Internal waves in a two-layer liquid of finite thickness with a charged interface

This article is devoted to the researching of internal waves in immiscible liquids of finite thickness with a charged interface. The parameters of the internal waves are shown to depend on the thickness of the layers.     

Waves in a density stratified two-layer liquid of finite thickness with a charged interface

Using an analytical asymptotic procedure of the first order of smallness, the mechanisms of the onset of the wave motion in a two-layer liquid stratified with regard to its physicochemical properties and having a free surface and a hard bottom are investigated. It is shown that the presence of the hard bottom enhances the effect.     

On the drift properties of a wave packet propagating along a charged surface of a liquid

An analytical expression is constructed to estimate the influence of a surface electric charge on the drift velocity caused by the propagation of a wave packet on a horizontal surface of an ideal fluid. It has been shown that the surface electric charge affects the drift most effectively if the wavenumber of the carrier wave is equal to the inverse value of the capillary constant. Common regularities of the drift motion are established.     

Spectral analysis of surface waves in single and multi-layer slabs with finite thickness using finite element modelling

This paper presents the numerical modelling of spectral analysis of surface waves (SASW) method to find the surface wave velocities and to investigate if the numerical modelling of a multi-layer slab system can show the dispersive characteristics. In the modelling of a single-layer slab, the average surface wave velocities obtained from the finite element mode superposition analysis are reasonably close to the experimental value. The refinement of the finite element mesh from element size of 25.4×25.4 mm to 12.7×12.7 mm improves the surface wave velocity results. The numerical modelling of a three-layer slab shows that the dispersive characteristics of surface wave exist in the layer system and can be modelled by the finite element analysis. This study further advances the application of the SASW method to the assessment of existing concrete slab structures.     

On the role of the viscosity of liquids in the realization of Kelvin-Helmholtz instability

An ideal model of two immiscible liquids is analyzed, the lower of which is viscous and the upper one, moving with a constant velocity parallel to the interface, is ideal. It is shown that, in the linear approximation, the role of the viscosity of the two liquids results in the decrement of the damping of waves on the interface.     

底厚对镀锌钢压印接头失效模式影响分析

为研究压印接头底厚与其失效模式之间的关系以及不同失效模式下其静力学性能,对同种镀锌钢材料进行压印连接,再进行拉伸剪切试验。结果表明:对镀锌钢同种单搭压印接头,当底厚不同时,压印接头的失效形式不同。当接头底厚为0.95 mm时,接头失效模式为颈部断裂失效模式和颈部断裂混合失效模式;当底厚为0.95 mm到1.26 mm之间时,接头的失效形式为混合失效;底厚为1.37 mm时,接头失效模式全部为底部拉脱失效。随着失效形式从颈部断裂失效模式到混合失效,再到底部拉脱失效变化,其承载能力、失效位移、能量吸收值呈抛物线变化。当失效形式为混合失效时,其承载能力、失效位移及能量吸收值均最优。     

On electrostatic instability of a space-charged jet of dielectric liquid

On the basis of the dispersion equation for the nonaxisymmetric capillary waves at the surface of a strongly volumetrically charged cylindrical jet of an ideal incompressible dielectric liquid, it has been found that, for liquids with their dielectric permittivity changed in a wide range of values, there may occur electrostatic instability of the jet’s side surface.     

Hydrogen embrittlement and fracture toughness of a titanium alloy with surface modification by hard coatings

The effect of hydrogen embrittlement on the fracture toughness of a titanium alloy with different surface modifications was investigated. Disk- shaped compact- tension specimens were first coated with different .hard films and then hydrogen charged by an electrochemical method. Glow discharge optical spectrometry (GDOS), scanning electron microscopy (SEM), and x- ray diffractometry (XRD) were applied to analyze the surface characteristics. The results revealed that fracture toughness of the as- received titanium alloy decreased with the increase of hydrogen charging time. Fracture toughness of the alloy after plasma nitriding or ion implantation, which produced a TiN _x layer, decreased as well, but to a lesser extent after cathodic charging. The best result obtained was for the alloy coated with a CrN film where fracture toughness was sustained even after hydrogen charging for 144 h. Obviously, the CrN film acted as a better barrier to retard hydrogen permeation, but it was at the sacrifice of the CrN film itself.     

