Microstructure and mechanical properties of curved AZ31 magnesium alloy profiles produced by differential velocity sideways extrusion

Lightweight curved profiles are widely utilised in the transportation industry considering the increasing need for improving aerodynamic efficiency,aesthetics and cutting emissions.In this paper,curved AZ31 Mg alloy profiles were manufactured in one operation by a novel process,differential velocity sideways extrusion(DVSE),in which two opposed rams were used.Effects of extrusion temperature and velocity(strain rate) on curvature,microstructure,and mechanical properties of the formed profiles were examined.Profile curvature was found to be more readily controlled by the velocity ratio of the bottom ram v2to the top ram v1,whereas extrusion temperature(T=250,300,350℃)and extrusion velocity(v_(1)=0.1,1 mm/s) slightly affect curvature for a given velocity ratio.A homogeneous microstructure with equiaxed grains(~4.5 μm) resulted from dynamic recrystallisation(DRX),was observed after DVSE(v_(2)/v_(1)=1/2) at 300 ℃ and v_(1)=0.1 mm/s,where the initial billet had an average grain size of ~25 um.Increasing extrusion temperature leads to grain growth(~5 μm) at 350 ℃ and v_(1)=0.1 mm/s.DRX is incomplete at the relatively low temperature of 250℃(v_(1)=0.1 mm/s),and higher strain rate with v1=1mm/s(T=300℃),resulting in inhomogeneous bi-modal necklace pattern grains ranging in size around 1-25 μm for the former and 2-20μm for the latter.Grain refinement is attributed to DRX during the severe plastic deformation(SPD) arising in DVSE,and initiates at the prior boundaries of coarse grains in a necklace-like manner.Compared with the billet,micro-hardness and ultimate tensile strength of the profiles have been enhanced,which is compatible with grain refinement.Also,an obvious increase in tensile ductility was found.However,yield strength slightly decreases except for the complete DRXed case(300℃,v_(1)=0.1 mm/s),where a slightly higher value was found,indicating strengthening by grain refinement is greater than softening caused by texture modification.The initial billet had a strong basal texture wherein the {0002} basal plane is oriented parallel to the extrusion direction(’hard’ orientation),while DVSE results in the profiles having weak basal textures and the {0002} basal plane oriented ~5-10° to the extrusion direction(i.e.towards the orientation for easier slip).This significantly modified texture contributes to the softening of the profiles in the extrusion direction,in which tensile tests were performed,and the related elongation improvement.

Application of deep learning for informatics aided design of electrode materials in metal-ion batteries

To develop emerging electrode materials and improve the performances of batteries,the machine learning techniques can provide insights to discover,design and develop battery new materials in high-throughput way.In this paper,two deep learning models are developed and trained with two feature groups extracted from the Materials Project datasets to predict the battery electrochemical performances including average voltage,specific capacity and specific energy.The deep learning models are trained with the multilayer perceptron as the core.The Bayesian optimization and Monte Carlo methods are applied to improve the prediction accuracy of models.Based on 10 types of ion batteries,the correlation coefficients are maintained above 0.9 compared to DFT calculation results and the mean absolute error of the prediction results for voltages of two models can reach 0.41 V and 0.20 V,respectively.The electrochemical performance prediction times for the two trained models on thousands of batteries are only 72.9 ms and 75.7 ms.Besides,the two deep learning models are applied to approach the screening of emerging electrode materials for sodium-ion and potassium-ion batteries.This work can contribute to a high-throughput computational method to accelerate the rational and fast materials discovery and design.

Effect of preload forces on multidimensional signal dynamic behaviours for battery early safety warning

Providing early safety warning for batteries in real-world applications is challenging.In this study,comprehensive thermal abuse experiments are conducted to clarify the multidimensional signal evolution of battery failure under various preload forces.The time-sequence relationship among expansion force,voltage,and temperature during thermal abuse under five categorised stages is revealed.Three characteristic peaks are identified for the expansion force,which correspond to venting,internal short-circuiting,and thermal runaway.In particular,an abnormal expansion force signal can be detected at temperatures as low as 42.4°C,followed by battery thermal runaway in approximately 6.5 min.Moreover,reducing the preload force can improve the effectiveness of the early-warning method via the expansion force.Specifically,reducing the preload force from 6000 to 1000 N prolongs the warning time(i.e.,227 to 398 s)before thermal runaway is triggered.Based on the results,a notable expansion force early-warning method is proposed that can successfully enable early safety warning approximately 375 s ahead of battery thermal runaway and effectively prevent failure propagation with module validation.This study provides a practical reference for the development of timely and accurate early-warning strategies as well as guidance for the design of safer battery systems.

