recoverable shear

recoverable shear

[ri′kəv·rə·bəl ′shir]
(fluid mechanics)
Measure of the elastic content of a fluid, related to elastic recovery (mechanicallike property of elastic recoil); found in unvulcanized, unfilled natural rubber, and certain polymer solutions, soap gels, and biological fluids.
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Differences in the polymer architecture directly impact processability and flow behavior, such as flow rate, die swell, melt stability, recoverable shear and internal stresses in blow molding, injection molding, sheet forming, cable jacket extrusion, among other production processes (refs.
Other elastic parameters such as recoverable shear strain ([[gamma].sub.R]) or the Weissenberg number can be given by the relation (23), (25):
Recoverable shear strain ([[gamma].sub.R]) or Weisscnberg number vs.
Melt elasticity can also be determined by the recoverable shear strain [7] according to Eq.
Gullet and Seriai (2) stated that the swelling phenomenon is mainly due to the recoverable elongational strain induced by the converging flow at the die entrance, as well as by recoverable shear strain originating within the die.
(44) on blown polyethylene (PE) films has found that the total haze percent exhibited a complex parabolic relationship with the logarithm of the recoverable shear strain parameter.
Currently used criteria for the onset of gross melt fracture (OGMF) are based mainly on parameters associated with capillary flow, i.e., the apparent wall shear rate, the shear stress at the wall, or the recoverable shear strain.
The recoverable shear compliance versus blend composition for the stabilized blends is shown in Fig.
It is a measure of stored energy and may be characterized by quantities such as the "steady-state shear compliance" or "recoverable shear strain." Changes in "melt elasticity" have been related to changes in the values of viscoelastic functions such as normal stress differences, storage modulus and parameters of practical importance such as die (extrudate) swell [51-53], the latter representing a measure of recovery of stored elastic energy.
based on these studies, a hypothesis may be formulated that the melt fracture behavior of a polymer is affected by a balance between its viscous (viscosity) and elastic properties (recoverable shear).
Although it is understood that elastic behavior involves no dissipation of energy and no time-dependence, the term has been considered to be synonymous or has been related to viscoelastic functions such as normal stress differences and storage modulus; also, to extensional viscosity, recoverable shear strain, entrance-exit pressure drop (Bagley correction) (2-4), and parameters of practical importance in polymer processing such as extrudate swell and melt strength (5, 6).
For long dies Tanner (23, 27), showed that the swell is a function of the recoverable shear [[Gamma].sub.[infinity]] [approximately equal to] [N.sub.1]/(2[Tau]):
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