Fracture properties of quasi-isotropic carbon-fiber-reinforced polyamide 6 laminates with different crystal structure of polyamide 6 due to surface profiles of carbon fibers

In this study, the mechanical properties of quasi-isotropic composites were investigated. These composites comprised polyamide 6 (PA6) and two types of carbon fibers (CFs) (CFsmooth and CFrough), and showed comparable mechanical properties but different surface irregularities. The flexural strength and modulus of the two types of PA6/CF laminates were comparable, whereas their fracture patterns differed significantly. The falling weight impact test showed that the impact absorbed energy of the PA6/CFsmooth laminate was higher than that of the PA6/CFrough laminate, which caused extensive delamination and a large number of fiber fractures. In contrast, the low impact absorption energy of the PA6/CFrough laminate resulted in the lack of internal microfractures observed. A polarized micro-Raman study of PA6 in the vicinity of CFs showed that the failure behavior of PA6/CF laminates was related to the distribution of PA6 crystals oriented between CFs in the interlayer.