Abstract
This study investigates two aspects of discontinuous carbon fiber-reinforced thermoplastic (CFRTP) manufactured using long fiber thermoplastic-direct (LFT-D) method: the fiber volume fraction and orientation, and the material’s damage behavior during tensile loading. Fiber content and orientation were quantified using cross-sectional images processed through binarization and ellipse fitting. Fiber bundles, with random size and position, were observed in areas of high fiber content, reflecting the inherent challenges of controlling parameters in the LFT-D process. Orientation analysis revealed a predominance of in-plane fiber alignment, indicating superior tensile performance in the in-plane direction but reduced strength out-of-plane. These findings provide insights into the material’s structural characteristics, while a separate evaluation focuses on its damage behavior under mechanical loading. In-situ tensile testing and scanning electron microscope observation revealed that cracks initiated at resin-rich regions and notch tips, propagated through resin-rich areas, and followed fiber bundle orientations, ultimately leading to failure. Observations of fiber pullout and interfacial debonding emphasized the importance of improving fiber-resin adhesion to enhance mechanical performance. These findings highlight the critical influence of fiber distribution and interfacial bonding on the mechanical behavior of CFRTP materials.
