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The main aim of the current study is to evaluate the compressive quasi-static and fatigue properties of titanium alloy (Ti6Al4V) cellular materials, with different topologies, manufactured via Laser Powder Bed Fusion (LPBF) process. The topologies herein considered are lattice based regular and irregular configurations of cubic, star and cross shaped unit cell along with trabecular based topology. The results have indicated that the effective stiffness of all configurations are in the range of 0.3 – 20 GPa, which is desirable for implant applications. The morphological irregularities in the structures induce bending dominated behavior affecting more the topologies with vertical struts. The S – N curves normalized with respect to the yield stress indicate that the behavior of star regular structures is between purely stretching dominated cubic and purely bending dominated cross based structures. Trabecular structures have shown desirable quasi-static and fatigue properties despite the random distribution of struts.

Additive manufacturing is an evolving technology for fabricating porous structures used in a broad array of applications, ranging from the aerospace industry to biomedical engineering. Porous titanium alloy (Ti6Al4V) structures play a major role in biomedical implants and are preferred over conventional solid implants because their properties can be tailored to obtain the stiffness required to avoid stress shielding and improve osteointegration. The mechanical properties of these structures are dependent on unit cell topology and overall porosity. In the present work, three open cellular configurations were studied, namely regular (square), irregular (skewed square) and fully random structures, at three different porosity levels. The samples were manufactured using the selective laser melting of spherical Ti6Al4V powder. The deviations of manufactured samples from as designed were assessed using morphological characterisations and porosity analyses. The mechanical characterisations of the samples included monotonic and cyclic tensile tests, along with conventional compression tests under monotonic and cyclic conditions. The results from the study indicate a clear deviation of thickness values from as-designed values. The effect of inclination of the strut with respect to the loading axis has been studied in compression samples. The off-axis loading in compression led to the asymmetry in the Young's modulus in compression and tension. These led to finite element modelling of structures in the elastic regime and its validation using Gibson–Ashby model for cellular structures.

Laser-based Powder Based Fusion (LPBF) being one of the most widely used additive manufacturing (AM) process has not only impacted the design of components in aeronautical and automobile industries but also in development of porous components. The properties of these lattice structures can be tailored according to the structural and compatibility requirements depending on the application. Therefore, understanding the behavior of cellular structures under static and fatigue loading becomes necessary. The factors that influence their behavior include relative density, cell topology, cell geometry and microstructure of the material. In this current study, titanium alloy Ti6Al4V cellular structures with four different geometries (Cubic, Star-shaped, X-shaped and Trabecular) manufactured using LPBF are considered. The mechanical performances of the samples, designed in order to have an overall porosity of 70-75%, have been evaluated with static tests under tensile and compressive loading, and with compression-compression fatigue test (R=0.1). The results indicate a clear decrease in the mechanical properties with increase in the bending dominated behavior of the cell types. However, Cubic structures displayed a catastrophic fracture behaviour, while the other structures were more resilient. Furthermore, despite the facts being bending dominated and with the lowest number of struts per node, the Trabecular structures showed good fatigue resistance thanks to the presence of struts in all the directions.

Selective Laser Melting (SLM) is a technology that allows for the realization of metallic porous solids that cannot be produced with other methods. Nevertheless, a geometric discrepancy between the as-designed and as-built part is a well-known issue that can be critically important for biomedical metallic lattices with pore size and strut thicknesses of a few hundred microns. In practice, any geometric imperfection introduces a degree of uncertainty that can alter the mechanical properties of the as-built lattice. A quantitative relationship between the as-designed geometry and the real geometry is a very useful design tool because it makes possible to predict the final morphology of the lattice by considering the manufacturing errors: a more predictable geometry of the lattice structure means more predictable mechanical properties of the implant. In this work, we investigate the relationship between the as-designed strut thickness and the printed strut thickness for regular cubic cell lattices. The joints between the struts are filleted to reduce the stress concentration and increase fatigue resistance. The size of the unit cell is scaled to find the smallest radius which can be accurately reproduced. Moreover, we also studied the effect of the printing direction on geometrical accuracy

In this work we study the mechanical behavior of Ti6Al4V cellular structures by varying the randomness in the cell topology from regular cubic to completely random and the porosity of the structure. The porosity of the structure is altered by changing the strut thickness and the pore size to obtain a stiffness value between 0.5-12Gpa. The geometrical deviation in the structures from the as-designed values is studied by morphological characterization. The samples are subjected to compression and tensile loading to obtain the stiffness and the elastic-plastic behavior of the samples. Finite element modelling (FEM) is carried out on the as-designed structures for both tensile and compressive loading to study the effect of deviation between the as-designed and as-built structures. FEM is also carried out for as-built regular structures, by introducing the geometrical deviation to match the porosity of the as-built structures. Comparison of FEM and experimental results indicated that the effect of cell topology depends on the porosity values. Simulation results of as-built structures demonstrated the importance of defects in the structure.

The main aim of the current study is to evaluate the compressive quasi-static and fatigue properties of titanium alloy (Ti6Al4V) cellular materials, with different topologies, manufactured via Laser Powder Bed Fusion (LPBF) process. The topologies herein considered are lattice based regular and irregular configurations of cubic, star and cross shaped unit cell along with trabecular based topology. The results have indicated that the effective stiffness of all configurations are in the range of 0.3 – 20 GPa, which is desirable for implant applications. The morphological irregularities in the structures induce bending dominated behavior affecting more the topologies with vertical struts. The S – N curves normalized with respect to the yield stress indicate that the behavior of star regular structures is between purely stretching dominated cubic and purely bending dominated cross based structures. Trabecular structures have shown desirable quasi-static and fatigue properties despite the random distribution of struts.

Additively manufactured porous structures find increasing applications in the biomedical context to produce orthopedic prosthesis and devices. In comparison with traditional bulk metallic implants, they permit to tailor the stiffness of the prosthesis to that of the surrounding bony tissues, thus limiting the onset of stress shielding and resulting implant loosening, and to favor the bone in-growth through the interconnected pores. Mechanical and biological properties of these structures are strongly influenced by the size and spatial arrangement of pores and struts. In the present work irregular and regular cellular as well as fully random porous structures are investigated through tensile and compression uniaxial tests. Specific point of novelty of this work is that, beside classical compressive tests, which are standard characterization methods for porous/ cellular materials, tensile tests are carried out. Mechanical tests are complemented with morphological analysis and porosity measurements. An attempt is made to find correlations between cell arrangements, porosity and mechanical properties.

Laser Powder Bed Fusion (L-PBF) provides ample freedom to fabricate lattice materials with tailored micro-architecture. Nevertheless, small-scale structures often suffer from a wide range of morphological defects, which impact the macro-scale mechanical properties. In this work, prominent morphological factors including geometric irregularities (surface notches and cross-section deviation), node geometry and printing direction are assessed for four batches of L-PBF Ti-6Al-4 V cubic lattice specimens, and their fatigue behavior compared. The results show that smoothing the strut fillets at their node remarkably improves the S-N curves and that the printing direction impacts both the fatigue strength and the failure behavior.

The Strain Energy Density (SED) based fatigue criterion proposed in Benedetti et al. Int. J. Fatigue 2020;133:105397 is further developed to incorporate residual stresses (RS). Mechanical and residual stresses are treated separately. The formers are encapsulated in the form of SED associated to stress range and maximum SED. The work done when tensile mechanical strains fluctuate in the presence of compressive RS is added to the equivalent SED of the fatigue criterion. This is calibrated and validated using the results of an extensive experimental campaign aimed at exploring the effect of shot-peened induced RS on plain and notch fatigue strength of Al-7075-T651.