Search

The flow field distribution in the star herringbone gearbox lubricated by oil injection is very complex, and there are many difficulties in the flow simulation analysis. Based on the smooth particle hydrodynamics (SPH) method, the particle simulation model of the flow field in the star herringbone gearbox with oil injection lubrication is established, and the oil-gas two-phase distribution characteristics at different cross-section positions in the gearbox are obtained. The oil-liquid distribution and velocity distribution of flow field under different gear speeds and oil injection speeds are compared and analyzed. The results show that the oil flow field distribution is obviously different at different cross-section positions in the gear shaft direction, the oil flow in the middle cross-section position of the gearbox is the largest, and the local eddy current phenomenon occurs in the area between the solar wheel, planetary wheel and oil injection port. The gear speed and oil injection speed have great influence on the oil distribution in the gearbox.

The three degrees of freedom parallel robot with is simple to control, convenient for design and research and has compact structure. In order to study the influence of parallel robots' joint configuration on the size of workspace, two Tau variant parallel robots, 3-RSS and 3-RUU, are taken as the research objects. Then, the spherical hinge and the Hooke hinge are respectively used for analyzing and solving the workspace of the 3-RSS and 3-RUU coaxial drive layout parallel robots. Firstly, a simplified model of the robot is established, and its forward kinematics is solved. Then, the motion range of spherical hinge and Hooke hinge are analyzed as the constraints of the joint so that the three-dimensional workspace of 3-RSS and 3-RUU coaxial drive layout parallel robots is analyzed so as to obtain the workspace boundary. The analysis results show that the 3-RUU coaxial drive layout parallel robot of the same size has a larger workspace than the 3-RSS coaxial drive layout parallel robot. It provides theoretical and technical support for subsequent research on joint selection and workspace of different parallel robots.

Controllable variable stiffness compliant actuator mechanism has the characteristics of high compliance, high environmental adaptability and good man-machine interaction. The variable stiffness compliant actuator mechanism is based on the transmission principle of a four-bar linkage with a zero-length rack. The variable stiffness control can be realized by changing the properties and the winding mode of the elastomer, or the configuration scheme. Through configuration analysis and structure design, the stiffness and torque models of the compliant actuator mechanism are established to reveal its stiffness behavior. The Lagrangian method is used to establish the dynamic model of the compliant actuator mechanism, and the frequency theoretical results are obtained by solving the average stiffness. The virtual prototype is established to motion simulation, which reveals its performance characteristics and verifies the correctness of theoretical analysis. Compared with other similar designs, the compliant actuator mechanism proposed has the characteristics of miniaturization and lightweight with strong applicability. It can be used as a single module and integrated into the exoskeleton system.

Based on the physiological characteristics of crab,a bionic crab- like robot composed of eight legs and two pincers is designed by using bionics principle. The cross direction moving and turning of the bionic crab- like robot are realized by controlling the walk stepping motor to drive gear crank connecting rod mechanism,the lifting and falling of pincers is realized by controlling the lifting stepping motor to drive gear and rack mechanism,the left and right swing of pincers is realized by controlling the swing steering engine,the snatching of pincers is realized by controlling the snatching steering engine drive intermittent gear and double- rocker linkage mechanism. The bionic crab robot has three good merits such as agile transmission,high driving efficiency,convenient maintaining,which is seasoned with different road surface. The robot has a good application potential under complex road conditions to search and detection. The design method is helpful for transmission design of multi- legged bionic robot in execrable environment.

The effect of vibration on the micro-forming ability of Zr55Cu30Al10Ni5 bulk metallic glass in its supercooled liquid region was studied. The experiment of micro-extrusion was carried out under different amplitude (38 ∼ 760 N) and different frequency (0.1 ∼ 2.0 Hz) at a fixed temperature of 723 K. The extrusion length was taken as a measure to characterize the micro-forming ability. Results reveal that the extrusion length of bulk metallic glass is effectively improved under vibration loading, and increases with increasing loading frequency and amplitude, whereas the frequency dependence is stronger. The viscosity of bulk metallic glass declines under vibration loading because of a larger free volume concentration and surface effect caused by vibration. This research indicates that the vibration forming is an effective method to enhance the micro-forming ability of bulk metallic glasses.

