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.
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.
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.
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.
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.