Double yielding behaviors of polyamide 6 and glass bead filled polyamide 6 composites

Double yield points before necking were observed in injection molded specimens of polyamide 6 (PA6) and PA6/glass bead (GB) composites under tensile loading. The results indicated that the unusual phenomenon was in correlation with the tensile velocity, the composition of the composites and the crystallinity of the matrix at different stages in the course of the tensile test. With higher tensile velocity, addition of glass beads and bead content increasing, the phenomenon of double yielding was depressed. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) studies indicated that the double yielding was only present in samples with less than 50% crystallinity and the crystalline structure and the size of crystallite of the samples in different tensile stages were also changed.