Papers by Keyword: Microtube

Abstract: The objective of this study was to clarify whether the surface roughness suppression orientation actually suppresses surface roughness by using the crystal plasticity finite element method (CPFEM), which is based on the relationship between the surface roughness suppression orientation and deformation in the inner surface direction that we have clarified in the past. In order to simplify the calculation and reduce the computational cost, a model was created by embedding cylinders in a rectangular body, which was then divided into 1/4 for the analysis. A dislocation density increase model that takes work hardening into account was applied to the model, and values obtained from tensile tests were used for material constants. The model was divided into 2130 elements. The simulation results show that the surface roughness suppression orientation is actually more difficult to deform than its surroundings.

Abstract: The paper presents microscale experimental investigation performed on microtubes that were prepared with a novel laser dieless drawing (LDD) technique from difficult-to-work AZ31 magnesium alloy (nominally 3wt.%Al-1wt.%Zn-0.3wt.%Mn-Mg balanced). A microstructure analysis was performed via various microscopic techniques. Mechanical response of individual grains with various orientations was tested using instrumental nanoindentation and the results were compared with the microstructure. Distributions of elastic modulus, hardness and visco-elastic properties were analyzed. In addition, microtubes were also characterized in terms of their surface roughness and morphology based on different modes of surface treatment. The grain size is practically not changed when LDD is applied after extrusion showing low thermal and straining effect of the process. Local mapping of mechanical properties does not show weak spots and imply feasibility of the novel production technology.

Abstract: This study is mainly based on five sets of mold cone angle and friction coefficient of micro-tube tube end necking forming analysis, and the tool cone angle of 60° experimental verification is carried out to analyze the titanium alloy (Grade 1) micro-tube for different mold cone angle and the different friction coefficient caused by the difference between the shrinkage forming. In this paper, Prandtl-Reuss's plastic flow rule, combined with finite element deformation theory and updated Lagrangian formulation (ULF) concept, establish an incremental elasto-plastic finite element analysis program for simulating the miniature tube end necking. The forming process also uses the generalized r_min algorithm to deal with elasto-plastic state and contact problems. From the simulation data of necking process, deformation history, punch load and punch stroke, stress and strain distribution is obtained. The analysis results show that by increasing the mold cone angle and friction coefficient, the thickness tends to be thicker in the certain area.

Abstract: A heat assisted superplastic dieless drawing process that requires no dies or tools is applied to the drawing of a Zn-22Al and β titanium superplastic alloy for not only circular but also noncircular microtubes such as square, rectangular and noncircular multi core tubes having square inner and rectangular outer cross sections. As a result, the tendency has been to increase the limiting reduction in area with increasing strain rate sensitivity index m value. We successfully fabricate Zn-22Al alloy, AZ31 magnesium, β titanium circular microtubes with outer diameter of 191μm, 890μm and 180μm, respectively. Furthermore, a noncircular micro tube, which has inner square tubes with a 335μm side, and an outer rectangular tube of 533×923μm were fabricated successfully. During the dieless drawing process, the geometrical similarity law in cross section which the tube is drawn while maintaining its initial shape can be satisfied. The smooth surface can be obtained in case of superplastic dieless drawing process without contact situation with dies and tools. Consequently, it is found that the superplastic dieless drawing is effective for the fabrication of circular and noncircular multicore microtubes.

Abstract: In this paper, single phase model was used to investigate the effect of base fluid in enhancing the heat transfer for forced convection flow of SiO₂ in microtube. Four different types of base fluid such as water, ethylene glycol, engine oil and glycerin were used in this investigation. Reynolds number used was ranged from 10 to 120. The results are presented in terms of axial and wall temperature along the tube radius and tube axis, axial velocity and Nusselt number. The result shows that the glycerin has the highest Nusselt number followed by engine oil, ethylene glycol then water.

