The distribution of fibre lengths in injection moulded polyamide composite components

Injection moulding of long glass fibre reinforced polyamide 6-6: guidelines to improve flexural properties

“…This segregation effect is visible for example in the beginning section of the part (Figure 12). These results confirm the observations made by other authors [15,16,17] on different long fibre reinforced thermoplastics injection-mouldings, such a fibre segregation being attributed to fibre breakage or pull-out at the interface between frozen and molten layers and subsequent sweeping along during the filling stage of the injection-moulding cycle. In summary, increasing the initial fibre fraction in the LFT pellets allows to improve the flexural mechanical properties due the globally higher fibre content.…”

“…This typical multi-layered structure also greatly influences the mechanical performances of the manufactured parts [10]. Finally, different authors have highlighted that the flow of the reinforced polymer melt in the mould cavity induces a concentration gradient of fibres along the flow axis, along the plate width and through the part thickness [5,6,[15][16][17]. This segregation effect is noticed for both short and long fibre reinforced thermoplastics.…”

“…The fibre accumulation (higher fibre contents) towards the end and in the centre (core) of the part have been attributed to the shear stresses at interfaces between the molten core and the frozen skin layers, which produce breakage of partially embedded fibres. The broken fibres are then pulled out and swept along by the melt flow and thus feed the next section of the part [15,16]. Kamal and Singh have also explained the fibre content decrease at the cavity edges by the peculiarities of the velocity flied at this location [18].…”

Injection moulding of long glass fiber reinforced polyamide 66: Processing conditions/microstructure/flexural properties relationship

“…10). Such a concentration gradient has also been observed by some authors both for short 6,21 and long fibers, 22 as mentioned in the introduction of this paper, and may be attributed to the sweeping toward the part's end of the fibers, which are partially embedded at the interface between the frozen and molten layers and broken by flow-induced shear stresses.…”

“…According to these authors, the shear flow favors the matrix migration to the cavity end section in the case of a fan gate part feeding. O'Reagan and Akay 22 have also shown a nonhomogeneous fiber content distribution on injection moulded 10 mm long fiber reinforced PA66. The volume fraction increases of about 4% along the plate axis, and the fiber content becomes lower in the skin layers and higher in the core layers.…”