Mechanism of improvement of formability in pulsating hydroforming of tubes

The mechanism of improvement of formability by the oscillation of internal pressure in a pulsating hydroforming process of tubes was examined. Free bulging hydroforming experiments of mild steel tubes under oscillating and constant inner pressures were performed. For a high constant pressure, a round bulge with local thinning was observed, whereas wrinkling occurred for a low constant pressure. The occurrence of these defects was prevented by oscillating the internal pressure in the pulsating hydroforming. In the pulsating hydroforming, a uniform expansion in the bulging region was obtained, and thus the formability was improved by preventing the local thinning. It was found from an observation of deformation behaviour, using a video camera, that the tube is uniformly expanded by repeating the appearance and disappearance of small wrinkling. The cause of the uniform expansion for the pulsating hydroforming was also interpreted from the variation of stress components. In addition, a similar deference in deformation behaviour between the oscillating and constant inner pressures was also obtained in finite element simulation.     

钢材打捆机控制系统智能化技术的研究

钢材打捆机是一种用于轧钢精整工艺的新型自动化设备，其控制系统基于SiemensS7 PLC和TP7触摸屏。系统的智能化技术主要包括：液压高低压自动控制、在线监视、离线故障检测、多台设备协同工作、可视化人机交互技术。本文描述了这些技术的原理与实现方法。     

Comparison of the effects of small additions of silicon or aluminum on the oxidation of iron-chromium alloys

A study has been undertaken of the oxidation behavior of Fe-26 wt.% Cr-1 wt.% Al and Fe-26 wt.% Cr-1 wt.% Si at 800° and 1000°C in oxygen, in order to determine the usefulness of the two tertiary elements in facilitating the development of the Cr₂O₃ external scale. The research has also permitted a comparison of the modes of internal oxidation of these elements, with a view to ascertaining the ease of establishment of the tertiary element oxides as healing layers at the scale/alloy interface. It has been shown that aluminum is the more effective addition in this respect, due to formation of a higher population density of internal oxide nuclei in the early stages. However, in the 1% Al alloy, the precipitates penetrate inward, to considerable depths, as continuous platelets, making development of a complete healing layer difficult. In practice, a higher aluminum concentration is necessary for the closely spaced precipitates to coalesce to form the healing layer, but the process then occurs rapidly. The initial internal oxide nuclei in the 1% Si alloy have a much smaller population density and are restricted to a location very close to the surface. Thus, a healing layer can be established, but the large interparticle spacing makes this a very slow process. Even at a higher silicon concentration, it takes a significant period to be completed. The effects are discussed and accounted for, particularly in terms of the relative stabilities of the various oxides.     

Effect of porosity of phosphate coating on corrosion resistance of galvanized and phosphated steels Part I: Measurement of porosity of phosphate

The corrosion resistance of phosphated and painted steels is associated with the integrity of phosphate and paint layers. In this work, a methodology to measure the porosity of phosphated coatings based on cathodic polarization technique with an electrolyte of a sodium sulfate aqueous solution was developed. The morphology and mass of phosphate layers were determined. Phosphating was performed using the spraying and immersion techniques, varying the refiner content of bath in the immersion operation. The phosphate coatings obtained by immersion with a refiner showed the lowest values of porosities among the samples studied. The phosphate layers, obtained by spraying, immersion without a refiner, and immersion with a half content of refiner, showed the lowest porosity on electrogalvanized steel. The phosphate layer obtained by immersion with a refiner displayed the lowest porosity on the substrate of ungalvanized steel.     

The method of production of damask steel

The Russian term is "bulat" steel and to bulat is related the understanding of steel with high elastic and cutting properties, for which a unique microstructure, a patterned surface, is characteristic. To it was imparted special value and it was assumed to be a compulsory component of damask steel. The word "bulat" is of Iranian origin (pulad).In the modern understanding steel is a material with a certain chemical composition and damask steel does not fit under it.     

Foundations of topological characterization of surface texture

More than a hundred years ago Maxwell proposed dividing a landscape into regions consisting of hills or alternatively consisting of dales. A hill is a set of points from which maximum uphill paths lead to one particular peak, and a dale is the set of points from which maximum downhill paths lead to one particular pit.Starting with Maxwell's ideas this paper sets out to develop the foundations of topological characterization of surface texture. This leads to a system of surface texture characterization which is complementary to published areal parameters based on the mean line system. In a similar manner that R&W system is complementary to the mean line system for profiles (the dale is the areal equivalent of a motif on a profile).An important example of a true areal characterization contained within this system is the connectability of surface valleys. This is important for applications such as lubrication and paintability of a surface. It is also important for characterizing extruded aluminium that has been anodized. The anodizing has cracks (connected valleys) and isolated pits, both of which require characterizing separately for production control.     

