PSI - Issue 28

6

James Allum et al. / Procedia Structural Integrity 28 (2020) 591–601 J.Allum et al. / Structural Integrity Procedia 00 (2019) 000–000

596

Fig. 4. The change of load-bearing capacity with mean load-bearing area of all specimens, with a linear trend line added. Two specimens (one F G and other Z) are highlighted with a black circle as they share similar load-bearing area and load-bearing capacity but differ in terms of their extruded-filament orientations.

Fig. 5. Micrographs of specimen types F NG (a), F G (b), and Z (c) demonstrating the cross-sectional filament-scale features, including shaded regions indicating the manually introduced groove in F G (b) and the natural groove in Z (c). F NG (a) and F G (b) share the same extruded-filament orientation (normal to the micrograph), so the extruded filament outlines are visible, whereas in the Z specimen (c), extruded filaments are oriented parallel to the plane of the micrograph; hence, the top of only a single extruded filament is observed. 3.3. Strain-at-fracture As with the UTS, the strain-at-fracture was calculated for each specimen. The mean strain-at-fracture of the F NG specimens was 0.044 (Fig. 7). The presence of manually applied grooves apparently had a significant impact on the F G specimen, with a reduction in mean strain-at-fracture by nearly half, to 0.026. The Z specimen had similar properties to F G , with a mean value of 0.021. The similarity between F G and Z, and their dissimilarity to the F NG , indicates that the introduction of manually applied grooves reduced the performance of the F G specimens to the extent that their characteristics resembled the Z specimens. This confirms that the geometry (presence of filament-scale grooves) at the interface is responsible for the anisotropic mechanical behaviour rather than any discrepancy in material properties caused by bonding. The inclusion of strain data for bulk PLA (Fig. 7) reported in the literature [15,23–29] demonstrates that all specimens fracture within the strain-at-fracture range identified for bulk PLA. The