Mechanical Properties and Flame Resistance of 3D-printed Coextruded Continuous Carbon Fiber Reinforced Polycarbonate

The active development of modern additive manufacturing technologies, namely continuous fiber extrusion based on fused deposition modeling (FDM), shows their significant potential for the creation of advanced materials based on fibrous polymer composites. These materials are widely used in the aviation industry, but their use as aircraft components is limited by the need to meet a number of requirements. One of such requirements is flame resistance. For such applications, it is of the utmost importance that a polymer composite is considered to be compliant with the type certificate prior to its integration. This research paper presents the results of a study that 3D-printed a continuously reinforced polymer composite with a polycarbonate matrix, with enhanced mechanical properties, and conducted flame resistance tests to demonstrate the feasibility of the printed materials in aviation applications. The study encompassed a series of interfacial shear strength, tensile strength, and flame resistance tests. The study presents a detailed characterization of the 3D-printed composite using ASTM D638-10, ASTM D635-22, optical microscopy, and pull-out tests of a single towpreg immersed in the matrix. The use of continuous carbon fiber coextrusion allowed for a fourfold increase in the tensile strength of the material (239.29 MPa) in comparison to unreinforced polycarbonate (54.92 MPa). The findings of the investigation into the flame resistance of printed continuously-reinforced polycarbonate indicate that the composite exhibited a burning time of less than 30 seconds following each flame application. Furthermore, the total burning time of a series of five samples after double flame application did not exceed 250 seconds, with an average of 56 seconds. The results obtained led to the conclusion that printed continuously reinforced polycarbonate is a viable material for its use in aircraft design. As to further support the use of the presented printing technology, the frame of an unmanned aerial vehicle was manufactured from continuously reinforced polycarbonate.