Tailoring mechanical properties of PμSL 3D-printed structures via size effect

Projection micro stereolithography (P μ SL) has emerged as a powerful three-dimensional (3D) printing technique for manufacturing polymer structures with micron-scale high resolution at high printing speed, which enables the production of customized 3D microlattices with feature sizes down to several microns. However, the mechanical properties of as-printed polymers were not systemically studied at the relevant length scales, especially when the feature sizes step into micron/sub-micron level, limiting its reliable performance prediction in micro/nanolattice and other metamaterial applications. In this work, we demonstrate that P μ SL-printed microfibers could become stronger and significantly more ductile with reduced size ranging from 20 μ m to 60 μ m, showing an obvious size-dependent mechanical behavior, in which the size decreases to 20 μ m with a fracture strain up to ∼100% and fracture strength up to ∼100 MPa. Such size effect enables the tailoring of the material strength and stiffness of P μ SL-printed microlattices over a broad range, allowing to fabricate the microlattice metamaterials with desired/tunable mechanical properties for various structural and functional applications. Projection micro stereolithography (P μ SL)-printed microfibers with diameters ranging from 20 μ m to 60 μ m shows size-dependent mechanical behavior. When diameter of microfibers decreases to 20 μ m, their fracture strains increase up to ∼100% and fracture strength up to ∼100 MPa. The size-dependent behavior of 3D-printed polymer can be mainly attributed to the surface effect and nonuniform distribution of defects. Strength and stiffness of P μ SL-printed microlattices can be therefore tailored over a broad range by utilized the microfiber size effect.