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Ghiassi, B., J. Xavier, D. V. Oliveira, and P. B. Lourenço. "Application of digital image correlation in investigating the bond between FRP and masonry." Composite Structures. 106 (2013): 340-349. Abstract


Pereira, J., J. Xavier, J. Morais, and J. Lousada. "Assessing wood quality by spatial variation of elastic properties within the stem: Case study of Pinus pinaster in the transverse plane." Canadian Journal of Forest Research. 44 (2014): 107-117. Abstract
Fernández-Cabo, J. L., R. Widmann, M. Arce-Blanco, R. Crocetti, J. Xavier, and A. Majano-Majano. "Assessment of wire-frame analysis models of a historical planked timber arch." Proceedings of the Institution of Civil Engineers - Structures and Buildings. 168 (2015): 680-694. AbstractWebsite
Xavier, J., J. C. R. Pereira, and A. M. P. de Jesus. "Characterisation of steel components under monotonic loading by means of image-based methods." Optics and Lasers in Engineering. 53 (2014): 142-151. AbstractWebsite
Xavier, J., U. Belini, F. Pierron, J. Morais, J. Lousada, and M. Tomazello. "Characterisation of the bending stiffness components of MDF panels from full-field slope measurements." Wood Science and Technology. 47 (2013): 423-441. Abstract
Raposo, P., J. Martins, J. Correia, Maria E. Salavessa, Cristina Reis, José Xavier, and Abilio M. P. de Jesus. "Characterization of the mechanical behaviour of wooden construction materials from quinta lobeira de cima." International Journal of Structural Integrity. 9 (2018): 396-410. AbstractWebsite

Purpose The antique structures are part of the inheritance that our elders left, being important to preserve their memories. It is important to preserve, rehabilitate and restore the historic buildings protecting the cultural patrimony, attending to the actual comfort and habitability requirements. It is necessary to study the behaviour of the various elements that compose antique structures (masonry and wood) in order to develop assessment measures according to the characteristics of the original materials. The paper aims to discuss these issues. Design/methodology/approach An experimental campaign to characterize the mechanical behaviour of the wood of the roof of the �sequeiro� of �Quinta Lobeira de Cima�, a building from the twentieth century located in Minho, was carried out. The tested wood specimens are from two different species: chestnut and oak. Compression, tension and static flexion tests according to parallel to the grain direction were performed. Other parameters, such as density, moisture content and longitudinal modulus of elasticity in compression and in tension, were also obtained. The measurement of displacements was made with Digital Image Correlation (DIC). Findings The results of this study show the similarity between experimental and empirical values for the studied woods species. Originality/value This original study aimed at characterizing the mechanical properties using DIC of wood of the roof of the �sequeiro� of �Quinta Lobeira de Cima�, a building from the twentieth century located in Minho (Portugal). This study is part of master thesis of Jo�o Martins, an original research work.

Raposo, P. C., J. Martins, J. A. F. O. Correia, M. E. Salavessa, C. Reis, J. M. C. Xavier, and A. M. P. de Jesus. "Characterization of the Tensile Mechanical Behavior of Wooden Construction on Materials from Historic Building." Procedia Structural Integrity. 5 (2017): 1086-1091. AbstractWebsite

Abstract Ancient structures are part of the inheritance our elders left us. These historical inheritance needs to be preserved, so the historic structures need to be rehabilitated and restored, protecting the cultural patrimony and attending to the comfort and habitability required nowadays. In order to accomplish a good and economic rehabilitation is essential to study the behaviour of traditional structures elements (masonry and wood) in order to develop adequate assessment measures and techniques. In this context it was carried out an experimental campaign to characterize the tensile mechanical behavior of the woods from the �sequeiro� wood structure, integral part of the �Quinta de Lobeira de Cima� farm. This building from the 20th century is located in Minho, Portugal. Tensile Tests were carried out for two different species of wood, chestnut and oak. The tensile tests were performed to obtain the tensile strength parallel to the fibers, using the digital image correlation (DIC) for the extension measurement.

