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Lopes H.,Polytechnic Institute of Bragança | Araujo Dos Santos J.V.,University of Lisbon | Moreno Garcia P.,Institute Engineering Mecanica E Gestao Industrial INEGI | Ferreira F.,Polytechnic Institute of Porto
Civil-Comp Proceedings | Year: 2012

This paper proposes a damage localisation method based on the analysis of perturbations in the second, third and fourth order derivatives of experimental modal displacement field. The high spatial resolution modal rotation fields are measured using speckle shearography with stroboscopic illumination and time phase modulation. The mode shape derivatives up to the fourth order are obtained by numerical differentiation. A new numerical differentiation strategy is proposed with the objective of minimising the propagation of experimental noise. This study is performed on a laminated composite plate where internal damage at two locations was created by two low energy impacts. A comparative analysis of the results between this method and the one proposed in previous studies is presented. The low experimental noise obtained in the measurements and the new differentiation method has led to a significant improvement in the damage localisation. © Civil-Comp Press, 2012.


Moreno-Garcia P.,Institute Engineering Mecanica E Gestao Industrial INEGI | Lopes H.,Polytechnic Institute of Bragança | Araujo Dos VSantos J.V.,University of Lisbon | Maia N.M.M.,University of Lisbon
Civil-Comp Proceedings | Year: 2012

A new vibration based damage localisation method relying on differences of third and fourth order spatial derivatives of modal displacements of composite laminated plates is proposed in this paper. The damage is simulated by decreasing the laminate stiffness of specific finite elements. Since the displacement fields of the damaged plate are discrete, they are differentiated using higher order finite differences. The modal displacement fields of the undamaged plate are obtained using the Ritz method and, therefore, the spatial derivatives are computed analytically. Parametric studies relating the number of measured degrees of freedom to the quality of the damage localisations are carried out. The results of the present method are compared with the results obtained with an extension of the well-known rotation and curvature methods. It was found that higher order derivatives, in particular fourth order derivatives, are very promising for damage localisation in composite laminated plates. © Civil-Comp Press, 2012.


Durao L.M.P.,Polytechnic Institute of Porto | Goncalves D.J.S.,Polytechnic Institute of Porto | Tavares J.M.R.S.,University of Porto | Tavares J.M.R.S.,Institute Engineering Mecanica e Gestao Industrial INEGI | And 5 more authors.
Composite Structures | Year: 2010

In this work, a comparative study on different drill point geometries and feed rate for composite laminates drilling is presented. For this goal, thrust force monitoring during drilling, hole wall roughness measurement and delamination extension assessment after drilling is accomplished. Delamination is evaluated using enhanced radiography combined with a dedicated computational platform that integrates algorithms of image processing and analysis. An experimental procedure was planned and consequences were evaluated. Results show that a cautious combination of the factors involved, like drill tip geometry or feed rate, can promote the reduction of delamination damage. © 2009 Elsevier Ltd. All rights reserved.


Guedes R.M.,Institute Engineering Mecanica e Gestao Industrial INEGI | Guedes R.M.,University of Porto | Pereira C.M.C.,Institute Engineering Mecanica e Gestao Industrial INEGI | Fonseca A.,University of Aveiro | Oliveira M.S.A.,University of Aveiro
Composite Structures | Year: 2013

Nanocomposites of ultra-high molecular weight polyethylene reinforced with multiwalled carbon nanotubes (UHMWPE/MWCNT) have been prepared with different volume fractions of MWCNTs: 0.2, 0.4, 0.6, 0.8 and 1.0%. DMTA experiments were carried out using a TA Instruments Q800 equipment and the samples were cut from the compressed sheets of polymer and composites. The experiments were conducted on each sample at 12 different frequencies varying from 0.1. Hz to 100. Hz over the temperature range of 22-82. °C at an interval of 5. °C where the reference temperature was kept at 37. °C. It was verified that both horizontal and vertical shifts are necessary to superimpose the dynamic modulus/frequency curves of all cases. The MWCNT did not seem to change the viscoelastic nature of the UHMWPE, i.e. incorporation of up to 1. wt.% of MWCNTs has negligible influence on the viscoelastic behaviour of the UHMWPE. Hence the same analytical model is applicable for the viscoelastic description of the nanocomposites. © 2013 Elsevier Ltd.


Ramos C.A.,Polytechnic Institute of Porto | De Oliveira R.,Institute Engineering Mecanica e Gestao Industrial INEGI | Marques A.T.,University of Porto | Frazao O.,INESC Porto
Optica Applicata | Year: 2011

This study seeks the development of adaptive composites capable to monitor and actively damp vibrations. In the proposed material, vibrations measurements are performed by an embedded low finesse optical fibre extrinsic Fabry-Pérotinterferometer, while active damping will be performed by embedded piezoelectric ceramics. This paper focuses on the development of the monitoring procedure. The proposed interrogation procedure for the low finesse optical fibre extrinsic Fabry-Pérot interferometer was successfully used to monitor the composite plate when submitted to four-point bending dynamic tests at different frequencies. The embedding of both sensing and actuating components in carbon-fibre reinforced composite laminates is also presented. In the case of the actuator, the efficiencyof the embedding process was merely analysed from the capability of the piezoelectric ceramic to monitor dynamic strain of the composite using the PZT piezoelectric inverse effect.


