Low-pressure additive manufacturing of continuous fiber-reinforced polymer composites

Continuous fiber-reinforced polymer composites have found a wide range of applications in the automotive and aerospace industry due to their lightweight properties. Recently the use of additive manufacturing (AM) has been developed for the fabrication of these composites. This study investigates the use of both atmospheric and, for the first time, low-pressure (1 Pa) processing conditions for the AM of continuous carbon, glass, and Kevlar fiber-reinforced nylon composites. Differential scanning calorimetry was used to compare the thermal properties of the three types of fiber-reinforced filament prior to printing. It was found that the melting peak was dependent on filament type, which can be related to the polymer processing conditions used during their fabrication. Based on computed tomography measurements, it was found that the use of low-pressure printing conditions yielded a reduction in porosity for the carbon, glass, and Kevlar printed composites of 5.7%, 1.0%, and 1.7%, respectively. The mechanical properties of the composites were compared, using a short beam shear test, which assisted in the measurement of interlaminar properties. An increase in interlaminar shear strength of 33%, 22%, and 12% was obtained for the carbon, glass, and Kevlar fiber-reinforced polymer composites, respectively, when printed under low pressure, compared with that obtained at atmospheric pressure.