Search

To provide intelligent control options during sheet metal forming process, magnetorheological (MR) fluid has been applied as a property-adjustable flexible-die. However, the mechanism of the magnetic field effect on the sheet deformation behavior is not clear yet. In this paper, to clarify the deformation mechanism, the bulging behavior of thin-walled Al1060-O sheet was systematically investigated through experiment and numerical simulation. Special attention was paid to the effect of magnetic field on loading curve, bulge dome height, and thickness strain distribution. Results showed that the maximum bulging force increased obviously with the increase of magnetic flux density. The bulge dome height and thickness strain were influenced by magnetic field condition and magnetic particle content synthetically. Appropriate magnetic field condition and magnetic particle content can improve formability. However, excessive magnetic flux intensity and magnetic particle volume fraction, for example, B = 0.20 T and φ = 46%, would lead to premature rupture. Finite element analysis was adopted to assist in explaining the bulging behavior. Detailed analysis indicated that the flow stress variations caused by magnetic field affect the stress states, velocity distribution of MR fluid, and sheet/MR fluid contact condition, further leading to different stress and strain distribution of sheet metal. Finally it causes the great difference in specimen geometry and wall thickness distribution. [ABSTRACT FROM AUTHOR]

In conventional bulging process, it is usually assumed that sheet metal deforms under normal pressure regardless of the frictional force between the sheet and the pressure-carrying medium. However, there is a phenomenon that sheet metal is bulged under the combined action of normal pressure and beneficial frictional force, which is resulted from the special characteristics of the pressure-carrying medium. Effects of constant tangential stress (beneficial frictional force) caused by rubber or urethane have been studied analytically and experimentally in previous works. Yet, the tangential adhesive stress imposed on sheet metal by viscous medium is correlated with its flow velocity due to its rate-dependent property, which can be controlled and measured by loading equipment. This kind of rate-dependent tangential adhesive stress has been taken into account to establish an analytical model to analyze its effects on the viscous pressure bulging (VPB) process. Then a numerical approach is presented to solve the problem, which utilizes incremental strain to start an iteration loop by considering different magnitudes of adhesive stress. Results have shown that rate-dependent beneficial frictional force in VPB process can promote longitudinal deformation of the bulged part to help make the strain distribution more uniform. The location of maximum thickness strain point deviates from the pole the outer radius, which means that when polar strains remain at the same level, higher bulging height can be obtained for larger magnitude of rate-dependent tangential stress; this characteristic mainly accounts for the postponement of fracture instability of sheet metal in VPB. The theoretical predictions of strain components and geometric parameters are analyzed and compared with experimental results. The comparisons have shown good agreement to validate the analytical model. [ABSTRACT FROM AUTHOR]

The Alkyl Polyglucoside (APG) is a nonionic surfactant with no toxicity and with high biodegradability, its drag-reduction behavior in a circular pipe flow is measured, and the rheological characteristics are investigated with a rheometer with a cone-plate flow cell. From the measured results, the APG is shown to have a high drag-reduction capacity, whose shear viscosity is shear-ratedependent at high concentrations, while its solution at concentrations with drag-reduction effects is non-viscoelastic as verified by zero relaxation time in the relaxation process of the shear stress, which contradicts the general viewpoint that there is a correlation between the viscoselastic characteristics and the turbulent drag reduction for the drag-reduction surfactant. However, the APG solution is birefringent as observed through a birefringent test, which indicates that there are rod-shaped micelles in the solution under the shearing flow. The higher extensional viscosity inferred from the extensional phenomenon observed in the measurements of the shear viscosity could be responsible for the drag reduction property of this nonionic surfactant. [ABSTRACT FROM AUTHOR]

In order to study the mechanisms of the turbulent frictional drag reduction by surfactant additives, the drag reduction, the shear viscosity and the shear stress relaxation were measured for solutions of a cationic surfactant cetyltrimethyl ammonium bromide (CTAB) with the same molar sodium salicylate as a counter-ion. It is found that the first step relaxation time decreases with increasing concentration and, thus, with the maximum drag-reducing rates, which indicates that the stiffness of the micellar structures with the first relaxation time, increases with the increase of the concentration of CTAB. Furthermore, for this surfactant, a viscoelastic property is necessary for reducing drag, while a stronger viscoelasticity characterized by a tail relaxation time does not necessarily mean a higher drag-reducing rate. [ABSTRACT FROM AUTHOR]

In order to develop technologies of friction drag reduction with a flexible tube to be used for water transport, experimental studies were carried out on the influence of Young’s modulus on the turbulent drag reduction. The friction coefficients of flexible tubes with different Young’s modulus were examined by using a sleeve-tube structure. The fluctuating vibration of the outer wall and the fluctuating pressure on the inner wall of the tubes were measured with a laser displacement sensor and a pressure sensor. The results are as follows. The smaller the Young’s modulus of a flexible tube and the larger the Reynolds number, the larger the turbulent drag reduction rates become. The transition from laminar flow to turbulent flow can be delayed with an appropriate Young’s modulus. Non-dimensional amplitude of fluctuating vibration on the outer wall is smaller than that of a viscous sub-layer thickness, and is positively correlated with the friction drag reduction. [ABSTRACT FROM AUTHOR]

To analyze the mechanism of drag reducing effect by coupling flexible tubes with turbulent flow, based on experimental examination of more obvious turbulent drag reduction effect in flexible tubes than in rigid tubes, experimental investigation was performed on the effect of turbulent drag reduction, fluctuating vibration characteristics of flexible tube and the correlations by using a double-tube system and laser displacement sensor. The results are as follows: with the decrease of the thickness of the flexible tubes, the root mean square of fluctuating amplitude of the outer wall of the tubes increases, and the non-dimensional burst period increases, resulting in the increase of the reduction rate of drag coefficient by coupling flexible tubes with turbulent flow. At applied pressure-balanced air on the outer wall and the Reynolds number of about 1.75 × 104, the non-dimensional burst periods of the flexible tubes with the thickness of 2 mm, 3 mm, 4 mm are 141, 126, 105, respectively. [ABSTRACT FROM AUTHOR]

The feasibility of the nozzle of self-excited oscillation pulsed jet (SEOPJ) as the breaker and loosing device for the air-lift pump was researched. The dynamic characteristics of the SEOPJ to crush the hard clay and loose the layer of ore deposit were explored experimentally under the submerged condition. The results show that the SEOPJ not only effectively breaks the hard clay or loose the particles of sand on the placer bed, but also produces fluctuating uplift force acting on particles of sand. The oscillating cross flow caused by the SEOPJ makes particles of sand move to the end of the suction pipe easily. Energy efficency of the airlift and concentration of the solids for the solid-liquid mixture sucked by the air-lift pump are increased obviously with the breaker of SEOPJ. [ABSTRACT FROM AUTHOR]