Flow instabilities occur in a variety of commercial polymer processing operations including extrusion, film blowing, fiber spinning and coating. During the extrusion of molten polymer through capillary or slit die geometries, a transition from a smooth surface to a nearly periodic ridge-like surface distortion has been observed at a critical shear rate or wall shear stress (Petrie and Denn 1976...

An investigation has been carried out into the microstructures developed during the early stages of equal channel angular extrusion (ECAE) in a polycrystalline single-phase Al-0.13Mg alloy, with emphasis on the substructural alignment with respect to the die geometry and the crystallographic slip systems, which is essentially related to the grain refinement and texture development during deform...

Micromechanic theory of fatigue crack initiation by Lin and his associates is reviewed. Intrusions and extrusions have been observed in fatigue specimens. An initial stress field favorable for the growth of extrusion or intrusion can be produced by arrays of dislocation dipoles as shown by Lin (1969). These dipoles cause an initial tensile strain giving an elongation which is called the static ...

In this paper, a generalized expression for the flow field in axisymmetric extrusion process is suggested to be valid for any dies and the boundary shapes of the plastic deformation zone. The general power terms are derived and the extrusion force is calculated by applying upper bound technique for a streamlined die shape and exponential functions for shear boundaries. It is shown that assuming...

The shear behavior of polymers obtained by means of devices such as capillary and cone-and-plate rheometers is commonly used to assess their processing performance and as a characterization tool. However, the number of instances when two polymers have the same shear properties but perform differently during certain types of processing operations (e.g. film blowing and sheet extrusion) indicate ...

Many fabrication processes for polymeric objects include melt extrusion, in which the molten polymer is conveyed by a ram or a screw and the melt is then forced through a shaping die in continuous processing or into a mold for the manufacture of discrete molded parts. The properties of the fabricated solid object, including morphology developed during cooling and solidification, depend in part ...

dehbid mylonite nappes associated with the tutak gneiss dome as the zagros hinterland involved-basement window in the zagros orogenic belt has significant components of dextral sense of shear along the mylonite nappes and are related to the high proportion of simple shear relative to pure shear deformation. kinematic vorticity analysis (wk) was made in order to determination of relative amounts...

Polymer – surface interactions strongly influence many important industrial and rheological flows. In particular, polymer melts and solutions slip against the surface; this has long been associated with sharkskin and spurt in extrusion, and recent experimental observations suggest that slip also plays a role in the formation of enhanced concentration fluctuations in entangled polymer solutions....

Semisolid powder processing (SPP) is a promising approach for near net-shape forming of features in micro/meso-scale. By combining the concept of forming in the semisolid state and conventional powder metallurgy, SPP provides a novel solution to various processing and materials engineering challenges faced in micromanufacturing. Replacing bulk materials with powdered materials adds a new dimens...

3.1 Abstract Rheological behavior of reactively extruded starch-PCL nanocomposite blends was evaluated in an off-line capillary rheometer. Power law models for blends with different nanoclay volume fractions were developed using appropriate correction factors. Consistency coefficients K for blends containing starch were significantly higher than 100% PCL. Starch-PCL nanocomposite blends showed ...