@article {ma13030745, title = {Experimental Evaluation of Mode II fracture Properties of Eucalyptus globulus L.}, journal = {Materials}, volume = {13}, number = {3}, year = {2020}, note = {n/a}, abstract = {

Eucalyptus globulus Labill is a hardwood species of broad growth in temperate climates, which is receiving increasing interest for structural applications due to its high mechanical properties. Knowing the fracture behaviour is crucial to predict, through finite element models, the load carrying capacity of engineering designs with possibility of brittle failures such as elements with holes, notches, or certain types of joints. This behaviour can be adequately modelled on a macroscopic scale by the constitutive cohesive law. A direct identification of the cohesive law of Eucalyptus globulus L. in Mode II was performed by combining end-notched flexure (ENF) tests with digital image correlation (DIC) for radial-longitudinal crack propagation system. The critical strain energy release for this fracture mode, which represents the material toughness to crack-growth, was determined by applying the Compliance Based Beam Method (CBBM) as data reduction scheme and resulted in a mean value of 1.54 N/mm.

}, issn = {1996-1944}, doi = {10.3390/ma13030745}, url = {https://www.mdpi.com/1996-1944/13/3/745}, author = {Majano-Majano, Almudena and Lara-Bocanegra, Antonio Jos{\'e} and Jos{\'e} Xavier and Morais, Jos{\'e}} } @article {ma12010023, title = {Measuring the Cohesive Law in Mode I Loading of Eucalyptus globulus}, journal = {Materials}, volume = {12}, number = {1}, year = {2019}, note = {n/a}, abstract = {

Assessing wood fracture behavior is essential in the design of structural timber elements and connections. This is particularly the case for connections with the possibility of brittle splitting failure. The numerical cohesive zone models that are used to simulate the fracture behavior of wood make it necessary to assume a cohesive law of the material that relates cohesive tractions and crack opening displacements ahead of the crack tip. This work addresses the determination of the fracture cohesive laws of Eucalyptus globulus, a hardwood species with great potential in timber engineering. This study centres on Mode I fracture loading for RL and TL crack propagation systems using Double Cantilever Beam tests. The Compliance-Based Beam Method is applied as the data reduction scheme in order to obtain the strain energy release rate from the load-displacement curves. The cohesive laws are determined by differentiating the relationship between strain energy release rate and crack tip opening displacement. The latter is measured by the digital image correlation technique. High strain energy release rates were obtained for this species, with no big differences between crack propagation systems. The difference between the crack systems is somewhat more pronounced in terms of maximum stress that determines the respective cohesive laws.

}, issn = {1996-1944}, doi = {10.3390/ma12010023}, url = {https://www.mdpi.com/1996-1944/12/1/23}, author = {Majano-Majano, Almudena and Lara-Bocanegra, Antonio Jos{\'e} and Jos{\'e} Xavier and Morais, Jos{\'e}} } @article {Raposo2018396, title = {Characterization of the mechanical behaviour of wooden construction materials from quinta lobeira de cima}, journal = {International Journal of Structural Integrity}, volume = {9}, number = {3}, year = {2018}, note = {

n/a

}, pages = {396-410}, abstract = {

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.

}, doi = {10.1108/IJSI-06-2017-0039}, url = {https://doi.org/10.1108/IJSI-06-2017-0039}, author = {P. Raposo and J. Martins and J. Correia and Maria E. Salavessa and Cristina Reis and Jos{\'e} Xavier and Abilio M.P. de Jesus} } @article {Pereira2018448, title = {Determination of mode II cohesive law of bovine cortical bone using direct and inverse methods}, journal = {International Journal of Mechanical Sciences}, volume = {138-139}, year = {2018}, note = {n/a}, pages = {448 - 456}, abstract = {

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.

}, keywords = {Bovine cortical bone, Cohesive law, End notched flexure, Mode II}, issn = {0020-7403}, doi = {https://doi.org/10.1016/j.ijmecsci.2018.02.009}, url = {http://www.sciencedirect.com/science/article/pii/S0020740317327479}, author = {F.A.M. Pereira and de M.F.S.F. Moura and N. Dourado and J.J.L. Morais and J. Xavier and M.I.R. Dias} } @article {Crespo2018, title = {Determination of the resistance-curve in Eucalyptus globulus through double cantilever beam tests}, journal = {Materials and Structures}, volume = {51}, number = {3}, year = {2018}, note = {n/a}, pages = {77}, abstract = {

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.

