Unidade de Investigação - CDRsp – Centro para o Desenvolvimento Rápido e Sustentado de Produto
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- Study on the fatigue strength of AA 6082-T6 adhesive lap jointsPublication . Pereira, António; Ferreira, J.M.; Antunes, F.V.; Bartolo, PauloA research study on the fatigue behaviour of aluminium alloy adhesive lap joints was carried out to understand the effect of surface pre-treatment and adherends thickness on the fatigue strength of adhesive joints. The adherend material used for the experimental tests was an aluminium alloy 6082-T6 in the form of thin sheets, and the adhesive used was a high strength epoxy (Araldite 420 A/B). The surface preparation included an abrasive preparation (AP joints) and sodium dichromate-sulphuric acid etch (CSA joints). A maximum fatigue strength was obtained for the CSA surface treatment with a 1.0 mm adherends' thickness. The fastest fatigue damage was related with a high surface roughness and a high stress perpendicular to adhesive surface, which helps to promote the adhesive failure. A numerical analysis was also performed to understand the effect of the adherends thickness on the stress level. Results showed an increase of the out-of-plane peak stresses with the increase of adherends thickness.
- Rheological behavior of alginate solutions for biomanufacturingPublication . Rezende, Rodrigo Alvarenga; Bartolo, Paulo; Mendes, Ausenda; Filho, Rubens MacielThe rheological behavior of alginate solutions were investigated for the optimal design of a biomanufacturing system to produce alginate structures for tissue engineering. Its rheological properties were determined by a rheometer through rotational and oscillatory I tests. Experimental results were used to model the alginate solutions characteristics. The findings suggest that alginate solutions undergo shear-thinning effects with increasing shear rates. It is also possible to observe that its loss modulus is higher than the storage modulus ones being both modulus dependent upon the frequency, which is a typical characteristic of dilute solutions.
- Fracture toughness of the heat affected zone on Nd-YAG laser welded jointsPublication . Costa, J.M.; Ferreira, J.M.; Capela, C.; Capela, CarlosLaser deposit welding based on modern Nd-YAG lasers is a new mould repair process with advantages relatively to the traditional methods (Micro-plasma and TIG methods). For moulds steels there are no research studies about the laser deposit welding process effects in respect to fracture toughness, hardness and residual stresses variations in the laser-deposited layer and in the heat affected zone. These variations will have an important influence in the thermal-mechanical fatigue strength of the moulds parts. This paper is concerned on the study of the fracture toughness of transient microstructure regions in Nd-YAG laser welded joints performed in mould steels. Fracture toughness tests were performed in two hot-working tool steels: AISI H13 and AISI P20. Small welded specimens were prepared with U notches and filled with laser welding deposits. The hardness profiles were obtained at the middle cross-section of specimens against distance to the surface in order to identify the microstructures present at the crack tip region. Fracture toughness was evaluated and plotted against the Vickers hardness measured at the fatigue crack tip. Depending of the crack tip depth two very different toughness levels were observed in the H13 steel, while a lower variation of toughness was observed for the P20 steel. The values of fracture toughness observed in each specimen are consistent with the correspondent crack tip microstructure hardness.
- Optimization of Scaffolds in Alginate for Biofabrication by Genetic AlgorithmsPublication . Rezende, Rodrigo; Rezende, Mylene; Bártolo, Paulo; Mendes, Ausenda; Filho, Rubens Maciel; Bartolo, Paulo; Mendes, AusendaWith an increasing in the rate of transplants due to damaged or affected tissues or organs by accidents or diseases and also by the aging of the population in many countries as Brazil, have motivated the research of some novel and alternative ways focused on restoring and replacing tissues. Biofabrication by means of Rapid Prototyping techniques can help in the fashioning and final production of scaffolds devoted to support and stimulate the growth of new tissues. For soft tissues, a biomaterial known as Alginate has been studied and used as raw-material for scaffolds fabrication. A scaffold must guarantee good strength and stiffness at the same time the material degrades gradually. In this work, a single mathematical model experimentally obtained that describes an interesting mechanical behavior of the degradation of alginated-scaffolds is developed. The optimization process scheme using Genetic Algorithms to maximize the elastic modulus and therefore to aid the design of scaffolds in alginate is proposed. The optimization is very welcome to tissue engineering and Biofabrication.
- Modeling and simulation of photofabrication processes using unsaturated polyester resinsPublication . Matias, João Manuel; Bartolo, Paulo; Pontes, António VilelaSeveral kinetic models have been proposed to simulate thermosetting cure reactions. The most complex models, based on a mechanistic approach of cure reactions, are developed based on the concepts of free radical polymerization and the mechanism of reactions with diffusion. However, mechanistic models are usually quite impractical for engineering purposes because of the difficulty in obtaining the model parameters. An alternative to these mechanistic models are the phenomenological models, formulated in terms of the degree of cure and much easier to apply. Phenomenological models have been largely used to study thermal-initiated cure reactions, although only few works used them to model the kinetics of ultraviolet-initiated cure reaction. This work proposes a photo-thermal-kinetic model to study the behavior of unsaturated polyester resins during ultraviolet-initiated cure reactions. The model considers samples with different amounts of initiator concentration and cure reactions performed under different ultraviolet light intensities. The model has been numerically solved using the finite element technique.
