News

    Volume 26,Issue 6 of Journal of SJTU (Science)!
    Pubdate: 2021-12-02
  • Metal Welding Technology

    1.Influence of Thermal Modification on Al-Si Coating of Hot-Stamped 22MnB5 Steel: Microstructure, Phase Transformation, and Mechanical Properties

    Authors WANG Qiongyan (王琼燕), LIN Wenhu (林文虎), LI Fang (李芳), SHEN Chen (沈忱), HUA Xueming (华学明). 

    AbstractThe hot-stamped steel with ultrahigh strength is a promising material for the fabrication of automotive components. However, the coating on the sheet surface leads to a softening problem in the welded joint. Instead of the costly coating removal process, heat treatment is an economical and effective method for the diffusion process, which can decrease the Al concentration in the coating. In this study, a preheating treatment was carried out on Al-Si-coated 22MnB5 hot-stamped steels for the homogeneity of Al, followed by laser welding and hot stamping. The effects of the preheating on the microstructure and mechanical properties of the laser-welded joints were investigated. With the preheating treatment, the Al-Si coating transformed into an Fe-Al intermetallic compound and the difference in Al content between the coating and substrate was reduced. The Al content in the weld of the specimen with the preheating treatment was reduced, compared with that without the preheating treatment. The amount of δ-ferrite in the weld after laser welding was reduced largely. The distribution of long-bland-like segregation was changed to a fine and uniform distribution. With the preheating treatment, the tensile strength of the welded joint was significantly improved and comparable to that of the decoated joint. In conclusion, the preheating treatment before the welding is an effective method to suppress the formation of δ-ferrite and improve the mechanical properties of the welded joint.


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    2.Effect of Cu Addition on the Microstructure and Mechanical Properties of U-MIG Welds on Galvanized Steel Sheets

    Authors YU Xiaokang (俞小康), YE Jia (叶佳), WU Chunxiang (吴春祥), MA Guohong (马国红)

    AbstractUltrasonic-assisted metal inert gas (U-MIG) welding experiments were performed to analyze the effect of Cu addition on the microstructure and mechanical properties of galvanized steel sheet welds, and first-principles calculations were undertaken to predict the effect of Cu on the mechanical properties of α-Fe based structures. As shown by scanning electron microscopy analysis, Cu is conducive to the refinement and uniformity of the microstructure in the weld zone. Energy-dispersive spectrometry data indicated the presence of Cu in the welds after welding with Cu powder. The elastic moduli of the welds without and with Cu powder, obtained from nanoindentation tests, were (217.66 ± 5.11) GPa and (223.13 ± 9.12) GPa, respectively, which were close to the calculated results. The mechanical properties of the crystal structures of α-Fe and α-Fe1.9Cu0.1 were calculated using Materials Studio software. Both the experimental and calculated results showed that Cu doping reduced the bulk modulus of the weld but increased its shear modulus.


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    Material, Structure, Mechanics

    3.Experimental Study on Medium and Low Cycle Fatigue Properties of Cast Steel GS20Mn5V

    Authors JIN Hui (靳慧), MO Jianhua (莫建华), SUN Sijia (孙思嘉), ZHAO Jing (赵静)

    AbstractOwing to the remarkable advantages in mechanical behavior, cast steel nodes have been widely used in static structures. Nowadays, cast steel nodes also gain increasing popularity due to the superior fatigue performance in dynamic structures, but they are not yet widely used because the fatigue properties of cast steel are not well understood. In this paper, the fatigue test of cast steel GS20Mn5V commonly used in steel castings is carried out. The strength of medium and low cycle fatigue and the fatigue limit are obtained. The feasibility of the estimated S-N (fatigue stress versus life) curve is tested. The double logarithmic linear model (DLLM) and the reversed generalized Pareto model (RGPM) are used to fit the experimental data, and the comparison is made. The P-S-N (the relationship between fatigue stress and life at different survival rates) curve obtained by the RGPM is proposed. The results show that the estimated S-N curve is not suitable for low cycle fatigue life, fitting the experimental data with the RGPM is the best, and obtaining the P-S-N curve from the RGPM is feasible.


