Improving Properties of Additively Manufactured Carbon Fiber Composites via Post Pressing

Abstract

Additive manufacturing, specifically the fused filament fabrication (FFF), has recently begun to explore its role in the composites industry, bringing the capability of engineered fiber orientation and placement, complex part geometry, and tailored internal structure to the traditionally high strength, high stiffness, and low-density material class. Despite conventional manufacturing, however, AM composites suffer from large void fractions and poor interlaminar adhesion, artifacts of the FFF, resulting in premature failure of AM parts. This study investigates the hot isostatic pressing (HIP) post-processing to improve the flexural and interlaminar properties of AM composites. Isostatic pressure and elevated temperatures were used in combination to compress internal voids in AM composite parts and induce the diffusion of molecular chains across printed layers to improve the interlaminar bond strength. This treatment can be applied to parts with complex geometries and in general is not limited by part size. The flexural strength, flexural stiffness, and interlaminar shear strength of the AM composites were found to increase by 36%, 35%, and 33%, respectively following a 1-hour treatment, accompanied by a corresponding reduction in void volume fraction. This method demonstrates a fast and robust method to post-process continuous carbon fiber reinforced polymer AM printed parts, resulting in a significant improvement in their mechanical performance.