BRIEF PAPER: EVALUATING EFFECTS OF ULTRAVIOLET EXPOSURE STRATEGIES ON MULTI-MATERIAL INTERFACES IN DIRECT INK WRITE ADDITIVE MANUFACTURING

Direct Ink Write (DIW) is a material extrusion additive manufacturing (AM) technique in which viscous inks are extruded through a nozzle and selectively patterned in a layer-wise manner to create three-dimensional parts. In UV-assisted DIW, ultraviolet light is used to quickly cure the extruded bead to limit spreading, and to induce sufficient strength to support subsequent layers. Printing and UV curing multiple inks within the same layer enables the fabrication of multi-material components; however, it also creates distinct interfaces in the printed part, which can become regions of failure after undergoing cyclic loading and unloading. The aim of this work is to understand how UV irradiance, UV exposure, and the sequence of UV dosing affects the resultant multi-material part's mechanical properties and failure mode (i.e., whether it fails at the multi-material interface or inside the weaker material). To understand the effect of UV irradiance, UV exposure, and sequence of UV dosing on the properties of the multi-material parts, we explore two tool-pathing strategies on a two-component tensile specimen printed in the XY plane using photocurable urethane acrylate resins: (1) 'Ex-situ' curing strategy applies UV irradiation across the entire layer following deposition of both materials; (2) 'Alternate' UV curing applies UV irradiation following deposition of each individual material. Multi-material specimens printed using the 'ex-situ' UV cure strategy consistently failed within the gauge region irrespective of the UV irradiance and exposure, and also exhibited the highest adhesion strength. However, for specimens fabricated via 'alternate' UV cure strategy, the failure mode (within gauge or at the interface) was found to be a function of cure depth, UV irradiance, and UV exposure. The findings will help inform the process with relevant processing parameters - amount of UV irradiance, UV exposure, sequence of UV cure, and the tool-pathing strategy required to print multi-material parts with desired and tunable properties and performance.