Interlaminar strength in large‐scale additive manufacturing of slow crystallizing polyaryletherketone carbon composites

Abstract

Fusion bonding theory is applied to the additive manufacturing process to predict the strength developed across the interface between the deposited layers in material extrusion based large‐scale additive manufacturing. Relaxation times were determined through rheology investigations of the neat polymers and were extrapolated across the entire process temperature range to estimate the required welding times for optimal bond formation. For the calculation of bond formation during cooling from the melt, the semicrystalline polyaryletherketone is considered amorphous until the onset of crystallization which is determined by recreating the process thermal history in DSC measurements. A significant improvement in bond development during additive manufacturing is achieved through the use of specifically designed polymers with slower crystallization kinetics. Both in small‐scale additive manufacturing, achieving full bonding, and in large‐scale additive manufacturing, they achieve significantly higher interlaminar strength than the reference material, validated by three‐point bending. A very good match between the estimated degree of bonding and the tested strength of upright printed specimens in three‐point bending was found. While the fusion bonding model calculates a degree of bonding of 42.07%, mechanical testing showed 42.54% of the bulk flexural strength. The study outlines a procedure to evaluate materials for additive manufacturing by material extrusion based on small material samples to shorten and improve the process development. © 2020 The Authors. Polymer International published by John Wiley & Sons Ltd on behalf of Society of Industrial Chemistry

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“…As this time frame for the chosen nozzle is between 0.075 and 0.013 s for slow and fast traversing speeds, the assumption of intimate contact occurring instantaneously is made. [ 45 ] Therefore, the degree of intimate contact can be reduced to where is the volume fraction of voids at the polymer interface. With the assumption of no in intimate contact over time: .…”

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