1. Introduction
Fused deposition modelling parts exhibit layer-dependent anisotropy that is well documented for static strength but comparatively under-characterised for fatigue behaviour, which governs the service life of parts subject to repeated loading such as functional brackets and enclosures.
2. Methodology
Dogbone specimens were printed in PLA at 0, 45 and 90-degree raster orientations relative to the loading axis and subjected to fully reversed axial fatigue testing across five stress amplitude levels, with cycles to failure recorded for each of 45 specimens (15 per orientation), and a modified Basquin S-N model fitted incorporating a raster-angle correction term.
3. Results
The 45-degree raster orientation exhibited the highest fatigue endurance, sustaining 38 percent more cycles than the 90-degree orientation at an equivalent stress amplitude of 18 MPa, while the 0-degree orientation performed intermediately. The corrected Basquin model predicted fatigue life within an average of 12 percent of experimental values across all three orientations, compared with 31 percent average error for the uncorrected isotropic model.
4. Conclusion
Raster orientation materially affects fatigue life in FDM-printed PLA parts, and orientation-corrected S-N models substantially improve prediction accuracy for design purposes. Future work will extend the correction framework to fibre-reinforced filaments.
References
[1] Basquin O. H., The exponential law of endurance tests, ASTM Proceedings, 1910. [2] Afrose M. F. et al., Effects of part build orientations on fatigue behaviour of FDM-processed PLA, Progress in Additive Manufacturing, 2016.