Kinetics of chemical n-doping of polyacetylene

Polyacetylene (PA) films were doped with tetrahydrofuran and benzene solutions of organo potassium and lithium compounds. The kinetics for doping were determined from the variation of the dopant concentration with time, as a function of film thickness, dopant concentration and doping temperature. The experimental doping rates were compared to computed values deduced from a doping model taking into account the interfibrillar diffusion, separately measured with an inert hydrocarbon. This comparison allows a minimum value (10⁻¹⁵ cm²/s) to be determined for the intrafibrillar diffusion coefficient D_f of doped sites and cations. With such a value no homogeneous doping can be carried out at intermediate doping levels, for films thicker than about 50 microns, by a simple control of doping time or dopant concentration. This may, however, be achieved by a thermodynamic control using dopants of suitable redox potential.     

Effect of electroosmotic flow of aqueous suspension of nanosilica on the properties of carbonated concrete

The paper investigates the possibility to use electroosmosis to transport nanosilica (NS) particles inside carbonated concrete, in order to exert a filler effect and enhance its durability performance. This method aims to extending possible beneficial effects of NS to existing reinforced concrete structures, where the presence of a carbonated layer of concrete is very likely. Injection tests were performed with electrochemical cells on carbonated concrete discs with water/cement (w/c) ratios of 0.50, 0.55 and 0.65, using a NS aqueous suspension at the anode. The results indicated that a flow did occur through the concrete disc and it was directed from the anode towards the cathode. A linear relationship between flux and applied voltage gradient was obtained, which is typical of electroosmotic phenomena. The bulk properties of concrete, such as density, water absorption and sorptivity, were not affected by the injection tests, whilst electrical resistivity increased indicating a mild ‘sealing’ effect on the surface. Also microstructural analyses highlighted the local presence of NS that decreased the local porosity close to the surface.     

Theoretical analysis of diffusion of solutes during the solidification of alloys

When an alloy solidifies and the composition of the solid differs from the composition of the liquid, atoms of the alloying elements rejected at the solid-liquid interface have to diffuse toward the bulk liquid. Diffusion may be supported by convection. Theoretical calculations have been made for a liquid without convection, for a liquid involving natural convection, and for solidification of a liquid alloy at the surface of a rotating disk as an example of forced convection.     

Demonstration of probability of detection taking consideration of both the length and the depth of a flaw explicitly

This study proposes the construction of the probability of detection (POD) as a function of both the depth and length of a flaw. In addition, this study discusses how to censor signals in constructing the POD. The general effects of the flaw parameters on signals are evaluated by numerical simulations, and the scattering of signals, which is critical to the POD, is estimated by signals obtained in experiments. A new likelihood function is introduced, and the proposed method is demonstrated using eddy current signals caused by various artificial flaws on a flat type 316L stainless steel plate obtained in a laboratory test. The demonstration confirms that the proposed method can provide a reasonable POD with a small amount of experimental signals, and reveals that proper censoring significantly decreases the detrimental effect of noise on the POD.     

A study of electropolymerization of N,N-dimethylaniline

Electrochemical oxidation and polymerization of N,N-dimethylaniline at a gold electrode have been studied in an acidic solution. Both potential cycling and electrolysis at a controlled potential yield a thin film of a polymer that shows electrochemical activity in acidic and pH-neutral solutions. Raman spectra of sulfate- and polystyrenesulfonate-doped polymer have been obtained and analyzed. Two possibilities for electropolymerization have been considered – a simple polymerization yielding a “true” poly(N,N-dimethylaniline), and polymerization accompanied by a partial demethylation yielding poly(N-methylaniline). Based on the results obtained, the first one has been considered as most likely.     

Causes of Fracture of Welded Joints of Flexible Tubing String

Metal Science and Heat Treatment - Results of a study of failure of a continuous flexible tubing string transporting working environments under the conditions of alternate bending and corrosive...     

Modeling of thermal conductivity of stainless-steelmaking dust pellets

The thermal conductivity of stainless-steelmaking dust pellets, an important parameter for the direct recycling of the dust, is naturally of interest to metallurgists. The measurement of central temperature and surface temperature was taken in a furnace. The physical model and calculation model for the heating process were set up to check the thermal conductivity of the dust pellets. The physical structure parameters δ and γ of the basic unit are 0.92 and 0.45 based on the calculation. The temperature in the pellet can be expressed in a linear equation α5 Tp =α1TN α2TM α4. This is convenient to determine the central temperature of a pellet in the direct recycling process.     

