Influence of Jet Angle and Ion Density of Cathode Side on Low Current Vacuum Arc Characteristics

In this study, the influence of the initial jet angles （IJAs） and ion number densities （INDs） at the cathode side on the low current vacuum arc （LCVA） characteristics is simulated and analysed. The results show that the ion temperature, electron temperature, ion number density, axial current density and plasma pressure all decrease with the increase of the cathode IJAs. It is also shown that LCVA can cause a current constriction for lower cathode IND, and the anode sheath potential is more nonuniform, which is mainly related to the nonuniform distribution of the axial current density at the anode side.

Influence of thickness and initial groove angle in M–K model on limit strain of 7B04 by considering through-thickness stress

Marciniack–Kuczinski(M–K)model is widely used to predict material's forming limit curve(FLC).The prediction of FLC traditionally neglected through-thickness normal stress.However,it cannot be neglected in some forming processes.Much work has been done to study the effect of through-thickness normal stress on FLC with constant through-thickness normal stress or constant ratio of through-thickness normal stress and maximum principal stress.In addition,based on Nakazima test process,the ratio of through-thickness normal stress and maximum principal stress has been derived,which was a function of instantaneous thickness and loading path.Here,initial groove angle in M–K model was not considered.In this paper,uniaxial tension tests and Nakazima tests were performed on 7B04 aluminum alloy.Based on Hill 48 yield criterion and M–K model,the prediction model of FLC was established.The increase of thickness can enhance FLC.Meanwhile,it is necessary to consider through-thickness normal stress and initial groove angle in prediction model.On the left side of FLC,the effect of initial groove angle on FLC is weakened by increasing sheet thickness.On the right side of FLC,the effect of initial groove angle on FLC is strengthened by increasing sheet thickness.On the right side of FLC,the relation between limit strain points with different thicknesses is linear under one certain loading path.Thickness has decisive effect on through-thickness normal stress level and the changing trendy of through-thickness normal stress during calculation is different under different stress condition.

ROCK FRACTURE PROCESS ZONE AND ITS INFLUENCE ON MODEⅡFRACTURE BEHAVIOR

On the basis of that rock material usually has a larger fracture process zone,a new fracture criterion which is different from that of linear elastic fracture theory was presented.On this basis,the fracture behavior and influencing factors under modeⅡor compressive shear loading were investigated.

Why a mosquito leg possesses superior load-bearing capacity on water:Experimentals

Mosquitoes possess the striking ability to walk on water because each of their legs has a huge water supporting force（WSF） that is 23 times their body weight.Aiming at a full understanding of the origins of this extremely large force,in this study,we concentrate on two aspects of it：the intrinsic properties of the leg surface and the active control of the initial stepping angle of the whole leg.Using a measurement system that we developed ourselves,the WSFs for the original leg samples are compared with those whose surface wax and microstructures have been removed and with those of a different stiffness.The results show that leg f exibility plays a dominant role over surface wax and microstructures on the leg surface in creating the supporting force.Moreover,we discuss the dependence relationship between the maximum WSF and the initial stepping angle,which indicates that the mosquito can regulate this angle to increase or decrease the WSF during landing or takeoff.These finding are helpful for uncovering the locomotion mechanism of aquatic insects and for providing inspiration for the design of microfluids miniature boats,biomimetic robots,and microsensors.

Research on Angular Output Velocity of a Drive Shaft with Double Cross Universal Joints

The study object is the angular output velocity of the drive shaft which is made up of two series-wound cross universal joints. We have deduced the function relation between the angular output velocity and initiative input angle of the drive shaft with double cross universal joints that is based on the calculation formula of the angular output velocity of a single cross universal joint, and by analyzing the relation between the two input angles. By using this function relation, the constant velocity condition of the drive shaft with double cross universal joints＂ is verified. The step-by-step searching algorithm is adopted to obtain the optimal phase angle that leads to the minimum fluctuate index of the angular output velocity in the vary velocity condition. At the same time, we worked out the maximal and minimum value of the angular output velocity, and their initiative input angle. The correctness of the function of the angular output velocity and the step-by-step search algorithm are verified by an ADAMS simulation example.

Fracture Mechanism of the Formation with a Natural Flaw Under a Single-Tooth Cutting

The process of a single-tooth cutting formation is taken as the representative to analyze the fracture mechanism of the formation with natural flaws under the PDC drill bit.The modeling of the stress field distribution of the formation under a single tooth is proposed first.Subsequently,the modeling of the stress intensity factor K,T-stress and the initiation angleθof the flaw under two far-field compressive loads in two cases are presented based on the mode-II fracture.Finally,the results of theoretical calculations and simulations are given and discussed.Based on the analysis undertaken,it can be concluded that the confinement ratioλapplying on the flaw changes nonlinearly with the variation inα+φ.The relationship between the dimensionless ratioβx/βy of T-stress and the rotational polar angleφis a parabola with an upward opening.When the direction of the cutting force is consistent with the flaw,the stress intensity factor K and the initiation angleθat the tip of the flaw reach the maximum.In addition,the angle between the cutting force and the flaw weakens the T-stress and inhibits the crack initiation and propagation of the flaw.The results of numerical simulations show good agreement with theoretical calculations.