A novel critical distance-based homogenised material approach to estimate fatigue lifetime of plain/notched polylactide 3D-printed with different in-fill levels

• Fatigue strength of 3D-printed PLA with varying infill is tested. • 3D-printed PLA with varying infill is modelled as a cracked elastic material. • Critical distance methods are used to estimate fatigue lifetime. • Proposed methods combine with commercial FE codes. This study presents a novel approach to predict the fatigue life of plain and notched polylactide (PLA) components 3D-printed with different in-fill levels. The proposed method models 3D-printed PLA with manufacturing voids as a continuous, homogeneous, linear-elastic, isotropic material weakened by equivalent cracks that scale with the size of the voids. This allows for accurate estimation of both plain material strength and notched component fatigue life, considering various in-fill levels. The proposed design method’s accuracy and reliability were validated against extensive fatigue testing data from plain and notched specimens, fabricated with varying in-fill levels and raster angles. The strong correlation between predicted and experimental fatigue lives confirms that the method accurately assesses the fatigue strength of additively manufactured PLA components, even without explicitly modelling fabrication voids.