Mechanical properties and fracture characterization of additive manufacturing polyamide 12 after accelerated weathering

The additive manufacturing (AM) methods, selective laser sintering (SLS) and multi jet fusion (MJF), are increasingly used for end-use polymer parts. Chemical reactions caused by ionizing radiation and catalyzed by oxygen, moisture, and heat are known to degrade the polymer structure, result in visual defects, and loss of mechanical properties. However, the effects of the AM layer-wise manufacturing process on polymer degradation are not widely studied. Yet, they may have implications on the mechanical properties and fracture mechanisms of the components. This paper presents an open access data repository of mechanical properties after weathering for AM plastics, conventionally manufactured plastics, and for two clear protective coatings. All materials were exposed to a 1500-h accelerated weathering cycle (ISO-4982-3) followed by tensile testing (ISO-527). Special attention was given to polyamide 12 (PA12) produced via powder bed fusion AM in two build orientations. The fracture surfaces of PA12 and glass-filled PA12 were further studied with scanning electron microscopy. The AM materials were PA12, glass-filled PA12, and carbon reinforced PA12. Traditionally manufactured materials included glass-filled and molybdenum disulfide-filled PA66, PMMA, ABS, PC, and cast PA12. No clear differences were found between the AM build orientations in fracture mechanisms or weathering performance. AM and cast PA12 were strongly affected by accelerated weathering. Carbon reinforced PA12 with a UV varnish experienced the least changes. Weathering resistance was increased with protective coatings. However, an increase in the deviation of mechanical properties with the coatings was observed. The contrary results in ductility for the glass-filled and molybdenum disulfide-filled PA66 after weathering would merit further studies.

Automated summary

This study compared the mechanical properties of additive manufacturing and conventionally manufactured plastics after weathering, finding that PA12 and PA66 from additive manufacturing were significantly affected by weathering, while carbon reinforced PA12 showed the best aging resistance due to the UV varnish. Protective coatings can increase materials' weathering resistance, but also lead to an increase in the deviation of mechanical properties.