The dimensional accuracy and microstructure affect the service performance of parts fabricated by wire arc additive manufacturing (WAAM). Regulating the geometry and microstructure of such parts presents a challenge. The coupling method of an artificial neural network and finite element (FE) is proposed in this research for this purpose. Back-propagating neural networks (BPNN) based on optimization algorithms were established to predict the bead width (BW) and height (BH) of the deposited layers. Then, the bead geometry was modeled based on the predicted dimension, and 3D FE heat transfer simulation was performed to investigate the evolution of temperature and microstructure. The results showed that the errors in BW and BH were less than 6%, and the beetle antenna search BPNN model had the highest prediction accuracy compared to the other models. The simulated melt pool error was less than 5% with the experimental results. The decrease in the ratio of the temperature gradient and solidification rate induced the transition of solidified grains from cellular crystals to columnar dendrites and then to equiaxed dendrites. Accelerating the cooling rate increased the primary dendrite arm spacing and δ-ferrite content. These results indicate that the coupling model provides a pathway for regulating the dimensions and microstructures of manufactured parts. [ABSTRACT FROM AUTHOR]

Abstract Comprehensive understanding of continuous cooling transformation behaviors is important in heat treatment of steels, but there is still a lack of research in the phase transition behaviors of 300M steel, which would greatly hinder the microstructure controlling and finally affect the application of this material. In this work, in-situ observations by high temperature confocal laser scanning microscope (HTCLSM) was introduced by considering its superiorities in clarity, accuracy, and directness, to systemically investigate the microstructure evolutions of 300M steel under various cooling rates (0.01–100 °C/s). Pearlite, bainite, and martensite were observed to form at the cooling rate range of 0.01–0.15, 0.03–1, and 0.3–100 °C/s, respectively. A continuous cooling transformation diagram was constructed based on the in-situ observations, verified by metallography, and compared with dilatometry. Results showed that the transition temperatures by in-situ observations agreed well with the results of dilatometry, while the transition starting temperatures by in situ observation were lower and the phase transition termination temperatures were higher. Finally, models accurately describing the relationships between Vickers hardness, retained austenite content, and cooling rates were established, and the phase transformation mechanisms and kinetics were analyzed. Our finding not only understands fundamentally the transformation mechanisms of different microstructures, but also provides a useful reference for practical microstructure control in heat treatment of 300M steel. Highlights • Phase transitions at various cooling rates are in-situ observed. • The continuous cooling transformation diagram of 300M steel is constructed. • The result by in-situ observation is verified and compared with traditional methods. • A new transformation mechanism of pearlite is proposed. [ABSTRACT FROM AUTHOR]

A metal surface finishing method by micro plasma beam irradiation was examined and presented in this study. Gray cast iron was used as the experimental material to examine the finishing effect by the micro plasma beam. This experimental setup consists of a compressed air system, a plasma torch, and a power supply. The compressed gas was ignited by high voltage direct current pulsed gas discharge and facilitated the generation of plasma, as well as a plasma beam with a maximum diameter of 0.6 mm was used for finishing the metal surface instantly. The experimental results show that it was possible to remove the peak points which exist on the metal surface. It was showed clearly that after the irradiation by the micro plasma beam, the initial rusty and rough surface becomes a clean and smooth surface under a proper finishing condition. [ABSTRACT FROM AUTHOR]

Abstract: The synthesis and antibacterial activity of oxazolidinones containing dihydro-1,2-oxazine and 2-pyrazoline ring systems are described. Linezolid analogs utilizing dihydro-1,2-oxazines as morpholine mimics were prepared utilizing a nitrosoamine/diene 4+2 cycloaddition strategy. Pyrazolidine, hexahydro-pyridazine, and 2-pyrazoline analogs more closely related to eperezolid were also prepared. The most active of these new oxazolidinones were the dihydro-1,2-oxazine 6 and the 2-pyrazoline 20 both of which had potency similar to linezolid against a panel of Gram-positive bacteria. [Copyright &y& Elsevier]

