PSI - Issue 34

D. Rigon et al. / Procedia Structural Integrity 34 (2021) 199–204

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Rigon D. et al. / Structural Integrity Procedia 00 (2021) 000–000

adoption of recycled materials is to use Additive Manufacturing technology combined with the optimization techniques that minimize the mass of a structural component (Dizon et al 2018). For the feasibility of combining recycled compounds with AM in the industrial sectors for structural applications, the mechanical properties and the fatigue behaviour must be deeply studied.

Nomenclature E

material elastic modulus [MPa]

L m,ad L w,ad

adjusted numerical mean fiber length [µ m] adjusted weighted mean fiber length [ µ m] reference number of cycles [cycles] number of cycles to failure [cycles]

N A N f

R σ a

load ratio (σ min /σ max )

stress amplitude of the cyclic load ((σ max - σ min )/2) σ A,50% stress amplitude evaluated at N A for 50% survival probability σ min minimum stress of the cyclic load [MPa] σ m tensile strength [MPa] AM additive manufacturing IM injection moulding F0°, F90°, F±45° build orientation of the AM specimens and the relevant infill pattern rPPMF-GF

100% recycled polypropylene mineral-filled and reinforced by short glass fibers virgin polypropylene mineral-filled and reinforced by short glass fibers

vPPMF-GF

This work deals with the fatigue characterization of specimens produced by pellet-based additive manufacturing made of a recycled mineral-filled polypropylene reinforce by short glass fibers (PPMF-GF). In the literature, there are several works on the mechanical properties of virgin or recycled SFRPCs (Abdelhaleem el al. (2018), Carneiro el al. (2015), Parandoush el al. (2018), Tekinalp el al. (2014), Weng el al. (2016), Wang el al. (2017), Spoerk et al. (2019, 2020)). However, for the material considered in this work, the quasi-static mechanical properties were studied only in a recent work (Rigon et. al. (2021), while there is a lack of data regarding its fatigue behaviour. Therefore, the aim of this work is to provide experimental data on the fatigue behaviour of the recycled PPMF-GF specimens produced by AM, to compare the data with those obtained on the same material produced by injection moulding (IM). Regarding the latter technology, the effect of recycling was also studied by testing IM specimens made of virgin PPMF-GF. Preliminary analyses of the macroscopic damage mechanisms were also discussed in the last section of the paper. 2. Materials and methods Two different types of pellets materials were used to produce specimens for fatigue tests. One batch of pellets was produced using mineral filled virgin polypropylene reinforced by short glass fibers (vPPCC-GF), while the second one has post-costumer recycled polypropylene (rPPCC-GF). These two batches are the same of those employed to produce the specimens for tensile tests in (Rigon et al. 2021). The contents of the fibers and filler were intentionally omitted for confidentiality reasons. In previous work, the numeric and weighted mean values of the fibers were measured starting from optical images of the fibers, after having burned off the matrix in a muffle (Rigon et al. 2021). The summary of these results is reported in Table 1, while for more details about the method and the distribution of the fiber length the reader is referred to the work (Rigon et al. 2021). The effect of the recycling on the fatigue properties of the materials was investigated only in specimens produced by injection moulding. The manufacturing of IM specimens consisted of producing, first, net-shape samples according to the type I geometry reported in standard ASTM D638-14 by adopting the process parameters reported in (Rigon et