On the stability of a bending mode of a charged jet of viscous dielectric liquid with the ultimate electroconductivity in a collinear electric field

The instability of the bending mode of a charged cylindrical jet of a viscous liquid with its ultimate electroconductivity in a collinear electrostatic field was studied theoretically using an analytical estimation. The development of the bending instability was found to be more feasible for weakly conductive liquids with small values of the surface diffusion coefficient of the electric charge.     

Effects of material creep on displacement instability in a surface groove under thermo-mechanical cycling

Displacement instability along the interface between a zirconia top coat and thermally-grown oxide (TGO) forming metal substrate is a fundamental source of failure in some thermal barrier coatings (TBCs). In this work, the effects of material creep on displacement instability near the surface groove on Fecralloy substrate subjected to thermo-mechanical cycling are investigated using finite element analysis (FEA). Assumptions and references about material properties are minimized for a more realistic analysis. Most material properties, such as TGO growth and creep parameters, are based on in-house experimental measurements. Our results show that under a small magnitude of tensile stress, cyclic history plays a major role in displacement instability, and that this role significantly fades as stress increases. We also show that creep in the substrate material predominates at the holding time of a cycle. Creep significantly enhances the deformation near the groove without mechanical load applied on the specimen, while it contributes to length change rather than deformation of the groove as the load level increases.     

斜底大圆角盒形件拉深成形工艺与模具设计

从变形区单元体的应力状态方面叙述了斜底、大底部圆角盒形拉深件的拉深工艺与模具设计,重点是如何控制拉深过程中的材料变薄。生产实践证明,改进后的模具和工艺生产的产品完全达到质量要求。     

硬质合金齿面的高频堆焊

为满足石油井下工况的要求 ,三牙轮铣齿钻头齿面要堆焊一层硬质合金颗粒 ,目前主要用氧乙炔火焰堆焊 ,工艺有两种 :一种用管装碳化钨焊条 ;另一种是“胶焊法” ,即先将碳化钨颗粒用氧化铜和水玻璃粘附在待焊表面 ,然后加热 ,使钢基体熔化后碳化钨颗粒沉积在齿面上。就生产现场情况看 ,气焊的主要不足是 :①变形较大 ,影响牙轮轴承孔加工精度 ,甚至出现钻头组装后牙轮互相干涉 ;②管装焊条堆焊层中碳化钨密度低 ,影响抗磨性能 ;③容易产生气孔 ;④焊层厚度不均匀。用“胶焊法”也经常因碳化钨颗粒粘附不牢被气体火焰吹失。为了避免气焊时因热…     

Instability of the lateral surface of strongly charged jets in a collinear flow of material environment

On the basis of the analysis of the dispersion equation for nonaxisymmetric capillary waves with an azimuthal number equal to two on a surface of a charged cylindrical jet of an ideal incompressible conductive fluid, it is shown that the influence of the flow has a destabilizing character. The instability of the nonaxisymmetric waves with an azimuthal number equal to two has a threshold character based on both the speed and on size of the electrical charge per unit of length of the jet.     

Linear analysis of oscillations of a charged viscous liquid drop in the context of boundary layer theory

The boundary layer theory in connection with a periodically moving free surface of viscous liquids is applied to solving the problem of calculating linear oscillations of a charged viscous liquid drop. The approximate solution is compared with the exact one.     

