Fiber migration in compression molded LFT-D materials: characterization proposal and first results

Fiber mass content (wf) is a key characteristic of long fiber reinforced thermoplastic (LFT) composites. It is defined in LFT-Direct (LFT-D) processing of continuous fiber rovings by the choice of processing parameters. However, in compression molding, the phenomenon of shear induced fiber migration, where wf does change across the flow path, was observed to varying degrees. A density-based method to quickly quantify wf in entire plates is presented and benchmarked against two approaches to thermographic analysis (TGA). The density-based approach was found to deviate from complete wf measurements by -0.4 % improving upon the state-of-the-art TGA results overestimating wf by 1.3 %. This work provides insight into the extent of the fiber migration for glass fiber (GF) reinforced polyamide 6 (PA6) LFT-D materials. For PA6 GF LFT-D with a wf = 33.0 % this deviation is at up to ±16.6 %. Different material combinations of PA6, polycarbonate and GF as well as CF are characterized at low and high wf. Fiber migration is present to various extends for all material combinations.