Data InterpretationEffect of crystallinity level on the double yielding behavior of polyamide 6

A complex double yielding behavior is observed in the engineering stress-strain curves of injection molded specimens of polyamide 6 (PA6) under tensile loading, and a simple method is put forward to judge the apparentness of the double yielding process. By thermal treatment, the effect of the crystallinity level on the double yielding behavior is studied in some detail. The results show that the second yield stress becomes larger than the first after the thermal treatment, which is contrary to the case without thermal treatment. With the annealing time decreasing and the annealing temperature increasing, the percentage crystallinity becomes higher, and the second yield point is much more apparent with a decrease of crystallinity of the specimens. A possible crystallinity window may exist in double yielding behavior of PA6 material. These results indirectly show that the second yield point is not only associated with the deformation of the crystalline region.