Experimental and Numerical Investigation of the Influence of Crack Front Orientation in Mode 1 Plane Strain Fracture Toughness of a Vero Material System via Poly Jet Additive Manufacturing

Abstract

Polyjet printing, a multi-jet Additive Manufacturing technique, has been used to fabricate 3-Dimensional structures for various polymeric material systems. This technique uses a layer-by-layer deposition method and allows for the fabrication of parts with different material compositions and varying thermomechanical properties. The current research investigates the influence of process-induced variation on Mode 1(K1C) fracture toughness of the Vero material system. Compact Tension (C-T) specimens with crack fronts parallel and perpendicular to the print direction were fabricated. The orientation of the crack front relative to the print and build directions influenced the Mode I fracture toughness values. When the crack front was parallel to the print plane, K1C decreased by 49.54%, G1C decreased by 41.56%, and peak load intensity decreased by 52.76% compared to the perpendicular crack front orientation. C-T samples were modeled in CAD to correlate with the experimental results and then analyzed in the Ansys workbench. The FEA yielded a Mode 1 fracture toughness value of 2.48 MPa m0.5 for a perpendicular configuration of the crack front and a fracture toughness value of 1.15 MPa m0.5 for a parallel configuration of the crack front. The Representative Volume Element method is used for a composite containing the Vero material system as a matrix and carbon nanofibers as reinforcement. Carbon nanofibers are integrated using a customized material configuration, and their influence on fracture is studied. A tailored network perpendicular to the crack front in a 3D printed C-T specimen stiffens the specimen. In contrast, a tailored network parallel to the crack front has a relaxing impact, indicating that an additively created part may be prone to softening under certain conditions.