction of the brake disc the temperature distribution in the friction zone is non-uniform and the temperature starting from the contact position of the brake disc and the brake pad decreases along the counterclockwise direction. The thermal stress caused by the temperature field during the braking process is the main factor causing the brake disc/pad failure. The effectiveness of the method and the model is verified by the designed inertia braking experiments. The analytical method proposed in this article provides a reference for simulating the friction braking process of large-size disc brakes.

Outward Foreign Direct Investment of Chinese Enterprises: Review and Analysis

This paper examines the unique motivations and strategies for outward foreign direct investment (OFDI) undertaken by Chinese multinationals, and addresses the challenges associated with these unique motivations and strategies. The findings show that Chinese OFDI is significantly driven by strategic asset seeking, and state ownership serves as a unique type of ownership advantages. Chinese multinationals typically use aggressive modes such as wholly-owned subsidiaries and acquisitions to enter foreign markets, but the associated challenges of those aggressive modes in post-entry integration are not negligible. This paper provides a comprehensive view on theory of Chinese OFDI and offers practical guidance for Chinese multinationals in their global expansion by outlining the strategies and challenges of Chinese OFDI.

Multiobjective structure topology optimization of wind turbine brake pads considering thermal-structural coupling and brake vibration

Brake pads of disc brake play an important role in the stable braking process of a large-megawatt wind turbine. There is always vibration, screaming, and severe nonuniform wear under the effect of both retardation pressure and friction. To solve these issues, this article aims to find a new structure of the brake pads to improve brake performance. A multiobjective structure topology optimization method considering thermal-structural coupling and brake vibration is carried out in this article. Based on topology optimization method of Solid Isotropic Microstructures with Penalization (SIMP), the compromise planning theory is applied to meet the stiffness requirement and vibration performance of brake pads. Structure of brake pads is optimized, and both the stiffness and vibration performance of brake pads are also improved. The disadvantages of single-objective optimization are avoided. Thermal-structural coupling analysis is tested with the actual working conditions. The results show that the new structure meets the stiffness requirement and improves the vibration performance well for the large-megawatt wind turbine. The effectiveness of the proposed method has been proved by the whole optimization process.

Study on Breakdown Probability of Multimaterial Electrodes in EDM

With the development of EDM technology, some multimaterial electrodes which have some special functions are regularly taking the place of traditional single material electrodes on some machining occasions and becoming widely used. In this paper, the influence of material on discharge breakdown in EDM with multimaterial electrodes is studied. A comparison model about material influence on discharge breakdown under both single discharge condition and continuous discharge condition is established, and the material property factors affecting the probability of discharge breakdown are also analyzed. Finally, a series of experiments are carried out to study the effects of different electrode materials on the discharge breakdown of EDM, a fitting formula of breakdown probability is presented, and the effectiveness of the comparison model is also verified by comparing with experimental results.

Explicit computational model of dielectric elastomeric lenses

Deformable lenses have many advantages over traditional lens assemblies in respect of compactness, cost benefit, efficiency, and flexibility. We propose a computational model based on the nonlinear elasticity to characterize the performance of dielectric elastomeric lenses in terms of the focal length variation with respect to the actuation voltage, with theoretical predictions fitting well with experimental data. This model can also be used to predict the relationship between the maximum focal length change and parameters of the lenses including geometry and the internal liquid volume. It is expected that our work could provide insight into designing this particular type of lens for experimental researchers in the field of tunable lenses.

The effect of high frequency pulse on the discharge probability in micro EDM

High frequency pulse improves the machining efficiency of micro electric discharge machining (micro EDM), while it also brings some changes in micro EDM process. This paper focuses on the influence of skin-effect under the high frequency pulse on energy distribution and transmission in micro EDM, based on which, the rules of discharge probability of electrode end face are also analysed. On the basis of the electrical discharge process under the condition of high frequency pulse in micro EDM, COMSOL Multiphysics software is used to establish energy transmission model in micro electrode. The discharge energy distribution and transmission within tool electrode under different pulse frequencies, electrical currents, and permeability situation are studied in order to get the distribution pattern of current density and electric field intensity in the electrode end face under the influence of electrical parameters change. The electric field intensity distribution is regarded as the influencing parameter of discharge probability on the electrode end. Finally, MATLAB is used to fit the curve and obtain the distribution of discharge probability of electrode end face.

Adaptive PID controller for cloud smart city system stability control based on chaotic neural network

Stability is an essential component in system control especially with those systems exhibiting a non-linear dynamic behaviour. PID controllers are an integral and most commonly used tuning method for control over non-linear systems due to their simplicity and ease of computational complexity. PID controllers are most useful to systems in real time in which the system control parameters vary very slowly or exhibit uncertainty consequently making prediction very complicated and delayed. Continuous and quick adaptation of PID controllers towards varying input determines the efficiency of the non-linear system and this research paper presents a radial basis neural network model in a chaotic configuration for tuning the PID controller in an adaptive manner. However, because mobile cloud computing inherits some characteristics of mobile computing itself, there may be problems such as network congestion, no signal area and crosstalk, which leads to the frequent failure of computing resources and service cooperation, which makes the availability of mobile cloud computing more difficult than traditional cloud calculate the more severe challenges. The scope of this research work is limited to training the neural network with a chaotic map and time series plots are obtained using the experimental results. The efficiency of the proposed chaotic network model is justified by the evaluation of accuracy and robustness of the model even in presence of disturbances.