横向厚差与宽厚比对冷轧带钢临界失稳板形的影响

基于秒流量相等的体积不变条件和弹性薄板稳定性理论,推导了理想条件和实际工况下冷轧带钢横向厚差、宽厚比与板形之间的耦合关系,分析各因素对临界失稳板形的综合影响规律。参考理想条件下横向厚差与板形的基本关系,建立实际工况下的影响模型。结果表明,0.3mm以下厚度薄带的横向厚差变化量对板形的影响明显;根据弹性薄板稳定性模型,分析横向厚差和宽厚比对临界失稳板形的影响。结果表明,当冷轧带钢的宽厚比大于3000时,临界失稳应力明显减小。通过实测1450六辊冷轧机的两卷典型带钢横向厚差,得到在生产不同宽厚比的超薄规格带钢时,需要根据入口带钢的横向厚差,调整负载辊缝形状,以保证出口带钢的横向厚差变化量满足板形不失稳条件,从而获得了良好的板形。     

The surface tension of a solid in the presence of adsorption and electric charge on its surface taking account its finite strain

Studies of the thermodynamic theory of equilibrium single-component adsorption from a liquid on a charged solid surface taking into account its finite strain are continued. The adsorption isotherm equation and surface tension of a solid are derived in the special case of the surface-layer equation within the model of two parallel capacitors. The constraint equations are obtained for parameters of the theory with capacitive curves measured on an unstrained metallic surface.     

Friction and the development of hard alloy surface microstructures during wear

Investigations of wear in sliding friction of WC-Hadfield steel hard alloy against cast tool steel have been carried out in a broad range of velocities and pressure values. Structural and phase composition variations have been revealed. Friction-affected zone was found to be 450 μm in depth. Structural γ → α, γ → transformation regions are located within 100 μm of the surface. These transformations contributed to the total solid solution deformation hardening.     

Arc plasma nitriding of graphite surface towards production of a hard carbon nitride case

Electrode grade graphite substrates were exposed in a nitrogen plasma produced in a pot type 35 kW dc extended arc furnace/reactor operating in non-transferred mode. Different gas (Ar, N₂, H₂) configurations were employed to nitride graphite for 15-20 min in the thermal plasma. Characterization of the plasma-nitrided graphite surface made by XRD revealed the presence of carbon nitride in a mixed form consisting of different phases. The 120-160 μm thick nitrided case exhibited enhanced microhardness values by more than 7 times. XPS studies confirmed the carbon and nitrogen bonding in the nitrided layer/case grown on surface. A comparison of morphologies between the un-nitrided and nitrided graphite surface showed a significant difference in the microstructure. Micro Raman spectra of the nitrided graphite surface showed further evidence of nitrogen incorporation and corroborate the XPS and SEM results. The new compound, carbon nitride, which was recently predicted from theoretical studies, is found to have been formed by the interaction between carbon (graphite) and nitrogen plasma due to a favourable free energy condition available in the high temperature plasma ambient.     

On the possibility of the full stabilization of the capillary instability of a dielectric liquid jet by a longitudinal static field

The dispersion equation for axisymmetric capillary waves at the surface of a cylindrical jet of an ideal incompressible dielectric liquid in a symmetry axis electrostatic field collinear to the jet has been analyzed. It was shown that, in contradiction with the idea put forward previously, no full stabilization of the capillary instability occurs at any arbitrarily large values of the field intensity.     

The effects of cryogenic cooling on surface integrity in hard machining: A comparison with dry machining

This paper presents results of an experimental study of cryogenic machining of hardened AISI 52100 steel, focusing on surface integrity. Experiments were performed under dry and cryogenic cooling conditions using CBN tools varying cutting speeds, workpiece hardness and tool geometry. Surface integrity parameters (surface roughness, white layer thickness, residual stresses, metallurgical conditions including grain size, phase transformation, etc.) were investigated to establish the effects of cryogenic cooling on the surface integrity of the machined component, and results were compared with those from dry hard machining. Overall, cryogenic cooling provides improved surface integrity leading to extended product life and performance.