Hardening mechanism and thermal-solid coupling model of laminar plasma surface hardening of 65 Mn steel

In the present work,the laminar plasma surface hardening method is employed to enhance the service life of metal components fabricated from 65 Mn steel.The mechanical and wear behaviors of the laminar plasma surface hardened 65 Mn steel were analyzed.The martensite transition transformation of the temperature of the laminar plasma-hardened 65 ferrite Mn steel was determined by a thermal-solid coupling model.Based on the orthogonal experimental results,the optimal hardening parameters were confirmed.The scanning velocity,quenching distance and arc current are 130 mm/min,50 mm and 120 A,respectively.The pearlites and ferrites are transformed into martensites in the hardened zone,while the ratio of martensite in the heataffected zone decreases with the increase in the hardening depth.Compared to the untreated 65Mn steel,the average hardness increases from 220 HV_(0.2)to 920 HV_(0.2)in the hardened zone and the corresponding absorbed power increases from 118.7 J to 175.5 J.At the same time,the average coefficient of friction(COF)decreases from 0.763 to 0.546,and the wear rate decreases from 5.39×10^(-6)mm^(3)/(N·m)to 2.95×10^(-6)mm^(3)/(N·m),indicating that the wear resistance of 65Mn steel could be significantly improved by using laminar surface hardening.With the same hardening parameters,the depth and width of the hardened zone predicted by the thermal-solid coupling model are 1.85 mm and 11.20 mm,respectively,which are in accordance with the experimental results;depth is 1.83 mm and width is 11.15 mm.In addition,the predicted hardness distributions of the simulation model are in accordance with the experimental results.These results indicate that the simulation model could effectively predict the microstructure characteristics of 65 Mn steel.

Flow Control with Intermittent Disturbance for the Laminar Separation Bubble on a NACA633-421 Airfoil

This study investigates the aerodynamic performance of the NACA 633-421 airfoil and the effectiveness and feasibility of intermittent disturbance flow control methods on laminar separation bubbles(LSBs).It is found that the average velocity and influence range of the synthetic jet actuator increase with the increasing of driving frequency and driving amplitude.LSB occurs at Re=1.0×10^(5),and ruptures atα=6°.But with intermittent disturbance control,the stall angle of attack(AoA)increases while significantly reducing drag.Research shows that although certain disturbance cannot fully recover from LSB stall,decreasing driving amplitude partially restores wing aerodynamic performance,more effectively than increasing driving amplitude.

Numerical Predictions of Laminar Forced Convection Heat Transfer with and without Buoyancy Effects from an Isothermal Horizontal Flat Plate to Supercritical Nitrogen

Numerical predictions are made for Laminar Forced convection heat transfer with and without buoyancy effects for Supercritical Nitrogen flowing over an isothermal horizontal flat plate with a heated surface facing downwards.Computations are performed by varying the value ofΔT from5 to 30 K and P_(∞)/P_(cr)ratio from1.1 to 1.5.Variation of all the thermophysical properties of supercritical Nitrogen is considered.The wall temperatures are chosen in such a way that two values of Tw are less than T∗(T*is the temperature at which the fluid has a maximum value of Cp for the given pressure),one value equal to T∗and two values greater than T∗.Three different values of U∞are used to obtain Re∞range of 3.6×10_(4)to 4.74×10^(5)for forced convection without buoyancy effects and Gr_(∞)/Re^(2)_(∞)range of 0.011 to 3.107 for the case where buoyancy effects are predominant.Six different forms of correlations are proposed based on numerical predictions and are compared with actual numerical predictions.It has been found that in all six forms of correlations,the maximum deviations are found to occur in those cases where the pseudocritical temperature TT∗lies between the wall temperature and bulk fluid temperature.

