Abstract:In this paper， the Shear Thickening Polishing （STP） method is proposed to realize the low-cost， high-efficiency overall high-quality polishing of the complex double helix surface of the carbide drilling tool，aiming at the problem of low efficiency of surface processing of cemented carbide drilling tools. First， non-Newtonian polishing fluid with shear-thickening properties was prepared. Then their rheological properties were tested using an MCR302 rotational rheometer. Based on the rheological properties of the shear thickening polishing slurry， the body clearance， the margin， and the helical surface of the flutes of the cemented carbide twist drill were polished. Using the control variable method， the influence of the rotational speed of the polishing groove and the rotational speed of the workpiece on the surface quality and material removal rate of the cemented carbide twist drill was analyzed. The experimental results show that the overall surface roughness Ra of the processed twist drill first decreases and then increases with the increase of the rotational speed of the polishing groove， and the effect of processing is the best when the rotational speed of the polishing groove is 90 r/min. The overall Ra of the twist drill first decreases and then remaines basically unchanged or slightly increases with the increases of the rotational speed of the workpiece， and the effect of processing is the best when the rotational speed of workpiece is 3 500 r/min. The material removal rate of the twist drill is positively correlated with the rotational speed of the polishing groove， and the rotational speed of the workpiece. Under the optimal processing parameters of the rotational speed of the polishing groove of 90 r/min and the rotational speed of the workpiece of 3 500 r/min， the twist drill was processed using STP technology for 60 min， the Ra of the body clearance， the margin and the helical surface of the flutes change from the original 310 nm， 450 nm and 270 nm to 10 nm， 243 nm and 15 nm， respectively， the grinding marks of the body clearance and the helical surface of the flutes almost disappeared， and the defects at the cutting edge of the flutes were significantly reduced.

Abstract:To predict the vehicle handling stability risk earlier， and to solve the problem of unknown prior information of“road”in the traditional“driver-vehicle-road”coupling system and the resulting difficulty in predicting“driver”input， a handling stability prediction method combined with the driver steering model and the vehicle nonlinear dynamics model was put forward using the forward preview path provided by advanced driver assistance systems. In this paper，firstly，a driver-vehicle-road closed-loop feedback driver model is constructed to compute the potential steering input， then the current vehicle speed and predicted steering are input into the three degrees of freedoms nonlinear dynamics model， and the prediction of handling stability state is subsequently accomplished. Finally， Simulink-Carsim co-simulation and the driver simulator in the loop are performed and compared， and the results of double-lane change， variable curvature path， and snake-shaped path show that the predicted values of thehandling stability states of the proposed method are in good agreement with the actual values.

Abstract:In the obstacle avoidance condition of the human-machine cooperative driving system， a human-machine cooperative obstacle avoidance controller is designed considering the driver’s characteristics， aiming at the problem that the driver cannot control the car in time due to the driver’s inattention. Based on the dual-driver and dual-control man-machine co-driving structure， the automatic driving system uses a Linear Quadratic Regulator （LQR） to control the vehicle to track the planned trajectory， and the driver model is established based on the optimal preview lateral acceleration model.To allocate driving rights more reasonably in the process of obstacle avoidance， a driving simulator is used to collect fatigue driving data to train a BP neural network to identify the driver’s fatigue operation behavior. The human-machine cooperative obstacle avoidance strategy is designed by modeling the driver fatigue factor and space risk of collision. Carsim，PreScan and Simulink co-simulation platform is built to conduct obstacle avoidance simulation experiments under high-speed conditions. The simulation results show that， compared with the traditional method， the proposed strategy reduces the lateral acceleration， sideslip angle and yaw rate by 8.9%， 18.2% and 11.1%， respectively， during the static obstacle avoidance process， and in the process of dynamic obstacle avoidance， the corresponding indicators are reduced by 51.5%， 53.4% and 50.6%， respectively. Therefore， the stability of the vehicle during obstacle avoidance is improved.

