I. Yield in melt extension
As a second theoretical prediction from our new model that recognizes the important destructive role of residual elastic stress due to the retraction force in each deformed chain, we set out to look for breakup of a stretched filament due to the retraction force that produces chain disentanglement.
shows yielding of SBR filaments due to the elastic retraction force after extended to two different levels of stretching. See our recent publications publications (PDF PRL, PDF JOR).
illustrates the essence of the discovered elastic breakup upon shear cessation can be demonstrated in stretching a piece of rubber band and subsequent loss of grab.
J.Shear strain localization at die entry during extrusion
The so called gross melt fracture arises from unsteady strain localization in the die entrance region. The PTV observation shows how the state of chain entanglement is spatially varying when the resting entangled melts are forced to enter a narrow die. The shear banding indicates that the deformation field cannot be depicted by a constitutive equation whose materials parameters are constant spatially.
Movie 19 shows the entry deformation of a polybutadiene melt of Mw = 200 kg/mol above the stick-slip transition.
Movie 20 shows both wall slip in the reservoir and internal slip (bulk strain localization) of a SBR of Mw = 616 kg/mol.