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.     

Spectral analysis of surface wave response of multi-layer thin cement mortar slab structures with finite thickness

The method of spectral analysis of surface waves (SASW), a nondestructive testing method, has mainly been developed and used for many years in the fields of geotechnical engineering and highway engineering, such as for examining the material properties of pavement systems and soil media under an infinite half-space condition. Extensive research in this area has been focused on understanding the applicability and limitations of the SASW method in recent decades. This method consists of generation, measurement, and processing of dispersive surface waves. During an SASW test, the surface of the medium under investigation is subject to an impact to generate surface wave energy at various frequencies. Two vertical accelerometer receivers are set up near the impact source to detect the energy transmitted through the testing media. By recording signals in digitized form using a data acquisition system and processing them, surface wave velocities can be obtained by constructing a dispersion curve. Through forward modeling, the shear wave velocities can also be found, which can be related to various material properties. This paper presents the relationship between the theoretical and experimental compact dispersion curves when the SASW method is applied to multi-layer thin cement mortar slab systems with a finite thickness. The test results of surface wave velocity obtained from the experimental compact dispersion curve are found to have higher values than the results obtained from the theoretical dispersion curve due to different boundary conditions and reflections from the boundaries. An experimental study was conducted to examine if the dispersive characteristics of a Rayleigh wave exist in the multi-layer cement mortar slab systems. This study can be utilized in examining structural elements of general concrete structures and can be applied in the integrity analysis of concrete structures with a finite thickness.     

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。     

Wave propagation in water-immersed adhesive structure with the substrates of finite thickness

In previous theoretical studies on the adhesive structure, the substrate is mostly considered as a semi-infinite solid space and corresponding theoretical derivation is rarely related to the thickness of the substrate. In the paper, based on the transfer matrix method, we studied in the water-immersed trilaminar plate-like adhesive structure with the substrates of finite thickness and the perfect/sliding interfaces in the case of plane longitudinal wave incidence and deduced the expressions of reflection and transmission coefficients of longitudinal waves. In order to verify the accuracy and applicability of the deduced formula, this formula was firstly applied to the water-immersed steel–epoxy resin–steel adhesive structure with perfect interfaces and the calculated result was compared with the existing data. Taking the water-immersed aluminum–epoxy resin–aluminum adhesive structure with perfect/sliding interfaces as an example, the impacts of incident angle and frequency on the reflection and transmission characteristics of the longitudinal wave were then analyzed. Finally, the theoretical method was experimentally verified and the experimental results were well consistent with the numerical calculation results. The reflection and transmission coefficient curves of longitudinal wave showed the obvious resonance when the longitudinal wave was normally incident. Regardless of the substrate thickness, the frequency of acoustic waves or the incident angle, it can only confirm whether a sliding interface exists, but the interface to slide cannot be determined.     

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.     

Surface conductive films via polymerization on a liquid surface

Surface conductive crosslinked polybutyl acrylate (c-PBA) films were prepared in two steps. In the first step, a mixture containing the monomer of the conductive polymer (pyrrole or 3-methylthiophene) and the precursors of c-PBA (butyl acrylate, a crosslinking reagent, and the initiator 2,2′-azobisisobutyronitrile) was spread over the surface of a hot 2 wt.% poly (vinyl alcohol) aqueous solution, and allowed to polymerize. In the second step, the pyrrole or 3-methylthiophene containing c-PBA film was immersed into an iron chloride solution in ethyl acetate for the monomer present in the film to be oxidatively polymerized and to generate a conductive coating layer near the surface of the film. The highest conductivities achieved were 1 S/cm for polypyrrole and 18 S/cm for poly (3-methylthiophene). The effects of the oxidation polymerization time, the amount of monomer precursor of the conductive polymer, the concentration of the oxidant solution, and the extent of crosslinking of c-PBA were investigated.     

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.     

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.     

Variation of temperature at the bottom surface of a hole during drilling and its effect on tool wear

The temperature at the bottom surface of a hole being drilled is measured by using an infrared-radiation pyrometer equipped with two optical fibers. One of the optical fibers is inserted into the oil hole of an internal coolant carbide drill and passes through the machine-tool spindle. This optical fiber is connected to another optical fiber at the end of the spindle. Infrared rays radiating from the bottom surface of the hole being drilled are accepted and transmitted to the pyrometer by the two optical fibers. Temperature increases as drilling progresses, and it increases considerably near the bottom surface of the workpiece. In case of a 10-mm-thick carbon–steel workpiece, temperature reaches 190, 250, and 340 °C at drilling depths of 6, 8, and 10 mm, respectively. To investigate the effect of the increase in temperature on drill wear, a series of 10-mm-deep blind holes are drilled in workpieces with thicknesses of 10 and 25 mm. Tool wear is greater when the drill cuts a hole at the bottom of a 10-mm workpiece than that when the drill cuts a hole at the mid-depth of a 25-mm workpiece. This indicates that the rapid increase in temperature near the bottom of the workpiece effects the progress of drill wear.     

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.     

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.     

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。     

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。     

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.