Abstract:Aiming to handle the complex situation where the parameters of the powertrain mounting system （PMS） of an electric vehicle were both uncertain and correlated， the global sensitivity analysis of the PMS inherent characteristics to system parameters was investigated by considering the correlation of uncertain parameters. Firstly， the PMS uncertain parameters was treated as probabilistic variables with correlation， and the first-and total-order global sensitivity formulas were derived based on variance decomposition. Then， a method for solving the global sensitivity indexes was proposed based on the Monte Carlo Method （MCM）. Next， the global sensitivity formulas were further derived for the case where the probabilistic variables are normally distributed， and the required sample sets to calculate the global sensitivity indexes were constructed by using MCM. Finally， the effectiveness of the proposed method was demonstrated by the numerical example of an electric vehicle PMS. The analysis results show that the parametric correlation has some effect on the sensitivities of the intrinsic frequency and decoupling rate responses to uncertain parameters， and the parametric correlation should be taken into account to obtain more reasonable results of sensitivity analysis.

Abstract:Considering the influence of car seat adjustment parameters on body pressure distribution， three parameters of seat back angle， seat height， and the seat fore-aft position were selected as factors. The orthogonal test of three factors and five levels was designed， and the collection experiment of body pressure distribution of 95th percentile， 50th percentile human and H-Point Machine（HPM） under different adjustment parameters was carried out. Firstly， the collected body pressure data weredenoised and extracted from the body pressure index， and gray correlation analysis was used to analyzethe factors with a large correlation with body pressure distribution index. Then single-factor experiments were performed on factors with a large correlation with the body pressure index， describing the change of each body pressure index under the dynamic adjustment of a single factor. The results show that seat back angle and the seat fore-aft position have a great influence on the body pressure distribution. When the back angle increases， the backrest body pressure index of different percentile human increases， and the overall body pressure index of the cushion becomes slightly smaller. When the position of the seat fore-aft increases， the 95 th percentile human backrest body pressure index decreases and the cushion contact area decreases， while the 50 th percentile human backrest body pressure index changes little and the cushion contact area decreases.

Abstract:To improve the aerodynamic characteristics of a cabin-over-engine truck and reduce wind resistance， the contribution of different components to the drag coefficient was studied through the wind tunnel test of the truck. It was found that the air deflector， neckline plate， rearview mirror and side skirt contributed greatly to the drag coefficient. According to the aerodynamic principle， aerodynamic drag reduction optimization design is carried out for the parts which make a great contribution to the drag coefficient such as the air deflector， and the drag reduction effect is verified by experiments. The flow field in the front of the truck is improved through the modification design of the rearview mirror and air deflector， and the flow field in the rear of the truck is improved through the parameter combination design of the deflector at the rear of the cargo box. Finally， the schemes with good drag reduction effect of each component are combined. The wind tunnel test results show that the aerodynamic performance of the truck body has been significantly improved through the aerodynamic drag reduction design. Compared with the initial model， the drag reduction effect of the optimal aerodynamic performance combination scheme is about 7%.

Abstract:Welds in structures are often subjected to both axial and tangential loads. The mechanical properties of welds in a single direction cannot reflect the real service condition. Therefore， this study compared the tensile shear and peel mechanical properties of Conventional Friction Stir Spot Welding （CFSSW）， Probeless Friction Stir Spot Welding （PFSSW） and Swept Friction Stir Spot Welding （SFSSW） joints under the optimal parameters. Moreover， a multi-condition welds service performance evaluation method was proposed for a small all-aluminum electric vehicle. And the service performance of the three types of weld was compared. The results show that the service performance of SFSSW joints in the connection region of body side surround and top cross beam under the optimal parameters was improved by 28.97% and 48.86%， compared with CFSSW and PFSSW， respectively. Moreover， in the front longitudinal beam connected region， the three types of weld showed the highest service performance. Meanwhile， the connecting parts on the floor crossbeam and floor longitudinal beam exhibited the lowest welding service performance， and the number of welding spots needs to be increased appropriately to ensure the structure’s safety.

