Processing-driven mechanical performance of discontinuous carbon fibre-reinforced composites

The mechanical performance of discontinuous carbon fiber-reinforced polymers (DFRPs) is significantly influenced by material selection and changes in fiber morphology resulting from processing. This study evaluates four fabrication techniques: injection molding, long fiber thermoplastics (LFT), sheet molding compounds (SMC), and additive manufacturing (AM). The investigation examines how these techniques affect fiber alignment, aspect ratio, and volume fraction and how these factors influence tensile strength, stiffness, and other mechanical properties. LFT and SMC exhibit enhanced tensile properties due to their ability to preserve fiber length and maintain quasi-aligned orientation during processing. Injection molding and AM, on the other hand, have significantly limited load transfer efficiency due to fiber attrition, random alignment, and weak interfacial bonding. Using micromechanical models, such as the rule of mixtures and orientation tensor-based frameworks, provides more insight into the differences in microstructure caused by the processes. Beyond mechanical behavior, this study explores trends in recyclability and sustainability. The study reveals that thermoplastic-based processes (LFT and injection molding) offer notable advantages in terms of energy consumption and closed-loop material reuse compared to thermoset-based systems, such as SMC. Each technique is linked to lightweight, impact-resistant, or high-throughput composite manufacturing. These techniques are presented in application-specific process recommendations. Finally, the key limitations of DFRPs, including limited modulus and fatigue vulnerability, are highlighted. Future research directions focused on hybrid reinforcement strategies and durability in harsh environments are also proposed. Overall, the findings provide comprehensive guidance on tailoring discontinuous CFRP systems to meet the evolving demands of high-performance, sustainable composite applications.