Dias, G. F., M. F. S. F. de Moura, J. A. G. Chousal, and J. Xavier. "Cohesive laws of composite bonded joints under mode I loading." Composite Structures. 106 (2013): 646-652. Abstract
Silva, A. L. L., A. M. P. de Jesus, J. Xavier, J. A. F. O. Correia, and A. A. Fernandes. "Combined analytical-numerical methodologies for the evaluation of mixed-mode (I+II) fatigue crack growth rates in structural steels." Engineering Fracture Mechanics. 185 (2017): 124-138. AbstractWebsite

Abstract This paper proposes an experimental study aiming to evaluate stress intensity factors (SIFs) for fatigue cracks propagating under pure mode I and mixed-mode I+II for a S235 structural steel. Compact tension (CT) specimens with a side hole were manufactured in order to generate a stress field, ahead of the crack tip, resulting in mixed-mode fatigue crack propagation. Specimens with distinct side hole locations were submitted to fatigue tests under stress controlled conditions for a stress rati

Pinto, V. C., Tiago Ramos, Sofia Alves, J. Xavier, Paulo Tavares, P. M. G. P. Moreira, and Rui Miranda Guedes. "Comparative Failure Analysis of PLA, PLA/GNP and PLA/CNT-COOH Biodegradable Nanocomposites thin Films." Procedia Engineering. 114 (2015): 635-642. AbstractWebsite

Abstract Biodegradable polymers such as poly(lactic) acid (PLA) have been studied for biomaterials applications such as natural human ligament replacement, however these materials could be applied to other sectors as aerospace, aeronautics, automotive, food packaging. \{PLA\} presents a relatively brittle with a mode I fracture behavior, being often blend with other biodegradable or non-degradable polymers to improve its fracture energy. For some existing applications, \{PLA\} components exhibit accumulated permanent deformation resulting from dynamic mechanical inputs, resulting on failure by laxity of parts. Aiming the improvement of \{PLA\} mechanical properties, the inclusion of carbon nanofillers into \{PLA\} matrix, in particular, CNT-COOH and \{GNP\} have been developed, due to their strong sp2 carbon-carbon bondings and their geometric arrangement that enhance mechanical properties of the polymer matrix. \{PLA\} and nanocomposites were produced by melt blending followed by compression molding in a hot press, with small weight percentages of nanofillers added to the matrix. Quasi static tensile tests were performed on a mechanical testing machine (Instron™ ElectroPuls E1000) along with failure analysis of specimens with centered crack with digital image correlation, revealing strain distribution along specimens.

Fernandes, A., J. Lousada, J. Morais, J. Xavier, J. Pereira, and P. Melo-Pinto. "Comparison between neural networks and partial least squares for intra-growth ring wood density measurement with hyperspectral imaging." Computers and Electronics in Agriculture. 94 (2013): 71-81. Abstract
Xavier, J. C., N. M. Garrido, M. Oliveira, J. L. Morais, P. P. Camanho, and F. Pierron. "A comparison between the Iosipescu and off-axis shear test methods for the characterization of ıt Pinus pinaster Ait." Composites Part A: Applied Science and Manufacturing. 35 (2004): 827-840. Abstract


Sousa, A. M. R., J. Xavier, M. Vaz, J. J. L. Morais, and V. M. J. Filipe. "Cross-correlation and differential technique combination to determine displacement fields." Strain. 47 (2011): 87-98. Abstract


Silva, F., J. Xavier, F. A. M. Pereira, J. Morais, N. Dourado, and M. F. S. F. de Moura. "Determination of cohesive laws in wood bonded joints under mode I loading using the DCB test." Holzforschung. 67 (2013): 835-959. AbstractWebsite
Silva, F. G. A., J. J. L. Morais, N. Dourado, J. Xavier, F. A. M. Pereira, and M. F. S. F. de Moura. "Determination of cohesive laws in wood bonded joints under mode II loading using the ENF test." International Journal of Adhesion and Adhesives. 51 (2014): 54-61. AbstractWebsite


Fernandes, R. M. R. P., J. A. G. Chousal, M. F. S. F. de Moura, and J. Xavier. "Determination of cohesive laws of composite bonded joints under mode II loading." Composites Part B: Engineering. 52 (2013): 269-274. Abstract


Cidade, Rafael A., Daniel S. V. Castro, Enrique M. Castrodeza, Peter Kuhn, Giuseppe Catalanotti, Jose Xavier, and Pedro P. Camanho. "Determination of mode I dynamic fracture toughness of IM7-8552 composites by digital image correlation and machine learning." Composite Structures. 210 (2019): 707-714. AbstractWebsite

An optical experimental procedure for evaluating the J-Integral from full-field displacement fields under dynamic loading is proposed in this work. The methodology is applied to measure the J-integral in the dynamic compressive loading of fiber-reinforced composites and to calculate the dynamic fracture toughness associated with the propagation of a kink-band. A modified J-Integral that considers inertia effects is calculated over the full-field measurements obtained by digital image correlation, for double edge-notched specimen of IM7-8552 laminates dynamically loaded in a split-Hopkinson pressure bar (SHPB). A sensibility study is conducted to address the influence of the speckle parameters. The results show good agreement with experimental observations obtained by using a different data reduction method, suggesting the existence of a rising R-curve for the studied material under dynamic loading. Furthermore, it was noticed that the inertia effect can be negligible, indicating a state of dynamic equilibrium in which quasi-static approaches may comfortably be used.

