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Fused filament fabricated (FFF) parts generally show anisotropic mechanical properties. Moreover, the anisotropy in FFF-printed parts varies with polymeric materials, depending on their characteristic relaxation and/or crystallization behavior. To acquire an in-depth understanding of the mechanical anisotropy induced by the FFF technique, polyphenylene sulfide (PPS) was chosen to investigate the effect of nozzle temperatures and nozzle speed on the mechanical properties of FFF-printed parts. In addition annealing of the samples at different times was chosen as a post-processing method to improve the mechanical properties. The optimized conditions through the highest value were selected by analyzing the Gray Relational Grade (GRG) values in the 16th trial using ANOVA and S/N investigation. It is found that increasing nozzle temperature gives rise to a decrease in crystallinity, slightly improving the tensile strength of the PPS parts with the deposited strands parallel to the loading direction (i.e. raster angle = 90°). Finally, manufacturing an impeller with optimized parameters was investigated by probing the surface through SEM and analyzing the geometrical accuracy from a 3D scanner.

This study numerically and experimentally investigates an optimized centrifugal compressor, fabricated by additive manufacturing technology. Additive manufacturing has attracted a lot of attention in industry and research and development studies due to its ability to fabricate parts of complex shapes with economic costs. In this regard, the compressor is designed based on iterative calculations of a 0D model in combination with loss models. The model can provide a preliminary geometry of the compressor according to the specifications. Then, the three-dimensional geometry of the compressor was optimized through the computational fluid dynamics calculation to find the best geometry and predict its performance. In addition, the structural aspect of the compressor rotor was analyzed through a numerical model. The components including the impeller and volute are fabricated by fused filament fabrication and stereolithography apparatus methods with polymers. The experimental results show the printed polymer rotor works properly at the speed of 52,000 r/min and can provide an expansion ratio of 0.66 with a maximum power of 250 W.

The use of additive manufacturing has been widely developed in the industry due to its ability to make complex shapes. The use of reinforcing fibers has provided a wider design capability in this field. Due to the effect of the number of fibers reinforced used on the mechanical properties, the study of the obtained mechanical properties is of great importance. This paper presents the experimental findings of tensile loading and three points bending fatigue tests performed on polymer-based composites (Onyx (which is CF-PA6) and reinforced Onyx with continuous glass fiber (CF-PA6 + GF) using Fused Filament Fabrication. Tensile properties of various types of printing conditions (Solid, Triangular, Rectangular, and Hexagonal fill patterns) have been compared. The coupled frequency amplitude affects the nature of the overall fatigue response which can be controlled by the damage mechanisms accumulation and/or by the self-heating. For fatigue loading, self-heating has been observed and yielded a temperature rise to about 60°C which is more than the glass transition temperature of the polymer. Multi-scale damage analysis of the sample in fatigue showed that the first observed damage phenomenon corresponds to the debonding of the filaments which leads to the propagation of transverse cracks.

This work studied the effect of sonication time and dispersing medium on the dispersion state of 0.1%wt multi-wall carbon nanotube (MWCNT) in the MWCNT/epoxy nanocomposite system. Epoxy, hardener, and epoxy/solvent were used as dispersing mediums in this study. Tensile strength, strain at failure, Young's modulus and fracture toughness were measured under different dispersion state of MWCNT. The results indicate that with the increase in sonication time, initially there was an increase in tensile strength and fracture toughness values which was followed by a drop in values at longer sonication times. The highest Young's modulus values were seen in epoxy dispersion and the highest tensile strength and fracture toughness values were observed when the hardener was used as dispersing medium. The results also indicated that the effect of sonication time was more pronounced in the case of epoxy dispersion. The effect of time was least when the epoxy / solvent system was used as CNT dispersing medium. It should also be pointed out that the Young's modulus for the nanocomposite sample obtained after 1h of dispersion in hardener showed good agreement with a modified Halpin-Tsai theory. The scanning electron microscope (SEM) was used to characterize the dispersion state of MWCNT. A good dispersion was obtained when either hardener or solvent were selected as the dispersing medium.

The viscoelastic properties of composites multi walled carbon nanotube / epoxy at different weight fractions (0.1, 0.5 and 1wt %) were evaluated by performing dynamic mechanical thermal analysis (DMTA) test. The MWCNT/ epoxy composite were fabricated by sonication and a cast molding process. The results showed that addition of nanotubes to epoxy had a significant effect on the viscoelastic properties. However, the use of 0.5wt% increased the viscoelastic properties more significantly. Concerning viscoelastic modeling, the COLE-COLE diagram has been plotted by the result of DMTA tests. These results show a good agreement between the Perez model and the viscoelastic behavior of the composite.

From a comparison of tensile properties of two epoxy networks crosslinked, respectively, with an aromatic diamine or an anhydride and from the available literature data on the fracture properties of thermosets, it has been tried to establish structure‐property relationships in this field. Attention was focused on possible specific aspects of the crosslinked polymers. Surprisingly, the crosslink density does not seem to play a crucial direct role in fracture. In contrast, there is a relation between toughness and Tg: Aliphatic networks of low Tgare generally tougher than aromatic ones. The local mobility plays a very important role because it partly controls the value of Poisson's ratio (which determines the relative importance of dilatant stresses and shear stresses responsible, respectively, for brittle rupture and yielding) and, presumably, the activation volume of yielding (which partly determines the broadness of the temperature interval of ductility).