PSI - Issue 41

N.A. Fountas et al. / Procedia Structural Integrity 41 (2022) 638–645 Author name / Structural Integrity Procedia 00 (2019) 000–000

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As far as the organic biocompatible composites is concerned, i.e. PLA mixed with wood flours materials (PLA/W); research effort was directed towards examining strength properties in relation to material synthesis and FFF parameters (Chansoda et al. 2020; Faludi et al. 2013, Bulanda et al. 2020; Bhagia et al. 2020; Yang and Yeh 2020; Zandi et al. 2020; Ayrilmis et al. 2019; Camposeco-Negrete et al. 2022). Interfacial adhesion between PLA and wood flours was mentioned in Faludi et al. (2013). Chansoda et al. (2020), examined the effect of using parawood powder derived from the furniture industry as an infill gradient in PLA matrix. Zandi et al. (2020) investigated the influence of crucial FDM parameters, i.e., layer height, nozzle diameter, infill density and printing speed on fatigue behavior of a PLA/W (Timberflll, 8% wood fibers). Their experiment was based on an L27 orthogonal array design and it was observed that layer height was the dominant parameter. Kain et al. (2020) examined two wood fiber contents (75% and 25% Wood fibers, ARBOCEL C100) mixed with PLA (lngeo™ 3251D) under different raster deposition angles during FDM. It was shown that the 25% wood content gave better strength than that having 15% whilst infill has the strongest effect on strength. Guessasma et al. (2019) examined the strength properties of PLA/W parts, changing the nozzle temperature NT between 210 o C and 250°C where it was shown that by increasing NT from 210°C to 230°C higher part strength is achieved. However if NT exceeds 230°C, strength is negatively affected by the wood particles’ degradation therefore it is not recommended. Ayrilmis et al. (2019) investigated the impact of LT on water absorption and strength of FFF-PLA/W specimens. It was observed that by increasing LT, both water absorption and cross-section porosity increase whilst durability decreases. Moreover, the density of PLA/W printed parts increased as printing speed PS decreased while UTS and flexural properties of FFF-PLA/W specimens did not exhibit significant changes under different layer deposition rates (Yang and Yeh, 2020). The above researchers examined the effect of FDM independent parameters on strength of various PLA wood flour contents. The authors strongly believe that the effect of such parameters on 3D printed PLA/W is yet to be studied. Therefore, the experimental domain with the independent parameters selected in this work is investigated, to the authors’ knowledge, for the first time. Present work is an extended experimental follow-up of the work presented by Kechagias et al. (2022) under the research question of how main FFF parameters, i.e., layer thickness (LT), nozzle temperature (NT), raster deposition angle (RDA), and printing speed (PS), affect ultimate tensile strength UTS when it comes to hybrid PLA/wood flour fabricated parts. In Kechagias et al. (2022) the results were analyzed and presented using statistical tools such as analysis of variances (ANOVA) and analysis of means to examine the effects of FFF control parameters on UTS and Young’s modulus E . However in their work layer thickness is investigated using two discrete values, thus; a generalized prediction model was not created. In this study a full quadratic regression model is built by considering the independent variables as continuous ones. By generating robust regression relations among FFF independent variables and responses under study (i.e. UTS), optimal settings may be found if optimization techniques are applied to further enhance strength referring to organic biocompatible hybrid FFF-PLA/W materials. 2. Experimental set-up and results Having in mind the current state of literature concerning additive manufacturing technology, experimental specimens in the form of “dog bone” geometry according to ASTM D638 were tested for their ultimate tensile strength. The order of experiments for destructive testing was as per the L18 Taguchi’s orthogonal array suggests under a mixed level design, i.e. 2 levels for layer thickness (LT) and three levels for the rest of parameters; nozzle temperature (NT), raster deposition angle (RDA) and printing speed (PS) as Table 1 summarizes.

Table 1. Operational (input) FFF parameters and corresponding levels according to L18 mixed level OA design. FFF process parameter Symbol Unit Level 1 Level 2 Level 3 Layer thickness LT (mm) 0.1 0.3 - Nozzle temperature NT ( o C) 180 200 220 Raster deposition angle RDA (deg.) 0 45 90 Printing speed PS (mm/sec) 30 40 50