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    4.Nonlinear Finite Element Method Considering Martensite Plasticity for Shape Memory Alloy Structure

    Authors ZHOU Bo (周博), KANG Zetian (康泽天), WANG Zhiyong (王志勇), XUE Shifeng (薛世峰)

    AbstractThis work presents a nonlinear finite element method to simulate the macroscopic mechanical responses and the effects of martensite plasticity in a shape memory alloy (SMA) structure. A linear relationship formulation is adopted to express the influence of martensite plasticity on the inverse martensitic phase transition of SMA material. Incorporating with a trigonometric-type phase transition evolution law and an exponential-type plastic flow evolution law, an incremental mechanical model with two internal variables is supposed based on the macroscopic experimental phenomena. A nonlinear finite element equation is formulated and solved by the principle of virtual displacement and Newton-Raphson method respectively. By employing the proposed nonlinear finite element method, the uniform tensile bar and three-point bending beam are simulated and analyzed. Results illustrate that the presented nonlinear finite element method is suitable to act as an effective computational tool for the wide applications based on the SMA material considering the effects of martensite plasticity because all material constants related to the method can be obtained from macroscopic experiments.


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    5.Speed Planning Algorithm Based on Improved S-Type Acceleration and Deceleration Model

    Authors LUO Huimiao (罗晖淼), ZHAO Dongbiao (赵东标), FU Wenqiang (付文强)

    AbstractThe acceleration saltation of the traditional S-type acceleration model in the speed planning of the NURBS curve will result in the vibration and flexible impact of the machine tool. It will affect the surface quality of the components. The high speed smooth S-type acceleration and deceleration model deals with flexible impact, but the calculation is tedious. Aimed at the above problems, the traditional S-type acceleration and deceleration model is improved to make the jerk change linearly at a certain slope to reduce the flexible impact. Before the speed planning, it is needed to find the arc length and curvature of each point on the NURBS curve with a tiny step, and to determine the speed sensitivity point on the curve accordingly. According to the speed sensitive point, the NURBS curve is segmented. The attribute parameters of each section are determined by adaptive speed planning. Then, the speed planning can be performed on the NURBS curve according to the speed characteristics classification. The simulation results show that the algorithm can effectively reduce the flexible impact, improve the machining precision and efficiency, and simplify the classification of speed characteristics.


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    6.Hysteretic Model for Corroded Rectangular Reinforced Concrete Bridge Column Under Seismic Loading

    Authors YANG Shuyan (杨淑雁), SONG Xiaobing (宋晓冰), JIA Hongxue (贾红学), CHEN Xi (陈溪), LIU Xila (刘西拉)

    AbstractAdditional hysteretic experiments for corroded rectangular reinforced concrete (RC) columns with an axial load ratio of 0.27 were implemented. A quasi-static cyclic lateral loading with constant axial force was subjected to tests. Herein, a modified ductility factor model for corroded RC column is developed on the basis of the previous work and additional experiments. The model involves the influence of both the corrosion ratio of longitudinal rebar and the axial load ratio. A four-linear envelope curve model concerning lateral load and displacement is proposed in a combination of determination rules of the peak point and the failure strength point. The hysteretic model of corroded RC columns is developed by considering both degraded unloading stiffness and reloading stiffness on the history peak point. The hysteretic model can predict the residual life of corroded RC columns under seismic loading.


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    7.Bond Mechanical Properties of Glass Fiber Reinforced Polymer Anti-Floating Anchor in Concrete Baseplate

    Authors BAI Xiaoyu (白晓宇), ZHENG Chen (郑晨), ZHANG Mingyi (张明义), LIU Xueying (刘雪颖), KUANG Zheng (匡政)

    AbstractCombined with fiber Bragg grating (FBG) sensing technology, four glass fiber reinforced polymer (GFRP) anti-floating anchors and four steel anti-floating anchors were tested for on-site destructive failure to investigate the anchoring performance and the bonding characteristics between GFRP anti-floating anchor and concrete floor. The test results show that bending GFRP anchor will be broken at the common boundary between vertical anchorage section and bending section during the pullout process, and the spring-back load provided by the rupture contributes to a decrease of bearing capacity and an inflection point on the load-slip curve. The loaddisplacement curve of the straight anchor GFRP anti-floating anchor is smoother and has better predictability than the same type of steel anchor. Additionally, different forms of GFRP anti-floating bolt have different bondslip constitutive relations. By introducing the sliding-slip correction factor of bending bolt, constitutive models describing the rising-section of sliding-slip relation of bending and straight-anchored GFRP anti-floating bolt are established respectively. The model can fit the test results rightly.


