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The sheet forming using flexible-die has been presented the great development potential, which uses the liquid, polyurethane rubber, rubber bladder, viscous medium, or magnetorheological fluid as the force transmission medium and shows some advantages. In this paper, the new method on the sheet flexible-die forming using the magnetorheological elastomer (MRE) is proposed. The MRE consists of magnetically polarizable particles locked into an elastomer matrix and has the magnetorheological effect under the action of a magnetic field. The mechanical property like the shear modulus of MRE can up to 160% in microseconds when the magnetic field is applied. Therefore, the performance behavior of MRE is controllable and adjusted, which can adapt the force requirements at different positions during the sheet metal forming process. Finite element analysis of Al1060 sheet bulge using MRE with different shear modulus was carried out. Results show that the right side of the FLD is obtained by using elliptical dies with different length–width ratios. On the basis of that a new method is proposed to obtain forming limit diagrams of sheet metal using the magnetorheological elastomer forming process at variable magnetic fields, bulging tests of the Al1060 sheet under different magnetic fields were implemented. FLD at different elliptical dies under the action of MRE is determined. An increase in forming limits of Al1060 with the increase in the magnetic field is observed. [ABSTRACT FROM AUTHOR]

Classical consolidation theory ignores the influence of soil liquid phase acceleration. This paper considers the influence of liquid phase acceleration on the stress balance equation during the consolidation of soil, obtains the one-dimensional equation governing quasi-hydrostatic consolidation under large deformation with the consideration of the inertia of the liquid phase, and solves the governing equations by finite element method. The calculation results show that the liquid phase inertia effect of the soil will cause excess pore pressure in the soil, obviously increasing in the initial stage of consolidation, and the self-weight of soil exerts an influence on the excess pore pressure at the later stages of consolidation. The liquid phase inertia effect parameter Dc determines the strength of the liquid phase inertia effect. A larger Dc value results in a larger increase in the excess pore pressure, and the later the liquid phase inertial effect occurs, the longer the duration is. In the large strain consolidation analysis, especially at the initial stage of consolidation, it is necessary to consider the liquid phase inertia effect of the soil. [ABSTRACT FROM AUTHOR]

The distribution of temperature in sand soils was measured through laboratory tests, and the temperature influence on friction resistances at the concrete-soil interface was analyzed. Based on the results of laboratory tests, the finite element model was established using the sequential thermal coupling method. The influences of temperature on the bearing characteristics of energy pile were analyzed. The analysis results show that the cyclic temperature will cause additional displacement along pile depth. It is pointed out that if applied vertical loads at energy pile head exceed the value from which nonlinear settlements would be initiated, irrecoverable additional settlement will occur at pile head. Based on the analysis results, a simplified approach was proposed to estimate the zero point of additional displacement along pile shaft and the additional axial pile force. The comparison between the calculated results obtained by the proposed method and that of ABAQUS on single energy pile was given to verify the accuracy of the proposed method. It is shown that reasonable predictions can be obtained without expensive and time-consuming analyses by the proposed method in this paper. [ABSTRACT FROM AUTHOR]

Magnetorheological fluid (MR fluid), a kind of smart material, has been used as a new pressure-carrying medium in magnetorheological pressure forming (MRPF). The mechanical property of MR fluid under the pressure significantly affects the sheet formability. However, there is little knowledge on the deformation behavior of MR fluid under three-dimensional stress states. In this paper, a new procedure via a combination of extrusion test and FEM simulation has been proposed to determine the flow stress of MR fluids. The experimental device for extrusion test of MR fluids was designed. The flow stresses of a MR fluid (MRF-J01T) under four different magnetic fields were determined through the proposed procedure. In addition, the obtained flow stresses were used in the following FEM simulations to verify the accuracy by comparing with the experimental results. The simulation results were in good agreement with the experimental data, which supports the correctness and practicability of the proposed method. [ABSTRACT FROM AUTHOR]

The viscosity of viscous medium used in viscous pressure forming (VPF) is one of the most significant processing parameters, which is rather complicated and lack of systematical investigation. In this paper, the viscosities of six kinds of viscous mediums with different molecular weights are measured and compared by using a dynamic shear rheometer. Then, extrusion tests for different viscous mediums are conducted, and the cavity pressures during different extrusion processes are acquired. The flow stresses of viscous mediums are determined by using a combination of extrusion test and FEM simulation, which can provide material parameters input for related FEM simulation of VPF. In addition, bulging specimens and three kinds of conic parts of Al1060-O sheet are obtained by VPF using different viscous mediums. The results show that the viscosity of viscous medium has a significant influence on specimen configuration. The viscosity difference leads to different flow stresses of viscous mediums, which further leads to the variation of stress loading and transmission in forming process. And the higher viscous adhesive stress generated by using viscous medium with a higher viscosity can make metal flow more easily and improve sheet formability. [ABSTRACT FROM AUTHOR]

