Application of Stand-off Double-Pulse Laser-Induced Breakdown Spectroscopy in Elemental Analysis of Magnesium Alloy

In this study, a stand-off and collinear double pulse laser-induced breakdown spectroscopy （DP LIBS） system was designed, and the magnesium alloy samples at a distance of 2.5 m away from the LIBS system were measured. The effect of inter-pulse delay on spectra was studied, and the signal enhancement was observed compared to the single pulse LIBS （SP LIBS）. The morphology of the ablated crater on the sample indicated a higher efficiency of surface pretreatment in DP LIBS. The calibration curves of Ytterbium （Y） and Zirconium （Zr） were investigated. The square of the correlation coefficient of the calibration curve of element Y reached up to 0.9998.

支援干扰掩护下反辐射无人机突防技术

针对高速或低速平台配合高速战机突防时,速度距离协同精度要求高、随队干扰时间短以及干扰掩护效率不高的问题,提出了两型机动能力相当的低速平台无人机配合突防的策略,即采用远距离支援干扰机掩护反辐射无人机突防至一定区域,雷达干扰无人机全程随队掩护反辐射无人机,仿真结果表明,该策略具有干扰掩护效率高、干扰资源节省、航迹配合容易的优点。

Effects of heat treatment on the intermetallic compounds and mechanical properties of the stainless steel 321–aluminum 1230 explosive-welding interface

The effects of heat treatment on the microstructure and mechanical properties of intermetallic compounds in the interface of stainless steel 321 explosively bonded to aluminum 1230 were investigated in this study. Experimental investigations were performed by optical microscopy, scanning electron microscopy, and microhardness and shear tensile strength testing. Prior to heat treatment, increasing the stand-off distance between samples from 1 to 2.5 mm caused their interface to become wavy and the thickness of intermetallic layers to increase from 3.5 to 102.3 μm. The microhardness increased from HV 766 in the sample prepared at a stand-off distance of 1 mm to HV 927 in the sample prepared at a stand-off distance of 2.5 mm; in addition, the sample strength increased from 103.2 to 214.5 MPa. Heat treatment at 450°C for 6 h increased the thickness of intermetallic compound layers to 4.4 and 118.5 μm in the samples prepared at stand-off distances of 1 and 2.5 mm, respectively. These results indicated that increasing the duration and temperature of heat treatment decreased the microhardness and strength of the interface of explosively welded stainless steel 321-Al 1230 and increased the thickness of the intermetallic region.

Response of masonry systems against blast loading

In this paper eight successive experimental blast tests with an increasing TNT equivalent charge weights ranging from 0.56 kg to 17.78 kg were conducted on unreinforced,ferrocemented overlay masonry and confined masonry walls.The pressure-time history caused by the blast was recorded by pressure sensors installed on the test specimen.The resulting damage pattern was observed during each test.Weak zones in the three systems of masonry were identified.Scaled distances for different damage levels in the three masonry systems were experimentally obtained.The results provide a basis for determining the response of each masonry system against blast loading.Consequently,efficiency of ferrocemented overlay masonry and confined masonry was found established in mitigation against blast loads.

Self-Adaptive Control System for Additive Manufacturing Using Double Electrode Micro Plasma Arc Welding

Wire arc additive manufacturing(WAAM)has been investigated to deposit large-scale metal parts due to its high deposition efficiency and low material cost.However,in the process of automatically manufacturing the high-quality metal parts by WAAM,several problems about the heat build-up,the deposit-path optimization,and the stability of the process parameters need to be well addressed.To overcome these issues,a new WAAM method based on the double electrode micro plasma arc welding(DE-MPAW)was designed.The circuit principles of different metal-transfer models in the DE-MPAW deposition process were analyzed theoretically.The effects between the parameters,wire feed rate and torch stand-off distance,in the process of WAAM were investigated experimentally.In addition,a real-time DE-MPAW control system was developed to optimize and stabilize the deposition process by self-adaptively changing the wire feed rate and torch stand-off distance.Finally,a series of tests were performed to evaluate the control system’s performance.The results show that the capability against interferences in the process of WAAM has been enhanced by this self-adaptive adjustment system.Further,the deposition paths about the metal part’s layer heights in WAAM are simplified.Finally,the appearance of the WAAM-deposited metal layers is also improved with the use of the control system.

Theoretical investigation of shock stand-off distance for non-equilibrium flows over spheres

We derived a theoretical solution of the shock stand-off distance for a non-equilibrium flow over spheres based on Wen and Hornung＇s solution and Olivier＇s solution. Compared with previous approaches, the main advantage of the present approach is allowing an analytic solution without involving any semi-empirical parameter for the whole non-equilibrium flow regimes. The effects of some important physical quantities therefore can be fully revealed via the analytic solution. By combining the current solution with Ideal Dissociating Gas（IDG） model, we investigate the effects of free stream kinetic energy and free stream dissociation level（which can be very different between different facilities） on the shock stand-off distance.

An Investigation of Effect of Stand-Off Distance on the Material Removal Characteristics and Surface Generation in Fluid Jet Polishing

Fluid jet polishing(FJP)is a versatile polishing process that has many advantages compared to other polishing processes.Stand-off distance(SOD)is one of the key parameters in flu id jet polishi ng.However,relatively little research work has been carried out to investigate its effect of SOD on material removal characteristics and surface generation in FJP.In this paper,a systematic investigation of the effect of SOD on the tool influence function and surface topography in FJP was conducted.Experiments were designed for FJP two kinds of materials corresponding to ductile and brittle materials.They are nickel copper(NiCu)alloy and BK7 optical glass,respectively.In this study,the SOD was varied from 2 to 35 mm.Analysis and discussions were made on its effect on the shape of TIF,material removal rate,and surface topography.It is interesting to note that the TIF shape becomes a Gaussian-like shape with large SOD both on NiCu and BK7,which provides a novel way to optimize the TIF in FJP.The variation of the material removal rate and surface roughness versus SOD on NiCu and BK7 were also determined from the experimental results.Moreover,the surface topography of NiCu and BK7 were characterized from the results measured from the white light interferometer and scan electron microscope.The outcome of the study provides a better understanding of the material removal characteristics and surface generation mechanism in FJP.

A quasi-one-dimensional model for hypersonic reactive flow along the stagnation streamline

This study proposes a quasi-one-dimensional model to predict the chemical nonequilibrium flow along the stagnation streamline of hypersonic flow past a blunt body. The model solves reduced equations along the stagnation streamline and predicts nearly identical results as the numerical solution of the full-field Navier-Stokes equations. The high efficiency of this model makes it useful to investigate the overall quantitative behavior of related physical-chemical phenomena. In this paper two important properties of hypersonic flow, shock stand-off distance and oxygen dissociation, are studied using the quasi-one-dimensional model with the ideal dissociating gas model. It is found that the shock stand-off distance is affected by both chemical and thermal non-equilibrium.The shock stand-off distance will increase when the flow conditions are changed from equilibrium to non-equilibrium, because the average density of the shock-compressed gas will decrease as a result of the increase in translational energy. For oxygen dissociation, the maximum value of its dissociation degree along the stagnation line varies with the flight altitude. It is increased at first and decreased thereafter with the altitude, which is due to the combination effect of the equilibrium shift and chemical non-equilibrium relaxation. The overall variation of the maximum dissociation is then plotted in the speed and altitude coordinates as a reference for engineering application.