PSI - Issue 41

Fabio Distefano et al. / Procedia Structural Integrity 41 (2022) 470–485 Author name / Structural Integrity Procedia 00 (2019) 000–000

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In the IWP unit cell, for all the configurations, the collapse mode is gradual and dominated by wall crushing. For IWP cells with relative density 0.05, the central portion of the structures collapse first, and the deformation behaviour is symmetric. Both cell sizes analysed do not reach a displacement of 75% due to the collapse of the structure. For IWP cells with relative density 0.1 and 0.2, at displacements of 25% and 50% the deformation behaviour is asymmetric for all the configurations analysed. In the IWP_2.1mm and IWP_3.5mm, the superior part collapse before the inferior one, while in the IWP_1.4mm and IWP_5mm the inferior part collapses first. The configurations with higher size values do not reach a displacement of the 75% because of the collapse of the structure, while the IWP_1.4 and IWP_2.1 cells reach a displacement of 75% following the same deformation behaviour described for displacements of 25% and 50%. 4. Conclusions The G7 cell fulfils the mechanical requirements for the application in the biomechanical field for all the configurations analysed. The actual values of the face size are lower than the designed ones; however, the G7 cells with relative densities 0.05 and 0.1 meet the morphological requirement, since the actual face sizes are greater than the minimum value of 0.6 mm necessary to promote the osteointegration process. Despite the G7 cell with relative density 0.2 presents a designed face size greater than 0.6 mm, the actual value is lower than the minimum allowed, thus the cell does not meet the morphological requirements. The compression tests allowed the evaluation of Gibson-Ashby coefficients for G7 cells and the analysed collapse modes showed that an improvement of the mechanical behaviour of the structure is required. FE analyses allowed the definition of G7 and IWP unit cells failure modes and the evaluation of cell size and shape effects on the mechanical properties. The G7 cell showed a collapse dominated by buckling and central node twisting, while IWP cell showed a gradual collapse, dominated by progressive walls crushing. Both G7 and IWP unit cells, for a given relative density, present an increase in structural performance while decreasing the cell diameter. The mechanical behaviour, the collapse modes as well as the morphological characteristics allowed to assess that IWP cell is suitable for the production of biomedical devices.