Fracture toughness characterization of 3D-printed advanced structured specimens by digital image correlation

We use digital image correlation to investigate the influence of filament deposition direction on the fracture toughness of single edge notch bend specimens manufactured by fused filament fabrication. Two methods of filament deposition were tested. The first one consists of putting the filaments in (+/- 45 degrees) crisscross pattern, while in the second method, the filaments around the notch tip were oriented according to the principal stress direction. Three points bending tests were carried out on these samples. The onset of the crack growth was detected by tracking the crack opening displacement. The displacement field in the notch tip vicinity has been employed to reveal the notch stress intensity factor using William's equation specific for wide V notch. To that end, the non-linear least-square method has been used to fit the coefficient of William's equation. The predicted and measured displacement fields were found to be consistent with a coefficient of determination close to 1. Thus, the linear elastic fracture mechanics assumption is valid in this case. The results show that the filament optimization leads to an improvement in the fracture toughness of the sample of about 10% in this case. The kinked crack observed in the classic crisscross sample indicates that the crack growth is driven by the weak interface between filaments. However, the crack extension in the optimized sample is driven by the remote stress.