Abstract
Mechanical performance of additively manufactured (AM) Ti6Al4V scaffolds has mostly been studied in uniaxial compression. However, in real-life applications, more complex load conditions occur. To address this, a novel sample geometry was designed, tested and analyzed in this work. The new scaffold geometry, with porosity gradient between the solid ends and scaffold middle, was successfully used for quasi-static tension, tension-tension (R = 0.1), tension-compression (R = −1) and compression-compression (R = 10) fatigue tests. Results show that global loading in tension-tension leads to a decreased fatigue performance compared to global loading in compression-compression. This difference in fatigue life can be understood fairly well by approximating the local tensile stress amplitudes in the struts near the nodes. Local stress based Haigh diagrams were constructed to provide more insight in the fatigue behavior. When fatigue life is interpreted in terms of local stresses, the behavior of single struts is shown to be qualitatively the same as bulk Ti6Al4V. Compression-compression and tension-tension fatigue regimes lead to a shorter fatigue life than fully reversed loading due to the presence of a mean local tensile stress. Fractographic analysis showed that most fracture sites were located close to the nodes, where the highest tensile stresses are located.
Highlights
Ti6Al4V is the most popular material for implant production today because of its high strength, high corrosion resistance and good biocompatibility[1]
The novel sample design with a porosity gradient between the solid ends and scaffold middle presented in this study was successfully used to perform quasi-static tension, tension-tension (R = 0.1), tension-compression (R = −1) and compression-compression (R = 10) fatigue tests
The Haigh diagram shows that, for the R-values tested here, a decrease of global stress amplitude is necessary if a mean global tensile stress is applied and a constant fatigue life is required
Summary
Ti6Al4V is the most popular material for implant production today because of its high strength, high corrosion resistance and good biocompatibility[1]. Just like conventionally processed material, governed by surface roughness, residual stress, manufacturing defects, microstructure, and loading conditions[3]. The aim of this work was to make a detailed study of the mechanical properties of SLM based Ti6Al4V ELI scaffolds with diamond unit cells in compression-compression, tension-tension and tension-compression fatigue for different stress amplitudes. For this purpose, a novel sample geometry with gradient porosity was designed and successfully tested in fatigue, which resulted in the construction of an S-N curve for every load condition. Experimental data was analyzed by applying local stress based fatigue analysis, which resulted in new insights in the failure of SLM based Ti6Al4V scaffolds under clinically and industrially relevant load conditions
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