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    8.Notched Component Fatigue Life Prediction in Torsional Loading

    Authors LIU Jianhui (刘俭辉), L ¨U Xin (吕鑫), WEI Yaobing (韦尧兵), ZHANG Rupeng (张如鹏), ZHANG Yonggui (张永贵)

    AbstractConsidering the situation that fatigue life prediction of notched component is an indispensable part in the process of design in engineering, it is necessary to find some ways to solve such problems effectively. The stress and strain state of notched specimen is more complex, compared with smooth specimen. As a result, some researchers take advantage of the finite element method to analyze the mechanical properties of these kind of specimens, they can get the stress and strain state at the dangerous point directly instead of using theoretical methods. At the same time, the equation of shear stress is fitted by analyzing stress distribution of the section of notch root. The integral of shear stress in the section is equal to the external load, and the true stress value of notch root is derived. Then, the fatigue damage evolution equation of notched specimens under torsional load is proposed based on the closed-form solution in this paper. Meanwhile, the nonlinear fatigue life prediction model of notched specimens under the torsional load is given by using the damage mechanics theory. The proposed model is validated by experimental data (30CrMnSiNi2A steel and 45# steel). The results show that the predicted life is not only close to the experimental results, but also tends to be safe. The fatigue life of notched specimen is predicted by using notch geometric parameters and material constants. The model has more concise calculation process, avoids complicated fatigue tests, and facilitates engineering application.

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    9.Parameter Identification of Structural Nonlinearity by Using Response Surface Plotting Technique

    Authors LIU Xin (刘鑫), WANG Lixiao (王力晓), CHEN Qidong (陈启东), SUN Beibei (孙蓓蓓)

    AbstractWith rigorous dynamic performance of mechanical products, it is important to identify dynamic parameters exactly. In this paper, a response surface plotting method is proposed and it can be applied to identify the dynamic parameters of some nonlinear systems. The method is based on the principle of harmonic balance method (HBM). The nonlinear vibration system behaves linearly under the steady-state response amplitude, which presents the equivalent stiffness and damping coefficient. The response surface plot is over two-dimensional space, which utilizes excitation as the vertical axis and the frequency as the horizontal axis. It can be applied to observe the output vibration response data. The modal parameters are identified by the response surface plot as linearity for different excitation levels, and they are converted into equivalent stiffness and damping coefficient for each resonant response. Finally, the HBM with first-order expansion is utilized for identification of stiffness and damping coefficient of nonlinear systems. The classical nonlinear systems are applied in the numerical simulation as the example, which is used to verify its effectiveness and accuracy. An application of this technique for nonlinearity identification by experimental setup is also illustrated.


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    Automation, Image Processing

    10.Snubber Circuit for Marine Controlled-Source Electromagnetic Transmitter

    Authors SONG Hongxi (宋红喜), ZENG Yijin (曾义金), ZHANG Wei (张卫)

    AbstractA high-power marine controlled-source electromagnetic transmitter (HP-MCSET) transmits a highfrequency conversion current on the sea floor. Some problems exist when the direct-current to alternating-current (DC-AC) launch bridge (LB) is used in the marine controlled-source electromagnetic transmitter (MCSET). There is a high voltage peak in the LB when the insulated gate bipolar transistor (IGBT) is turned on and off. In some cases, the voltage stress of the IGBT can be exceeded, which may cause IGBT damage. Because the rise of the current steepness is relatively low and the output voltage has a voltage peak in the LB, a snubber circuit is added to the IGBT to suppress the voltage peak to improve the output current and voltage waveform. The suppression of the voltage peaks is analyzed and compared for several groups of snubber circuits. To meet the performance requirements of the MCSET, the optimal snubber circuit is selected to effectively suppress the voltage peaks at an output current of 1 kA. This method is verified by using a 70 kW MCSET and the experimental waveforms are provided. The simulation of the inductance obstruction load in seawater is necessary to determine the conditions for actual marine environment experiments.


