A statistical framework proposed for estimating fracture resistance of additively manufactured PLA components considering crack tip plasticity effects

Abstract

This study presents a statistical framework for assessing the fracture behavior of Polylactic Acid (PLA) specimens fabricated using the Fused Filament Fabrication (FFF) technique. Specifically, the model is developed to predict the fracture load of a specimen under predominant bending conditions, based on the tensile properties of the base material and the fracture resistance of a pre-cracked specimen subjected to predominantly tensile loading. To achieve this, tensile tests were first conducted on dogbone specimens, and the corresponding material properties were determined using the Digital Image Correlation (DIC) technique. Fracture tests were then performed on pre-cracked Semi-Circular Bending (SCB) and Single Edge Notched Tension (SENT) specimens to collect the fracture data. These experiments were conducted at two environmental temperatures (-10 degrees C and 25 degrees C) to further assess the efficacy of the proposed framework in predicting fracture loads under different levels of plasticity. The results of fracture tests were statistically analyzed using the Weibull model. Fracture mechanics criteria within the Theory of Critical Distances (TCD), especially the Point Method (PM) and the Line Method (LM), were then combined with the Weibull model to predict the fracture loads of target specimens (SCBs). Additionally, the Fictitious Material Concept (FMC) was employed to account for the plastic deformation around the crack tip in the SENT specimens. The results show that the proposed framework provides accurate predictions under both environmental conditions, with maximum discrepancy of 6.3 % at -10 degrees C and 2.7 % at 25 degrees C. Beyond the primary objective, this study also investigates the geometry effects on fracture behavior of the tested specimens. This analysis was conducted by examining the fracture surfaces and performing elastic-plastic Finite Element (FE) analyses to compare the size of their plastic zones. The findings from this investigation indicate that SENT specimens exhibited more pronounced plastic deformation compared to SCB counterparts.