Growth characterization of anodic film on AZ91D magnesium alloy in an electrolyte of Na_2SiO_3 and KF

Anodization of AZ91D magnesium alloy in the electrolyte solution of 0.5 mol/L of sodium silicate and 1.0 mol/L of potassium fluoride was investigated. The anodic films were characterized using optical microscopy （OM）, scanning electron microscopy （SEM）, and X-ray diffraction （XRD）. The corrosion resistance of the various anodized alloys was evaluated by a fast corrosion test using the solution of hydrochloric acid and potassium dichromate. The results showed that the addition of KF resulted in the presence of NaF in the anodic film. The thickness of the anodic film formed under a constant current density of 20 mA/cm^2 for 16 rain at 60℃ exceeded 100 gm. The growth of the anodic film could be divided into three stages based on the anodizing time; the growth rate was much faster during stage Ⅱ than in stages I and Ⅲ. The anodic film exhibited the highest corrosion resistance for the AZ91 alloy, which is attributed to the fact that the anodization was maintained until the end of stage Ⅱ.

A Physical Model of Electromagnetic Force from PEMA Acted on Metal Projectiles

Electromagnetic armor is a new conceptual combat vehicle technology, which improves remarkably the defensive capability and maneuverability of vehicles. The authors present definitely to apply the electromagnetic theory to analyze the electromagnetic armor. Based on electromagnetics, the experienced expression of projectile and the physical model of PEMA (passive electromagnetic armor) are obtained when electric current flows through the system, and a computer simulation is given.

Indoor measurement method of smoke screen disturbance efficiency based on Gaussian diffusion model

Because of ground clutter wave interf e rence,it is difficult to measure smoke screen disturbance in the field.In this pape r,a kind of indoor measurement method of smoke screen disturbance efficiency ba sed on Gaussian diffusion model is put forward.As a characteristic,the measur ement result of smoke screen area density proves that the indoor measurement met hod of smoke screen disturbance efficiency based on Gaussian diffusion model is fea sible.

Comparison of Laboratory Measurements for IR Imaging System Performance

Sensitivity and human performance are two important parameters for IR imaging system. Noise equivalent temperature difference (NETD) and minimum resolvable temperature difference (MRTD) can describe sensitivity and human performance of IR imaging system. So a lot of engineers apply themselves to studying the methods to measure NETD and MRTD for IR imaging system. The classical laboratory measurement methodologies for NETD and MRTD are introduced. And, two new approaches to three-dimensional (3-D) noise and MRTD/MRC are also portrayed, which can overcome some of the disadvantages existed in classical testing of NETD and MRTD. With the help of the new laboratory measurements, the disadvantages of the classical methods to measure NETD and MRTD can be solved.

Numerical Investigation of the Effects of Rate-Shaped Main Injection on Combustion and Emission in an OPOC Two-Stroke Diesel Engine

The effects of various split injection strategies on the opposed-piston opposed-cylinder(OPOC)diesel engine combustion and emission characteristics have been studied numerically using AVL-Fire CFD tools.The five rate-shaped main injections were used in split injection strategies.The results show that ignition delay from a rectangular injection rate is the shortest.Maximum pressure of the trapezoid injection rate is the largest.And the NOx emission of the rectangular injection rate is the largest.Meanwhile,the soot emission of the trapezoid injection rate is the least among the five injection rates.

Plasticity and melting characteristics of metal Al with Ti-cluster under shock loading

Impurity agglomeration has a significant influence on shock response of metal materials.In this paper,the mechanism of Ti-clusters in metal Al under shock loading is investigated by non-equilibrium molecular dynamics simulations.Our results show that the Ti-cluster has obvious effects on the dislocation initiation and melting of bulk Al.First,the Ti clusters induces the strain concentrate and leads the dislocations to be initiated from the interface of Ti cluster.Second,dislocation distribution from the Ti-cluster model results in a formation of a grid-like structure,while the dislocation density is reduced compared with that from the perfect Al model.Third,the critical shock velocity of dislocation from the Ti-cluster model is lower than from perfect Al model.Furthermore,it is also found that the temperature near the interface of Ti-cluster is100 K–150 K higher than in the other areas,which means that Ti-cluster interface melts earlier than the bulk area.

Effects of Strain Rate on the Mechanic Performance of Lattice Materials

Split Hopkinson pressure bar(SHPB)was utilized to explore the effects of loading strain rate on the dynamic compressing strength of the titanium alloy lattice material.Results reveal that the yield strength of alloy lattice material reaches 342 MPa initially and then drops to 200 MPa before it rebounds to 252 MPa while the loading strain rate correspondingly increases from the static value 1401/s to 2084/s.Numerical simulations were then carried out to explore the possible reason underlying.Results show that the lattice structure changed the stress distribution and caused significate stress concentration at finite strain with high strain rate.It is believed that the strain rate strengthening effect and layer-wise failure mode are the main reasons of the above mechanical properties change.