Development of mathematical models of superplasticity properties as a function of parameters of aluminum alloys of Al-Mg-Si system

The article discusses the superplasticity properties and structure parameters of cold-worked alloys of a quasi-binary section of the Al-Mg-Si system with a volume fraction of eutectic particles of 0.08–0.18. Mathematical models of yield stress and effective elongation as a function of the structure and engineering parameters have been developed for alloys of this system. An analysis of the developed models shows that, in the temperature range of 520–560°C, superplastic deformation is controlled by the rate of diffusion of aluminum atoms in the grain bulk.     

Effect of Rigidity of Die and Press on Blanking Accuracy of Electronic Machine Parts

Blanking accuracy is decided by the relative displacement of an appear die to a lower die in the blanking. Deformation of a die-set subjected to an accentric load in a press is analysed, and the bending moment M and the lateral force Q acting on the end of each guide post are expressed by the inclination θ and the lateral displacement DX of the upper die. In the experiment, a die-set of sub-guide construction is installed on a 1250kN straight side frame press and 100kN C-type frame press, and θ DX are measured user static loading and dynamic loading of 100sdm. The calculated M and Q using the measured θ and DX show that the M and Q acting on the guide post end are smaller on the straight side frame press than on the C-type frame press though the capacities of both presses are almost the same. The analytical method proposed in this paper can be used in the selection of a press suitable to a given die set and a given accentric load.     

Metallurgy of granules of high-strength titanium alloys

Centrifugal spraying of a melt to obtain fine granules is a method of the technology of fast hardening. Each granule is a microscopic ingot having the composition of the sprayed alloy. Subsequent compaction of the granules gives performs or parts with uniform structure and chemical composition. This is especially important for producing large semifinished products from high-alloy titanium alloys with a capacity for segregation and structural inhomogeneity. The present work is devoted to optimization of the compaction regimes of granules of alloy VT22 and the choice of regimes of deformation and heat treatment of parts from granulated alloy VT22 in order to a obtain a combination of high properties.Translated from Metallovednie i Termicheskaya Obrabotka Metallov, No. 6, pp. 28–30,June, 1995.     

Regularities of formation of the structure of Al-containing nanocomposites upon interaction of ASD-6 powder with polymer suspension

A new approach toward development of nanosize materials based on water-soluble polymers is suggested. Nanosize aluminum-containing structures screened by a polymer sodium carboxymethyl cellulose shell are obtained at temperatures of 70–80°C by introducing Al microparticles with a size of up to 10 μm into an aqueous solution of sodium carboxymethyl cellulose. The methods of XRD and IR spectroscopy were used to establish that metallic aluminum is present in nanoparticles and the polymer Na CMC matrix is preserved without fundamental changes. Electron microscopy is used to characterize the morphological regularities and elemental composition of nanoparticles. Agglomerates of the obtained particles reach a size of about 300–500 nm and consist of tubular structures with a size of up to 150 nm with a total thickness of 3–5 nm. This approach may form the basis for a comparatively simple and cheap method of obtaining nanosize particles that can serve as modifying agents in protective corrosion-resistant coatings.     

Investigation of Femtosecond Laser-assisted Micromachining of Lithium Niobate

Lithium Niobate has a potential for applications in electronics and communication industries due to its unique electro-optical, piezoelectric and nonlinear properties. Femtosecond laser machining offers the best alternative to machine the mechanically fragile and optically delicate lithium niobate crystal. This paper reports a study of the effect of femtosecond laser machining on the surface integrity of lithium niobate. The transmission electron microscopy reveals a 100nm thin amorphous region and a void. The chemical analysis shows a loss of lithium and oxygen from the surface and sub-surface. Optical illumination facilitates the selective readout of the written spots of 2 microns size.     

Determination of material constants and prediction of fracture in sintering of ceramic products

Methods of determining material constants required for finite element simulation of sintering of ceramic green bodies are proposed. The flow stress and shrinkage strain-rate in sintering are measured from a simple compression test with a constant load. The critical difference in volumetric strain in the criterion for sintering fracture is determined from a three-point bending test with a constant load. Using the measured material constants, the densification behaviour in compaction and sintering processes of circular tiles composed of a coloured upper layer and uncoloured substrate with a groove is simulated by the viscoplastic finite element method. The occurrence of sintering fracture is predicted from the difference of volumetric strain calculated by the finite element simulation. The accuracy of the calculated results is improved by using the flow stress with strain-rate and temperature sensitivities and the history of shrinkage strain-rate.