IPS - ESTS – DEM - Artigos científicos
URI permanente para esta coleção:
Navegar
Percorrer IPS - ESTS – DEM - Artigos científicos por autor "Baptista, Ricardo"
A mostrar 1 - 2 de 2
Resultados por página
Opções de ordenação
- An algorithm for fatigue crack growth applied to mixed and biaxial mode loadingsPublication . Baptista, Ricardo; Infante, V.; Freitas, M.Fatigue is still one of the main concerns when dealing with mechanical components failure. While it is fundamental to experimentally determine the fatigue material behavior using standard specimens, testing large and complex component geometries can be complicated. In these cases, the Finite Element Method can be a cost-effective solution but developing fatigue crack growth models is still a complicated task. In order to solve this problem, an algorithm for automatic crack propagation was developed. Using three different modules, the algorithm can generate a complex Finite Element Method model including a fatigue crack; solve this model considering complex loading conditions, by applying the superposition method; and calculate the fatigue crack propagation rate, using it to update the original model. In order to benchmark this solution two different problems were analyzed, a modified compact tension specimen and a cruciform specimen. By modifying the compact tension specimen hole location and simulating an initial crack, it was possible to understand how mixed mode conditions influence the fatigue crack path. Different load ratios and initial crack directions on the cruciform specimen were analyzed. Increasing the load ratio will increase the crack deflecting angle. The obtain solutions were compared with experimental results, showing good agreement. Therefore the developed algorithm can be used to predict the fatigue crack growth behavior on complex geometries and when different types of loads are applied to the component.
- Fatigue behavior of different geometry scaffolds for bone replacementPublication . Baptista, Ricardo; Guedes, M.When transplanting bone tissue is not a possibility, tissue engineering is responsible for developing solutions to substitute the functions of the missing bone structure or support the process of bone regeneration. Scaffolds can be used to fulfill this mission by supporting loads that were applied to the missing bone, supporting the cell regenerating process, allowing for the necessary nutrients and oxygen diffusion and delivering growth factors or drugs. Scaffold geometry design must support static and dynamic loads up to 20 MPa in order to replace human trabecular bone. Also, it should generate macro and micro pores to support cell growth and mineral precipitation, while all pores should be interconnected for nutrient and oxygen diffusion. Scaffolds were fabricated according to ASTM-695 standard, using two different layouts, 50% porosity and a theoretical distance of 0.8 mm between each filament. A 400 µm diameter nozzle was used, and scaffolds were produced at 215 ºC with deposition rate of 30 mm/s. Both designs were fatigue tested until 3600 cycles, using different load amplitudes and a frequency of 0.25 Hz. The orthogonal scaffold showed improved behavior, with compression modulus reaching 680 MPa, when a maximum stress of 14.5 MPa was applied.