Interface fracture characterization of 3D-printed rigid/flexible dissimilar polymers

Interface fracture in additively manufactured multi-materials is a leading cause of failure and it is critical to understand and characterize it. Here a simple methodology is presented to quantify the interfacial failure in additively manufactured acrylonitrile butadiene styrene (ABS) and thermoplastic polyurethane (TPU) bimaterials. Double cantilever beam (DCB) specimens were 3D-printed where a TPU layer is sandwiched between two ABS substrates. The printed specimens were loaded under mode I until failure, and the crack initiation load was identified using a verified stiffness drop method. This method overcame the significant crack blunting issues in visual crack detection methods, caused by the TPU inelastic deformation. A finite element model was used to obtain the J-integral fracture energy values. The measured fracture energy presented the adhesion strength between ABS and TPU, as the failure was purely adhesive in nature. The effect of the specimen geometry on the ABS/TPU interface fracture energy was then analyzed. It was found that the fracture energy is independent of the precrack length, but it is strongly affected by the TPU layer thickness, which was related to enlargement of the damage zone ahead of crack tip. This methodology provides a simple route to characterize interfacial adhesion in various additively manufactured multi-materials.