In order to avoid the highly complex process sequences and the potential instable metal flow in the manufacture of thin-walled metal circular rings with corrugated meridians, a forming method without use of axial compression on blank end is developed specially. A highly viscous polymer, i.e., the viscous medium, is utilized as pressure carrying medium in the proposed method. Since the lack of axial feeding leads to the insufficient metal flow into the die cavity, which finally causes severe wall thickness thinning, the tangential adhesive stress at blank/medium interface is used to promote metal flow. The limit of diameter variation of thin-walled metal circular rings produced by employing different types of viscous medium is predicted by finite element analysis (FEA) and resulting strain-based FLD. The numerical results show that employing viscous medium with proper strain rate sensitive exponent ( m) will be feasible to extend the limit of diameter variation. Based on the evaluation on the achievable diameter variation in compression forming and expansion forming, a multistep forming process was presented. Accordingly, nickel-based superalloy parts with one and two convolutions were manufactured successfully. The end displacement of ring-shaped blank is considerable and the resulting wall thickness reduction is relatively small (9 %), which demonstrates the metal flow is promoted effectively. The proposed forming method is considered to be simple and convenient for the fabrication of ring-shaped parts with extremely thin wall and complex shapes. [ABSTRACT FROM AUTHOR]

Aluminum alloy car panels are difficult-to-form, complex components, with low formability at room temperature and high springback, and are easily scraped after forming. Although several advanced forming technologies have been developed to improve the formability of aluminum alloys, currently, there are no viable and cost-effective methods for the manufacture of high-quality aluminum alloy car panels. In this paper, a newly-developed flexible die forming approach called viscous pressure forming (VPF) is proposed to manufacture car hoods with scaled-down dimensions. The use of VPF technology provides decreased springback and improved surface quality, and manufacturing expense can be decreased by taking advantage of the characteristics of this technology. Both forming experiments and the finite element method (FEM) were adopted to investigate the forming of the panels and to verify the accuracy of the simulation model. The FEM was then used to further investigate key forming process parameters, such as sheet blank shape and blank holder force (BHF), particularly their role in the main defect of local wall thinning. Results indicated that the maximum thinning of a formed hood was 32.4 % when using an initial sheet blank under a constant BHF of 40 kN, while it decreased by 41.7 % when using the optimized sheet blank under variable BHF with segmented binders. This is mainly because material flow can be efficiently controlled under variable BHF. VPF technology combined with an appropriate sheet blank and variable BHF is an advantageous approach for manufacturing high-quality aluminum alloy car panels. [ABSTRACT FROM AUTHOR]

• A general form of kinematically admissible velocity field has been proposed for three-dimensional upset forging of elliptical disks and rings. • Three control functions with free parameters have been introduced to take consideration into sidewise spread, lateral bulging and movement of neutral surface in the upset forging of elliptical rings. • By changing the proposed three control functions, different forms of the assumed general kinematically admissible velocity fields can be derived for the upset forging of various shapes of disks and rings. • The forging load and deformed profiles of the billet can be calculated by minimizing the total plastic dissipation power using the upper-bound method and simplex algorithm. An analysis is carried out for three-dimensional upset forging of elliptical disks and rings based on the upper-bound method. A general form of kinematically admissible velocity field has been proposed by introducing three control functions, each of which contains a free parameter, thus the sidewise spread, lateral bulging along thickness direction as well as movement of neutral surface which occurs in the upset forging of elliptical rings can all be taken into consideration. It is shown that the kinematically admissible velocity fields proposed in previous references by other researchers can be obtained by choosing different control functions in the proposed general form. By optimizing the free parameters using the simplex algorithm in the upper-bound method, the forging load and deformed profiles of the billet can be calculated at certain stages of deformation. Calculation for different billet shapes and friction conditions have been conducted, the obtained theoretical results are in good agreement with the experimental results in previous studies and results obtained from finite element analysis carried out in this paper. Image, graphical abstract [ABSTRACT FROM AUTHOR]