Pereira, F. A. M., M. F. S. F. de Moura, N. Dourado, J. J. L. Morais, J. Xavier, and M. I. R. Dias. "Determination of mode II cohesive law of bovine cortical bone using direct and inverse methods." International Journal of Mechanical Sciences. 138-139 (2018): 448-456. AbstractWebsite

This study presents two alternative methods to determine the cohesive law of bovine cortical bone under mode II loading, employing the End Notched Flexure (ENF) test. The direct method results from the combination of the progress of the mode II strain energy release rate with the crack tip shear displacement, obtained by digital image correlation. The resulting cohesive law is determined by differentiation of this relation relatively to the crack shear displacement. The inverse method employs finite element analyses with cohesive zone modelling, in association with an optimization procedure. The resulting strategy enables determining the cohesive law without establishing a pre-defined shape. The significant conclusion that comes out of this work is that both methods offer consistent results regarding the estimation of the cohesive law in bone. Given that the inverse method dispenses the use of sophisticated equipment to obtain the cohesive law in bone, it can be used as a more convenient procedure to accomplish efficient studies in the context of bone fracture characterization under mode II loading.

Kuhn, P., G. Catalanotti, J. Xavier, M. Ploeckl, and H. Koerber. "Determination of the crack resistance curve for intralaminar fiber tensile failure mode in polymer composites under high rate loading." Composite Structures. 204 (2018): 276-287. AbstractWebsite

This paper presents the determination of the crack resistance curve of the unidirectional carbon-epoxy composite material IM7-8552 for intralaminar fiber tensile failure under dynamic loading. The methodology, proposed by Catalanotti et al. (2014) for quasi-static loading conditions, was enhanced to high rate loading in the order of about 60 ?s-1. Dynamic tests were performed using a split-Hopkinson tension bar, while quasi-static reference tests were conducted on a standard electromechanical testing machine. Double-edge notched tension specimens of different sizes were tested to obtain the size effect law, which in combination with the concepts of the energy release rate is used to measure the entire crack resistance curve for the fiber tensile failure mode. Digital image correlation is applied to further verify the validity of the experiments performed at both static and dynamic loading. The data reduction methodology applied in this paper is suitable for intralaminar fiber failure modes without significant delamination. Sufficient proof is given that quasi-static fracture mechanics theory can also be used for the data reduction of the dynamic tests. It is shown, that the intralaminar fracture toughness for fiber tensile failure of UD IM7-8552 increases with increasing rate of loading.

Crespo, J., A. Majano-Majano, J. Xavier, and M. Guaita. "Determination of the resistance-curve in Eucalyptus globulus through double cantilever beam tests." Materials and Structures. 51 (2018): 77. AbstractWebsite

The prediction of the fracture behaviour through reliable and practical criteria in the design of structural timber elements and connections has become of great importance and demands a proper fracture characterization of the material. Eucalyptus globulus Labill is envisioned as a hardwood species with great potential for high performance structural purposes because of its major mechanical and durability properties, being so far mainly used in paper industry. Experimental research on the identification of the resistance curves to derive the critical strain energy release rate in Eucalyptus globulus L. under pure mode I and RL crack propagation system is performed by means of Double Cantilever Beam tests. Three different data reduction schemes are compared: the Modified Experimental Compliance Method; and two approaches of the Compliance Based Beam Method. These methods take into account the non negligible damage mechanisms at the fracture process zone and have the advantage of being based exclusively on the specimen compliance following an equivalent crack concept, for which crack length monitoring during testing is not required. The Compliance Based Beam Method turns out to be the most appropriate data reduction scheme to obtain the critical energy release rate in eucalyptus because of its simplicity. Concerning this, a high average value of 720�J/m2 was obtained confirming Eucalyptus globulus L. as a promising hardwood species for timber structural design.

