Energy Direction in Ultrasonic Impregnation of Continuous Fiber-Reinforced Thermoplastics

Dietmar Drummer,Tobias Mattner,Julian Popp,Michael Wolf

doi:10.3390/jcs5090239

Dietmar Drummer, Tobias Mattner + Show 2 more

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https://doi.org/10.3390/jcs5090239

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Abstract

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.

Highlights

In times of increasing global warming, the reduction of CO2 emissions is a major societal challenge
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
Samples manufactured with a welding time of 5 s show partial air pockets, which can be interpreted as a sign of insufficient impregnation quality

Summary

Introduction

In times of increasing global warming, the reduction of CO2 emissions is a major societal challenge. Short or long fiber reinforced plastics are sufficient since higher moduli can be reliably reached with lower fiber lengths [3,4]. Applications that require high strength and impact properties, such as those in the transportation sector, necessitate the highest possible fiber length, as only the maximum weightspecific impact properties can be achieved [5,6]. In comparison to thermoset-based CFRPs, continuous fiber-reinforced thermoplastics (CFRTs) typically have several advantages: a higher impact strength, simple storage possibilities without refrigeration, and practically unlimited shelf time, as well as short cycle times [7]. CFRT parts are typically manufactured via hot press processes from semi-finished products such as pre-consolidated sheets or comingled yarn systems

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