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Using local continuous fiber reinforcements in highly stressed component areas, the mechanical properties of injection molded structural parts can be significantly improved while maximizing the potential for lightweight design. The 3D skeleton winding process (3DSW) is a robot-based 3D filament winding approach which enables the winding of thermoplastic impregnated continuous fiber reinforcements, based on commingled yarns (CY), to complex skeleton-like fiber structures. These fiber skeletons (FS) can subsequently be embedded in the final component geometry as local continuous fiber reinforcements using conventional injection molding. The robot-based generation of FS in combination with injection molding means that this manufacturing process can also be applied in the production of highly optimized structural thermoplastic components in larger quantities. This paper presents how the characteristics of the PPS matrix used as thermoplastic filaments in the CY and as overmolding matrix affect the mechanical properties of glass fiber-reinforced tensile loop specimens. Furthermore, the general lightweight potential using wound continuous reinforcements in combination with polyphenylene sulfide (PPS) is demonstrated on a generic 3D structural component. [ABSTRACT FROM AUTHOR]

Sheet Molding Compound (SMC) has proven to be a suitable process for the manufacturing of automotive body parts. Thermosetting matrix materials combined with glass fiber reinforcement deliver a good performance to weight ratio at a competitive cost. The downside of SMC, as with all thermoset-based composites, is the limited recycling potential, especially compared to thermoplastic alternatives. A recently introduced resin system based on acrylates enables, for the first time, the production of a thermoplastic SMC, combining the strengths of the SMC process with the advantages of the thermoplastic resin systems. Replacing conventional glass fibers by synthetic fibers as reinforcement enables the production of a completely thermoplastic material, which is suited for lightweight and eco-friendly design in automotive applications of the future. In the present work, the acrylic resin system Elium, a reactive thermoplastic material with processing characteristics similar to those of polyester resins, was used to produce semi-finished materials and mold parts thereof on industrial-scale production equipment. Aramid fibers were introduced to the SMC material in the form of non-woven fabrics, as, due to the tough nature of those fibers, direct processing on a conventional SMC fiber-cutting unit was not feasible. For reference, an Elium-based SMC with glass fiber reinforcement was also produced, as well as a thermoset epoxy SMC with aramid fiber reinforcement. The material variants were characterized in regard to their tensile and flexural properties, as well as their impact strength. The obtained mechanical characteristics were benchmarked against commercial SMC products. The aramid fiber-based SMC variants exhibited good strength under both tensile and flexural load. Stiffness, in both load cases, ranged in between those of comparable glass and carbon fiber SMCs, which is in line with the modulus of the respective neat fibers. The impact strength of both aramid fiber reinforced materials was also good. Between those two materials, the epoxy variant displayed better mechanical performance. The glass-reinforced Elium SMC performed on a similar level to commercially available vinyl ester SMC. Overall, the achieved material performance was very promising. Paired with the low density of the produced material and its recycling potential this new type of SMC forms a valuable proposition for the composite market. [ABSTRACT FROM AUTHOR]

Thermoforming of continuously fiber-reinforced thermoplastics (CoFRTP) is currently of great interest for the automotive industry due to low cycle times, material efficiency and recyclability. Depending on material parameters and process conditions, manufacturing defects are possible. Finite Element (FE) forming simulation offers the possibility of a detailed analysis of the deformation behavior of multi-layered thermoplastic blanks during forming, considering material behavior and process conditions by means of constitutive equations. Usually, thermoforming simulation is assumed to be isothermal, which is a reasonable assumption for semi-crystalline thermoplastics for temperatures above the onset of crystallization. However, it is not investigated so far, if the onset of recrystallization and its influence on formability is in general negligible for thermoforming simulation. In this study, characterization results for crystallization kinetics as well as for temperature-transient shear characterization for a unidirectional semi-crystalline thermoplastic tape (PA6-CF) are presented. A strong dependency on the cooling rate for recrystallization and shear behavior and a distinct increase in shear behavior with the onset of recrystallization is observed. To investigate temperature evolution and crystallization behavior on part level, a virtual forming study under variation of forming velocity is conducted. The results reveal that recrystallization during forming cannot be excluded for an unfavorable choice of process parameters. This reveals the necessity to take into account thermomechanics and crystallization kinetics in thermoforming simulation, especially in a process design phase. [ABSTRACT FROM AUTHOR]