PSI - Issue 28

3

D. Rigon et al. / Procedia Structural Integrity 28 (2020) 1655–1663 Rigon et al. / Structural Integrity Procedia 00 (2019) 000–000

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While experimental investigations are reported on mechanical properties and, in particular, on fatigue behaviour of 3D printed virgin polymer materials (see for example the literature review reported in (Safai et al. (2019)), few works exist on the mechanical properties for structural durability of 3D printed recycled polymers, particularly in comparison with the same materials obtained by injection moulding. Recycled plastic materials for 3D printing became recently available, such as recycled Acrylonitrile Butadiene Styrene (rABS), Polypropylene (rPP), PolyEthylene Terephthalate (rPET) or Polylatic Acid (rPLA) (see for example (Zander et al. (2019); Zhao (2018)). One of the most used 3D printing processes is the so-called Fused Deposition Modelling (FDM) (or Fused Filament Fabrication (FFF)). It is an extrusion process where the object is built by depositing melted material layer-by-layer. A continuous filament of thermoplastic material is rolled in a spool; it is pushed towards the printer extruder head through drive wheels where the material is molten and then deposited on the layer (see Fig. 1). With this technology, complex shape components can be produced by using a wide range of plastic materials which are easily changeable between each other. However, the parts produced by FDM have not negligible anisotropy with respect to the direction normal to the layers, high surface roughness and defects formed by the imperfect sealing between layers and toolpaths. The aim of this paper is to summarise the data available from the literature, regarding static and fatigue properties of virgin and recycled ABS, PP, and short glass fiber reinforced PP produced by Fused Deposition Modelling (FDM), since they are materials closely related to the ones that will be investigated by the authors in following works. Where available, the influence on the mechanical properties of some 3D printed process parameters will be presented including a general comparison between results of the relevant materials produced by conventional manufacturing (Injection Moulding (IM)) and by FDM. 2. Materials and Methods The materials considered in this work are Acrylonitrile butadiene styrene (ABS), Polypropylene (PP), and short glass fiber reinforced polypropylene with a mass fraction of fiber equal to 30%wt (PP-GF30). Both virgin and recycled states were considered, where the recycled materials derived from domestic appliances and used electronic equipment housings. Regarding the FDM process, three process parameters were taken into account. The first one is the percentage of infill density in which 0% corresponds to no infill, while 100% is equivalent to a solid part. Second is the way how to infill a volume i.e. the infill pattern. The third one is the specimen orientation with respect to the build direction. In this work, five infill patterns characterized by 100% of infill density were taken into account. The infill patterns are shown in Fig. 2a) and identified by the angles between the rasters and the load direction. Furthermore, considering the data available in the open literature for comparing virgin and recycled plastics, only the flat oriented specimens were considered (see Fig. 2b). Therefore, the influence of the orientation of the specimens on the mechanical properties is not the object of study in this work, although it is studied in the literature.

load direction

a)

b)

Figure 2. a) Infill patterns for 100% of infill density and b) orientation of the specimen.