Investigation of Experimental Devices for Finger Active and Passive Tactile Friction Analysis

Complicated tribological behavior occurs when human fingers touch and perceive the surfaces of objects.In this process,people use their exploration style with different conditions,such as contact load,sliding speed,sliding direction,and angle of orientation between fingers and object surface consciously or unconsciously.This work addressed interlaboratory experimental devices for finger active and passive tactile friction analysis,showing two types of finger movement.In active sliding experiment,the participant slid their finger freely against the object surface,requiring the subject to control the motion conditions themselves.For passive sliding experiments,these motion conditions were adjusted by the device.Several analysis parameters,such as contact force,vibration acceleration signals,vibration magnitude,and fingerprint deformation were recorded simultaneously.Noticeable friction differences were observed when comparing active sliding and passive sliding.For passive sliding,stick-slip behavior occurred when sliding in the distal direction,evidenced by observing the friction force and the related deformation of the fingerprint ridges.The employed devices showed good repeatability and high reliability,which enriched the design of the experimental platform and provided guidance to the standardization research in the field of tactile friction.

Vibration-based bearing fault diagnosis of high-speed trains:A literature review

Due to the advantages of comfort and safety,high-speed trains are gradually becoming the mainstream public transport in China.Since the operating speed and mileage of high-speed trains have achieved rapid growth,it is more and more urgent to ensure their reliability and safety.As an important component in the bogies of highspeed trains,the health state of the bearing directly affects the operational safety of the trains.It is therefore necessary to diagnoze the faults of bearings in the bogies of high-speed trains as early as possible.In this paper,the bearing fault diagnostic methods for high-speed trains have been systematically summarized with their challenges and perspectives.First,it briefly introduces the structure of bearings in the bogies as well as the fault characteristic frequencies.Then,a brief review of the research on vibration-based signal processing methods and machine learning methods has been provided.Finally,the challenges and future developments of vibrationbased bearing fault diagnostic methods for high-speed trains have been analyzed.

Advances in Active Suspension Systems for Road Vehicles

Active suspension systems(ASSs)have been proposed and developed for a few decades,and have now once again become a thriving topic in both academia and industry,due to the high demand for driving comfort and safety and the compatibility of ASSs with vehicle electrification and autonomy.Existing review papers on ASSs mainly cover dynamics modeling and robust control;however,the gap between academic research outcomes and industrial application requirements has not yet been bridged,hindering most ASS research knowledge from being transferred to vehicle companies.This paper comprehensively reviews advances in ASSs for road vehicles,with a focus on hardware structures and control strategies.In particular,state-of-the-art ASSs that have been recently adopted in production cars are discussed in detail,including the representative solutions of Mercedes active body control(ABC)and Audi predictive active suspension;novel concepts that could become alternative candidates are also introduced,including series active variable geometry suspension,and the active wheel-alignment system.ASSs with compact structure,small mass increment,low power consumption,high-frequency response,acceptable economic costs,and high reliability are more likely to be adopted by car manufacturers.In terms of control strategies,the development of future ASSs aims not only to stabilize the chassis attitude and attenuate the chassis vibration,but also to enable ASSs to cooperate with other modules(e.g.,steering and braking)and sensors(e.g.,cameras)within a car,and even with high-level decision-making(e.g.,reference driving speed)in the overall transportation system-strategies that will be compatible with the rapidly developing electric and autonomous vehicles.

Investigation of FE Model Size Definition for Surface Coating Application

An efficient prediction mechanical performance of coating structures has been a constant concern since the dawn of surface engineering. However, predictive models presented by initial research are normally based on traditional solid mechanics, and thus cannot predict coating performance accurately. Also, the high computational costs that originate from the exclusive structure of surface coating systems （a big difference in the order of coating and substrate） are not well addressed by these models. To fill the needs for accurate prediction and low computational costs, a multi-axial continuum damage mechanics （CDM）-based constitutive model is introduced for the investigation of the load bearing capacity and fracture properties of coatings. Material parameters within the proposed constitutive model are determined for a typical coating （TIN） and substrate （Cu） system. An efficient numerical subroutine is developed to implement the determined constitutive model into the commercial FE solver, ABAQUS, through the user-defined subroutine, VUMAT. By changing the geometrical sizes of FE models, a series of computations are carried out to investigate （1） loading features, （2） stress distributions, and （3） failure features of the coating system. The results show that there is a critical displacement corresponding to each FE model size, and only if the applied normal loading displacement is smaller than the critical displacement, a reasonable prediction can be achieved. Finally, a 3D map of the critical displacement is generated to provide guidance for users to determine an FE model with suitable geometrical size for surface coating simulations. This paper presents an effective modelling approach for the prediction of mechanical performance of surface coatings.