同步辐射Laminar光栅的研制

采用全息离子束刻蚀和反应离子刻蚀相结合的新工艺 ,在熔石英基片上成功地刻蚀出 2 0 0l/mm、线空比 4:6、槽深 70nm、刻划面积 60× 2 0mm2 的浅槽矩形Laminar光栅。对改进光栅线条粗糙度和线空比的方法进行了系统的研究。这一新工艺相对简单 。

Fabrication of superaligned carbon nanotubes reinforced copper matrix laminar composite by electrodeposition

A new kind of laminar metal matrix nanocomposite（MMC） was fabricated by an electrodeposition process with copper and superaligned carbon nanotubes film（SACNT film）.The SACNT film was put on a titanium plate and then a layer of copper was electrodeposited on it.By repeating the above process,the laminar Cu/SACNT composite which contains dozens or hundreds of layers of copper and SACNT films was obtained.The thickness of a single copper layer was controlled by adjusting the process parameter easily and the thinnest layer is less than 2 μm.The microscopic observation shows that the directional alignment structure of SACNT is retained in the composite perfectly.The mechanical and electrical properties testing results show that the tensile and yield strengths of composites are improved obviously compared with those of pure copper,and the high conductivity is retained.This technology is a potential method to make applicable MMC which characterizes high volume fraction and directional alignment of carbon nanotubes.

Analytical Solution for Laminar Viscous Flow inthe Gap Between Two Parallel Rotary Disks

Aim To get the analytical for laminar viscous flow in the gap of two parallel rotating disks. Methods By estimating the order of magnitude of each term in the Navier-Stokes equations to drop small terms and achieve the required simplified differential equations, and by integrating the equations to obtain the solution for theflow between two rotary disks. Results Parameters related to the laminar viscous flow in the gap between two parallel rotary disks, such as the velocity, the pressure, the flowrate, the force, the shearing stress, the torque and the power derived. Conclusion The result provides a theoretical basis and an effective method for the designs of the devices connected with the laminar viscous flow in the gap between two parallel rotary disks.

Self-Learning and Its Application to Laminar Cooling Model of Hot Rolled Strip

The mathematical model for online controlling hot rolled steel cooling on run-out table （ROT for abbreviation） was analyzed, and water cooling is found to be the main cooling mode for hot rolled steel. The calculation of the drop in strip temperature by both water cooling and air cooling is summed up to obtain the change of heat transfer coefficient. It is found that the learning coefficient of heat transfer coefficient is the kernel coefficient of coiler temperature control （CTC） model tuning. To decrease the deviation between the calculated steel temperature and the measured one at coiler entrance, a laminar cooling control self-learning strategy is used. Using the data acquired in the field, the results of the self-learning model used in the field were analyzed. The analyzed results show that the self-learning function is effective.

Opti mization and Model of Laminar Cooling Control Systemfor Hot Strip Mills

The structure of laminar cooling control system for hot rolling was introduced and the control mode, cooling strategy, segment tracking and model recalculation were analyzed. The parameters of air/water cooling models were optimized by regressing the data gathering in situ, and satisfactory effect was obtained. The coiling temperature can be controlled within ±15℃.

Preparation of super-aligned carbon nanotube-reinforced nickel-matrix laminar composites with excellent mechanical properties

A homogeneous and compact super-aligned carbon nanotube(SACNT)-reinforced nickel-matrix composite was successfully prepared by electrodeposition. The mechanical properties of the laminar SACNT/Ni composites were substantially improved compared with those of pure nickel. With increasing content of SACNTs, the tensile strength of the composite increased and the elongation decreased because of the high-strength SACNTs bearing part of an applied load and the fine-grained strengthening mechanism. The nanohardness of the SACNT/Ni composites was improved from 3.92 GPa(pure nickel) to 4.62 GPa(Ni-4 vol%SACNTs). The uniform distribution of SACNTs in the composites and strong interfacial bonding between the SACNTs and the nickel matrix resulted in an improvement of the mechanical properties of the SACNT/Ni composites. The introduced SACNTs refined the nickel grains, increased the amount of crystal twins, and changed the preferred orientation of grain growth.

