Microcracking Resistance of 3D Printed Fibre Composites at Cryogenic Temperatures

Abstract

Thermoplastic composites present considerable promise for the 3D printing of cryogenic fuel storage tanks, offering enhanced recyclability and repairability compared to thermoset composites. However, a significant knowledge gap remains regarding their ability to withstand cryogenic environments without suffering ply cracking. This study investigates the microcracking behaviour of continuous carbon fibre reinforced thermoplastic (CFRTP) composites fabricated through extrusion-based 3D printing. The experimental results reveal that CFRTP composites printed at room temperature exhibit a remarkable ability to withstand an applied strain of 0.60% without ply cracking at liquid nitrogen temperature. This performance surpasses that of conventional carbon fibre reinforced epoxy composites, which typically experience ply cracking even with any applied strain. Some of microcracks were traced back manufacturing defects. The defects were found to be fused by a post-heat treatment at 180℃ for 60 min. Unexpectedly, however, the treatment reduced the ply-cracking strain to 0.40% at the liquid nitrogen temperature. Computational micromechanical modelling revealed that this unexpected decline in ply-cracking resistance resulted from the increased thermal residual stresses induced by the heat treatment. The findings of this study suggest that 3D-printed thermoplastic composites exhibit robust resistance to microcracking at cryogenic temperatures, making them a promising solution in the quest for sustainable lightweight cryogenic fuel storage solutions.