Co-authors​ :

 Rosanna FORSTER (UNITED KINGDOM), Antonio FETEIRA , Dimitra SOULIOTI , Sotirios GRAMMATIKOS (NORWAY), Evangelos KORDATOS (UNITED KINGDOM) 

Fused filament fabrication (FFF) is an extrusion based additive manufacturing (AM) technique used to produce fibre-reinforced polymer matrix composites (FRPs) due to its resource efficiency, part geometric flexibility and ease of use. Composite materials generally have superior properties such as being stiffer and more robust than conventional materials at a reduced weight leading to their application in a wide variety of sectors such as aerospace, biomedical and automotive. However, composites manufactured in this way are highly susceptible to defects such as high void content and poor bond quality at the fibre and matrix interfaces and these defects are hard to detect during the manufacturing due to the printing method. Early defect detection such as missing layers and excess vibration causing the print head to divert from its program can be detected by some FFF machines, but the technology isn’t consistently reliable and cannot detect smaller defects such as voids or porosity in the printed samples. These defects stop fibre-reinforced composite materials manufactured this way meeting industry standards and being used for structural applications.
In the present work, a novel combination in-line monitoring methodology including Infrared Thermography (IR) and acoustic emission (AE), benchmarked against micro-computerised tomography was developed for the monitoring of the FFF AM process manufacturing pure polymer, short fibre-reinforced and continuous fibre reinforced polymer matrix composite samples. The method allows for the detection of anomalies during the printing process and the verification of their presence after printing without the need for destructive testing. Tensile testing alongside a methodology of IR and AE was also used to investigate the structural integrity and mechanical properties of AM FRPs with pure polymer, short fibre-reinforced and continuous fibre-reinforced tensile samples being produced through FFF AM. For both the in-line monitoring and the structural assessment, the correlation between the printing parameters, the presence of defects and anomalies and the mechanical properties was investigated.
It was found that the in-line monitoring method can detect anomalies during the printing process and can provide information on the efficacy of the printing. This is substantiated by the presence of defects found during the offline assessment. It was also concluded there was a correlation between the structural integrity and print quality of the printed samples and their printing parameters which was identified during both the in-line monitoring work and structural assessment.