Santos, Telmo; NOVA School of Science and Technology - NOVA University Lisbon; Portugal

Pontes, A.; University of Minho; Portugal
Simão, C.; NOVA School of Science and Technology; Portugal
Nunes, J.; University of Minho; Portugal
Pinto, J.; University of Aveiro; Portugal
Viana, J.; University of Minho; Portugal
Ferreira, M.S.; University of Aveiro; Portugal
Santos, T.G.; University of Lisbon; Portugal

ID: ECNDT-0305-2018
Download: PDF
Session: Additive Manufacturing – various methods
Room: H1
Date: 2018-06-12
Time: 11:30 - 11:50

Additive manufacturing (AM) using 3D printing is one of the most promising manufacturing technologies nowadays. However, the development of reliable Non-Destructive Testing (NDT) techniques for AM products is a big challenge. In fact, AM introduces new defect morphologies, dimensions and locations demanding new, and more reliable NDT techniques. These issue is even more pronounced in the case of AM of composites. In this case, possible defects that may arise include: delamination between matrix layers, lack of bonding between matrix and reinforcements, porosities (inter-filament discontinuity and path discontinuity), trapped support material between internal surfaces, misalignment of reinforcements or excessive surface roughness (staircase defect). Detecting such defects with existing NDT techniques presents major limitations as they were developed for other requirements and operational conditions.
This paper focuses on one of the most difficult challenges in NDT: the challenge of detecting defects in composite materials produced by Additive Manufacturing (AM), in particular, using continuous fibre reinforcement thermoplastics (FRTP). For those products, structural applications and safety requirements are envisaged, increasing the demand for NDT.
Four different NDT techniques were studied: active thermography, eddy currents, digital X-ray and ultrasound. Tests were performed in composite samples produced by Fused Deposition Modelling (FDM) AM containing different artificial defects, using polymeric matrix (PLA, ABS, Polyamide and PEEK) and continuous reinforcement fibres introduced externally (carbon and glass fibres and NiTi wires).
Active thermography with customized heat sources showed to be adequate for detecting voids and delaminations parallel to the surface, while X-ray and eddy currents with customized probes allow the identification of the NiTi wires and their arrangement inside polymeric matrix. Ultrasonic inspection presents major limitations due to the high acoustic attenuation of polymers (not so intense for PEEK) and due to high surface roughness when a 3D printing nozzle of 1.4 mm was used.