Two single track multi-layer walls with linear energy inputs (LEIs) of 219 and 590 J/mm were deposited by cold metal transfer-based wire arc additive manufacturing system. Combined with the X-ray diffraction technique, scanning electron microscope and uniaxial tensile tests, the influences of LEI and cooling rate (CR) on the microstructure evolution, mechanical properties and fracture mechanisms of the studied steel are analyzed. It is observed that the microstructures of the studied steel are mainly composed of δ-ferrite and austenite dendrites. σ phase is formed on the δferrite–austenite interface under low CR. Meanwhile, the primary dendrites' spacing decreases with the decrease in LEI or the increase in CR, and the maximal primary dendrites' spacing is 32 μm. The values of elongation to fracture roughly decline with the decrease in LEI or the increase in CR, but the variations of ultimate tensile strength and yield stress show an opposite trend. In addition, the mesoscopic damages in the studied steel under low LEI are mainly caused by the coalescence of pores. While under high LEI, the cracks are induced by the dislocations piling up around δ-ferrite. [ABSTRACT FROM AUTHOR]

In order to improve the tribological performance of the slanted guide pillar, Cu particle reinforced composite coatings were synthesized on the surface of GCr15 steel using the plasma transferred arc (PTA) alloying technique. A systematic experimental investigation was conducted to study the effects of PTA current on the microstructure and microhardness of alloyed coatings. In addition, tribological behaviors at room temperature (RT) and high temperature (HT) were investigated. The results indicate that at low PTA current (70A), due to the insufficient current, no Cu particles are dissolved in the alloyed coating and a Cu-rich layer is observed on the surface. With the increase in the PTA current, Cu particles are gradually dissolved into the alloyed layer and the microstructure of alloyed coating mainly consists of bamboo-like martensite, retained austenite, and dispersed Cu particles. The microhardness of the PTA samples is approximately four times that of the untreated sample. The tribological results exhibit that an abrasive wear at RT and slight abrasive wear with oxidation wear at HT are the dominant wear mechanisms of alloyed coatings. The PTA samples show far superior antifriction properties compared to the untreated and remolten samples at both RT and HT, which can be attributed to the formation of lubricating Cu films and the improvement in microhardness. [ABSTRACT FROM AUTHOR]

The relationships between initial microstructures, process parameters, and grain evolutions in isothermal holdings have drawn wide attention in recent years, but the grain growth behaviors of 300M steel were not well understood, resulting in a failure in precise microstructure controlling in heat treatment. In this work, in situ observations were carried out to characterize the grain evolutions of 300M steel with varying holding time, holding temperatures, and initial microstructures. The intriguing finding was that the grain refinement by austenization of 300M steel was followed by a dramatic grain growth in the initial stage of holding (≤~600 s), and with increasing time (~600–7200 s), the average grain size appeared to have a limit value at specific temperatures. The austenization process accelerated the grain growth by generating large quantity of grain boundaries at the initial stage of holdings, and the growth rate gradually slowed down after holding for ~600 s because the driven force was weakened due to the reduction of grain boundary energy. The initial structure and the initial grain size of 300M steel had no obvious influences on the grain size evolutions. The mechanisms of grain growth were analyzed based on in situ observations and transmission electron microscope (TEM) characterizations. A grain evolution model considering the grain boundary migration of 300M steel was established for the isothermal holding process. Good agreement was obtained between the in situ observation results and the model calculation results. This investigation aimed to understand fundamentally the grain evolutions of 300M steel in the isothermal holding process. [ABSTRACT FROM AUTHOR]

