DSpace Collection:

Analytical sensitivity matrix for the inverse identification of hardening parameters of metal sheets

Tue, 01 Jan 2019 00:00:00 GMT

Title: Analytical sensitivity matrix for the inverse identification of hardening parameters of metal sheets Authors: Prates, P.A.; Pereira, A.F.G.; Oliveira, M.C.; Fernandes, J.V.

Structural, chemical, optical and mechanical properties of Au doped Al-N sputtered coatings

Thu, 25 Sep 2014 00:00:00 GMT

Title: Structural, chemical, optical and mechanical properties of Au doped Al-N sputtered coatings Authors: Figueiredo, N. M.; Vaz, F.; Cunha, L.; Rodil, S. E.; Cavaleiro, A. Abstract: This paper is focused on the structure, chemical composition, optical and mechanical properties of coatings consisting in an Alsingle bondN matrix incorporating different Au contents (up to 2.5 at.%). The Au was incorporated in the matrix atomically or in the form of very small nanoparticles (< 1 nm). With the increase in the Au content both the refractive index and the coefficient of extinction were increased. The AlN matrix presented a crystalline wurtzite phase, stable up to 1000 °C. With annealing at 400 °C the precipitation of XRD detectable Au nanoparticles was possible, originating SPR light absorption. The Alsingle bondN + Au coatings exhibited hardness values between 15 and 24 GPa, with no significant changes after the annealing treatments at low temperatures. These coatings are of interest to the decorative applications.

Mechanical and wear behaviours of nano and microfilled polymeric composite: effect of filler fraction and size

Mon, 01 Sep 2014 00:00:00 GMT

Title: Mechanical and wear behaviours of nano and microfilled polymeric composite: effect of filler fraction and size Authors: Antunes, P. V.; Ramalho, A.; Carrilho, E. V. P. Abstract: The addition of ceramic reinforced material, SiC particles, to resin matrices, results in the improvement of the overall performance of the composite, allowing the application of these materials as tribo-materials in industries such as: automotive, aeronautical and medical. Particle-reinforced polymeric composites are widely used as biomaterials, for example as dental filler materials and bone cements. These reinforced composites have improved mechanical and tribological performance and have higher values of elastic modulus and hardness, and also reduce the shrinkage during the polymerisation compared with resin matrices. However, the effect of the filler level in mechanical and tribological behaviour is not quite understood. The aim of this work is to determine the influence of the particle volume fraction and particle size in the wear loss of the composites and their antagonists. Reciprocating wear tests were conducted using a glass sphere against resin polyester silica reinforced composite in a controlled medium, with an abrasive slurry or distilled water. For 6 μm average particle dimension, seven particles contents were studied ranging from 0% to 46% of filler volume fraction (FVF). Afterwards, filler volume fractions of 10% and 30% were selected; and, for these percentages, 7 and 4 average particle dimensions were tested and were evaluated regarding their wear behaviour, respectively. The reinforcement particle dimensions used ranged from 0.1 μm to 22 μm with the 10% filler fraction, and for 30% of filler content the range extended from 3 μm to 22 μm. The results allow us to conclude that in an abrasive slurry medium the composite abrasion resistance decreases with the increase of the particle volume fraction, in spite of the accompanying rise in hardness and elastic modulus. With constant FVF, and abrasive slurry, the composite wear resistance increases with increasing average particle dimension. In a distilled water medium and with several FVF values, the minimum wear was registered for a median particle content of 24%. In this medium and with constant FVF the highest wear resistance occurred for average reinforcement particles of 6 μm. The removal mechanisms involved in the wear process are discussed, taking into account the systematic SEM observations to evaluate the wear mechanisms.

Factors affecting moment redistribution at ultimate in continuous beams prestressed with external CFRP tendons

Sat, 01 Nov 2014 00:00:00 GMT

Title: Factors affecting moment redistribution at ultimate in continuous beams prestressed with external CFRP tendons Authors: Lou, Tiejiong; Lopes, Sergio M. R.; Lopes, Adelino V. Abstract: A numerical investigation of redistribution of moments in continuous concrete beams prestressed with external carbon fiber reinforced polymer (CFRP) tendons at failure loads is described. A finite element analysis (FEA) model is introduced, and an extensive parametric study is carried out on two-span continuous beams. The factors examined in this study include the content of non-prestressed steel, tendon eccentricities, tendon area, effective prestress, span-to-height ratio, concrete strength, CFRP modulus of elasticity and load type. The results obtained from FEA are compared with those obtained from various codes. The study shows that the importance of some factors is not reflected in the codes. When used to calculate the degree of moment redistribution in these beams, the parameter εt (net strain in extreme tension steel) seems to be more reasonable than the parameter c/d (ratio of neutral axis depth to section effective depth). A simplified equation for calculating the degree of moment redistribution at ultimate is proposed.