The main objective of this investigation was to determine the fatigue behaviour of polyamide 12 processed via the additive manufacturing technique as selective laser sintering and to compare it with that manufactured by the conventional technique as injection moulding. The fatigue assessment was carried out from the two approaches in design: the safe life approach and the damage tolerant approach. In the first case, the S-N or Wohler curves and the fatigue limit were computed for finite and infinite lifetime, respectively. In the second case, the fatigue crack propagation curves as well as the threshold values were measured. Due to the layer-wise structure of the parts fabricated by selective laser sintering, which may induce an anisotropic mechanical response, two loading directions with respect to the layered structure were evaluated, one with the load applied parallel to the layered structure and the other with the load applied perpendicularly. To attain this main goal, the following key objectives were defined:
▪ Measurement of the physical and thermal properties as well as the microstructural features of the polyamide 12 manufactured via selective laser sintering and injection moulding.
▪ Characterization of the mechanical properties through tensile and fracture characterizations of the materials under study.
▪ Determination of the fatigue behaviour of plain specimens and the fatigue crack growth behaviour at a frequency of 1 Hz and a stress ratio of 0.1, analysing the effects of orientation and manufacturing technique.
▪ Development of a map of fatigue through the generalised Kitagawa-Takahashi diagrams. Special attention was paid to the physically short crack regime, and the empirical model of El Haddad was also evaluated for all the materials and conditions under study.
▪ Identification of the micromechanisms of failure as a function of orientation and manufacturing technique.