Fatigue and Tensile Behavior of 3D-Printed Polylactic Acid Matte: Effects of Infill Pattern and Density

Abstract

Abstract. This study systematically investigates the static tensile and cyclic tension-tension fatigue behavior of 3D-printed polylactic acid (PLA) to understand the effects of key printing parameters using fused deposition modeling (FDM). ASTM D638 Type IV dog-bone specimens were fabricated with varying infill orientations (0 deg/90 deg and +45 deg/−45 deg), infill densities (25%, 50%, 75%, and 100%), and build orientations (flat and edge). Uniaxial tensile tests and tension-tension fatigue tests (R = 0.1, 1 Hz) were conducted, with fatigue loading set at 90% of each configuration's ultimate tensile strength (UTS). Statistical analysis via three-way analysis of variance (ANOVA) revealed that while infill density was the dominant factor for static properties (UTS and Young's modulus), fatigue life was primarily governed by the interaction between build orientation and raster angle. The highest UTS (28.99 MPa) was achieved with a flat, 100% infill, +45 deg/−45 deg configuration. In contrast, the highest fatigue life (637.5 cycles) was observed in the flat, 25% infill, +45 deg/−45 deg configuration, which was over 14 times more durable than the worst-performing specimen (edge, 100% infill, 0 deg/90 deg). These findings demonstrate a critical trade-off between designing for static strength and designing for fatigue durability, providing essential guidelines for optimizing FDM-printed PLA in mechanically demanding applications and establishing a baseline for predictive fatigue modeling.