- Effect of asymmetrical rolling and annealing the mechanical response of an 1050-o sheetPublication . Simões, Fábio; Sousa, Ricardo J. Alves de; Grácio, José J. A.; Barlat, Frédéric; Yoon, Jeong WhanThe asymmetrical rolling process has been studied as a way to promote intense shear deformations across the sheet thickness. These shear deformations may lead, given the proper conditions, to the development of shear texture components ({001}<110>, {111}<110> and {111}<112>) and also grain refinement. In this work, a 1050-O sheet is asymmetrically rolled and annealed. Conventional rolling is also performed, for comparison purposes. Shear texture components are obtained for the asymmetrically rolled specimens, and seem to be retained after annealing. Differences in mechanical response between asymmetrical and conventionally rolled specimens, as well as texture evolution after heat treatment processing are inferred based on experimental tensile and shear tests. Numerical simulations are used to help explain the differences found on experimental tests. It is proven that it is difficult to spread shear texture through the entire sheet thickness from a general asymmetric rolling process. Based on the fact, future research is discussed at closure.
- High-pressure range shock wave data for syntactic foamsPublication . Ribeiro, J.; Mendes, R.; Plaksin, I.; Campos, J.; Capela, Carlos; Elert, Mark; Furnish, Michael D.; Anderson, William W.; Proud, William G.; Butler, William T.Syntactic foams [SF] are a porous composite material resulting from the mixture of Hollow Glass Micro Spheres [HGMS] with a polymeric binder. Beyond a set of technological advantages over the polymer considered alone, SF present as an essential feature the possibility to control in wide limits the amount, the shape and the size of the pores and for that reason are being used for benchmarking in the area of shock wave [SW] behavior of porous materials. In this paper, SW loading experiments of SF samples were performed in order to assess the high-pressure range Hugoniot equation of state as a function of the SF initial density. Hugoniot data were assessed coupling the SW velocity within the SF samples with the SW velocity in a reference material or with manganin gauge results. The results obtained present a significant variation with the initial specific mass and can be described with appreciable precision by the Thouvenin/Hofmann Plate Gap model, while the concordance between the experimental results and the Gruüneisen model seems to be very dependent on the Gruüneisen coefficient values.
- Biomanufacturing for tissue engineering: Present and future trendsPublication . Bartolo, Paulo; Chua, C. K.; Almeida, Henrique de Amorim; Chou, S. M.; Lim, A. S. C.Tissue engineering, often referred to as regenerative medicine and reparative medicine, is an interdisciplinary field that necessitates the combined effort of cell biologists, engineers, material scientists, mathematicians, geneticists, and clinicians toward the development of biological substitutes that restore, maintain, or improve tissue function. It has emerged as a rapidly expanding approach to address the organ shortage problem and comprises tissue regeneration and organ substitution. Cells placed on/or within constructs is the most common strategy in tissue engineering. Successful cell seeding depends on fast attachment of cell to scaffolds, high cell survival and uniform cell distribution. The seeding time is strongly dependent on the scaffold material and architecture. Scaffolds provide an initial biochemical substrate for the novel tissue until cells can produce their own extra-cellular matrix (ECM). Thus scaffolds not only define the 3D space for the formation of new tissues, but also serve to provide tissues with appropriate functions. These scaffolds are often critical, both in vivo (within the body) or in vitro (outside the body) mimicking in vivo conditions. Additive fabrication processes represent a new group of non-conventional fabrication techniques recently introduced in the biomedical engineering field. In tissue engineering, additive fabrication processes have been used to produce scaffolds with customised external shape and predefined internal morphology, allowing good control of pore size and pore distribution. This article provides a comprehensive state-of-the-art review of the application of biomanufacturing additive processes in the field of tissue engineering. New and moving trends in biomanufacturing technologies and the concept of direct cell-printing technologies are also discussed.
- High-k oxidesPublication . Silva, E. L.; Santos, M. C.Due to the need of increasing the gate capacitance of metal-oxide-semiconductor (MOS) devices, the layer thickness of the SiO2 gate dielectric is reducing to such thickness that the leakage current is becoming too large to control. Suitable high-oxides hence need to be found in order to replace the existing gate dielectric, because the thicker layer of the oxide contender may exponentially decrease the tunnelling currents, while achieving the same level of capacitance as the actual devices of SiO2.
- Computation of the volume of triangulated polyhedraPublication . Gaspar, Miguel