چكيده به لاتين
Biomaterials are natural or artificial materials which facilitate organ recoveriy due to the interaction with alive textures. They can be used as a total organ replacement or an enhancement in phsyologic functions. In order to reduce the manufacturing costs and enhance the in-vivo behavoiur of these Materials, new methods are being designed and investigated. One of the newest methods is Additive Manufacturing or 3D-printing. The core feature of this method is the ability to manufacture complex structures and topologies such as porrous lattice structures to be used as Implants. The reason of using these porrous lattice structures is to hinder the possibility of occouring Stress Shielding phenomenon, due to mechanical mismatch between bone and implant, specially deference in Young Modulus. As a living organ, the bone will grow and be recovered only if it’s being used and functioning in the target ambient. Clinical studies have shown that using stronger and stiffer Materials as a combined system with bone, such as bone-implant combination, gradually leads to degradation of bone in the system. This happens due to stress repartition in the combined system, as the stiffer implant bears the whole imposed stress on the system, leading to gradual bone degradation as it’s not much being used. Thus, the porous lattice structures were designed, manufactured and their mechanical behavior was simulated and then evaluated by actual mechanical tensile and compression tests. First, the unit cell of Diag structure was investigated and proven to have some stress concentration spots in the struts intersection, due to special geometrical orientaion. Thus, the Unit cell was redesigned, inorder to hinder the stress concentration and softening the material, resulting in generating 2 new unit cells named Arr-Diag and Sph-diag. then an optimization code was applied on the unit cells, in order to modify the dimentional properties, followed by lattice structures generation by successive
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repetition of these unit cells in 3 directions. A 10 % strain was later imposed on the Structures and the reaction forces of all nodes were then calculated. Results showed that new structure modification leads to a better stress distribution and also hindering the stess concentration spots. The Strucres were then manufactured by selective Laser Melting 3D printing machine, using Ti-6Al-4V powder. Imposing same tesile and compression tests on the Samples, obtained same results as simulation, where the residual tesile strain in Sph- , Arr- and Simple-Diag was recorded 0.37, 0.89 and 1.01 mm respectively. The Ultimate Tensile Strength of three structures was reported as 950, 1050 and 1060 Mpa respectively as before. The results of compression test were reported as 0.73, 0.66 and 0.60 mm of residual strain in Simple-Diag, Arr-diag and Sph-Diag respectively. Each structure showed a different Ulmate Tensile Strength reported as 1350, 1060, 1050 Mpa respectively as before. The obtained results presented a noticeable enhancement in mechanical properties of the lattice structures due to unit cell modification resulting in improved Elastic and Elasto-plastic behavior.