Process-induced property loss of prepreg filaments with continuous fiber content of 65 vol% suitable for direct 3D printing

Continuous carbon fiber reinforced composite 3D printing is a hot research topic in additive manufacturing. Preparing high-content composite prepreg filaments, suitable for direct 3D printing, is the key to realizing highperformance composite materials. However, high fiber content will make the processability of prepreg filament worse. Composite prepreg filament (3K-PLA/CCF) with good infiltration and high fiber content was prepared by in-situ impregnation. The preparation and 3D-printing process of prepregs was divided into 6 stages to evaluate tensile property loss at different stages systematically. Fiber content is 65 vol% by various characterization methods. Tensile strength and modulus are 1713 MPa and 120.96 GPa, respectively, which are 25.34 % and 19.47 % lower than the theoretical value (RoM). The effects of layer thickness, preload, and printing angle on tensile properties were studied. Printing parameters corresponding to the smallest loss of performance are 0.2 mm and 0.25 N, and tensile strength and modulus are reduced by 34.33 % and 21.6 %, respectively, compared with prepregs. It is worth noting that the property loss was further reduced after the nozzle inclination was changed from 90 degrees to 60 degrees. The microstructure of prepreg filament shows that fiber damage and uneven distribution are the main reasons for the loss of properties. In addition, experimental results show that the conductivity of prepreg filaments is related to fiber defects. This study evaluated the performance loss caused by the 3Dprinting process, revealed the relevant mechanism, and explored the measures to reduce the loss, which will contribute to the development of high-performance composite 3D-printing technology.