Plane strain compression in a channel die is kinematically very similar to drawing; however, the possibility of void formation is limited due to a compressive component of stress. In drawing, voids were detected by small-angle X-ray scattering (SAXS) and density measurements in poly(methylene oxide) (POM), polypropylene (PP), and high-density polyethylene (HDPE), but no voiding was found in polyamide 6 (PA 6), low-density polyethylenes (LDPEs), and ethylene-octene copolymer (EOC). The slope and shape of the initial elastic part of true stress-true strain curves are similar in tension and in channel die compression. When drawn samples of POM, PP, HDPE, and PA 6 already show yielding, the channel die compressed samples still undergo elastic deformation to a much larger deformation and respond with a much larger stress. Channel die compressed POM, PP, HDPE, and PA 6 exhibit strong and rapid strain hardening up to 400 MPa in contrast to their behavior in tension. The difference in strain hardening is related to preservation of chain entanglement density in channel die compression and disentanglement in tensile drawing. True stress-true strain curves for polymers having crystals with low plastic resistance and not cavitating are very similar in channel die compression and in tension. In tensile drawing there is a competition between cavitation and activation of crystal plasticity. Cavitation occurs in polymers with crystals of higher plastic resistance, while plastic deformation of crystals in polymers with crystals of lower plastic resistance. The necessary conditions for cavitation and for plastic deformation of crystal are defined. They explain why the cavitation is observed in POM, PP, and HDPE but not in LDPEs. In PA 6 negative pressure causes cavitation but the cavities, due to their small sizes and healing action of surface tension, are unstable, close quickly, but leave the traces of a structural damage. A model of plastic deformation of crystalline polymers accounting for cavitation is outlined.

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The process of cavitation during tensile deformation of polypropylene was studied. It was shown that in injection-molded polypropylene samples cavities appear in the center of a sample shortly before yielding. With increasing deformation the cavities change their size, number, and orientation from elongated perpendicular to parallel to deformation. The cavitation process is visible also as a rapid increase of volume of deformed material. The cavitation could be suppressed by changing internal morphology of polypropylene by fast cooling. The samples prepared by compression molding followed by quenching, with less perfect crystals, were able to deform by plastic deformation of crystals without cavitation. However, for faster draw rate the cavitation in amorphous phase was preferred again due to stronger response of crystals.