Diffusion of chemically reactive species in third grade fluid flow over an exponentially stretching sheet considering magnetic field effects

This article addresses the magnetohydrodynamics(MHD) flow of a third grade fluid over an exponentially stretching sheet. Analysis is carried out in the presence of first order chemical reaction. Both cases of constructive and destructive chemical reactions are reported. Convergent solutions of the resulting differential systems are presented in series forms. Characteristics of various sundry parameters on the velocity, concentration, skin friction and local Sherwood number are analyzed and discussed.

Damage prediction of 7025 aluminum alloy during equal-channel angular pressing

Equal-channel angular pressing （ECAP） is a prominent technique that imposes severe plastic deformation into materials to en- hance their mechanical properties. In this research, experimental and numerical approaches were utilized to investigate the mechanical prop- erties, strain behavior, and damage prediction of ECAPed 7025 aluminum alloy in various conditions, such as die channel angle, outer comer angle, and friction coefficient. Experimental results indicate that, after the first pass, the yield strength, ultimate tensile strength, and hardness magnitude are improved by approximately 95%, 28%, and 48.5%, respectively, compared with the annealed state, mainly due to grain re- finement during the deformation. Finite element analysis shows that the influence of die channel angle is more important than that of outer comer angle or friction coefficient on both the strain behavior and the damage prediction. Also, surface cracks are the main cause of damage during the ECAP process for every die channel angle except for 90°; however, the cracks initiated from the neighborhood of the central re- gions are the possible cause of damage in the ECAPed sample with the die channel angle of 90°.

High-efficiency forming processes for complex thin-walled titanium alloys components: state-of-the-art and perspectives

Complex thin-walled titanium alloy components play a key role in the aircraft,aerospace and marine industries,offering the advantages of reduced weight and increased thermal resistance.The geometrical complexity,dimensional accuracy and in-service properties are essential to fulfill the high-performance standards required in new transportation systems,which brings new challenges to titanium alloy forming technologies.Traditional forming processes,such as superplastic forming or hot pressing,cannot meet all demands of modern applications due to their limited properties,low productivity and high cost.This has encouraged industry and research groups to develop novel high-efficiency forming processes.Hot gas pressure forming and hot stamping-quenching technologies have been developed for the manufacture of tubular and panel components,and are believed to be the cut-edge processes guaranteeing dimensional accuracy,microstructure and mechanical properties.This article intends to provide a critical review of high-efficiency titanium alloy forming processes,concentrating on latest investigations of controlling dimensional accuracy,microstructure and properties.The advantages and limitations of individual forming process are comprehensively analyzed,through which,future research trends of high-efficiency forming are identified including trends in process integration,processing window design,full cycle and multi-objective optimization.This review aims to provide a guide for researchers and process designers on the manufacture of thin-walled titanium alloy components whilst achieving high dimensional accuracy and satisfying performance properties with high efficiency and low cost.

Ductile fracture behavior of TA15 titanium alloy at elevated temperatures

To better understand the fracture behavior of TA15 titanium alloy during hot forming, three groups of experiments were conducted to investigate the influence of deformation temperature, strain rate, initial microstructure, and stress triaxiality on the fracture behavior of TA15 titanium alloy. The microstructure and fracture surface of the alloy were observed by scanning electronic microscopy to analyze the potential fracture mechanisms under the experimental deformation conditions. The experimental results indicate that the fracture strain increases with increasing deformation temperature, decreasing strain rate, and decreasing stress triaxiality. Fracture is mainly caused by the nucleation, growth, and coalescence of microvoids because of the breakdown of compatibility requirements at the α/β interface. In the equiaxed microstructure, the fracture strain decreases with decreasing volume fraction of the primary α-phase(αp) and increasing α/β-interface length. In the bimodal microstructure, the fracture strain is mainly affected by α-lamella width.

Investigation of the friction coefficient evolution and lubricant breakdown behaviour of AA7075 aluminium alloy forming processes at elevated temperatures

The lubricant behaviour at elevated temperatures was investigated by conducting pin-on-disc tests between P20 tool steel and AA7075 aluminium alloy. The effects of temperature, initial lubricant volume, contact pressure and sliding speed on the lubricant behaviour(i.e. evolutions of the coefficient of friction(COF) and the breakdown phenomenon) were experimentally studied. The evolutions of COF at elevated temperatures consisted of three distinct stages with different friction mechanisms. The first stage(stage Ⅰ) occurred with low friction when the boundary lubrication was present. The second stage(stage Ⅱ) was the transition process in which the COF rapidly increased as the lubricant film thickness decreased to a critical value. In the final plateau stage(stage Ⅲ), lubricant breakdown occurred and intimate contact at the interface led to high friction values. At the low friction stage(stage Ⅰ), the value of COF increased with increasing temperature. The increase in temperature, contact pressure and sliding speed as well as the decrease in initial lubricant volume accelerated the lubricant breakdown.