The formability of aluminum alloy sheet in electromagnetic impaction deformation has attracted the attention of numerous researchers for the past decades. However, the influences of die geometry and high-speed impaction electromagnetic deformation on formability have not been well established, thereby resulting in the formability of the sheet not being developed fully. In this study, the influence of die geometry on the formability of 5052 aluminum alloy in electromagnetic deformation was investigated by comparing the formability of 5052 aluminum alloys formed using a hemispherical die and a cylindrical die. The intriguing finding is that the formability of the 5052 aluminum alloy formed using a cylindrical die is considerably higher than that formed using a hemispherical die. Therefore, die geometry significantly influences the formability of 5052 aluminum alloy. The influence of die geometry on the formability of 5052 aluminum alloy in high-speed impaction electromagnetic deformation was explained in terms of strain rate, pressure stress, and stress state. This investigation enhances insight into the interaction between sheets and dies, and provides a reference for the studying influence of dies on the forming limit of sheets in high-speed impaction deformation. [ABSTRACT FROM AUTHOR]

The relationships between hot deformation parameters and flow behaviour have attracted many researchers’ attention for the past few decades, whilst precise constitutive modelling of GH4169 remained a problem, which seriously affected the process and microstructure control of alloys. In this work, a modified Arrhenius type model was introduced to describe the flow stresses of various compression conditions. The model showed high precision in flow stress prediction. In order to facilitate workability evaluation for engineering applications, the hot processing maps were established at the strain of 0.4~0.6. The processing maps revealed an instability domain at 900~950 °C and 0.1~1 s−1, a high dissipation efficiency domain at 1060~1100 °C and 0.001~0.01 s−1, and a stable deformation domain for the rest of processing parameters. Microstructures of each domain were observed via optical microscope (OM) and electron backscattered diffraction (EBSD). The intriguing finding was that the microstructures morphology agreed well with the descriptions in “discontinuous mechanism”, and incompletely recrystallized microstructures were found in the instability domain. Fully recrystallized microstructures were found in the stable deformation domain, and grain coarsen in the high dissipation efficiency domain. Optimal hot working conditions were suggested based on the microstructure analysis. This investigation contributed to a comprehensive understanding of the workability of GH4169. [ABSTRACT FROM AUTHOR]

The relationship between microstructure and flow behaviour has attracted attention from many researchers for the past decades, whilst the influences of dislocation and recrystallization on flow stress have not been well understood, which led to failure in flow stress prediction at high temperature compressions. In this work, we tried to provide a novel explanation of the relationship between microstructure evolutions and flow behaviour, and the influence of dislocation and recrystallization on flow stress was investigated. A dislocation based flow stress model was proposed and applied for 300M steel at the strain rate of 0.01–10 s−1 and the temperature of 950–1150 °C. Results showed the established model could predict the flow stress both at constant strain rate conditions and at variable strain rate conditions. The present investigation is helpful to a better understanding of hardening and softening mechanisms in hot compression of 300M steel. [ABSTRACT FROM AUTHOR]

[Display omitted] • Methods to control the surface roughness during polishing process are analyzed. • Autocorrelation function of the polished surface is investigated. • Areal roughness S a can be reduced to 0.81 ± 0.01 μm from 8.67 ± 0.12 μm. • Possible changes of chemical composition and nano-hardness are discussed. Industrial products used in medical equipment and food manufacture are usually made from AISI 304 and place great demands on surface polishing. The application of plasma beam in the field of energy beam polishing is a new technology to obtain a desired level of surface roughness. Therefore, this paper details an investigation conducted to focus on the effect of process parameters on the surface morphology of AISI 304 stainless steel during plasma beam polishing. The main arc current, nozzle height, scanning speed and plasma gas flux that have the greatest influence on the arc plasma characteristics and energy input values are considered to be the key experimental parameters. While the measured roughness values and their intensity autocorrelation functions are applied to evaluate the polished surfaces. The capacity of plasma beam polishing to produce glossy and defect-free surfaces on AISI 304 has been successfully verified. Under the specific combination of main arc current, nozzle height and scanning speed, the energy input could reach approx. 90 J/mm ∼ 110 J/mm, corresponding to the more than 85.9% fall in areal roughness S a. Although the plasma gas flux had no discernible impact on the energy input, it was observed that the surface uniformity varied from 0.81 ± 0.01 μm S a to 1.04 ± 0.04 μm S a with the increase of plasma gas flux. Possible changes of chemical composition and nano-hardness during plasma beam polishing of AISI 304 stainless steel are analyzed. [ABSTRACT FROM AUTHOR]

