Porto, Portugal
Porto, Portugal
Time filter
Source Type

Barbosa A.Q.,INEGI | da Silva L.F.M.,University of Porto | Abenojar J.,Charles III University of Madrid | Figueiredo M.,University of Porto | Ochsner A.,Griffith University
Composites Part B: Engineering | Year: 2017

Structural adhesives are increasingly being used for new applications, replacing conventional bonding methods. Epoxy resins are the most common structural adhesives used due to their suitable mechanical, thermal and chemical properties, as well for their low ductility and low toughness. Several researchers, have in the past decades, found it necessary to reverse these properties and find new ways to increase the toughness of these adhesives. There are many processes depicted in the literature on how to increase the toughness of brittle adhesives, the use of rubber particles being one of the most common. The inclusion of particles (nano or micro) is a successful method to improve toughness of structural adhesives. In the present study, natural micro particles of cork are used with the objective of increasing the toughness of a brittle epoxy adhesive. The concept is for the cork particles to act like as a crack stopper leading to more energy absorption. The influence of the cork particle size, amount and the presence of a surface treatment were studied. Cork particles ranging from 38 to 53 and 125 to 250 μm were mixed into adhesive Araldite 2020. The amount of cork in the adhesive varied between 0.25 and 1% in volume. The toughness of the adhesive was assessed through fracture tests, using three-point bending specimens. A Taguchi design experiments was used to understand the influence of each parameter under study (amount, size and presence of surface treatment) and the interaction between them. With this research it was possible to conclude that cork can improve toughness and cork amount, size and the use of plasma surface treatment have influence on the mechanical properties. © 2016 Elsevier Ltd

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.

Catalanotti G.,INEGI | Catalanotti G.,University of Porto | Katunin A.,Silesian University of Technology
Computational Materials Science | Year: 2016

Modern trends in materials dedicated for aircraft applications are focused on development of highly multifunctional materials that allow not only to carry mechanical loading, but also to possess several other types of functionality, e.g. be thermal resistant, electrically conductive, etc. The material of such a type, with a possibility of conducting electrical current without loss of mechanical properties is the main topic of presented research results. The work presented here deals with the determination of the overall stochastic mechanical and electrical properties of a blend of polypyrrole (PPy) and epoxy. The material properties are obtained applying appropriate periodic boundary conditions (PBCs) to the representative volume elements (RVEs) of the material nano-structure. A strategy to model numerically the electrical percolation network in the framework of Finite Element Method (FEM) is proposed and discussed. Electrical and mechanical properties of the material are calculated as a function of the filler volume fraction. Finally, the numerical results are compared with experiments found in literature and an overall good agreement is found. © 2015 Elsevier B.V. All rights reserved.

Ferreira J.J.,1 FEUP INEGI | Zagalo C.M.,ISCSEM IPO | Oliveira M.L.,INEGI | Correia A.M.,FMDUP | Reis A.R.,1 FEUP INEGI
Prosthetics and Orthotics International | Year: 2015

Background: Mandibular reconstruction has been experiencing an amazing evolution. Several different approaches are used to reconstruct this bone and therefore have a fundamental role in the recovery of oral functions. Objectives: This review aims to highlight the persistent problems associated with the approaches identified, whether bone grafts or prosthetic devices are used. A brief summary of the historical evolution of the surgical procedures is presented, as well as an insight into possible future pathways. Study design: A literature review was conducted from September to December 2012 using the PubMed database. The keyword used was "mandible reconstruction." Articles published in the last three years were included as well as the relevant references from those articles and the "historical articles" were referred. This research resulted in a monograph that this article aims to summarize. Results: Titanium plates, bone grafts, pediculate flaps, free osteomyocutaneous flaps, rapid prototyping, and tissue engineering strategies are some of the identified possibilities. The classical approaches present considerable associated morbidity donor-site-related problems. Conclusion: Research that results in the development of new prosthetics devices is needed. A new prosthetic approach could minimize the identified problems and offer the patients more predictable, affordable, and comfortable solutions. Clinical relevance This review, while affirming the evolution and the good results found with the actual approaches, emphasizes the negative aspects that still subsist. Thus, it shows that mandible reconstruction is not a closed issue. On the contrary, it remains as a research field where new findings could have a direct positive impact on patients' life quality. The identification of the persistent problems reveals the characteristics to be considered in a new prosthetic device. This could overcome the current difficulties and result in more comfortable solutions. Medical teams have the responsibility to keep patients informed about the predictable problems related with each elected approach, even understanding that a perfect reconstruction is a secondary goal when compared with maintenance of life. © International Society for Prosthetics and Orthotics 2014.