An investigation into ball burnishing process of magnesium alloy on CNC lathe using different environments

Ball burnishing routine permits through a simple,fast and economical manner to obtain free chip on the manufactured parts.It generates a superior surface finish by rotating a ball tool against a workpiece.The burnishing process is commonly developed in industry in order to improve the surface quality,which is a critical issue in the manufacturing sector.An experimental study were carried out to determine the best surface quality for magnesium alloy subjected to d iff ere ni medium.Burnishing of magnesium alloy was performed varying four different mediums and combining different burnishing parameters.To design the experiment were used the classical Taguchi method through which were developed the L16 orthogonal array.This strategy allowed to detect the driving parameters that generate the best surface roughness value by computing the signal-to-noise ratio.The driving parameters values for this study are 400 N(force),0.05 mm/min(feed rate),three number of passes and boron oil as medium.The results are paramount important for designing heavy parts used in transportation vehicles such as automobiles,airplanes,high-speed trains etc.

Coil-to-Stretch Transition of Binder Chains Enabled by“Nano-Combs”to Facilitate Highly Stable SiO_(x) Anode

The commercialized binder carboxymethyl cellulose sodium(CMC-Na)is considered unsuitable for micro-sized SiO_(x) anode as it cannot endure the large volume change to retain the conductive network during repeated charge/discharge cycles.Herein,a small amount of silicon nanoparticles(SiNPs)is added during slurry preparation process as“nano-combs”to unfold the convoluted CMC-Na polymer chains so that they undergo a coilto-stretch transition by interaction between polar groups(e.g.,-OH,-COONa)of polymer and SiNPs’large surface.Through maximizing the utilization of binders,a uniform conductive network is constructed with increased interfacial contact with micro-sized SiO_(x).As a result,the SiO_(x) electrode with optimized(10 wt%)SiNPs addition shows significantly improved initial capacity and cycling performance.Through revisiting CMCNa,a currently deemed unqualified binder in SiO_(x) anode,this work gives a brand-new perspective on the failing mechanism of Si-based anode materials and an improving strategy for electrode preparation.

Model-guided design of a high performance and durability Ni nanofiber/ceria matrix solid oxide fuel cell electrode

Mixed ionic electronic conductors(MIECs)have attracted increasing attention as anode materials for solid oxide fuel cells(SOFCs)and they hold great promise for lowering the operation temperature of SOFCs.However,there has been a lack of understanding of the performance-limiting factors and guidelines for rational design of composite metal-MIEC electrodes.Using a newly-developed approach based on 3 D-tomography and electrochemical impedance spectroscopy,here for the first time we quantify the contribution of the dual-phase boundary(DPB)relative to the three-phase boundary(TPB)reaction pathway on real MIEC electrodes.A new design strategy is developed for Ni/gadolinium doped ceria(CGO)electrodes(a typical MIEC electrode)based on the quantitative analyses and a novel Ni/CGO fiber-matrix structure is proposed and fabricated by combining electrospinning and tape-casting methods using commercial powders.With only 11.5 vol%nickel,the designer Ni/CGO fiber-matrix electrode shows 32%and 67%lower polarization resistance than a nano-Ni impregnated CGO scaffold electrode and conventional cermet electrode respectively.The results in this paper demonstrate quantitatively using real electrode structures that enhancing DPB and hydrogen kinetics are more efficient strategies to enhance electrode performance than simply increasing TPB.

Orthogonal On-Rotor Sensing Vibrations for Condition Monitoring of Rotating Machines

Thanks to the fast development of micro-electro-mechanical systems(MEMS)technologies,MEMS accelerometers show great potentialities for machine condition monitoring.To overcome the problems of a poor signal to noise ratio(SNR),complicated modulation,and high costs of vibration measurement and computation using conventional integrated electronics piezoelectric accelerometers,a triaxialMEMS accelerometer-based on-rotor sensing(ORS)technology was developed in this study.With wireless data transmission capability,the ORS unit can be mounted on a rotating rotor to obtain both rotational and transverse dynamics of the rotor with a high SNR.The orthogonal outputs lead to a construction method of analytic signals in the time domain,which is versatile in fault detection and diagnosis of rotating machines.Two case studies based on an induction motor were carried out,which demonstrated that incipient bearing defect and half-broken rotor bar can be effectively diagnosed by the proposed measurement and analysis methods.Comparatively,vibration signals from translational on-casing accelerometers are less capable of detecting such faults.This demonstrates the superiority of the ORS vibrations in fault detection of rotating machines.

