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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influence. This was supported by the linear trend observed relating the load-bearing capacity with the load-bearing area for all specimen types, irrespective of the orientation of their extruded filaments or the inclusion (or lack of) filament-scale grooves.

Fig. 9. Fractographic micrographs of F NG (a), F G (c) and Z (d) specimens. Shear lips in F NG (a) are labelled.

4. Conclusions This study demonstrated that the interface between layers in MEAM has strength equivalent to that of the bulk polymer, and that such properties are readily attainable by use of common manufacturing parameters. A reduced load bearing capacity when loading in Z direction, normal to the direction of the extruded filaments, was caused by the filament-scale geometric grooves that occur naturally at the interface in MEAM. These grooves resulted in a reduction of the load-bearing area. This was confirmed by the introduction of manual grooves into specimens that were tested longitudinally along the extruded filaments, which were found to perform almost identically to the Z specimens, having reduced mechanical properties compared to longitudinally tested specimens without grooves. The use of a specially developed tensile specimen enabled improved fundamental analysis of fracture characteristics and microscopic measurement, at the scale of individual extruded filaments. Development of specimens formed by individual extruded filaments was critical for gaining this new understanding; investigation of role of grooves would be impossible with larger specimens produced with multiple filaments through their thickness. Fractography supported the mechanical characterisation, indicating the presence of bulk material in all tested specimens and the importance of the microscale geometry for plastic deformation and strain-at-fracture. 5. Future Work As demonstrated by the findings in this study, the future work should consider ways of addressing the mechanical limitations caused by reduced load-bearing area in the interfacial region between layers as this is the predominant cause of interlayer weakness. The authors addressed this by developing a novel ZigZagZ nonplanar deposition toolpath [30], which eliminates planar interfaces and results in significant mechanical improvement. The present study illustrated the benefits of reducing specimen complexity and increasing control of deposition to support the improved specimen design for fundamental mechanical characterization; future studies should consider these potential benefits when developing test specimens.