Cousseau T.,Institute Engineering Mecanica e Gestao Industrial INEGI | Graca B.,Institute Engineering Mecanica e Gestao Industrial INEGI | Campos A.,Polytechnic Institute of Porto | Seabra J.,University of Porto
Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology | Year: 2011

Thrust ball bearings lubricated with several different types of grease, including three biodegradable low-toxicity greases, were tested in a modified four-ball machine in order to evaluate the bearing friction torque. At the end of each test, grease samples were obtained and analysed through ferrography, allowing the quantification and evaluation of the bearing wear. In order to compare the grease performance in terms of friction and wear, a correlation between the grease characteristics (base oil, bleed oil, thickener structure, and rheological parameters) and the experimental results was established. © Authors 2011.


Cousseau T.,Institute Engineering Mecanica e Gestao Industrial INEGI | Graca B.,Institute Engineering Mecanica e Gestao Industrial INEGI | Campos A.,Polytechnic Institute of Porto | Seabra J.,University of Porto
Lubrication Science | Year: 2010

The reduction of the power loss generated in mechanical transmissions and the use of low friction biodegradable lubricants has been attracting considerable attention in recent times. Therefore, it is necessary to develop methods to test and evaluate the performance of such lubricants and compare them with conventional ones. In this sense, a Four-Ball Machine was modifi ed allowing the test of rolling bearings. A 51107 thrust ball bearing was used to test two different greases and the corresponding base oils. Friction torque and operating temperatures were continuously monitored to quantify the power loss and the heat evacuation for each lubricant tested. Copyright © 2010 John Wiley & Sons, Ltd.


Cousseau T.,Institute Engineering Mecanica e Gestao industrial INEGI | Graca B.M.,Institute Engineering Mecanica e Gestao industrial INEGI | Campos A.V.,Polytechnic Institute of Porto | Seabra J.H.O.,University of Porto
Tribology International | Year: 2012

The friction torque and the operating temperatures in a thrust ball bearing were measured for seven different types of greases, including three biodegradable greases having low toxicity. These friction torque tests were performed using a modified Four-Ball machine. Rheological evaluations of the lubricating greases were made using a rheometer. Bleed oils were extracted from the greases and the dynamic viscosities were measured. In order to compare the performance of the lubricant greases in terms of friction, the grease characteristics were related to experimental results, showing that the interaction between thickener and base oil have strong influences in the bearing friction torque. © 2011 Elsevier Ltd.


Silva A.C.F.,Institute Engineering Mecanica e Gestao Industrial INEGI | Braga D.F.O.,Institute Engineering Mecanica e Gestao Industrial INEGI | Figueiredo M.A.V.D.,University of Porto | Moreira P.M.G.P.,Institute Engineering Mecanica e Gestao Industrial INEGI
Materials and Design | Year: 2014

The increasing use of aluminium alloys in transportation industry, such as railways, shipbuilding and aeronautics, promotes the development of more efficient and reliable welding processes. Friction stir welding (FSW) is a prominent solid-state joining technology that arose as a possible reliable welding solution. Optimized process parameters are not regularly used in previous studies found in the literature, in particular T-joints, which difficult the process industrial application. This study is focused on the optimization of friction stir welded T-joints using the Taguchi method. Mechanical tests of 27 different welded joints were carried out, and results were analysed using ANOVA, mean effect and response surface methodology (RSM). The tool rotational speed was verified to be the most influent factor in the joint mechanical properties, and is strongly dependent on the shoulder/probe diameters ratio. It was also shown that using 1000. rpm, 3.90. mm of probe depth and shoulder/probe diameters ratio of 2.5 (shoulder diameter of 15. mm) it may be achieved improved joint strength. For the optimized parameters it was verified that the welding speed does not have a significant influence. Equations to predict the joints mechanical properties were also derived through multiple regression. © 2013 Elsevier Ltd.


Silva A.C.F.,Institute Engineering Mecanica e Gestao Industrial INEGI | Braga D.F.O.,Institute Engineering Mecanica e Gestao Industrial INEGI | de Figueiredo M.A.V.,University of Porto | Moreira P.M.G.P.,Institute Engineering Mecanica e Gestao Industrial INEGI
International Journal of Advanced Manufacturing Technology | Year: 2015

Friction stir welding (FSW) is a highly reliable joining process. However, there is still lack of optimized FSW parameters for different joint configurations. The present manuscript presents a set of optimization studies for different friction stir welding joint geometries of AA6082-T6 aluminium alloy: butt, lap and T joints. The optimization process was performed using Taguchi orthogonal arrays (OA) for designing experiments, analyses of the average effects (main effect plot) and variance (ANOVA). Welded joints were manufactured according to orthogonal arrays, selected using the Taguchi method, for each type of joint, and the ultimate tensile strength (UTS) was evaluated for statistical optimization. As a major asset for the current state of the art, this manuscript contribution is focused on the determination of the most relevant FSW parameters on UTS for a complete range of joints, as well as their interactions. In the particular case of lap and T joints, parameter optimization studies are lacking in the literature, and as such, this work aims at tackling the issue. The parameter combinations to achieve the best mechanical properties for each joint configuration were derived. © 2015, Springer-Verlag London.

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