MORPHOLOGY OF BULK NYLON-6 SUBJECTED TO PLANE-STRAIN COMPRESSION

The mechanisms of deformation of nylon 6 in plane strain compression were elucidated by density measurements, differential scanning calorimetry, polarized light microscopy, X-ray diffraction, and X-ray diffraction pole figures. A deconvolution procedure for separating overlapping X-ray diffraction peaks and the amorphous halo was used to generate pole figures for the various alpha- and gamma-phase reflections exhibited by nylon 6. At compression ratios above 1.6, specimens experienced intense shear at -45-degrees and +45-degrees with respect to the flow direction. Shear bands were formed most frequently at interspherulitic boundaries. This shearing produced a small volume fraction of gamma-phase crystals in samples that originally contained only alpha crystallinity. The X-ray diffraction studies showed that gamma-phase crystals were oriented with their macro-molecular chains along the directions of shear bands. The alpha crystals of nylon 6 underwent extensive deterioration in compression by a chain slip mechanism along the (002) planes containing hydrogen bonds. Slip also caused the rotation of fragmented lamellae that lead, at high compression ratios, to a peculiar bifurcated orientation state resembling a twinned monocrystal.