Xavier, J., M. Oliveira, J. J. L. Morais, and M. F. S. F. de Moura. "Determining mode I cohesive law of Pinus pinaster by coupling double cantilever beam test with digital image correlation." Fracture and Structural Integrity. 31 (2015): 13-22. AbstractWebsite

The direct identification of the cohesive law in pure mode I of Pinus pinaster is addressed. The approach couples the double cantilever beam (DCB) test with digital image correlation (DIC). Wooden beam specimens loaded in the radial-longitudinal (RL) fracture propagation system are used. The strain energy release rate in mode I (GI ) is uniquely determined from the load-displacement ( P ?? ) curve by means of the compliance-based beam method (CBBM). This method relies on the concept of equivalent elastic crack length ( eq a ) and therefore does not require the monitoring of crack propagation during test. The crack tip opening displacement in mode I ? ? I w is determined from the displacement field at the initial crack tip. The cohesive law in mode I I I (? ? w ) is then identified by numerical differentiation of the I I G ? w relationship. Moreover, the proposed procedure is validated by finite element analyses including cohesive zone modelling. It is concluded that the proposed data reduction scheme is adequate for assessing the cohesive law in pure mode I of P. pinaster.

Xavier, J., M. Oliveira, J. J. L. Morais, and M. F. S. F. de Moura. "Determining mode İI\} cohesive law of Pinus pinaster by combining the end-notched flexure test with digital image correlation." Construction and Building Materials. 71 (2014): 109-115. Abstract

Abstract This work addresses the direct identification of cohesive law of Pinus pinaster in mode II. The end-notched flexure (ENF) test is selected for mode İI\} loading. The strain energy release rate in mode İI\} (GII) is determined according to the compliance-based beam method (CBBM) by processing the global load�displacement curve, without requirements to monitor the crack length during test. The fracture test is coupled with digital image correlation (DIC) for the local measurement of the crack tip opening displacement in mode İI\} (wII). Using a direct method, the cohesive law in mode İI\} (sII�wII) is determined by differentiating the GII�wII relationship. The procedure is validated from both numerical, using finite element analyses including cohesive zone modelling, and experimental approaches. The methodology and accuracy on this reconstruction is discussed. It is concluded that the proposed data reduction scheme is suitable for assessing the cohesive law of P. pinaster in mode II.

Subramani, P., Sohel Rana, Bahman Ghiassi, Raul Fangueiro, Daniel V. Oliveira, Paulo B. Lourenco, and Jose Xavier. "Development and characterization of novel auxetic structures based on re-entrant hexagon design produced from braided composites." Composites Part B: Engineering. 93 (2016): 132-142. AbstractWebsite

Abstract This paper reports the first attempt of developing macro-scale auxetic structures based on re-entrant hexagon design from braided composite materials for civil engineering applications. Braided composite rods (BCRs) were produced and arranged as longitudinal and horizontal elements to produce three types of auxetic structures: (1) basic re-entrant hexagon structure, (2) basic structure modified by adding straight longitudinal elements and (3): structure-2 modified by changing structural angle. The influence of various material and structural parameters as well as structure type on Poisson's ratio and tensile properties was thoroughly investigated. The auxetic behaviour was found to strongly depend on the structural angle and straight elements, resulting in lower auxeticity with lower angles and in presence of straight elements. Material parameters influenced the auxetic behaviour to a lesser extent and a decrease in auxetic behaviour was noticed with increase in core fibre linear density and using stiffer fibres such as carbon. The reverse effect was observed in case of tensile strength and work of rupture. Among these structures, structure-3 exhibited good auxetic behaviour, balanced tensile properties, and high energy absorption capacity and their auxetic behaviour could be well predicted with the developed analytical model. Therefore, these novel structures present good potential for strengthening of civil structures.

Subramani, P., S. Rana, D. V. Oliveira, R. Fangueiro, and J. Xavier. "Development of novel auxetic structures based on braided composites." Materials & Design. 61 (2014): 286-295. AbstractWebsite
Pereira, F. A. M., M. F. S. F. de Moura, N. Dourado, J. J. L. Morais, J. Xavier, and M. I. R. Dias. "Direct and inverse methods applied to the determination of mode I cohesive law of bovine cortical bone using the DCB test." International Journal of Solids and Structures. 128 (2017): 210-220. AbstractWebsite

Abstract This work addresses the determination of the cohesive law under mode I loading of bovine cortical bone tissue using the Double Cantilever Beam (DCB) test. Direct and inverse methods were proposed to assess the cohesive laws representative of bone fracture under mode I loading. The direct method combines the evolution of the strain energy release rate under mode I loading with the crack tip opening displacement that is monitored by digital image correlation technique. According to this method, the cohesive law is obtained by differentiation of such relation with respect to the crack opening. The inverse procedure is performed through a finite element analysis including cohesive zone modelling, conjointly with a developed optimization algorithm. This identification strategy does not require a pre-established shape of the cohesive law as with the conventional inverse based procedures, which is viewed as a novelty of this work. It was concluded that both methods provide consistent results, being appellative tools concerning systematic and methodical studies dedicated to bone fracture characterization.