Systematic analysis of the mechanical anisotropy of fibre-reinforced polymer specimens produced by laser sintering

Selective laser sintering (SLS) is an additive manufacturing process which nowadays receives abundant attention from industry sectors. However, the number of materials which can be processed by SLS is still very limited and requires further research. The present work aims to contribute to this topic by investigating the mechanical properties of neat and short carbon fibre reinforced polyamide 1212 processed by SLS. The specimens were built in different spatial alignments to obtain ample details on the tensile behaviour. The detailed examinations of the fractured specimens were performed by means of optical microscopy, scanning electron microscopy and X-ray computed tomography. The comprehensive analysis revealed that most of the fibres (85 - 95%) were oriented in the plane of the powder layer and here, the majority along the direction of the moving roller coater, which distributes the powder on the powder bed of the SLS machine. It was shown that this effect has a direct impact on the strength and stiffness of the printed tensile bars and thus on the mechanical behaviour of SLS printed parts. Furthermore, the analysis results indicate the possibility to control this mechanical anisotropy through a systematic alignment of the components in the powder cake.