Defect analysis in additively manufactured scaffolds by 3D X-ray tomography

Details

Supervisors

Simar, Aude ; Pyka, Grzegorz

Faculty

Ecole polytechnique de Louvain

Degree label

Master [120] : ingénieur civil mécanicien, à finalité spécialisée

Abstract

Metallic alloys with healing properties have garnered interest due to their potential to shift the paradigm of damage prevention to damage management. Concurrently, lattice structures due to their lightweight properties have become popular in various applications. This study aims to explore and characterize the behavior of lattice structures produced with these advanced materials. Body-Centered Cubic (BCC) lattice structures were manufactured using Laser Powder Bed Fusion (LPBF) and characterized through images obtained via 3D X-ray tomography. Additionally, compression tests were conducted to evaluate the mechanical properties of the manufactured lattices. The investigation focused on identifying the critical processing parameters necessary for producing lattice structures with high geometric accuracy and part density. Digital Volume Correlation (DVC) analysis was employed to detect critical defects within the structures that lead to failure. Furthermore, the healing properties of the material used in the lattice structures were examined. The study revealed that lattice structures are highly sensitivity to processing parameters, requiring a careful balance. Optimal results for lattice structures with a 300μm beam diameter were achieved using a linear energy density (LED) of 0.409 J/mm, combined with pre-sintering and a contour-only scan path. Compressions tests highlighted the limitations of the Gibson-Ashby model in predicting the behavior of additively manufactured lattice structures; however, modifying the scaling pre-factors improved predictions for both elastic modulus and yield strength. Moreover, DVC analysis revealed that defects near nodes caused stress concentrations and localized strain, leading to buckling and structural failure. Finally, the diffusion healing mechanism was proved successful for a lattice structure with a final magnesium composition of 12.1% wt., using a healing heat treatment (HHT) at 400°C for 30 min followed by air cooling. However, further investigation is required to validate the liquid-assisted healing mechanism of the material.