Morphological alteration and strength of polyamide 6 subjected to high plane-strain compression

The present study attempts to find out the similarity and dissimilarity in structure and mechanical properties of PA6 deformed by channel die compression and by a new method combining the compression and rolling and which is known as rolling with side constraints. The resulting materials were characterized by texture investigation by WAXD and SAXS while mechanical properties by tensile tests and DMTA. The fractured surfaces of rolled samples at high deformation ratio was visualized by using SEM. The present study indicates that the crystalline texture and lamellar structure of PA6 samples after the deformation by the two methods are similar at the corresponding strains, some differences develop at a hardening stage at which the time allowed for creep under load plays an important role. Above the compression ratio of 1.8 an intense shear banding occurs at ±45°. With further deformation to compression ratio of 4.0 the shear band planes are tilted 20-26° from the flow direction only. In association with the appearance of shear bands a fraction of γ-form crystals is generated which are oriented with macromolecular chain axes along shear planes and in the direction of shear. Those γ-crystals are misaligned with α-crystals that are deformed and oriented along the flow direction. The bifurcation of orientation of α- and γ-crystals is a reason of a unique fracture behavior of highly oriented samples: fracture occurs along shear planes with γ-crystals and fracture surfaces are nearly flat.