effect of porosity and cell topology on elastic plastic behavior of cellular structures

Abstract 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

Tensile and compression properties of variously arranged porous Ti-6Al-4V additively manufactured structures via SLM

Abstract 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

Microstructure and properties of a silicon coating deposited on a titanium nickelide substrate using molecular-beam epitaxy equipment

The microstructure and properties of a silicon coating on a titanium nickelide substrate were studied to assess the possibility of using such a coating to improve the biocompatibility of medical implants. The silicon coating with thickness of 4.0±0.5 microns was applied to the TiNi substrate on a molecular beam epitaxy unit. The coating had a submicrocrystalline structure with a crystallite size of 0.1...0.2 microns, a developed surface, and high crack resistance

FROM THE ORIGINATOR

From the originator

Efficient optimization framework for L-PBF fatigue enhanced Ti6Al4V lattice component

Industries today face challenges in incorporating metallic additively manufactured lattice structures in critical components subjected to fatigue loading. This work explores the relationship between fatigue properties and the printing orientation of Laser-Powered Bed Fusion (LPBF) lattice structures. This relation is at the base of a cost-effective and time-efficient optimization workflow able to determine the optimal lattice printing orientation for improved fatigue life. Fatigue resistance is tested under uniaxial conditions on miniaturized specimens that mimic the lattice sub-unit elements: struts and nodes. The collected data is used as input for the optimization algorithm to determine the specimen orientation that maximizes fatigue life. The optimized specimens are manufactured, tested under three-point-bending conditions, and analysed using metrological x-ray computed tomography to verify the improvement. The proposed workflow is able to produce a 24 % increase in specimen fatigue life by simply adjusting the orientation on the printing plane

Comparative metrological characterization of Ti6Al4V lattice structures produced by laser powder bed fusion

The advancement of Additive Manufacturing (AM) technologies, such as Laser Powder Bed Fusion (LPBF), enables the fabrication of metallic lattice materials with a wide range of topologies and size scales. The possibility to manufacture these materials into complex shapes with good property-to-weight ratio stimulates a growing interest in several industrial sectors, including biomedical, aerospace, and automotive. Nevertheless, such structural features printed at a small-scale often suffer from a wide range of morphological defects that can lead to a marked deviation from the nominal geometry and consequently impact the mechanical, transport and thermal properties. An accurate metrological characterization of the lattice is thus of paramount importance for a more reliable prediction of the properties of the lattice. The most common characterization techniques used for as-built lattice materials are scanning electron microscopy (SEM), optical microscopy (OM) and X-ray computed tomography (CT). CT, contrary to the other methods, provides full 3D data including inaccessible geometries and features, in a non-destructive way, but it requires expensive equipment and considerable expertise. SEM and OM can be faster and less expensive, but can be non-destructive only when limited to the outer surface of the lattice. When combined with metallographic analysis, instead, they require destructive, careful and time-consuming specimen preparation, and the analysis is confined to selected sections. In this work, the three above-mentioned techniques are applied to the metrological characterization of LBPF Ti6Al4V regular cubic lattices of 4 mm unit cell size and struts with circular cross-section of diameter 0.760 mm. The results in terms of strut cross-section parameters and junction fillet radius are compared and the effect of the size of the analysis domain on the accuracy of the results is investigated by comparing lattice sub-volumes of different size. Via a thorough statistical analysis it is shown that CT and metallographic characterization are compatible, while microscope imaging can lead to an overestimation of the strut thickness