Abstract
The application of carbon fiber reinforced thermoplastic (CFRTP) composite materials in diverse fields, such as aerospace, automobiles, marine, and bio-medical industries, is increasing owing to their high strength-to-weight ratio, and processability. The increasing demand for lightweight and high-strength structures can be met by adopting technologies that enable rapid and demand-specific manufacturing of CFRTP. Automated fiber placement (AFP), with its high-production rate, decreased scrap-rate, fast processing speed, and increased productivity, has become one of the best choices for manufacturing CFRTP. The mechanical performance of CFRTP can be significantly enhanced by optimizing the process parameters of AFP as there are several interdependent process parameters involved. This thesis explores the manufacturing of CFRTP composites using infrared (IR)-assisted AFP. Systematic optimization of AFP process parameters based on a statistical approach is developed. Moreover, the thesis addresses the implementation of IR-assisted AFP for CFRTP and manufacturing methodologies for optimization. The mechanical properties and failure behaviors of CFRTP materials manufactured with IR-assisted AFP are investigated. The result of this research provides in-depth knowledge of processing using IR-assisted AFP for CFRTP with enhanced mechanical performance and reduced manufacturing-induced defects. Two different CFRTPs are explored in this thesis: (i) carbon fiber reinforced/ polyamide 6 (CF/PA 6) and (ii) carbon fiber reinforced polycarbonate (CF/PC). In this thesis, a statistical approach with the design of experiments (DoE) is adopted to analyze the effect of the various process parameters of IR-assisted AFP. Four studies are reported in this thesis. Study 1 covers the initial optimization of IR-assisted AFP using CF/PA 6; the critical process parameters are identified through screening analysis as layup speed and IR power. Furthermore, the interaction between the layup speed and IR power is investigated. Manufacturing-induced defects are decreased by optimizing the combination of critical process parameters, and the IR power is directly proportional to the layup speed. This study reveals the importance of IR power and layup speed and the interdependence of mechanical properties on compaction force and tool (heated bed) temperature. From the initial optimization study, the effect of compaction pressure and tool temperatures is determined. Hence, study 2 investigates the combined effect of compaction force, compaction roller type, and tool temperature on the flexural strength, lap-shear strength, and percentage of crystallinity of CF/PA 6. Four different combinations of compaction force and tool temperature are studied for steel compaction roller and elastomer (silicone) compaction roller. The elastomer compaction roller yields better results than the steel compaction roller. This study establishes the correlation between the process parameters, mechanical and thermal properties to analyze the combined effect of the two process parameters. The mechanical iii performance achieved in study 1 is improved upon in study 2 (Chapters 4 and 5). Study 3 is focused on utilizing the knowledge developed on processing with AFP amorphous-based CFRTP – CF/PC. The initial analysis with IR power and layup speed is conducted, and a higher layup speed than that used for CF/PA 6 is used for manufacturing CF/PC laminates. Analysis of the effect of the compaction roller on the processing reveals that the steel compaction roller cannot process CF/PC. Hence, four different processing conditions using an elastomer compaction roller are investigated. CF/PC has higher mechanical properties than CF/PA 6 and no manufacturing-induced defects. Thus, a flat laminate of size 500 × 500 × 1 mm is manufactured and demonstrated for potential applications. Studies 1 to 3 investigate the optimization of process parameters for IR-assisted AFP for CF/PA 6 and CF/PC. For both the materials, higher compaction force and tool temperature are important to enhance the mechanical properties. The optimized processing parameters are used to manufacture tensile samples, and the tensile strength and modulus are compared. Study 4 (Chapter 7) provides an overall comparison between processing, the effect of process parameters, and mechanical properties of CF/PA 6 and CF/PC. Further, future work on manufacturing CFRTP on curved laminates using IR-assisted AFP is explained as a proof of concept of the optimization study. This thesis provides the detailed effect of process parameters of IR-assisted AFP on CFRTP and an analysis of the processing knowledge and mechanical properties of CF/PA 6 and CF/PC process with IR-assisted AFP for future research and development.