Mechanical Properties of 3D-Printed Multi-Material Polymeric Composites

With the rise in the capabilities and complexity of additive manufacturing, it has become increasingly challenging to assess the quality and strength of 3D-printed heterogeneous components with unknown interfacial properties. Yet, this assessment is required prior to use in real-world applications. This research seeks to measure and quantify 3D-printed multiextrusion coplanar interfaces, both single-material and multi-material, as it applies to particle-reinforced polymeric composites. In addition, it seeks to understand the effect of time and spatially-varying irradiance of UV light sources on the preferential breaking of tensile specimens. The UV LED sources were first characterized, and a stabilization time of 30 minutes was found to be suitable for both the cure depth LED spotlight and the UV LED array used to make tensile specimens. Furthermore, the normalized irradiance was measured to be 96.83% at the center of the LED array and 85.07% or less at a distance of 4 cm from the center of the array. Cure depth measurements were performed on two different formulations of photocurable glass-reinforced polymer slurries (60 vol.% solids loading) as a function of exposure time while accounting for the stabilization time. Tensile specimens were designed and manufactured via casting and vibration-assisted printing (VAP). The specimens were designed to receive 95% or more of the maximum normalized irradiance within their gauge lengths to promote uniform mechanical properties. The tensile strengths of the specimens were measured on a universal testing machine Density measurements were also obtained using Archimedes' method. Preferential breaking occurred outside of the center half of the gauge lengths for all sets of tensile specimens, with 25 of the 35 tested specimens exhibiting this behavior. This is believed to be due to the spatially-varying UV irradiance, in addition to stress concentrations and localized porosity that need to be isolated from the UV curing effects. Overall, it was found that the combined effects of spatially-varying irradiance, potential internal defects, and stress concentrations affected the ultimate tensile strength far more than the inclusion of a multi-extrusion coplanar interface. Future work is necessary to better mitigate stress concentrations and porosity if the mechanical properties of multi-extrusion, multi-material coplanar interfaces are to measured and characterized.