Coil–stretch-like transition of elastic sheets in extensional flows

A thin soft sheet suspended in a fluid undergoing planar or biaxial flow displays a hysteretic transition between compact and stretched states as the flow strength changes. This transition is analogous to the “coil–stretch transition” observed for long linear polymers in these flows.

New Multistage Sheet-Bulk Metal Forming Process Using Oscillating Tools

A new sheet-bulk metal forming process for the production of bulk components out of a flat sheet has been developed. Superimposed oscillation has been applied to the new process. By this means, process limits regarding better mould filling were expanded, and forming forces could be reduced. In order to investigate the effects of superimposed oscillation on material behaviour, plane strain and ring compression tests were carried out. The superimposed oscillated plane strain compression test showed a reduction in biaxial flow stress and thus in plastic work. Furthermore, reduced friction and roughness were verified in ring compression tests using superimposed oscillation.

Determination of Uniaxial Flow Stress Curve Using Aero-Bulge Test for Very Thin Copper Sheet

Determination of the flow stress curve is an important step for precisely describing material behavior in Finite Element simulations. The flow stress curve is generally determined by taking a uniaxial tensile test as a standard. In the case of very thin sheet, since the fracture is generated at a low strain, there is not enough uniaxial data obtained to be applied in the FE simulation. The reason for this is that charactering plastic deformation at a large strain values by extrapolating a flow stress curve which is based on insufficient measurement data is highly susceptible to error. Bulge test is useful method for determining the equivalent biaxial flow stress curve up to a large strain. In this paper, the biaxial flow stresses curve for very thin copper sheet with thickness 35 and 50 μm were determined using the aero-bulge test. A new empirical model was derived for the estimation of the sheet thickness at the pole. After the compatibility between uniaxial and biaxial flow stresses was verified, the uniaxial flow stress curve was determined from the aero-bulge test using reverse engineering. The methodology of extrapolation of the flow stress curve at a large strain was finally proposed for application in FE simulations.