Abstract: We develop new drawing technologies of rotary laser dieless drawing for the fabrication of micro-tubes without the need for tools such as dies, plugs and mandrels. A rotary laser dieless drawing apparatus with local heating using a laser irradiated from one direction as the heating source has been focused on for the fabrication of micro-tubes. In this study, a dieless drawing with a semiconductor laser setup with power of 30W is designed and developed. A workpieces was rotated about a tensile axis by rotary stage with chucks for circumferential uniform temperature distribution. A tube of stainless steel SUS304, with an outer diameter of 0.5mm and thickness of 0.13mm is used in the experiments. In this experiment, we verify the effectiveness of the developed rotary laser dieless drawing apparatus.

Abstract: Nickel based alloy microtube was prepared by utilizing spider silk as template via electroless deposition. The spider silk fiber was choosed as template which can be removed easily by heat-treatment and dissolving with sodium hydroxide solution. The nickel based alloy microtube was characterized by TG-DSC, XRD, SEM and EDX. SEM show that the microtube is about 600nm in outer diameter, 400 nm in inner diameter and more than 20 μm in the length. The catalytic activity of different structure Ni-P products was studied in liquid-phase hydrogenation of nitrobenzene reaction. The results show that the catalytic property of amorphous nickel based alloy is better than crystalline nickel based alloy and Raney Ni.

Abstract: The flow characteristics of nitrogen in microtubes with diameters of 14.9, 10.1, 5.03 and 2.05μm are investigated experimentally under high pressure conditions. The results show that the high pressure flow characteristics of nitrogen in microtube with the diameter of 14.9μm are in accordance with the classical fluid mechanics theory. However, with the decrease of the inner diameter of microtube, gas flow shows an apparent microscale effect and the results depart from the theoretical predictions of the conventional theory, moreover the smaller the diameter, the stronger the microscale effect. Besides, the high pressure microscale effect can not be characterized by the Knudsen number, which is proposed for studying rarefaction effect at low-pressure. Because of the existence of high-pressure microscale effect, it is inappropriate to study the real gas seepage characteristic in reservoir through the flow experiment at low pressure.

Abstract: In this work, nickel glycolate polymer microtubes (NGPMs) were prepared via a facile solvothermal method using hydrous nickel nitrate and anhydrous sodium acetate as starting materials, and ethylene glycol as solvent. Furthermore, nickel oxide (NiO) microtubes were obtained by a high-temperature treatment of NGPMs in air atmosphere. The morphology and phase of the products were characterized by scanning electron microscope (SEM), Transmission electron microscope (TEM) and X-ray diffractometer (XRD). The results show that NGPMs are of hierarchical structure, which are composed of a lot of nanolamellas. The morphology of NiO microtubes directly derived from that of NGPMs. In addition, the experiments were conducted with atomic absorption spectrometer for adsorption of Cr2O72- in ultrapure water using these microtubes obtained as absorbers. The results reveal that NGPMs obviously possess a better ability of chromium absorption with a maximum absorbing value of 14.6 mg/g at pH of 4 than NiO microtubes. Thus, the as-prepared of NGPMs may be promising as a new type of absorber for heavy metal ion for water treatment.

Abstract: Micro flow experiments in microtubes with nominal radius of 5μm have been accomplished and the impacts of wettability on micro flow have been studied. Method of improving injection by resistance force reducing agent has been discussed in this paper. Research results show that the flux differences between hydrophobic and hydrophilic microtubes represent more obvious at low velocity and low pressure condition. Water flux in hydrophobic microtubes are higher than in hydrophilic microtubes when the pressure gradient is smaller than 1 MPa·m^-1, but the differences are no more obvious when the pressure gradient is greater than 1MPa·m^-1. Some surfactants (resistance force reducing agents) can be adsorbed and arranged tightly on the wall of the microtube, and the wettability of the wall surface can be changed in a certain extent. Thus, the attraction of wall to water molecule is decreased, the effective boundary layer is getting thinner and the flow resistance can be reduced as a result. Based on this research, it is foreseeable that resistance force reducing agents can be applied in low permeability reservoir to improve water injection and improve oil recovery.