On the Failure Assessment Diagram methodology in polyamide 12

Abstract

For the first time, the Failure Assessment Diagrams of Polyamide 12, PA12, processed via a conventional technique as injection moulding, IM, and an additive manufacturing technique as Selective Laser Sintering, SLS, were determined via Finite Element Analysis (FEA) using a stress–strain equation more appropriate to describe the mechanical behaviour of thermoplastics. These diagrams were compared with those computed from the options of the BS 7910 standard applied for metals. The diagrams of SLS PA12 were clearly above that of IM PA12, presenting almost constant fracture ratio values for all the load ratios. This indicates the brittle behaviour, with small deviation from linearity, of SLS PA12 in comparison with IM PA12 which exhibited plasticity effects. This trend was supported by the mechanical response shown by PA12 manufactured by the different processing techniques. On the other hand, the diagrams obtained via FEA showed significant differences with the options of the BS 7910 standard, employed for the determination of the failure diagrams in metals, particularly when a Ramberg-Osgood model is used to describe the mechanical behaviour.