Interlayer weakness limits the mechanical performance of material extrusion additive manufacturing (MEAM) parts. Interlayer behaviour is governed by two mechanisms: the quality of bonding at welded regions and naturally occurring interface notches formed by the extrudate’s geometry. This study aims to investigate the interplay between these mechanisms in polyethylene terephthalate glycol parts produced via fused granular fabrication.
Layer height was deliberately varied to generate a spectrum of notch severities and interlayer bonding qualities. Samples were tested in the transverse direction using tensile testing coupled with digital image correlation to quantify strain localization and failure mechanisms.
Results show that increasing layer height amplifies notch severity while enhancing interlayer bonding. While fracture consistently initiates at interface notches, the resulting strength reduction depends on the interplay between notch geometry and bonding quality. A less severe notch can cause greater strength loss if the interface bonding is weaker, revealing a competing effect which leads to an optimal condition where notch severity and bonding are balanced. Removal of interface notches through surface machining and comparison with as-printed samples reveal that ultimate tensile strength is largely restored, whereas recovery of strain at break remains incomplete in samples with weaker bonding, suggesting that conventional strength-based criteria may overestimate full interlayer bonding.
These findings demonstrate that interface notch geometry and interlayer bonding exert coupled effects on interlayer mechanical behaviour. Recognizing this interplay is essential for accurately interpreting mechanical performance in MEAM parts and for enabling reliable modeling and process optimization.