Abstract:Considering the lack of investigation on the dynamic distribution characteristics and the law of formaldehyde under the ventilation condition in passenger cars， this paper applied Computational Fluid Dynamics（CFD） theory and Fluent software to establish a numerical simulation model for analyzing formaldehyde concentration and its distribution in vehicles， and verified its reliability. On this basis， the present work firstly studied the distribution and dynamic variation of formaldehyde mass concentration in passenger vehicles based on the analysis of the air flow field by taking temperature， ventilation rate and ventilation mode factors as variables. Especially， this study investigated the influence of temperature， ventilation rate and ventilation mode on formaldehyde mass concentration at the breathing positions of drivers and passengers， as well as some typical sampling lines in vehicles. The results indicated that the temperature has a significant effect on the formaldehyde concentration in a car. It was also found that formaldehyde concentration at 0.5 m/s and 4.0 m/s ventilation rates presented different distribution characteristics of “hyperbola” and “hump”， respectively， due to vortex flow field. Formaldehyde mass concentration at the driver’s breathing position increased with the increase of ventilation rate. When the ventilation rate is not larger than1.6 m/s， the growth rate is 16.5%； When the ventilation rate is larger than 1.6 m/s， the growth rate decreases to 3.6%. The formaldehyde concentration at the vehicle detection point showed a linear growth trend with the air velocity rate at growth rate of 10.8%. The formaldehyde concentration in the rear row is higher than that in the front row in a car.

Abstract:The excavator usually needs to use linear excavation when excavating trenches and leveling slopes， and it requires a high-precision operation. This paper proposes a multi-joint motion planning and control strategy to realize high-precision linear mining operations. Firstly， the kinematic model of the excavator working device was established， the kinematic trajectory of each joint was obtained by inverse kinematic solution according to the linear motion trajectory of the bucket tooth tip， and the target angle of the boom was planned again according to the predicted angle of stick and bucket. The dynamic model parameters of each joint of the excavator online were identified by using recursive least squares， and the variation of joint angle in the delay time was predicted in real time to compensate for the tracking control errors caused by the system delay characteristics. Finally， the existing excavator was transformed into an intelligent excavator and the working device model of AMESim was built. The hydraulic system model parameters and excavator models are modified based on experimental data， and the control model is established in Simulink and the excavator model of AMESim is co-simulated to verify the reliability of the control algorithm. The simulation results show that， compared with the traditional PID control strategy， the strategy based on joint cooperative control has better performance in the trajectory control of linear excavating buckets.

Abstract:Aiming at the problems of insufficient leg stiffness and vibration of large hexapod robots during motion， a multi-objective comprehensive optimization method based on an approximate model is proposed. First， to determine the optimal space for the bionic leg， a finite element model is established to analyze the strength， stiffness， and modal frequency of the leg structure under various complex working conditions. A parametric model is established for the static and dynamic performance of the bionic leg， and the corresponding design variables are defined. To obtain the initial sample points， the Optimal Latin Hypercube Method was used to conduct an experimental design of the bionic leg hip linkage， thigh， and calf module. The response surface model， kriging model and radial basis function neural network model are fitted， and the approximate model with the highest accuracy is selected through error analysis. And combined with the Non-dominated Sorting Genetic Algorithm Ⅱ， the static stiffness， mass， and first-order natural frequency are targeted.Constraining the maximum stress， the bionic leg is optimally designed， and the optimized results are analyzed and verified. The results show that after the heavy-duty bionic leg is optimized by the method， under the premise of satisfying the structural strength， the maximum deformation of the flat ground condition is reduced by 9.73%， the maximum deformation of the slope condition is reduced by 9.46%， the first-order natural frequency is increased by 3.45%， and the overall quality fell by 8.63%.

Abstract:Aiming at the difficulty to satisfy the large flow rate and high sensitivity of the online wear detection system for mechanical instruments simultaneously， a multi-channel online wear particle detection sensor structure based on oppositely arranged ring magnets is proposed. By establishing the mathematical model of the magnetic properties of the sensor and the magnetization of ferromagnetic wear particles， the analytical solution of the magnetic perturbation， is derived when the wear particles pass through the sensor . Then， the influence law ofsensor structure parameters on the sensor performance is verified through simulation and experiment. The research results show that the magnetic flux density in a ferromagnetic spherical wear particle passing through the sensor is about three times the background magnetic induction intensity， and the sensitivity of the sensor， when the induction coil is arranged at the outer edge of the magnet， is about 10.1% higher than that the coil is arranged at the inner edge of the magnet. In addition， with the increase of the outer diameter of the magnet and the distance between the two magnets， the induction voltage output by the sensor shows a trend of increasing first and then decreasing， and the sensor with optimized structural parameters can effectively detect the ferromagnetic wear particles with a diameter of 80 μm.