Extraction Kinetics of Lanthanum in Chloride Medium by Bifunctional Ionic Liquid [A336][CA-12] Using a Constant Interfacial Cell with Laminar Flow

The extraction kinetics of La(III) from aqueous chloride solutions into n-heptane solutions of bifunctional ionic liquid extractant [A336][CA-12](tricaprylmethylammonium sec-octylphenoxy acetic acid) was investigated using a constant interfacial cell with laminar flow. The effects of stirring speed, temperature and specific interfacial area on the extraction rate were examined. The results indicate that mass transfer kinetics of La(III) is a mixed-controlled process influenced by interfacial reaction. On the basis of mass transfer kinetic results in the extraction of La(III) by [A336][CA-12], the extraction rate equation of La(III) is proposed in terms of pseudo-firstorder constants, which is supported by the measured thermodynamic equations. The mass-transfer kinetic model deduced from the rate controlling step is adequate to interpret the experimental data qualitatively.

Cortical laminar necrosis related to migrainous cerebral infarction

We present a 29-year-old woman with a long history of attacks of migraine with and without visual aura.She was a heavy smoker(20 cigarettes/d) and was currently taking oral contraceptives. During a typical migraine attack with aura, she developed dysarthria,left brachial hemiparesis and hemihypoesthesia and brief and autolimited left clonic facial movements. Four hours after onset, vascular headache and focal sensorimotor neurological deficit were the only persisting symptoms and, on seventh day, she was completely recovered. Brain magnetic resonance imaging on day 20 after onset showed a subacute ischemic lesion in the right temporo-parietal cortex compatible with cortical laminar necrosis(CLN). Extensive neurological work-up done to rule out other known causes of cerebral infarct with CLN was unrevealing. Only ten of 3.808 consecutive stroke patients included in our stroke registry over a 19-year period fulfilled the strictly defined International Headache Society criteria for migrainous stroke. The present case is the unique one in our stroke registry that presents CLN related to migrainous cerebral infarction. Migrainous infarction can result in CLN.

THEORETICAL ANALYSIS ON HYDRAULIC TRANSIENT RESULTED BY SUDDEN INCREASE OF INLET PRESSURE FOR LAMINAR PIPELINE FLOW

Hydraulic transient, which is resulted from sudden increase of inlet pressure for laminar pipeline flow, is studied. The partial differential equation, initial and boundary conditions for transient pressure were constructed, and the theoretical solution was obtained by variable-separation method. The partial differential equation, initial and boundary conditions for flow rate were obtained in accordance with the constraint correlation between flow rate and pressure while the transient flow rate distribution was also solved by variable-separation method. The theoretical solution conforms to numerical solution obtained by method of characteristics (MOC) very well.

Arc Voltage Fluctuation in DC Laminar and Turbulent Plasma Jets Generation

Arc voltage fluctuations in a direct current （DC） non-transferred arc plasma generator are experimentally studied, in generating a jet in the laminar, transitional and turbulent regimes. The study is with a view toward elucidating the mechanism of the fluctuations and their relationship with the generating parameters, arc root movement and flow regimes. Results indicate that the existence of a 300 Hz alternating current （AC） component in the power supply ripples does not cause the transition of the laminar plasma jet into a turbulent state. There exists a high frequency fluctuation at 4 kHz in the turbulent jet regime. It may be related to the rapid movement of the anode attachment point of the arc.

Element Tracking Strategies for Hot Strip Laminar Cooling Control

Feedforward control is the core to control function in the cooling process of hot strip. One of the most important tasks in feedforward control is to determine the arrival time of the strip at various locations on the runout table for effective control. Based on the principles of element tracking and tracking strategies for variable rolling speed and constant rolling speed, a simple diagonal tracking method for an existing hot strip mill was proposed and tested. The test results show that the proposed strategies are effective for improving tracking control.

