Effect of variable heat treatment modes on microstructures in Fe-Cr-B cast iron alloy

The effect of heat treatment mode on the microstructure of Fe-Cr-B cast iron alloys was investigated in this paper by comparing the difference of precipitation patterns of secondary particles after thermal cycling treatment (TCT) with those after normal heat treatment (NHT). No obvious differences were found in precipitation patterns of secondary particles between TCT and NHT when experimental temperature was below Ar. However, when temperature was over Ar, there were significant differences, with secondary particles prominently segregated at the grain boundaries under TCT, while the particles evenly distributed in the matrix under NHT. The reason for the microstructure differences could be associated with the development of non-equilibrium segregation of boron during TCT

Measurement of air shower cores to study the cosmic ray composition in the knee energy region

Since 1996, a hybrid experiment consisting of an emulsion chamber and a burst detector array and the Tibet-II air shower array has been operated at Yangbajing (4300 m above sea level) in Tibet. This experiment can detect air-shower cores, called burst events, accompanied by air showers in excess of about 100 TeV. Using the burst event data observed by this experiment, we discuss the primary cosmic ray composition around the knee in comparison with the Monte Carlo simulations. In this paper, we show that all the features of burst events are wholly compatible with the heavy enriched composition in the knee energy region.Comment: 20 pages, 21 figures, to appear in Physical Review

A study of the shadowing of galactic cosmic rays by the sun in a quiet phase of solar activity with the Tibet air shower array

We have shown that the Sun's shadow by high energy cosmic rays moves year by year and its behavior is correlated with a time variation of the large-scale structure of the solar and interplanetary magnetic fields. The solar activity was near minimum in the period from 1996 through 1997. Using the data obtained with the Tibet air shower array, we examined the shadowing of cosmic rays by the Sun in this quiet phase of solar cycle, and found that the Sun's shadow was just in the apparent direction of the Sun, though it was observed at the position considerably away from the Sun to the south-west in the period between 1990 and 1993. It is known that the magnetic pole of equivalent solar dipole was reversed during the previous active phase, and near solar minimum the dipole was aligned with the rotating axis, preserving its N-pole on the north pole side of the Sun. This causes the solar magnetic field to shift the Sun's shadow to the east. Thus, the observed results suggest that the shift of the Sun's shadow due to the solar magnetic field was pushed back by the effect of the geomagnetic field, since the geomagnetic field always make the shadow shift to the west. We discuss the Sun's shadow observed during the period near solar minimum in 1996-1997 and compare it with the simulation results.Comment: 13 pages, 6 figures, to appear in Ap

Design and Mechanical Analysis of Bionic Foldable Beetle Wings

In order to improve the flight performance of collapsible aircrafts, a novel mechanism of bionic foldable wings of beetle is designed based on the four-plate mechanism theory. The folding and unfolding movements of the bionic foldable wings are driven by motor and torsion hinges. Based on the D-H method, a kinematic model of wings is established to analyze the dihedral angle of adjacent plates. The folding ratio of an area in different plate creasing angles has been derived and calculated. Utilizing the kinematic and static models produced, as well as considering the folding ratio and output motor torque, the optimal physical parameters of folding wings are obtained. Dynamic models of rigid and flexible wings were established using ADAMS, and a motion simulation was performed. The relationship between dihedral angle and torque during the folding process of both rigid and flexible wings was obtained. The results provide a better understanding of the folding mechanism through the formulation of rigid-flexible wing analysis, as well as demonstrating a novel design of insect-mimicking artificial wings for small aerial vehicles

Study on the Behavior Mechanism of K and Na during the Synthesis of VN Alloy

In this paper, the sources of K and Na in vanadium-nitrogen (VN) alloys and their effects on the furnace structure were studied. The results show that K and Na are mainly present as counter-ions of decavanadate and dodecanadate in ammonium polyvanadate (APV) and vanadium trioxide (V2O3). In the production process of VN, the concentration of K in the scab produced in the kiln is 25 times higher than that of the vanadium raw material, the concentration of Na is 15 times higher than that of the raw material, and the degree of enrichment of K is stronger than that of Na. Additionally, in the VN products, K and Na are mainly distributed uniformly in the form of KCN and NaCN. The results also found that the K and Na vapors during the production of VN promoted the formation of VN. However, K, Na steam, KCN, NaCN, K2CO3, Na2CO3 and other potassium-sodium high-temperature corrosive substances cause strong corrosion of the furnace lining, graphite sagger, push plate, and heating elements. Therefore, in the process of synthesizing VN, the raw materials of K and Na content of impurity elements must be reasonably controlled. The results not only analyzed the source of K and Na, but also analyzed the characteristics of their enrichment and the influence on the equipment

Research on an Ankle Joint Auxiliary Rehabilitation Robot with a Rigid-Flexible Hybrid Drive Based on a 2-S′PS′ Mechanism

An ankle joint auxiliary rehabilitation robot has been developed, which consists of an upper platform, a lower platform, a dorsiflexion/plantar flexion drive system, a varus/valgus drive system, and some connecting parts. The upper platform connects to the lower platform through a ball pin pair and two driving branch chains based on the S′PS′ mechanism. Although the robot has two degrees of freedom (DOF), the upper platform can realize three kinds of motion. To achieve ankle joint auxiliary rehabilitation, the ankle joint of patients on the upper platform makes a bionic motion. The robot uses a centre ball pin pair as the main support to simulate the motion of the ankle joint; the upper platform and the centre ball pin pair construct a mirror image of a patient’s foot and ankle joint, which satisfies the human body physiological characteristics; the driving systems adopt a rigid-flexible hybrid structure; and the dorsiflexion/plantar flexion motion and the varus/valgus motion are decoupled. These structural features can avoid secondary damage to the patient. The rehabilitation process is considered, and energy consumption of the robot is studied. An experimental prototype demonstrates that the robot can simulate the motion of the human foot

Dynamic Modeling for Chatter Analysis in Micro-Milling by Integrating Effects of Centrifugal Force, Gyroscopic Moment, and Tool Runout

During micro-milling, regenerative chatter will decrease the machining accuracy, destabilize the micro-milling process, shorten the life of the micro-mill, and increase machining failures. Establishing a mathematical model of chatter vibration is essential to suppressing the adverse impact of chatter. The mathematical model must include the dynamic motions of the cutting system with the spindle–holder–tool assembly and tool runout. In this study, an integrated model was developed by considering the centrifugal force induced by rotational speeds, the gyroscopic effect introduced by high speeds, and the tool runout caused by uncertain factors. The tool-tip frequency-response functions (FRFs) obtained by theoretical calculations and the results predicted by simulation experiments were compared to verify the developed model. And stability lobe diagrams (SLDs) and time-domain responses are depicted and analyzed. Furthermore, experiments on tool-tip FRFs and micro-milling were conducted. The results validate the effectiveness of the integrated model, which can calculate the tool-tip FRFs, SLDs, and time responses to analyze chatter stability by considering the centrifugal force, gyroscopic effect, and tool runout

Insight into the role of Si on corrosion resistance of weathering steel in a simulated industrial atmosphere

This study investigates the role of Si on the corrosion resistance of weathering steel (WS) in a simulated industrial environment. With increasing Si content (0.15–0.50%), the corrosion resistance of WS is enhanced. On the one hand, the rust layer becomes compact and uniform because higher Si content promotes the formation of fine α-FeOOH. On the other hand, Si reacts with Fe3O4 to form a three-dimensional SiO2 network structure located around the cracks and holes of the rust layer. This structure has a protective effect, enhancing the corrosion resistance of WS and equipping the rust layer with self-healing functionality