Conditioned 3D-printed polyamides for structural optimization : Establishing the material data to advance in AM utilization

Abstract: Polyamides are commonly used in additive manufacturing for final part production, but the material performance can be affected by environmental conditions. The purpose of this project was to evaluate the effects of moisture and temperature on 3D printed polyamides and how structural optimization can benefit from condition-specific data. Conditioned and unconditioned specimens were tensile tested in regions of -20 °C, 23 °C and 60 °C. Two techniques were evaluated; multi jet fusion and selective laser sintering, and mainly two polyamides; polyamide 11 and polyamide 12. Simulations with the obtained data were performed as well as conceptual structural optimization with the intent of optimizing for the intended end-use environment. Infrared thermography provided specimen temperatures as well as temperature and strain relations present during testing. The stress-strain curves obtained showed generally decreasing stiffness and strength with increasing moisture and temperature, albeit moisture in certain cases increased the tensile modulus at freezing temperatures. Temperature affected stiffness and strength more so than moisture. Polyamide 11 absorbed moisture at a higher rate than polyamide 12. The mechanical performance of laser-sintered polyamide 12 was superior, while laser-sintered polyamide 11 showed great elongation before breakage. Further investigation of polymer crystallinity could explain the behaviour of the 3D printed polyamides.