Increased fracture toughness of additively manufactured amorphous thermoplastics via thermal annealing. (23rd May 2018) - Hart, Kevin R.
Abstract: Polymeric structures fabricated using Fused Filament Fabrication (FFF) suffer from poor inter-laminar fracture toughness. As a result, these materials exhibit only a fraction of the mechanical performance of those manufactured through more traditional means. Here we show that thermal annealing of confined structures manufactured using the FFF technique dramatically increases their inter-laminar toughness. Single Edge Notch Bend (SENB) fracture specimens made from acrylonitrile-butadiene-styrene (ABS) feedstock were isothermally heated in a supporting fixture, post-manufacture, across a range of times and temperatures. Fracture testing was then used to quantify the changes in inter-laminar toughness offered by annealing through measurements of the Mode I critical elastic-plastic strain energy release rate, J Ic . Under the most aggressive annealing conditions, the inter-laminar toughness increased by more than 2700% over the non-annealed baseline material. Void migration and aggregation during the annealing process was analyzed using X-ray tomography and provides insight into the toughening mechanisms. Time-scales of reptation and polymer mobility at the interface during annealing are also modeled and agree with fracture experiments. Graphical abstract: Image 1 Highlights: Compliance check fracture testing used to evaluate J Ic of 3D printed polymers. Up to 27x increase in fracture toughness achieved via thermal annealing. Void migration and coalescence during annealing observed via X-Ray tomography. Rheology performed to quantify time scales for reptation and intimate contact. Results suggest that intimate contact is poor in as-printed materials.