PSI - Issue 56

Dan Micota et al. / Procedia Structural Integrity 56 (2024) 144–152 Dan Micota / Structural Integrity Procedia 00 (2019) 000 – 000

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fiber reinforced polymers (SFRP) are the chosen materials for many components and assemblies, even for many applications that in the near past were considered completely metal dependent. This family of composite materials can offer many advantages as they blend plastic materials lightness and mass scale manufacturability with the glass or carbon fibers high mechanical properties. Thus, the preferred manufacturing technology for SFRP parts is plastic injection molding, which comes with a series of advantages but also with some challenges that need to be comprehensively understood even from design phases. Plastic injection molding is quite advantageous as a manufacturing technology due to the good mechanical properties of the resulted parts, repeatable tolerancing and dimensional stability as well as directly out of mold desired surface finishing, reduction of technological and manipulation operations, cost efficiency as a result of mass scale production and low takt times per part. But for all it’s advantages plastic injection molding technology is a very complex process with a lot of interdependent parameters and variables which have to be carefully balanced to get the best results, such as molding tool design, manufacturing and materials, raw materials state and quality, process temperatures, pressures and durations, but one of the greatest influence of SFRP parts quality, strength and behavior is the design of the part itself. As the injection molding technology is based on pressurized plastic melt flow through the mold cavity and simultaneously with liquid to solid phase transformation, the resulting part presents differentiated orientation of the fibers to the melt flow direction, and not only in different areas of the parts geometry but also throughout the thickness of the parts walls Bernasconi et al. (2007), Castagnet et al. (2021), Holmström et al. (2020); Huszar et al. (2015), Jørgensen et al. (2019), Stepashkin et al. (2018). This being such an high demand process and technology, but a very complex one, there is a high research interest with some of the works referenced in this paper being Bernasconi et al. (2007), Choi & Takahashi (1992), Hassan et al. (2004); Huang et al. (2019); Isaincu et al. (2021), Lohr et al. (2018), Micota, Isaincu, & Marsavina (2021), Ogierman & Kokot (2016), Oseli et al. (2020) ; Şerban et al. (2012, 2016), Skourlis et al. (1998), Takahashi et al. (2014), Zhang et al. (2014), Zhao et al. (2019). The effect of different wall thicknesses on the mechanical properties and strength of the resulted injected SFRP parts was investigated in this paper. The phenomena is that increased wall thicknesses create a higher volume mid plane flow channel, the fibers of the material in those channels cannot be aligned in the melt flow direction by the mold walls, thus freezing in a random orientation at the moment when the tool cavity is fully filled. Throughout the parts wall thickness the percentage of highly oriented fibers in the melt flow direction is decreasing with the increase of the overall designed wall thickness. 2. Tested materials This paper is continuing the work presented in Micota, Isaincu, & Marsavina (2021), so the same two thermoplastic materials were studied, once again provided by the Solvay group. One being a polyphthalamide (PPA) reinforced with 33% short glass fiber inclusions (GF33) and the other material a polyphenylene sulfide (PPS) with a higher quantity of the same type of inclusions, 40% (GF40). These two materials can be found under the commercial designations of AMODEL AE-4133 for the PPA and Ryton R-4-270BL for the PPS. Both materials have a semi crystalline structure of their matrix base polymers and are included in the high-performance class of engineering plastic materials. Also, they are widely used in the automotive industry in tough work environments regarding temperatures, loads and chemical agents. 3. Experimental testing As results obtained for this paper have been compared with ones from Micota, Isaincu, & Marsavina (2021), much of the specimen preparation and test methodology was kept the same, in order to influence as few variables as possible. The specimens for this test campaign were obtained from square injection molding plates of PPA and PPS, measuring approximately 100mm on their sides and approximately 3.2mm thick. The tool cavity was filled via a cold runner and a side positioned fan gate, in order to uniformly distribute the flow front along the plate ’s length, resulting in a highly oriented fiber orientation pattern in the fill direction.