Multiscale modeling and multiobjective optimization of the mechanical behavior of annealed and non-annealed material extrusion printed PLA

This study presents a multiscale finite element investigation of the mechanical behavior of Material Extrusion (MEX)-printed polylactic acid (PLA), considering the combined effects of raster orientation, strain rate, and thermal annealing. A homogenization-based modeling framework was developed to capture the anisotropic response of printed structures with raster angles of 0°, 45°, and 90°, subjected to strain rates ranging from 10⁻⁴ to 10⁻² s⁻¹. The numerical predictions were validated against experimental tensile data, showing good agreement in tensile strength and elongation, while stiffness was slightly underestimated due to simplified material assumptions. The results demonstrate that increasing strain rate enhances stiffness and strength but reduces ductility. Annealing further improves Young’s modulus and tensile strength (up to + 20.8% and + 15.8%) while decreasing elongation (–10.8%), which is consistent with DSC results indicating increased crystallinity (higher Tc) and density. A multi-objective optimization based on the Composite Desirability Function (CDF) identified the optimal configuration as a 90° raster orientation at a strain rate of 10⁻³ s⁻¹, providing the best compromise between stiffness, strength, and ductility. In addition to its predictive capability, the proposed numerical framework significantly reduces experimental effort, material consumption, and development time, offering an efficient decision-support tool for process optimization in industrial additive manufacturing.