Seabra M.R.R.,FEUP |
Cesar De Sa J.M.A.,FEUP |
Sustaric P.,C3M D.o.o. |
Rodic T.,University of Ljubljana
Computational Mechanics | Year: 2012
TheXFEM is a powerful method to handle strong discontinuities in a finite element environment, especially in the study of the final stages of material failure, modelling the propagation of cracks, suppressing the need of remeshing. Nevertheless, for some materials undergoing large strain processes without noticeable volume changes, the discretization technique employed must not only describe the material behaviour but also correctly address the incompressibility constraints. In order to develop a robust formulation for this type of problems, an approach based on the analyses of the underlying sub-space of incompressible deformations embedded in the XFEM approximation is used, in the context of both infinitesimal and finite strains. This study motivated the extension of the conventional formulations of B-bar and F-bar to include the XFEM enrichment functions, whose performance is evaluated through some numerical examples and compared with competingmethods such as the enhanced strain formulation.
Seabra M.R.R.,FEUP |
Sustaric P.,C3M D.o.o. |
Cesar De Sa J.M.A.,FEUP |
Rodic T.,C3M D.o.o. |
Rodic T.,University of Ljubljana
Computational Mechanics | Year: 2013
Originally Continuum Damage Mechanics and Fracture Mechanics evolved separately. However, when it comes to ductile fracture, an unified approach is quite beneficial for an accurate modelling of this phenomenon. Ductile materials may undergo moderate to large plastic deformations and internal degradation phenomena which are well described by continuum theories. Nevertheless in the final stages of failure, a discontinuous methodology is essential to represent surface decohesion and macro-crack propagation. In this work, XFEM is combined with the Lemaitre ductile damage model in a way that crack initiation and propagation are governed by the evolution of damage. The model was built under a finite strain assumption and a non-local integral formulation is applied to avoid pathological mesh dependence. The efficiency of the proposed methodology is evaluated through various numerical examples. © 2012 Springer-Verlag Berlin Heidelberg.
Puga H.,University of Minho |
Costa S.,University of Minho |
Barbosa J.,University of Minho |
Ribeiro S.,FEUP |
Prokic M.,MP Interconsulting
Journal of Materials Processing Technology | Year: 2011
A novel MMM (Multi-frequency, Multimode, Modulated) ultrasonic (US) technology was used to refine the as cast microstructure and improve the mechanical properties of a AlSi9Cu3 alloy. Ultrasonic vibration was isothermally applied to the melt for 120 s at different temperatures slightly above the liquidus temperature of the alloy, using different electric power values, before pouring into a metallic mould. The microstructure of the cast samples was characterized by optical and scanning electron microscopy and energy dispersive spectrometry. Ultrasonic vibration promoted the formation of small α-Al globular grains, changed the size and morphology of intermetallic compounds and distributed them uniformly throughout the castings. Ultimate tensile strength and strain were increased to 332 MPa and 2.9%, respectively, which are 50% and 480% higher than the values obtained for castings produced without vibration. The microstructure morphology and the alloy mechanical properties were found to depend on the electric power and the melt temperature, and by using a suitable combination of these parameters it is possible to achieve high refinement efficiency by treating the melts in the liquid state. © 2011 Elsevier B.V. All rights reserved.
Infante V.,University of Lisbon |
Braga D.F.O.,INEGI |
Duarte F.,INEGI |
Moreira P.M.G.,INEGI |
And 2 more authors.
International Journal of Fatigue | Year: 2016
Building lightweight structures is one of the key strategies to guarantee an efficient, competitive, safe and sustainable public transport system. The implementation of reliable and optimized lightweight structures needs to achieve high levels of performance, cost effectiveness and sustainability. The expected weight saving will significantly reduce fuel consumption and therefore CO2 emission per passenger-kilometer. Friction Stir Welding (FSW) is a solid state process enabling to develop new design concepts for lightweight metallic materials, where previously conventional manufacturing processes as riveting or classical welding were used. This study was conducted within the LighTRAIN project that aims to improve the life cycle costs of the underframe of a passenger railway car, with a novel lightweighted solution. The major objective of the research was to study the fatigue behaviour of dissimilar welded joints based on two different aluminium alloys: AA6082 and AA5754. The paper presents the experimental results obtained in two different structures: AA6082-T6 2 mm and AA5754-H111 2 mm thick joints, and AA6082-T6 2 mm thick joints. Fatigue tests were carried out on lap joints specimens with a constant amplitude loading with a stress ratio R = 0.1. The results of the fatigue tests are presented as well as detailed metallographic characterization of the weld zone and also the hardness distribution at the weld region. Fatigue tests performed on similar and dissimilar joints show low fatigue strength when compared with base materials AA5754 and AA6082, which is associated with the typical "hook" defect inherent to this welding process. The fatigue performance of AA6082 and AA5754 FSW welded joints suggests a shallower S-N curve than for the similar AA6082 FSW welded joints with an improvement in fatigue performance for lower applied stress ranges. © 2015 Elsevier Ltd. All rights reserved.
