Viability of 3D fused filament fabrication for aerospace applications

Abstract

This study investigates the possible utilization of modern three-dimensional (3D) fused filament fabrication (FFF) in engineering applications. These FFF machines use filament that are usually made from PLA or ABS, coiled up in spools. With the rapid development in every possible technical field, new materials arrive on the market faster than they can be examined. Two particular materials of interest are Onyx and a printable carbon fibre filament manufactured by the Markforged Company. The Onyx material and carbon fibre filament materials are used in the FFF machine called the Markforged Mark Two. This machine has the ability to reinforce Onyx FFF parts with continuous reinforcement fibre and the process is referred to as continuous filament fabrication (CFF). This technology, although currently limited and relatively new, drastically increases the performance of a 3D printed part. A potential application of this technology is in the aerospace sector, more specifically with gliders. The airworthiness directive for gliders, CS-22, specifies an operational temperature of 54°C. There is however limited information available about the mechanical properties of these materials, especially at elevated temperatures. Thus, the purpose of the study is to investigate the mechanical properties of the Onyx material reinforced with carbon fibre at 54°C. The material was tested under compression and tension. As there was no specific standard available for FFF testing, therefore, ASTM standards served as a basis for the development of these test procedures. The compression testing was based on the ASTM D695 and D6641 standards while the tension testing used the D3039 standard. The room temperature tests for the Onyx were executed to verify the testing methods so that they could be used to determine the mechanical properties of the materials at 54°C. The tensile tests of Onyx at room temperature resulted in the Young’s modulus to be 1512.16 MPa, which is 7.44% higher than the published values. The results of the ultimate tensile stress were found to be 34.27 MPa, which is 4.4% less than the published values. There were no compression values to compare the room temperature tests to. An alternative solution was to use two different compressive testing methods and compare the values for verifying the testing methods to be used for the tests at 54°C. Using ASTM D695 and D6641 the Young’s modulus was found to be 843.95 MPa with D6641 and 823.84 MPa with D695. The yield stress was found to be 7.51 MPa with D6641 and 6.07 with D695 for Onyx in compression at room temperature. The experimental properties of Onyx at an elevated temperature of 54°C showed a 38.27% lower value for the Young’s modulus in tension and 33.72% lower value for the ultimate stress in tension. While in compression, it showed a 78.45% decrease in the Young’s modulus in compression and a decrease of 57.81% in the ultimate stress in compression. The Continuous Carbon Fibre showed an increase of 13.39% and 1.49% for the Young’s modulus and ultimate stress in tension while showing an 80.38% decrease and 13.4% increase in compression respectively when compared to the values supplied by Markforged at room temperature.