Characterization of the deformation behavior of intermediate porosity interconnected Ti foams using micro-computed tomography and direct finite element modeling

Under load-bearing conditions metal-based foam scaffolds are currently the preferred choice as bone/cartilage implants. In this study X-ray micro-computed tomography was used to discretize the three-dimensional structure of a commercial titanium foam used in spinal fusion devices. Direct finite element modeling, continuum micromechanics and analytical models of the foam were employed to characterize the elasto-plastic deformation behavior. These results were validated against experimental measurements, including ultrasound and monotonic and interrupted compression testing. Interrupted compression tests demonstrated localized collapse of pores unfavorably oriented with respect to the loading direction at many isolated locations, unlike the Ashby model, in which pores collapse row by row. A principal component analysis technique was developed to quantify the pore anisotropy which was then related to the yield stress anisotropy, indicating which isolated pores will collapse first. The Gibson–Ashby model was extended to incorporate this anisotropy by considering an orthorhombic, rather than a tetragonal, unit cell. It is worth noting that the natural bone is highly anisotropic and there is a need to develop and characterize anisotropic implants that mimic bone characteristics.