Abstract:Comprehensively considering the various thermoelectric effects including the Thomson effect， a computational model of a series two-stage thermoelectric cooler that works in adiabatic surface space and non-adiabatic surface space is established. The effects of transient changes of parameters such as cold and hot junction temperature， and interstage temperature difference on the performance of a two-stage thermoelectric cooler are analyzed. The variation law of performance parameters such as cooling capacity， cooling space temperature and coefficient of performance with time is obtained. When the input current， the number of thermoelectric couples and the distribution ratio of thermoelectric couples are changed， respectively， the minimum cooling temperature， the time-consuming to reach the stable temperature， the refrigerating output and the change of the cooling coefficient of the two models are compared. The results show that， compared with single-stage refrigerators under the same conditions， two-stage refrigerators take longer to cool down but can achieve lower cooling temperatures. Appropriately increasing the current can effectively reduce the cooling time. There exists the optimal current， the number of thermoelectric couples and the distribution ratio of thermoelectric couples， which make the temperature of the cooling space the lowest and the coefficient of performance of the cooler to be the largest， respectively.

Abstract:Fluent simulation software is used to establish a variety of typical large-format forming bin structures， and SpaceClaim software is used to extract the flow field of the established large-format forming bin， to obtain the fluid domain inside the laser-selective melting forming bin， and to conduct flow field characteristics for various structures. The positions above the forming table and below the lens are used to analyze the flow field characteristics and flow field uniformity of various structures.The research results show that a stable and uniform gas flow field is formed inside the porous wind wall forming bin.At 20 mm above the top of the forming table， the flow rate is in the range of 284~308 mm/s； At the position below the laser lens， the overall shielding gas rate is in the range of 142~175 mm/s； and a circulating gas flow from the inlet to the outlet can be formed inside， and the soot that is not discharged in time can be discharged out of the forming bin after multiple flows.

Abstract:The autonomous movement of shotcrete robot in coal mine roadways requires an accurate environment map， and the weight degradation and particle dilution in large scenes are easy to happen in the Gmapping algorithm， which leads to excessive pose estimation error of robot and poor consistency such as map overlap and layering. Therefore a classification recovery resampling algorithm is proposed. When resampling， it modifies and recovers the low-weight particles in proportion， which makes full use of the existing information and tries to protect the particle diversity while restraining the weight degradation. The experimental results show that when mapping ACES building and MIT Killian Court data sets， using the traditional algorithm to locate and map the number of particles with extremely poor effect， the improved Gmapping algorithm can still maintain the translation error and rotation error of the robot at a low level， and can obtain a clear and accurate environment map .The particle distribution in the later stage of the classification recovery resampling algorithm is more in line with the requirements of the particle filter， which verifies the effectiveness of the classification recovery resampling algorithm.

Abstract:To study the influence of the input time delay of the controller on the stability and dynamic performance of the active magnetic bearing-rotor system， an equivalent model of the active magnetic bearing-rotor control system with input time delay is established， and the approximate value for the critical delay of the active magnetic bearing-rotor system is obtained by analyzing the existing conditions of Hopf bifurcation in the system. The influence of control parameters on system stability is analyzed by MATLAB/Simulink simulation， and the existence of Hopf bifurcation is further verified. The influence of input time delay on the ability of closed-loop systems to suppress external interference is explored from the perspective of system amplitude-frequency characteristics and phase frequency characteristics. Finally， experimental verification is carried out on the simulation content. The results show that the increase of the input time delay will leads to the Hopf bifurcation of the system. The peaking phenomenon of the amplitude-frequency response curve of the closed-loop system is aggravated， and the stability of the system is reduced. For PID controller， increasing the proportional gain and decreasing the differential gain can amplify the influence of input delay on system stability.

