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Silva F.G.A.,INEGI Institute Engineering Mecanica e Gestao Industrial | Morais J.J.L.,University of Tras os Montes e Alto Douro | Dourado N.,University of Tras os Montes e Alto Douro | Xavier J.,University of Tras os Montes e Alto Douro | And 3 more authors.
International Journal of Adhesion and Adhesives | Year: 2014

Cohesive laws of wood bonded joints under mode II loading were determined using two different methods. The direct method requires the establishment of the relation between the strain energy release rate under mode II loading (G II) and the corresponding crack tip shear displacement (CTSD II). An equivalent crack length procedure was used to assess the evolution of GII, with remarkable advantages relatively to classical data reduction schemes. The CTSDII was determined from displacements measured by digital image correlation. The cohesive laws were obtained by differentiation of a logistic function fitted to the GII=f(CTSD II) relation. The inverse method is based on an optimization procedure using a genetic algorithm with the objective to determine the cohesive law providing the best agreement between numerical and experimental load-displacement curves. Four parameters of the adjusted trapezoidal law were obtained in this optimization procedure. Both direct and inverse methods propitiated excellent agreement between numerical and experimental load-displacement curves, thus revealing their adequacy to determine cohesive laws of wood bonded joints under mode II loading. © 2014 Elsevier Ltd. Source

Fernandes R.,University of Porto | De Moura M.F.S.F.,University of Porto | Silva F.G.A.,INEGI Institute Engineering Mecanica e Gestao Industrial | Dourado N.,Royal University
Composite Structures | Year: 2014

In this work fracture characterization under mode I loading of a hybrid laminate composed by a unidirectional carbon-epoxy composite and cork was performed using the Double Cantilever Beam test. An equivalent crack length procedure based on specimen compliance and Timoshenko beam theory applied to the composed beam was adopted to evaluate the fracture energy. The procedure revealed to be quite effective and it was validated numerically by means of finite element analysis including cohesive zone modelling. The analysis of the experimental results has shown that an increase of 32% of mode I toughness relative to monolithic carbon-epoxy laminate was obtained, which proves that hybridization using cork results in a quite effective procedure to increase interlaminar toughness of composite laminates. © 2014 Elsevier Ltd. Source

Faria H.,INEGI Institute Engineering Mecanica e Gestao Industrial | Guedes R.M.,University of Porto
Polymer Testing | Year: 2010

The certification of glass-fibre reinforced plastic (GFRP) piping systems is regulated by normative standards in which test series of 10,000 h are required to estimate the residual properties at the end of the expected life (normally, 50 years). In this paper, the possibility to reduce the test duration, whilst maintaining an equivalent prediction of long-term properties, is discussed. Experimental results from standard test procedures conducted on GFRP pipes of four different types and respective data analysis support this possibility. The estimation error when using only data from shorter tests is consistently less than 10% if compared to the standard methods. © 2009 Elsevier Ltd. All rights reserved. Source

Falco O.,University of Girona | Lopes C.S.,IMDEA Madrid Institute for Advanced Studies | Lopes C.S.,INEGI Institute Engineering Mecanica e Gestao Industrial | Mayugo J.A.,University of Girona | And 2 more authors.
Composite Structures | Year: 2014

This paper presents an experimental study of the effects of tow-drop gaps in Variable Stiffness Panels under drop-weight impact events. Two different configurations, with and without ply-staggering, have been manufactured by Automated Fibre Placement and compared with their baseline counterpart without defects. For the study of damage resistance, three levels of low velocity impact energy are generated with a drop-weight tower. The damage area is analysed by means of ultrasonic inspection. Results of the analysed defect configurations indicate that the influence of gap defects is only relevant under small impact energy values. However, in the case of damage tolerance, the residual compressive strength after impact does not present significant differences to that of conventional straight fibre laminates. This indicates that the strength reduction is driven mainly by the damage caused by the impact event rather than by the influence of manufacturing-induced defects. © 2014 Elsevier Ltd. Source

Lopes C.S.,INEGI Institute Engineering Mecanica e Gestao Industrial | Gurdal Z.,Technical University of Delft | Camanho P.P.,University of Porto
Composites Part A: Applied Science and Manufacturing | Year: 2010

A large number of composite parts include cutouts to accommodate windows, doors, and bolted joints. These regions are hot-spots in terms of design because they concentrate stresses, hence becoming critical in terms of the structural integrity of the part. A traditional approach to the problem of stress concentrations around cutouts is to locally increase the laminate thickness in order to improve the strength margins. Often this practice attracts more loads to the cutout besides increasing part weight. A more effective solution is to tailor the panel in-plane stiffness by means of fibre-steered laminates, and avoid the stress concentrations altogether. The present research demonstrates that it is possible to design and manufacture composite panels whose buckling and first-ply failure responses are insensitive to the existence of a central hole. Moreover, it is shown that the structural performance of these designs more than doubles that of straight-fibre configurations. © 2010 Elsevier Ltd. All rights reserved. Source

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