An Analytical Framework for Correlation Between Laser Powder Bed Fusion Factors and Porosity-Induced Fracture Strength and Plasticity

Strain-stress properties of additively manufactured materials by laser powder bed fusion (LPBF) are substantially determined by the porosity level that is generated during the additive manufacturing. Accordingly, to optimally design of the LPBFed sample addressing the best stress-strain behavior, the porosity levels should be optimized through adjustment of process factors. In order to do so, in the present work, an integrated multi-physics-based analytical model has been developed to firstly correlate the LPBF process factors to porosity level using the mechanism of melt pool formation, vapor depression and identifying the lack-of-fusion. Then, the calculated porosity is used as an input of continuum damage mechanics model namely Gurson–Tvergaard–Needleman (GTN) to predict the stress-strain behavior. Through this hybrid approach, stress-strain curves together with ultimate tensile stress, elongation at peak and elongation at break have been successfully calculated and correlated to LPBF process factors. To verify the results, the LPBF samples made of stainless steel 316 L were subjected to micro-CT analysis and tensile testing and the measured values of porosity and stress-strain curves compared to the modded values. Also, comparisons were made on experimental values of porosity, UTS and elongation of other 3D printed materials i.e. Ti6Al4V, Inconel 718 and AlSi10Mg which reported in the literature with the values obtained from integrated framework in this research. The results based on relative root mean square error (RRMSE) showed that the developed model has excellent to good prediction accuracy with RRMSE values varies between the 3% to 20% accuracy in prediction of porosity, UTS and elongation of stainless steel 316 L, Ti6Al4V and Inconel 718. Also, for the aluminum alloy the RRMSE varies between 20% and 30% that shows the prediction accuracy is fair.