Abstract:SiCp/6013Al composites with a uniform structure and good particle dispersion were prepared by ball milling， cold isostatic pressing， hot isostatic pressing and hot extrusion process. Using transmission electron microscopy， scanning electron microscopy， and room temperature mechanical performance testing， the precipitation behavior and mechanical properties of 15% SiCp/6013Al composites under different artificial aging temperatures after solution treatment were studied. The results show that the precipitation behavior of the composites is controlled by thermal diffusion， and the precipitation accelerates when the temperature increases. The main strengthening phase of the composites is Mg2Si， while SiC particles can significantly enhance the strength of the composites， but also lead to a rapid decline in the plasticity of the composites. Compared with 6013 aluminum alloy matrix， 15% SiCp/6013Al composites can reach peak aging at a lower temperature and in a shorter time. After artificial aging treatment， the maximum hardness is 180 HV0.2 and the tensile strength is 522 MPa.

Abstract:The solid solution temperature affects the strengthening mechanism of thin-plate fine-grain 2A97 alloy with a grain size of less than 10 μm. It has been observed that the tensile strength of peak-aging 2A97 alloy obtained at 540 °C decreases by 40 MPa compared with 510 ℃ for the same solution time. X-ray diffraction， scanning electron microscopy， and transmission electron microscopy were applied to explain this phenomenon quantitatively from the perspective of strengthening mechanisms such as solid solution strengthening， grain boundary strengthening， dislocation strengthening and precipitation strengthening. It was found that the alloy solution-treated at 540 ℃ exhibited significantly grown grains， higher levels of recovery and recrystallization， lower dislocation density and wider grain boundary precipitate free zone than that at 510 ℃， resulting in a decrease in the properties.

Abstract:In this study， we report the first cobalt metal-organic framework containing zeolitic imidazolate framework （ZIF-67） immobilized on sodium bismuthate dehydrate nanoparticles to activate peroxymonosulfate （PMS）， which was named ZIF-67@NaBiO3. Characterization of X-Ray Diffraction， Scanning Electron Microscope and X-Ray Photo-electron Spectroscopy were applied to explore its morphology， structure and element valence， and it was found that ZIF-67 was successfully supported on NaBiO3. We chose Rhodamine B（RhB） as the target pollutant， and then we studied the effects of the catalyst dosage， pH， PMS concentration， temperature and other factors on the degradation of RhB in the ZIF-67@NaBiO3 activated persulfate system. When the temperature is 20 ℃， pH=7， the concentrations of RhB， PMS， ZIF-67@NaBiO3 are 80 mg/L、600 mg/L and 100 mg/L， respectively， the degradation rate of Rhodamine B was as high as 98% after 30 minutes. Furthermore， the degradation rate remained around 98% after 4 circulating. Quenching experiments showed that the main oxidants in the reaction process under neutral conditions are ， ?OH. In addition， due to the introduction of NaBiO3， the reacted materials are extremely easy to separate and can be reused， which further expands the industrial application range of organometallic frame materials.

Abstract:MoO3 and KSCN were taken as precursors to synthesize spherical flower-like MoS2 through the hydrothermal method， where MoO3 worked as the source of molybdenum for the reaction， and KSCN provided sulfur， KSCN also worked as the reducing agent of this reaction. With the method of controlling the reaction temperature， changing pH， adding a surfactant， and a large excess of sulfur source in the reagent， many experiments were explored to discover the effects of different experiment parameters on the crystal structure and morphology of MoS2. The optimal conditions of the reaction to obtain the spherical flower-like MoS2 were at 240 ℃， and the pH value is 0.6. Besides， with an excess of KSCN， the size of the MoS2 became smaller and the intervals between the surface sheets also increased. After adding the CTAB， the morphologies of the products became more structured and their sizes became more uniform.

