Fiber distribution of long fiber reinforced polyamide and effect of fiber orientation on mechanical behavior

The objective of this paper is to research fiber distribution and mechanical behavior (tensile, flexural, and Charpy impact properties) of long fiber reinforced thermoplastic (LFT) plates made by injection molding. The plates were made of long glass fiber reinforced polyamide 6,6 granules and injected using two types of molds, including center-gated and end-gated injecting modes, to obtain different fiber orientation state. In addition, end-gated plate was cut along three directions (0 degrees/45 degrees/90 degrees) to main flow path, in order to experimentally investigate the effects of fiber orientation on mechanical properties. It is found that there is skin-shell-transition-core structure across thickness of plate, resulted from different fiber orientation. Furthermore, end-gated plate has more obvious fiber orientation at shell and core regions than center-gated plate. The experimental results demonstrate that fiber orientation has significant effects on modulus, strength, toughness, and full-field strain evolution. Tensile and flexural properties decrease by over 50%, as the cutting angle with respect to flow direction changes from 0 degrees to 90 degrees in end-gated plate. Moreover, unnotched and notched strength drops by 66% and 33%, respectively, from 0 degrees to 90 degrees off-axis angle. These results show apparent mechanical anisotropy of LFT. Shell-core structure also significantly influences strain distribution and fracture morphology.