Interface behavior of multi-material polymeric structures manufactured by material jetting

Multi-material three-dimensional (3D) printing methods, like Polyjet™, can produce parts of different materials within a single print. Interfaces with unknown adhesion strength and mixing are formed in these parts and there is currently no established protocol to characterize interface cohesion. Characterization methods that address interface cohesion are needed as delamination at interfaces is a concern when printed parts are used. In this article, a method of characterizing the bulk and interfacial performance of multi-material 3D printed parts is presented. To test limiting cases, designed test parts exhibited an interface between a highly rigid and highly compliant material. Mechanical behavior of the interface between rigid thermoplastic (VeroUltra™) and compliant elastomeric (Elastico™) materials was observed through compressive loading with parts built in two configurations. Multi-material specimens were designed such that load would be applied either normal or parallel to the interface. It was observed that the multi-material parts did not fail through delamination in either loading configuration. Fracture occurred either in the rigid VeroUltra™ region between print layers or within the compliant Elastico™ region, with the interface remaining intact. Optical microscopy revealed a diffuse interface between the rigid and compliant materials measuring ~ 100 microns, indicating that interface mixing at the microscale may aid in prevention of delamination at the interface.