Abstract:In this study， the aging mechanism of commercial LiNi0.8Co0.15Al0.05O2/Graphite lithium-ion batteries at fixed nodes was studied experimentally， and the degradation modes in the whole life cycle were identified by differential voltage analysis method and electrochemical impedance spectroscopy analysis method， and verified by microscopic morphology observation. The results show that the capacity degradation of these lithium-ion batteries has two stages. In the first stage， the capacity degradation is slow， and the degradation modes in this stage are mainly composed of loss of anode active material and loss of lithium ions. In the second stage， the capacity degradation is sharp due to the lithium plating on the surface of the anode， which consumes a large number of recycled lithium ions directly， so the loss of lithium ions increases. The metallic lithium then reacts with the electrolyte and forms a dense covering layer， which increases the mechanical stress of the electrode in the process during the Li+ intercalation/deintercalation processes， and makes the loss of electrode active material increase. Generally speaking， the lithium plating causes the capacity plunge phenomenon， the formation of the passivation layer aggravates the loss of active material， and the continuous lithium plating causes drastic capacity decay in the second stage of aging.

Abstract:By reasonably designing and exploring the surface ligand of Quantum Dots（QDs）， this work adopts a one-step synthesis of perovskite QDs in the atmospheric environment. Utilizing 3-aminopropyl triethoxysilane as surface ligands， the core-shell structures of silica coated CsPbBr3 QDs （CsPbBr3@SiO2 QDs） were directly prepared by thermal injection method in the air. The effect of reaction time on the thickness of the silica shell was systematically studied， and the morphology and composition of core-shell QDs were characterized by transmission electron microscopy and X-ray photoelectron spectroscopy. The photoluminescence spectra were used to record the characteristics of light emission spectra under the environment of water， oxygen and lighting， and the time stability of spectra was analyzed and discussed. These results show that core-shell QDs with high-quality perovskite core and uniform silica shell were successfully prepared at a reaction time of 30 min. Benefitting from the coating of silica shell and organic supporting film， QDs optical film still maintained the high-efficiency photoluminescence， and its stability in water and oxygen environment had been greatly improved. The spectral peak and intensity of the optical film were even stable after 180 days. Furthermore， our core-shell perovskite QDs were applied in light emitting diode devices， showing bright light emissions with narrow full width at half maxima.

Abstract:A theoretical model for the free vibration characteristics of Functionally Graded Carbon Nanotubes Reinforced Composites （FG-CNTRCs） thin cylindrical shells considering the scale effect of Carbon Nanotubes （CNTs） was established. First， the nonlocal Eshelby-Mori-Tanaka （EMT） constitutive model of macroscopic CNTRCs was developed based on the EMT method and nonlocal theory by considering the orientation and scale effect of CNTs. Then， based on the Kirchhoff-Love cylindrical shell assumption， the free vibration governing equations for FG-CNTRCs cylindrical shells on the visco-Pasternak foundation in the thermal environment ware derived by applying the Hamilton principle. The natural frequencies of the simply supported cylindrical shells at both ends were obtained by the Navier method， and the results were compared with those in the literature to verify the correctness of the model and method. Finally， the effects of nonlocal parameters， volume fraction and distribution of CNTs， length-to-thickness ratio of cylindrical shell， ambient temperature， and foundation parameters on the free vibration characteristics of simply-supported FG-CNTRCs cylindrical shell were analyzed. It is found that considering the scale effect of CNTs can reduce the bending stiffness of FG-CNTRCs cylindrical shells. The influence of ambient temperature on the imaginary part of the natural frequency of simply supported FG-X-CNTRCs cylindrical shell increases with the increase of CNTs volume fraction， and the influence of length-thickness ratio and foundation damping parameters on the imaginary part is coupled.

Abstract:The traditional protection gears have the disadvantages of heavy weight and are difficult to deform. In recent years， the protection gears inspired by biological armor structures have been developed， which better solves the contradictory problem between protection performance and flexibility. This paper summaries the findings on multi-level structure and mechanical properties of biological armor， as well as the design and manufacture methods of biomimetic protection gears； and further discusses the chosen materials and structures， protection performance and mechanism， and application prospects of modern biomimetic scale-like protection gears. The main problems at the current stage are pointed out， and the future development directions of high-performance biomimetic flexible protection gears are prospected