Mechanical Properties of Interfaces in Inkjet 3D Printed Single- and Multi-Material Parts

Material jetting, commonly referred to as (inkjet) 3D printing, of polymers offers multiple advantages over other processes, such as a high resolution and multi-material capability. Most published research investigates the macroscopic properties of inkjet printed parts. This work studies the mechanical properties on the micron scale, in which metallurgical sample preparation and nanoindentation have proved to be appropriate tools for investigating parts with stiffnesses ranging over three orders of magnitude. First, interfaces in single-material parts that are created through jetting of material in layers and through nozzles are investigated. Visual inspections of the samples show a uniform layer thickness for rigid materials and irregular layers for flexible materials. The hardness and modulus near the layer interfaces show similar values to those further away, indicating a uniform curing throughout the layers. Second, the on-the-fly material mixing of the printer is investigated and shows a dominating base material with elongated features induced from the secondary material. This shows that the mixing is an introduction of particles, rather than molecular mixing. As a consequence, the local material characteristics differ strongly from the global properties of printed structures. Third, interfaces of dissimilar materials are investigated and show a smooth transition in the mechanical properties from one material to another.