• Plasma beam multi-track polishing can reduce the surface roughness of AISI 304. • S a decreased from 8.67 ± 0.12 μm to 0.79 ± 0.06 μm representing a 90.9% reduction. • A two-dimension transient model was developed to simulate the polishing process. • Modelling results verify that the offset distance affects the molten pool flow. The adoption of high energy beam in the area of metallic surface polishing is a novel technique to produce glossy surfaces. In particularly, plasma beam finishing is emerging as a workable and economical option to realize high quality irradiated surfaces. In this paper, effect of overlap between the adjacent tracks on surface morphology during plasma beam finishing was researched through using different offset distances, and AISI 304 austenitic stainless steel was selected to be the test material. Based on considering surface roughness, certain statistic features (e.g. material ratio function and power spectral density function) were analyzed to comprehensively reflect the influence of offset distance. To aid a deeper understanding of the molten pool flow and surface evolution during polishing process, a two-dimension transient model, which consists of magnetic field, electric field, laminar flow and heat transfer, was developed by means of the finite element approach. The multi-track polishing tests showed that although the irradiated surface became smoother, significant bulges were found in the overlapped region between adjacent tracks. The simulation model then verified that these bulges varied with different offset distances, reflecting different dynamic processes. Therefore, the selection of offset distance is important for the optimization of plasma beam polishing. [ABSTRACT FROM AUTHOR]

The effects of linear heat input (LHI) on the microstructure and corrosion behavior of an austenitic stainless steel processed by wire arc additive manufacturing (WAAM) are studied. It is found that the primary dendrites spacing of the studied steel increases from 18 μm to 23 μm, when the LHI increases from 219 J ⋅ mm - 1 to 590 J ⋅ mm - 1 . But the δ-ferrite contents under high and low LHIs are similar. Moreover, the passivation voltage range decreases and the corrosion current density increases with the increase of LHI. The poor corrosion resistance for the studied steel under high LHI is highly related with the segregation of Cr and Mo atoms in the Ni-poor δ-ferrite. • The effect of linear heat input on a stainless steel processed by WAAM is studied. • The primary dendrites grow quickly during the WAAM under high linear heat input. • The poor corrosion property is related with the segregation of Cr/Mo in δ-ferrite. [ABSTRACT FROM AUTHOR]

The hot tensile deformation and fracture behaviors of a typical ultrahigh strength steel are investigated by isothermal uniaxial tensile experiments over the tensile temperatures of 900–1150 °C and strain rates of 0.01–10 s - 1 . By combining the results of tensile tests and microstructural observation, the effects of deformation processing parameter (strain rate and tensile temperature) on the macroscopic plastic deformation behaviors, microscopic fracture morphologies and microstructural evolution are clarified. The studies indicate that the hot tensile behavior of the studied steel is greatly influenced by the competition of damage evolution, work hardening, and dynamic softening. With the increased strain rate, the strain rate sensitivity coefficients decrease, but the value of elongation to fracture increase from 0.38 to 0.50. The variations of microvoids or cracks in amounts and sizes show an increasing trend with the increased strain rate or the decreased tensile temperature. At the low tensile temperature (900 °C), the poor capability of necking diffusion hardly prevents the strain localization, and the mesoscopic damages easily take place. As the strain rate increases from 0.01 to 10 s - 1 , the neat fracture morphologies gradually change to the serrated. The main ductile fracture mechanisms transform from the intergranular fracture at the high tensile temperature and low strain rate to the transgranular fracture at the low tensile temperature and high strain rate. • The hot tensile deformation and fracture behaviors of a typical ultrahigh strength steel are studied. • With the increased strain rate, the strain rate sensitivity coefficient decreases, but the elongation to fracture increases. • The main fracture mechanisms transform from the intergranular to transgranular fracture with the decreased tensile temperature. [ABSTRACT FROM AUTHOR]