48th US Rock Mechanics / Geomechanics Symposium 2014 | Year: 2014
Discontinuity sample size influences the experimental shearing parameters of rock joints. To study how peak shear strength evaluation depends on sample size several shear tests were conducted on artificial joints prepared with molds used for encapsulating rock joints. Discontinuity surfaces were shaped with two different saw-tooth profiles. For each one three joint surface sizes were considered: 64, 100 and 144 cm2. The same series of shear tests with dry joint surfaces was repeated with wetted discontinuity samples. Some reduction was observed in peak shear strength values. Tests with dry surfaces were simulated in numerical calculations that reproduced satisfactorily experimental results. Size effect seems to be more important when normal stress is high. With low normal stress imbrication cohesion is influenced by sample size. Some reflection is advisable to propose a transition from one situation to the other. Calibration of numerical models with more laboratory tests will validate them to be used in later developments. Copyright © 2014 ARMA.
Numerical Methods in Geotechnical Engineering - Proceedings of the 8th European Conference on Numerical Methods in Geotechnical Engineering, NUMGE 2014 | Year: 2014
The simulation of mechanical behaviour of rock joints is a valuable contribution to the validation of shear strength criteria and to understand how experimental results can be influenced by scale effects and testing conditions. Two peak shear strength criteria are applied in numerical simulations of shear tests in order to understand how a geometrical predefined joint profile can be equivalent to applying specific shear criteria to a linear interface representing that joint. Saw-toothed and standard Barton's joint profiles were considered. It was found that numerical simulations can reproduce failure laws for peak shear strength calibrated from experimental results. The development of this study is expected to have a valuable contribution to joint roughness numerical modelling specially in post-peak behaviour. © 2014 Taylor & Francis Group.
International Conference on Intelligent User Interfaces, Proceedings IUI | Year: 2012
Virtual Marionette is a research on digital puppetry, an interdisciplinary approach that brings the art of puppetry into the world of digital animation. Inspired in the traditional marionette technology our intention is to study novel interfaces as an interaction platform for creating artistic contents based on computer animated puppets. The overall goal of this thesis is to research and deploy techniques and methods for the manipulation of articulated puppets in real-time with low-cost interfaces to establish an interaction model for digital puppetry. Copyright © 2012 ACM.
Occupational Safety and Hygiene IV - Selected, Extended and Revised Contributions from the International Symposium Occupational Safety and Hygiene, 2016 | Year: 2016
The present study describes the anthropometrics data comparison between two studies made in the north of Portugal, the current study presents 11 body measurements taken in standing posture with workers of food and nutrition unit. In a total of 29 employees, 13 participated in this study, three male and 10 female. The study used the traditional method of anthropometric measurements and to ensure reliable, the measurements were made in pairs. The second study, which served as the comparison was the most significant Portuguese study conducted in 2004 by the Portuguese Institute of Health and Hygiene. This study were measured 891 workers, with 492 male and 399 female, through the method computer-aided measurement, this method was used assessment for photos to make the acquisition of 24 static body measurements in the standing and sitting posture of the samples. The measures compared in the study were stature (body straight), eye height, shoulder height, elbow height, hand center height (arm stretched), hand center height (raised arm), arm length (in horizontal, to hand center), body depth (at the level of the chest), width of shoulders, hip width and distance elbow-fist. Still, was compared the standard deviations and possible differences in the studies. The studies differ in their purposes, the current study aims to create a local database for further dimensioning of the workstation for the population under study. The Portuguese study conducted in 2004, had two objectives the first obtain anthropometric database of the Portuguese population and second objective was to evaluate a new method of acquisition of anthropometric measurements. The results of the comparison between the two studies were showed consistently, the Portuguese study showed higher values on measurements, but with little variation between studies. The current study shown that workers average weight was 7% higher than the Portuguese study. It can be said that the current study has approximate values even with number of samples were smaller than the Portuguese study, it shows necessary more anthropometric studies of the Portuguese population in order to update the previous study data and include workers from other sectors and regions of Portugal. © 2016 Taylor & Francis Group, London.
De Quay Y.,FEUP
Proceedings of the 5th International Conference on Tangible Embedded and Embodied Interaction, TEI'11 | Year: 2011
Who never whispered a secret to a wind chime, or saw it scare off evil spirits will have the opportunity to do so on a massive scale. The Espanta Espíritos is an interactive sculpture that embodies the spiritual and physical features of a wind chime. This piece presents itself as a giant wind chime made out of recyclable material, the size of a person, ready for outdoors or indoors. People can whisper secrets to the Espanta Espíritos, and through a microphone and a camera, it will register these secrets forever. Natural wind, or a specially designed reactive fan, will cause the Espanta Espíritos to move, and then play these recordings through different audio effects, recreating the secret as if said by spirits. To enhance the illusion, phantasmagoric videos of those who whispered will be projected on the sculpture.
Ferreira A.P.,Polytechnic Institute of Bragança |
SDEMPED 2011 - 8th IEEE Symposium on Diagnostics for Electrical Machines, Power Electronics and Drives | Year: 2011
This paper presents a comprehensive study towards the determination of efficient pole-arc coefficients for axial flux permanent magnet (PM) machines, through investigation of the contribution of volume elements of PMs to the no load flux linkage. The proposed methodology involves the evaluation of flux linkage using a mathematical expression which integrates a function over the volume of PMs instead of the classical integration of the magnetic flux density over the coil surface. The process is implemented using 2D finite element (FE) analysis, and the results shows the pole-arc coefficients that maximize the ratio of the flux linkage over the PM volume is between 0.5 and 0.6. © 2011 IEEE.