Micro-CT based finite element models for mechanical strength assessment of glass ceramic scaffolds obtained through the robocasting technique

Sammanfattning

In this thesis, micro computed tomography (μ−CT) scans of a bio-glass scaffold produced by the robocasting technique was used to create finite element method (FEM) models with the purpose of determining its mechanical strength. Prior to this, a Matlab script was used to create several simplified geometries of the scaffold in an effort to determine the importance of scaffold design parameters (such as the fiber compenetration between two adjacent printing planes) on the strength of the scaffold. Furthermore, to assess the influence of micro-structural defects such as voids and micro-cracks that are intrinsic to the robocasting manufacturing process, the total number of voids and their respective volume was calculated using the μ-CT scan imagery and fitted to a statistical distribution. The distribution of voids was then used to create several scaffold models in Matlab with either spherical or ellipsoidal voids present. In the final two models, one scaled-down and one scaled-up FEM based on μ-CT scans were investigated.To model the crack initiation, propagation and final failure, the phase-field method was used. The method was implemented by the use of a publicly available Fortran user subroutine and was edited to account for asymmetric tension/compression energy degradation. The resulting strength of the produced models have been presented as non-dimensional values. The finite element analysis (FEA) of the Matlab produced scaffolds showed that the fiber shifting between two adjacent layers, porosity, and voids of ellipsoidal shape that were perpendicular to the loading direction had the highest effect on the strength of the scaffold. The resulting normalized strength values obtained from the μ-CT models was partially validated through a comparison with the literature available.The different failure modes and overall architectural arrangement of cracks also showed promising results.