STUDY ON COOLING RATE-DEPENDENT MECHANICAL PROPERTIES OF THERMOPLASTIC COMPOSITES

This study investigates the effect of solidification conditions on the crystallization behaviors and mechanical properties of thermoplastic resin and carbon fiber reinforced thermoplastics (CFRTP). In particular, the crystallinity, elastic modulus, plastic behavior, strength, and fracture toughness were investigated in Polyphenylene Sulfide (PPS) and CF/PPS manufactured by different cooling rates. Based on experimental results, the cooling-rate-dependent elasto-plastic constitutive law of resin was developed empirically. Finally, the homogenized simulations of CF/PPS were conducted using the developed empirical model, and predicted results were compared with experiments.

Energy Direction in Ultrasonic Impregnation of Continuous Fiber-Reinforced Thermoplastics

As a new and innovative processing method for fabrication for fiber-reinforced thermoplastic composites (CFRTs), the feasibility of ultrasonic welding technology was proven in several studies. This method offers potential for the direct manufacturing of CFRT–metal structures via embedded pin structures. Despite the previous studies, a deeper understanding of the process of energy input and whether fibers work as energy directors and consequently can, in combination with chosen processing parameters, influence the consolidation quality of the CFRTs, is still unknown. Consequently, the aim of this work is to establish a deeper process understanding of the ultrasonic direct impregnation of fiber-reinforced thermoplastics with an emphasis on the fiber’s function as energy directors. Based on the generated insights, a better assessment of the feasibility of direct, hybrid part manufacturing is possible. The produced samples were primarily evaluated by optical and mechanical test methods. It is demonstrated that with higher welding time and amplitude, a better consolidation quality can be achieved and that independent of the process parameters chosen in this study, no significant fiber breakage occurs. This is interpreted as a sign of a gentle impregnation process. Furthermore, based on the examination of single roving and 5-layer set-ups, it is shown that the glass fibers function as energy directors and can influence the transformation of sonic energy into thermal energy. In comparison to industrially available CFRT material, the mechanical properties are weaker, but materials and processes offer potential for significant improvement. Based on these findings, proposals for a direct impregnation and joining process are made.