Tensile failure mechanisms in additively manufactured brittle/ductile UV-curable resins and their nanocomposites with superior strength

Abstract

This paper investigates the mechanical performance of two different types of UV-cured resin types with significantly different mechanical responses when reinforced with nanoparticles having different characteristics. To achieve that, it employed stereolithography (SLA) by a desktop scale printer to manufacture tension and open-hole tension (OHT) tests specimens according to ASTM D638 testing standards. OHT samples contained a circular hole of 1 mm radius that was printed. A highly ductile resin grade and a brittle resin grade were employed as the matrix phase, whereas nano-scaled Al2O3 (metal oxide) and SiO2 particles were used as nano inclusions in 1 and 5 wt. %. A detailed fractographic analysis is then performed to identify and classify the active failure modes in specimen failure for each case. For ductile-grade resins, tensile failure primarily occurs due to CL(Core layer)-interface separation during yielding, followed by either interfacial crack propagation or tensile failure of building blocks (BB) forming the core layers. Notably, the D-SiO2-5 nanocomposite prevented CL-interface crack formation, allowing individual BB failure, while D-Al2O3 composites significantly increased tensile strength (60-70%) by resisting interface-related failure modes, making D-grade resins promising for further property tuning studies. The failure of brittle-grade nanocomposites was primarily driven by interfacial crack propagation between BBs and the coalescence of these cracks, with strengthening relying on nanoparticle-induced crack deflection without additional cracking. While B-Al2O3 composites achieved minor tensile strength increases (10-20%) through crack deflection, they introduced micro-cracks within BBs, whereas B-SiO2 nanocomposites exhibited the highest tensile strength without this issue, making them the most effective among the investigated cases. In overall, a comprehensive document discussing the development of strength and deformation in nanocomposite SLA samples is presented.