Study of the Mechanical Properties of 3D-printed Onyx Parts: Investigation on Printing Parameters and Effect of Humidity

Recently, an increasing number of parts have been produced using additive manufacturing technology. They are no longer simply prototypes but structural parts whose mechanical characteristics must be known before printing. One of the weaknesses of 3D printing is the significant variability in the dimensions and geometrical and mechanical properties of the printed parts. These properties depend on specific printing parameters and environmental conditions. This study aims to determine the influence of two printing parameters, namely, the orientation and positioning of the parts on the printing platform and the influence of humidity on the mechanical properties of the parts. The studied samples were fabricated with onyx using a Markforged X7 printer. The results showed that onyx could be considered an isotropic material to a certain extent because its mechanical properties do not vary sufficiently according to the orientation angle on the printing platform; a maximum deviation of 10% was observed between the different orientations. In contrast to the orientation, the positioning (flat or XY, on-edge or XZ, and upright or ZX) of the workpieces significantly influenced the mechanical properties. Positioning on the edge allowed the Young's modulus to be up to 50% greater than that of flat and upright positioning. The study of the sensitivity to humidity revealed that a specimen absorbs approximately 2% of the humidity and loses up to 65% of its Young's modulus after 165 days of exposure, significantly influencing the mechanical properties of the parts. Consideration should be given to this aging of onyx when using printed parts as structural parts.