Paiva B.,INEGI | Neto R.J.,INEGI | Lino J.,FEUP
Innovative Developments in Virtual and Physical Prototyping - Proceedings of the 5th International Conference on Advanced Research and Rapid Prototyping | Year: 2012

Nowadays there are an enormous variety of titanium (Ti) jewelry artifacts. These products have a high specific strength, are corrosion resistant, promote a warm feeling to the human touch and are easily surface modified by temperature or anodization to acquire a sophisticated aesthetic colour. Ti is more durable than gold or platinum, has a lower price and is a fashion material due to the successful use in challengeable applications. This paper describes the importance of using additive manufacturing and conversion processes to develop innovative jewelry titanium artifacts. Combining 3D modelling, stereolithography, conversion technologies with silicone and low melting point metallic molds and precision casting in ceramic shells molds in controlled atmosphere, we were able to manufacture complex shapes with shiny thin sections, that after an adequate heat treatment exhibit a variety of attractive colors that are more difficult and expensive to obtain with existing technology for manufacturing jewelry products (metal forming and machining). © 2012 Taylor & Francis Group, London.

Moreira P.M.G.P.,INEGI | de Jesus A.M.P.,University of Trás os Montes e Alto Douro | de Figueiredo M.A.V.,University of Porto | Windisch M.,MT Aerospace AG | And 2 more authors.
Theoretical and Applied Fracture Mechanics | Year: 2012

Aluminium-lithium (Al-Li) alloys offer attractive properties for lightweight aerospace structures, due to their low density, high strength and fatigue crack growth resistance. Although there are many advantages with Al-Li alloys, limitations remain while using conventional joining techniques. Friction stir welding is a well-established solid-state joining process that is expected to reduce many of the concerns about Al-Li welding. The work presented in this paper involves the characterisation of the fatigue performance of the AA2195-T8X at room temperature. SN and crack growth tests of base material and friction stir welded 5. mm thick specimens were performed. During crack growth tests, three different R ratios (minimum remote stress/maximum remote stress), 0.1, 0.5 and 0.8, were used per each three different material conditions: base material, heat affected zone (HAZ), and weldment. M(T) specimens containing notches at the centre of the weld, at the HAZ and at the base material, were tested. The fatigue crack growth specimens were left with an un-cracked ligament for final evaluation of fracture toughness. Novel results are presented for fatigue crack growth and toughness on T-L orientation. The results for SN fatigue behaviour, fatigue crack growth and toughness of the studied alloy and its friction stir weldments present high values when compared with data found in the literature. © 2012 Elsevier Ltd.

Melro A.R.,INEGI | Camanho P.P.,University of Porto | Andrade Pires F.M.,University of Porto | Pinho S.T.,Imperial College London
International Journal of Solids and Structures | Year: 2013

This paper presents the application of a new constitutive damage model for an epoxy matrix on micromechanical analyses of polymer composite materials. Different representative volume elements (RVEs) are developed with a random distribution of fibres. Upon application of periodic boundary conditions (PBCs) on the RVEs, different loading scenarios are applied and the mechanical response of the composite studied. Focus is given to the influence of the interface between fibre and matrix, as well as to the influence of the epoxy matrix, on the strength properties of the composite, damage initiation and propagation under different loading conditions. © 2013 Elsevier Ltd.