Achieving high ductility and strength in magnesium alloy through cryogenic-hot forming

Magnesium alloys are the lightest structural alloys and have attracted substantial research attention in the past two decades. However, their mechanical properties, including ductility and strength, are limited after forming due to the formation of coarse grains and strong texture. This study proposes and proves a new cryogenic-hot forming process concept. Cryogenic deformation is imposed before the hot deformation. The effect of the cryogenic step has been compared with a conventional direct hot deformation process. The mechanical properties, microstructure,and texture of both the novel and conventional process routes have been compared. The cryogenic-hot deformed sample exhibits the highest ductility and fracture strength(ultimate tensile strength: 321 MPa, ductility: 21%) due to effective grain refinement and texture weakening by cryogenically formed twin-twin interaction induced recrystallisation. The proposed cryogenic-hot forming process can be a potential innovative manufacturing method for producing high-performance magnesium components.

Flame Structure of Methane and Kerosene Combustion with a Compact Concave Flame-Holder using the LES-pdf Method

Compact flame-holders for afterburners are an increasing requirement for modern aero engines.However,flame-holder design is non-trivial since high inlet temperatures,velocities,and elaborate structures induce complex turbulence,combustion,and spray coupling in modern afterburners.In this work,the LES-pdf and stochastic fields-Lagrangian particle spray methods are used to investigate methane and aviation kerosene combustion structures formed by new-type concave flame-holders.The flow pattern,combustion mode,and flame structure of gaseous and liquid fuel around a concave flame-holder are analyzed,discussed,and compared with experimental results.Results reveal that the flame stability of a concave flame-holder is better than that of the non-concave one.Furthermore,when using liquid fuel,the concave flame-holder forms a stable and compact flame.These results suggest concave flame-holders are a promising design for compact afterburners.

Interactive mechanism and friction modelling of transient tribological phenomena in metal forming processes: A review

The accurate representation of tribological boundary conditions at the tool–workpiece interface is crucial for analysis and optimization of formability,material flow,and surface quality of components during metal forming processes.It has been found that these tribological conditions vary spatially and historically with process parameters and contact conditions.These time-dependent tribological behaviours are also known as transient tribological phenomena,which are widely observed during forming processes and many other manufacturing application scenarios.However,constant friction values are usually assigned to represent complex and dynamic interfacial conditions,which would introduce deviations in the relevant predictions.In this paper,transient tribological phenomena and the contemporary understanding of the interaction between friction and wear are reviewed,and it has been found that these phenomena are induced by the transitions of friction mechanisms and highly dependent on complex loading conditions at the interface.Friction modelling techniques for transient behaviours for metal forming applications are also reviewed.To accurately describe the evolutionary friction values and corresponding wear during forming,the advanced interactive friction modelling has been established for different application scenarios,including lubricated condition,dry sliding condition(metal-on-metal contact),and coated system.

Predicting the coefficient of friction in a sliding contact by applying machine learning to acoustic emission data

It is increasingly important to monitor sliding interfaces within machines,since this is where both energy is lost,and failures occur.Acoustic emission(AE)techniques offer a way to monitor contacts remotely without requiring transparent or electrically conductive materials.However,acoustic data from sliding contacts is notoriously complex and difficult to interpret.Herein,we simultaneously measure coefficient of friction(with a conventional force transducer)and acoustic emission(with a piezoelectric sensor and high acquisition rate digitizer)produced by a steel‒steel rubbing contact.Acquired data is then used to train machine learning(ML)algorithms(e.g.,Gaussian process regression(GPR)and support vector machine(SVM))to correlated acoustic emission with friction.ML training requires the dense AE data to first be reduced in size and a range of processing techniques are assessed for this(e.g.,down-sampling,averaging,fast Fourier transforms(FFTs),histograms).Next,fresh,unseen AE data is given to the trained model and the resulting friction predictions are compared with the directly measured friction.There is excellent agreement between the measured and predicted friction when the GPR model is used on AE histogram data,with root mean square(RMS)errors as low as 0.03 and Pearson correlation coefficients reaching 0.8.Moreover,predictions remain accurate despite changes in test conditions such as normal load,reciprocating frequency,and stroke length.This paves the way for remote,acoustic measurements of friction in inaccessible locations within machinery to increase mechanical efficiency and avoid costly failure/needless maintenance.