Recycling of CF-LM-PAEK long fiber reinforced thermoplastics using compression molding (Masterarbeit)

Abstract

This thesis investigates the optimal process parameters for producing defect-free parts using compression molding with recycled long-fiber thermoplastic material. The material, which is carbon fiber-reinforced low melt polyaryletherketone (LM-PAEK), was sourced from rest tape rolls from the automated fiber placement (AFP) process at the DLR facility in Stuttgart. The recycled tapes were cut into specific fiber lengths and firstly compression molded into small plates (300x300 mm). Five small plates were manufactured and analyzed using ultrasonic scans, optical 3D scans, micrograph analysis, and visual inspection to determine the optimal process parameters for defect-free parts. These parameters were then used to scale up the plates to a side length of 650x650 mm. To evaluate the effect of fiber length on tensile strength, two different chip sizes (25 mm and 50 mm) were used to manufacture two of the large plates. Tensile test specimens were cut from both plates in four directions to assess the quasi-isotropic behavior of the randomly oriented long fiber thermoplastic chip material used for the plates. The results demonstrated quasi-isotropic behavior, with tensile strengths comparable to lightweight materials like 6061 T6 aluminum and AZ80A T5 magnesium alloy. Additionally, the material's specific strength exceeded even that of 3 Al-2.5V titanium alloy and high strength 7075 T6 aluminum alloy. The study also found that increasing chip length has a significant positive effect on tensile strength.