Co-authors​ :

 Klaas PETERS (CANADA), Nicholas ELDERFIELD (CANADA), Les Joseph SUDAK (CANADA), Joanna WONG (CANADA) 

Continuous fiber-reinforced thermoplastic composites manufactured via material extrusion (MEX)-based additive manufacturing processes have typically suffered from poor interlaminar bonding and high void contents due to incomplete consolidation combined with decompaction of the fiber network during deposition. To counter these issues, discrete in-situ consolidation (DISC), a process that uses a flat heated tool to apply local consolidation pressure along the length of each bead after deposition, was previously introduced [1]. It has been observed that DISC significantly spreads the fiber network from its initially deposited state [2], but the behaviour of this fiber network rearrangement is not yet well understood. Here, micro-computed tomography (μ-CT) and optical microscopy techniques are used to examine the redistribution of the fibers during the deposition and consolidation processes. Additionally, a process parameter study is performed to investigate the effects of consolidation pressure, temperature, and speed. It is observed that the 90° angle bend that occurs in the filament as it exits the deposition nozzle causes twisting and non-uniform buckling of the fiber network due to path length inequalities. The lenticular cross-sectional geometry of the deposited bead (Figure 1a) is a result of this fiber network rearrangement. Applying the DISC process to this initial cross-sectional geometry causes the fiber network to spread via mechanisms of non-uniform translation and localized twisting. Bead cross-sectional geometry is found to be relatively insensitive to consolidation pressure, this is likely due to the generation of compression resistant fiber crossings via network twisting. Conversely, decreasing consolidation speed and increasing temperature is shown to result in increased fiber network spreading and matrix squeeze-out (Figure 1b and c). Furthermore, residual stresses caused by fiber network rearrangements and thermal history result in varying levels of transverse warping of the bead (Figure 1c). This investigation on the morphological evolution of the fiber network during DISC processing provides insights into areas of improvement that need to be addressed in MEX-based processes.