PSI - Issue 37

Theodoros Marinopoulos et al. / Procedia Structural Integrity 37 (2022) 139–144 T. Marinopoulos et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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variation was reported regarding the socket ’s load-bearing capacity, with many conventional products failing to meet the requirements (Current, Kogler, and Barth 1999; Gerschutz et al. 2012). 3D printing of polymer and composite components is also expanding its applications in the healthcare field (Jin et al. 2015). Still, despite the considerable progress of the 3D printing technology and the final quality of the parts becoming closer to that of conventional manufacturing techniques, mechanical characterisation of the additively manufactured products remains a challenge. The sockets produced using such methods must still be tested to evaluate both the manufacturing process and the final product (Schmidt et al. 2015). 2. Methodology 2.1. Socket manufacturing In this study, the stl file of a socket from a male transfemoral amputee was used. To achieve the paediatric size, the socket was scaled down to match the fitting size of a 15-year- old male’s residuum (NatCen Social Research and University College London 2017). Sockets were subsequently sliced with 0.2 mm layer height and 100% infill employing commercial software CURA and printed with a desktop 3D printer Ultimaker 2+ using PLA. A twin socket was produced in carbon-fibre reinforced nylon (CFN) for material comparison. The initial socket design allowed them to be attached to an Össur off-the-shelf pyramid using bolts leading to an internal disk insert (Fig. 1). A second design was also produced where the round distal end of the socket was redesigned in a square shape matching the pyramid dimensions to avoid stress concentration on the flat end and was printed with the same parameters as the original design (Fig. 2).

Figure 1. Socket attachment mechanism to pyramid using screwable insert

Figure 2. (A) Transfemoral socket with round distal end. (B) Redesigned square-ended socket

2.2. Experiment

To evaluate the structural integrity of prosthetic sockets, a dedicated testing rig was developed following the guidelines of BS EN ISO 1385. Two important features are reported in these standards that relate to (i) the load-bearing requirements of the tested component and (ii) the size of the load-application points. For static compressive tests, the standards describe three different load levels, refe rring to user’s weight a s follows: P3 for weight below 65 kg, P4 for weight below 85 kg and P5 for weight up to 100 kg with three minimum load-bearing requirements of 3220 N, 4130 N and 4480 N, respectively, applied at the top of the part. Since a product capable of withstanding the loads from the heaviest user is safe to be used for lower load level users the P5 class was selected for this study. A set of coordinates,