THE LOSS OF STABILITY OF LAMINAR FLOW IN OPEN CHANNEL AND THE MECHANISM OF SAND RIPPLE FORMATION

In the flow on a mobile bed in an open channel, sand ripple often appears after the sediment begins to move. Different scholars have different views on the formation of sand ripples. This paper holds that as the ripple in general is very small, its formation is due to the instability of the laminar flow or the evolution of the small-scale coherent structures in the sublayer adjacent to the wall of the open channel. When the shear stresses caused by the disturbing waves or the coherent structure near the bed surface boundary and the water flow itself are greater than the shields stresses, responses on the bed surface appear and the sand ripple forms. If the frequency of the shear stress caused by the disturbance is close to the natural frequency of the sand grains that produced resonance, such a phenomenon is called the 'detection property' of the sediment. It is at this point that the maximum resonance appears and the sand ripple develops rapidly.

Existence of multiple solutions for the laminar flow in a porous channel with suction at both slowly expanding and contracting walls

The asymptotic behavior of solutions of a similarity equation for the laminar flow in a porous channel with suction at both expanding and contracting walls has been obtained by using a singular perturbation method.However,in the matching process,this solution neglects exponentially small terms.To take into account these exponentially small terms,a method involving the inclusion of exponentially small terms in a perturbation series was used to find two of the solutions analytically.The series involving the exponentially small terms and expansion ratio predicts dual solutions.Furthermore,the result indicates that the expansion ratio has much important influence on the solutions.

Influence of the Laminar Plasma Torch Construction on the Jet Characteristics

Based on two typical laminar plasma torches （LPT）, i.e. a multi-electrode plasma torch （MEPT） with segmented anode structure and a two-electrode plasma torch （TEPT） with conventional structure, this paper studied the influence of the LPTs construction on the jet characteristics. Experiments were designed to measure their arc voltage, jet length, thermal efficiency and specific enthalpy using a home-made data acquisition system. With them, the jet characteristics of the two different LPTs were compared in detail. Results show that different plasma torch construction leads to distinctively different characteristics of the generated plasma jet. Based on the different jet characteristics, a plasma torch with appropriate construction could be used to meet the different application requirements.

Physics-informed deep learning for incompressible laminar flows

Physics-informed deep learning has drawn tremendous interest in recent years to solve computational physics problems,whose basic concept is to embed physical laws to constrain/inform neural networks,with the need of less data for training a reliable model.This can be achieved by incorporating the residual of physics equations into the loss function.Through minimizing the loss function,the network could approximate the solution.In this paper,we propose a mixed-variable scheme of physics-informed neural network(PINN)for fluid dynamics and apply it to simulate steady and transient laminar flows at low Reynolds numbers.A parametric study indicates that the mixed-variable scheme can improve the PINN trainability and the solution accuracy.The predicted velocity and pressure fields by the proposed PINN approach are also compared with the reference numerical solutions.Simulation results demonstrate great potential of the proposed PINN for fluid flow simulation with a high accuracy.

Robust design of natural laminar flow supercritical airfoil by multi-objective evolution method

Abstract A transonic, high Reynolds number natural laminar flow airfoil is designed and studied. The γ-θ transition model is combined with the shear stress transport （SST） k-w turbulence model to predict the transition region for a laminar-turbulent boundary layer. The non-uniform free-form deformation （NFFD） method based on the non-uniform rational B-spline （NURBS） basis function is introduced to the airfoil parameterization. The non-dominated sorting genetic algorithm-II （NSGA-II） is used as the search algo- rithm, and the surrogate model based on the Kriging models is introduced to improve the efficiency of the optimization system. The optimization system is set up based on the above technologies, and the robust design about the uncertainty of the Mach number is carried out for NASA0412 airfoil. The optimized airfoil is analyzed and compared with the original airfoil. The results show that natural laminar flow can be achieved on a supercritical airfoil to improve the aerodynamic characteristic of airfoils.

Preliminary Studies of Practicability of Laminar Plasma Surface Treatment Process

The basic remelting and cladding tests with laminar plasma technology on metals have been conducted in order to demonstrate the possibility of the technology applied in material surface modification. The experimental results show that the properties of the modified layers of the cast iron surface can be improved notably by the remelting treatment and those of the stainless steel by the cladding treatment. The related results are also verified by microscopic studies such as scanning electron microscopic （SEM） observations, energy dispersive spectra （EDS） analysis and the Vickers hardness measurements of the surface modified layers.