Dimensional Accuracy in 4D-Printed PLA Objects with Holes: Experimental and Numerical Investigations

Abstract

This study investigates the impact of material and process parameters—specifically, filament color, infill density, and pattern—on the dimensional accuracy of 4D-printed polylactic acid (PLA) objects featuring holes of varying diameters (6, 8, and 10 mm) that undergo a heat-induced recovery process. The objective was to understand how these factors affect shape retention and the dimensional accuracy of holes through a comparative analysis of the diameters before and after recovery. Increased variability in the hole diameters was noted after recovery, regardless of the values of the independent variables. The objects did not fully return to their original planar shape, and the holes did not completely return to their circular form, resulting in smaller diameters for each sample. No significant differences in the hole diameters could be determined. Additionally, there was no consistent trend in identifying the most influential parameter affecting the accuracy of the recovered holes. However, it was observed that higher infill densities improved shape retention. A quasi-static finite elements analysis model was developed to capture the mechanical behavior of the 4D-printed parts. This model incorporated temperature-dependent material characteristics to predict the strain occurring near the holes. Nodal displacements were defined according to the deformed shape. A correlation was established between the observed strains and the post-recovery dimensional accuracy of the specimens. The importance of this work was demonstrated through a case study involving a two-sieve filtering device for small objects.