PSI - Issue 28

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

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reduction in strain-at-fracture of the F G specimens highlights that mechanical damage, such as scratching or cracking, may result in reduced performance of parts manufactured with MEAM by causing stress concentrations within the affected region, which could result in premature fracture.

Fig. 6. Mean UTS of different types of specimen. For F NG , F G and Z, the error bars indicate the range of values attained for six replicates of each specimen type. For bulk PLA, the error bar indicates the range of values identified from the literature [15,23–29].

3.4. 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 reduction in strain-at-fracture of the F G specimens highlights that mechanical damage, such as scratching or cracking, may result in reduced performance of parts manufactured with MEAM by causing stress concentrations within the affected region, which could result in premature fracture.

Fig. 7. Mean strain-at-fracture of different types of specimens. Error bars indicate the range of values attained for six replicates of each type. For bulk PLA, error bars indicate the range of values identified from the literature [15,23–29].