Orientation-dependent mechanical response of photopolymer resin specimens fabricated by masked stereolithography-based 3D printing

This study evaluates the mechanical performance of ASTM standard specimens fabricated using a masked stereolithography (MSLA) based 3D printer in various build orientations. MSLA 3D printers employ ultraviolet (UV) light transmitted through an LCD screen mask to selectively cure liquid photopolymer resin in a layer-by-layer manner. This layer-wise stacking was hypothesised to induce apparent mechanical anisotropy, a phenomenon commonly observed in fused deposition modelling (FDM). Unlike FDM, where interlayer bonding is primarily led by thermal diffusion and physical chain entanglement without chemical crosslinking, MSLA involves photopolymerization-driven network formation, offering fundamentally different interlayer interactions. To isolate the effect of build orientation, printing parameters such as layer thickness and exposure time were kept constant across all prints. Tensile, flexural, and compression specimens were fabricated using a PLA-polyol-derived photopolymer resin at seven orientations: 45°-45°, 45° vertical, 90° vertical, 90° horizontal, 45° horizontal, 0° dorsal, and 45° dorsal. Standard mechanical tests were conducted to evaluate the influence of build orientation on mechanical properties and failure behaviour. One-way analysis of variance (ANOVA) revealed a statistically significant dependence of compressive strength on build orientation, whereas tensile and flexural properties did not show statistically significant differences within the tested sample size. Fracture surface analysis using optical microscopy indicated predominantly brittle fracture behaviour across all specimens, with crack initiation consistently associated with printing-induced defects such as pores and interlayer voids. No clear macroscopic evidence of interlayer delamination or orientation-dependent fracture mechanisms was observed under the employed imaging conditions.