Experimental characterisation of fused filament fabrication printed parts under tension, shear, and combined shear–tension loads via Arcan test

Abstract

The mechanical performance of fused filament fabrication printed parts is considered the weak point of the technology due to its high anisotropic structure and irregular behaviour. This research focuses on the application of the Arcan-based method to fused filament fabrication printed parts, to better understand their mechanical behaviour. In order to characterise and quantify the anisotropic behaviour, a butterfly type specimen was developed, taking into account the flaws presented by the process (e.g. need for support material for tilted surfaces, low resolution, etc.). Together with the Arcan type grip, a combination of vertical–transversal (VT), vertical-longitudinal (VL) and horizontal (H) printed samples were tested under three distinct loading conditions, 90° – tensile, 45° – combined loading and 0° – pure shear. For each set of samples, digital image correlation was used to analyse the deformation fields imposed by the distinct building orientations and loading conditions. Regarding the material, two different types of Nylon® (PA 12) were used, namely FX256 and CF15, being the second a short carbon fibre reinforced version of the first, allowing a comparison of the mechanical behaviour. The results show that the building orientation prevails, originating distinct fracture types and overall behaviour difference. It was shown that fibre presence does not create a stronger material, yet an increase in stiffness is observed for all building orientations, except VT, where both materials presented similar values, indicating that the fibre orientation is critical when taking into account the loading conditions. It was also observed that of all sample types, FX256 H specimens showed the closest to isotropic behaviour.