Fig. 3. Manufacturing-ready materials and resolution.
(A) Type I dog-bone structures made from an ABS-like polyurethane acrylate resin exhibit isotropic mechanical properties (ASTM D638) and are comparable to a part cast from the same resin (black line) as well as injection molded ABS (gray line). (B) HARP also enables high spatial resolution and print fidelity, as evidenced by the variation between designed and printed features as a function of feature size down to ~300 μm (below this, the ability to resolve parts becomes inconsistent) using a light-patterning engine with an optical resolution of 100 μm. Data points are mean values; error bars represent SD across 10 5-mm posts printed in differing regions of the print bed. Red dashed lines represent the bounding constraints of ±1 pixel for the light-patterning engine. (C) A computed tomography (CT) scan between a printed part (print rate, 120 μm/s; optical resolution, 100 μm) and its CAD design file reveals a volumetric correlation of 93%. Blue and purple volumes represent the printed object and the CAD object, respectively. Scale bar, 1 cm. (D) Representative height profile scans along the print direction for a series of 3-mm-thick dog bones for varying widths [red, 1 mm; green, 2 mm; blue, 4 mm; black, 6 mm; see additional data in (24) for dog bones 1 to 2.5 mm thick]. Red dashed lines represent the bounding constraints of ±1 pixel for the light-patterning engine. (E) Analysis of the profilometry data allows for the calculation of the arithmetic surface roughness, Ra, of the printed parts as a function of minimum feature dimension and reveals a strong linear correlation with a Pearson correlation coefficient of r = 0.90 (n = 20, rcrit = 0.444 for P = 0.05). (F) Despite this surface roughness, the maximum tensile stress remains invariant of the feature size (data points are mean values; error bars represent SD across five Type IV dog bones, ASTM D638). The inset shows a scatterplot for each dog bone, revealing a Pearson correlation coefficient between the surface roughness and maximum tensile stress of r = −0.34 (n = 25, rcrit = 0.396 for P = 0.05). The hard polyurethane acrylate resin was used for all experiments in (B) to (F).