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    11.Feature Selection Optimization for Mahalanobis-Taguchi System Using Chaos Quantum-Behavior Particle Swarm

    Authors LIU Jiufu (刘久富), ZHENG Rui (郑锐), ZHOU Zaihong (周再红), ZHANG Xinzhe (张信哲), YANG Zhong (杨忠), WANG Zhisheng (王志胜)

    AbstractThe computational speed in the feature selection of Mahalanobis-Taguchi system (MTS) using standard binary particle swarm optimization (BPSO) is slow and it is easy to fall into the locally optimal solution. This paper proposes an MTS variable optimization method based on chaos quantum-behavior particle swarm. In order to avoid the influence of complex collinearity on the distance measurement results, the Gram-Schmidt orthogonalization method is first used to calculate the Mahalanobis distance (MD) value. Then, the optimal threshold point of the system classification is determined through the receiver operating characteristic (ROC) curve; the misclassification rate and the selected variables are defined; the multi-objective mixed programming model is built. The chaos quantum-behavior particle swarm optimization (CQPSO) algorithm is proposed to solve the optimization combination, and the algorithm performs binary coding on the particle based on probability. Using the optimized combination of variables, a new Mahalanobis-Taguchi metric based prediction system is established to complete the task of precise discrimination. Finally, a fault diagnosis for the steel plate is taken as an example. The experimental results show that the proposed method can effectively enhance the iterative speed and optimization precision of the particles, and the prediction accuracy of the optimized MTS is significantly improved.


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    12.Fast Smooth Second-Order Sliding Mode Control with Disturbance Observer for Automatic Shell Magazine

    Authors YAO Laipeng (姚来鹏), HOU Baolin (侯保林), LIU Xi (刘曦)

    AbstractThis paper studies practical control design for a novel automatic shell magazine (ASM) with a new fast smooth second-order sliding mode (FSSOSM) control based on disturbance observer. The dynamic model of the ASM with parameter perturbations and nonlinear friction is established. A higher order sliding mode disturbance observer based on super-twisting algorithm is utilized as a robust compensator to estimate the lumped uncertainties. The proposed FSSOSM control is performed to obtain the continuous sliding mode control law and inhibit the chattering phenomenon. The finite time convergence is investigated by utilizing the Lyapunov stability theorem. Three controllers, the traditional sliding mode controller, the proposed FSSOSM controller and a continuous fixed-time second-order sliding mode (CFTSOSM) controller, are compared. Extensive comparative simulation results under three typical working conditions (no-loaded, half-loaded and full-loaded) demonstrate that the proposed control strategy has a high dynamic tracking performance along with a good robustness against model uncertainty.


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    13 .Poisson Image Restoration via Transformed Network

    Authors XU Xiaoling (徐晓玲), ZHENG Haiyu (郑海玉), ZHANG Fengqin (张凤芹), LI Hechen (李赫辰), ZHANG Minghui (张明辉)

    AbstractThere is a Poisson inverse problem in biomedical imaging, fluorescence microscopy and so on. Since the observed measurements are damaged by a linear operator and further destroyed by Poisson noise, recovering the approximate original image is difficult. Motivated by the decouple scheme and the variance-stabilizing transformation (VST) strategy, we propose a method of transformed convolutional neural network (CNN) to restore the observed image. In the network, the Conv-layers play the role of a linear inverse filter and the distribution transformation simultaneously. Furthermore, there is no batch normalization (BN) layer in the residual block of the network, which is devoted to tackling with the non-Gaussian recovery procedure. The proposed method is compared with state-of-the-art Poisson deblurring algorithms, and the experimental results show the effectiveness of the method.

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