Mechanical properties of trabecular structures produced by SLM, as a function of the trabecular morphology

Abstract: Eurocoating, Italy, is a company that works in the biomedical sector. They have for a long time created prostheses from CAD files achieved from customers, and now they want to build their own expertise about the design. The thesis work was a part of a three year long collaborative research project between Eurocoating and University of Trento that was aiming to investigate the prostheses with open-porous surface and trabecular structure, created by Selective Laser Melting. The purpose of the thesis was to investigate and characterize 30 different trabecular structures of Ti-6Al-4V, fabricated by Selective Laser Melting. That includes investigation the effect on the morphology and porosity fraction caused by the manufacturing and the effect on mechanical and physical properties due to the different characterizations of the structures. The thesis work had its foundation in literature studies to receive deep knowledge about the subject. Practical tests were performed to investigate mechanical behaviour under compressive and tensile loading, static friction and wear resistance. The findings from these tests were compared to the porosity fraction and the morphological characterizations. The result stated that the porosity fraction was lower than the designed porosity, and that is was strongly influenced by size of the voids and struts. The strut thickness was higher than the design values, especially on the lateral surface, while the voids size were approximately as designed. Result from the compression test showed a trend of decreasing stiffness and strength with increasing porosity fraction. Also structures with same porosity fraction could have a wide range in mechanical properties which indicates high dependence on the morphological geometry i.e. pore size and shape, strut size and pore distribution. Comparisons between tensile and compression behaviour stated that the structures had a lower strength but a significant higher stiffness in tensile load. All structures from the wear test showed a good resistance while the results from the friction test needs further investigation to be fully understood. The physical and mechanical properties of the trabecular structures was found to be close to those of cortical and trabecular bone in porosity, stiffness and strength. There is a range of variations leading to possibilities to adopt the application depending on customer. Thus, these can be considered as promising structures used biomedical application to optimize osseointegration and secondary long term fixation.