Fracture load predictions in 3D-printed ASA and carbon-fiber reinforced ASA notched specimens by using the ASED criterion

Abstract

Additive manufacturing (AM) is a versatile fabrication technology capable of producing intricate geometries from diverse materials, including polymers, metals, ceramics, and composites. This research focuses on fused deposition modelling (FDM), a prominent AM technique. FDM involves the extrusion of a molten filament through a heated nozzle, which is then deposited layer-by-layer onto a build platform to construct the final component [1]. Historically, FDM has been predominantly utilized for prototyping rather than for the production of load-bearing structural components. This is primarily due to the generally lower mechanical properties of 3D-printed components compared to those achieved via conventional methods such as injection molding or extrusion. Consequently, significant research efforts over the past years have aimed to clarify the correlation between FDM process parameters and resulting mechanical properties of different 3D-printed polymers (e.g., [2]–[10]). Complex geometries inherent to 3D-printed components often contain various stress risers. These can originate from manufacturing defects (e.g., poor surface finish, porosity), operational damage, or intrinsic design features (e.g., notches, holes, corners). Assessing the structural integrity of components with such stress risers necessitates specialized analytical approaches that extend beyond conventional fracture mechanics. It has been widely demonstrated that non-sharp stress risers, commonly referred to as notches, induce an apparent fracture toughness in the material that typically exceeds the intrinsic fracture toughness measured using cracked specimens. To account for this "notch effect", various methodologies have been developed, notably the Theory of Critical Distances [11] or the Average Strain Energy Density (ASED) criterion [12], in which this work is focused. The ASED criterion has been extensively validated across a range of brittle and quasi-brittle materials under various loading conditions (e.g., [12]–[16]). This methodology has been applied to 3D-printed polymers [17]–[20]. However, to the best of the author's knowledge, it has not yet been applied to 3D-printed acrylonitrile-styrene-acrylate polymer. Subsequently, linear elastic Finite Element (FE) analyses are conducted to delineate the resultant stress fields. Therefore, this Master Thesis presents a fracture analysis of 3D-printed pristine acrylonitrile-styrene-acrylate (ASA) and carbon-fiber reinforced acrylonitrile-styrene-acrylate specimens containing U-notches, utilizing the ASED criterion.