PSI - Issue 49

Theodoros Marinopoulos et al. / Procedia Structural Integrity 49 (2023) 81–87 T. Marinopoulos et al./ Structural Integrity Procedia 00 (2023) 000 – 000

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2. Results The CURA-sliced sockets demonstrated a mean maximum load of 5694.1 N with a range between 9828.0 and 4395.5 N. The custom-sliced sockets significantly outperformed the CURA-sliced ones, with a mean max load higher by at least 75% at 10000 N (at this magnitude the tests stopped). The range for the triple-pass sockets was between 8885.4 and 10000 N since only one sample out of four tested failed. The single-pass sockets exhibited a maximum load at failure ranging between 5495.8 and 10000 N, with only two out of five samples failing. All types of sockets exhibited the same stiffness during the tests (after the initial transition stage), confirming their consistency as structures (Fig. 3A). A significant improvement in the mechanical behavior of 3D printed structures was observed that was discussed more extensively in a recent publication that this study relies on [20,21]. It was previously proven that the actual area of contact between the printed layers was smaller than the nominal one measured with calipers. This was the result of inherent AM-induced internal porosity, formed by the overlapping material between neighboring paths during printing. The use of the custom slicing allowed the additional control over the material deposition paths and, thus, the increased surface area could be achieved by avoiding the porosity between neighboring filaments. In the same study, it was reported that the cause of failure was the unavoidable remaining surface notches (grooves) between printed layers. Such a notch acts as stress concentrator in the area and is the weak point of the structure, but, thanks to the increased width of the material deposition, the angle of the notch was larger decreasing stress concentration. In addition to the larger bonding area of the material, improved mechanical performance can be achieved for 3D printed structures.

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Fig. 3. (A) Comparison of load-displacement behaviors for original design of prosthetic sockets sliced with commercial and bespoke slicing software and printed using Ultimaker 2+. (Blue lines – triple pass, red – commercial CURA, black – single pass). (B) Range and mean values of maximum load at failure for sockets printed with paths created using three different methodologies (The red central mark indicates the median, and the bottom and top edges of the box indicate the 25 th and 75 th percentiles, respectively. The whiskers extend to the most extreme data points not considered outliers. Tests were up to 10000 N.)