Melro A.R.,INEGI | Camanho P.P.,University of Porto | Andrade Pires F.M.,University of Porto | Pinho S.T.,Imperial College London
International Journal of Solids and Structures | Year: 2013

Micromechanical analyses of unidirectional continuous-fibre reinforced composite materials were performed to study the mechanisms of deformation and fracture of the constituents, and their influence on the mechanical properties of the composite. Special focus was given to the matrix material behaviour as well as to the interface between constituents. The matrix was modelled using a pressure dependent, elasto-plastic thermodynamically consistent damage model. Cohesive elements were used to model the interface between matrix and fibres. Part I of this paper details the continuum model developed for a typical epoxy matrix. Part II will focus on micromechanical analyses of composite materials and the estimation of its elastic and strength properties. © 2013 Elsevier Ltd. All rights reserved.

Martins R.,University of Porto | Locatelli C.,INEGI | Seabra J.,University of Porto
Industrial Lubrication and Tribology | Year: 2011

Purpose - The purpose of this paper is to get a better understanding of roughness evolution and micropitting initiation on the tooth flank, as well as the evolution of surface topography during the test load stages in a modified DGMK short micropitting test procedure. Design/methodology/approach - A modified DGMK short micropitting test procedure was performed, using an increased number of surface observations (three times more) in order to understand the evolution of the surface during each load stage performed. Each of these surface observations consists in the evaluation of surface roughness, surface topography, visual inspection and also weigh measurements as well as lubricant analysis. Findings - This work showed that the larger modifications on surface took place in the beginning of tests, especially during load stage K3 (lowest load, considered as running-in) and on the first period of load stage K6, that is, during the first 200,000 cycles of the test. The 3D roughness parameters (St and Sv), obtained from the surface topographies, gave a more precise indication about surface roughness evolution and micropitting generation than the 2D parameters, especially in what concerns to inferring the depth of micropits and the reduction of roughness. Tooth flank topography allows to identify local changes on the surface and the appearance of first micropits. Research limitations/implications - This work was performed with gears holding a high surface roughness and with a ester-based lubricant. It was interesting to see the differences observed for surface evolution, for other base oils and also for gears with lower roughness. Practical implications - The main implication of this work is the understanding that major changes in the surface took place in the first cycles, indicating that the running-in procedure could be very important for the surface fatigue life. This work also showed that micropitting depends on local contact conditions. Depending on the roughness of the counter surface, micropitting can appear on the bottom of the deep valleys and/or do not appear on the tip of the roughness peaks. The surface topography, and implicitly 3D roughness parameters, is very useful for the observation of surface evolution. Originality/value - This paper shows in detail the evolution of the tooth surface during a micropitting test. The micropits generation and evolution and also surface wear evolution are presented. © Emerald Group Publishing Limited.

Mourao F.,INEGI | Matos J.C.,INEGI
European Wind Energy Association Conference and Exhibition 2014, EWEA 2014 | Year: 2014

The long-term significance of wind measuring campaign results is crucial for achieving a reliable projection of the energy yield. Despite the availability of NWP datasets and mesoscale generated time series, not always such series correlate well with the local times series and some further data processing may be required on such generated data. The here considered approach to that consists on a statistical downscaling method which is relatively common in climatological analysis. Our work was done in two stages: (1) quality analysis of the model in the simulation of the wind regime for four distinct locations; and (2) generation and application of a statistical downscaling method, to be applied to the output data of the simulation model, WRF, operated by Meteogalicia [1]. In the first stage, data attained from four meteorological stations located in northern Portugal was compared with the output data originated from the simulation model through the analysis of some statistical parameters. Results were reasonable in terms of reproduction of the mean wind regime. However, the level of correlation between the series varies slightly from location to location. Secondly, a spatial downscaling model was applied successfully, as results were quite satisfactory. Although results for some of the locations did not present improvement, results in terms of the resource maps obtained with the temporal output series of this model were very interesting. It is, nonetheless, understood, that results can yet be improved through future works that aim to further perfect the downscaling method that was developed.

Loading INEGI collaborators
Loading INEGI collaborators