Mechanical Performance and Structural Integrity of 3D-Printed Polylactic Acid in Tensile Testing: Influence of Hole Fabrication Technique and Process Parameters

Abstract

This study presents a systematic investigation of the tensile behavior of FFF-printed PLA specimens, with a specific emphasis on the role of hole fabrication methods—post-drilled versus integrated printed holes—on structural integrity. Unlike prior works that primarily addressed raster orientation and infill effects, this research isolates the influence of hole manufacturing techniques under standardized ASTM D638 and D5766 testing. Stress concentration factors (Kt) were calculated using classical analytical expressions, and their limitations for anisotropic FFF parts are acknowledged and further discussed in the Results and Discussion section. The results revealed that, although raster angle and infill density affected overall strength, the decisive factor was the method of hole generation: post-drilled holes consistently outperformed printed-hole counterparts in tensile resistance and failure behavior. Microscopic analysis confirmed that printed holes introduced interlayer misalignment and shell–infill discontinuities, accelerating crack initiation. These findings demonstrate that hole geometry alone is insufficient to guarantee mechanical reliability, and that the fabrication method of stress concentrators must be considered a critical design parameter in FFF applications.