}, issn = {1871-6873}, doi = {10.1617/s11527-018-1209-9}, url = {https://doi.org/10.1617/s11527-018-1209-9}, author = {J. Crespo and A. Majano-Majano and J. Xavier and M. Guaita} } @article {Pereiraetal2018, title = {Identification of transverse elastic properties of the diaphysis of cortical bone}, journal = {Journal of Mechanical Engineering and Biomechanics}, volume = {2}, number = {5}, year = {2018}, note = {n/a}, pages = {50-55}, abstract = {n/a}, doi = {10.24243/JMEB/2.5.172}, url = {https://doi.org/10.24243/JMEB/2.5.172}, author = {B. Pereira and J. Xavier and Pereira, F. and Morais, J} } @article {Xavier2018462, title = {Non-linear shear behaviour of bovine cortical bone by coupling the Arcan test with digital image correlation}, journal = {Optics and Lasers in Engineering}, volume = {110}, year = {2018}, note = {n/a}, pages = {462-470}, abstract = {

The non-linear shear behaviour of bovine cortical bone is measured by coupling the Arcan test with digital image correlation. The experimental study is carried out on specimens taken from bovine femur and oriented along the longitudinal-tangential material plane. An ad hoc Arcan fixture is built to transfer the cross-head displacement of the testing machine into a shear loading at the centre of the V-notched section. A validation of predominant shear behaviour at the gauge section is shown from full-field deformation measurements. Moreover, direct evaluation of the shear modulus is obtained by integrating the shear strain component along the V-notches, avoiding numerical correction factors required in the classical data reduction scheme. The shear modulus of bovine cortical bone is found in good agreement with references from literature. Moreover, the shear stress at maximum load is understood as a suitable estimation of the shear strength. Furthermore, the Ramberg�Osgood model is found to provide an accurate description of the non-linear shear behaviour of bone tissue.

}, keywords = {Arcan shear test, Cortical bone, Digital Image Correlation, Finite element method, Non-linear shear behaviour}, doi = {https://doi.org/10.1016/j.optlaseng.2018.07.004}, url = {http://www.sciencedirect.com/science/article/pii/S0143816618302288}, author = {J. Xavier and Morais, J and Pereira, F.} } @article {doi:10.1177/0309324718786351, title = {On the identification of earlywood and latewood radial elastic modulus of Pinus pinaster by digital image correlation: A parametric analysis}, journal = {The Journal of Strain Analysis for Engineering Design}, volume = {53}, number = {8}, year = {2018}, note = {n/a}, pages = {566-574}, abstract = {

This work addresses the reconstruction of strain gradient fields at the wood growth ring scale from full-field deformation measurements provided by digital image correlation. Moreover, the spatial distribution of the earlywood and latewood radial modulus of elasticity is assessed. Meso-scale tensile tests are carried out on Pinus pinaster Ait. wooden specimens oriented in the radial{\textendash}tangential plane under quasi-static loading conditions. A parametric analysis of the two-dimensional digital image correlation extrinsic and intrinsic setting parameters is performed, in a balance between spatial resolution and resolution. It is shown that the parametric module is an effective way to quantitatively support the choice of digital image correlation parameters in the presence of the high deformation gradient fields generated by the structure{\textendash}property relationships at the scale of observation. Under the assumption of a uniaxial tensile stress state, the spatial distribution of the radial elastic modulus across the growth rings is obtained. It is observed that the ratio of the radial modulus of elasticity between latewood and earlywood tissues can vary significantly as a function of the digital image correlation parameters. It is pointed out, however, that a convergence value can be systematically established. Effectively, earlywood and latewood stress{\textendash}strain curves are obtained and elastic properties are determined assuming the converged digital image correlation setting parameters.

}, doi = {10.1177/0309324718786351}, url = {https://doi.org/10.1177/0309324718786351}, author = {Jo{\~a}o Lu{\'\i}s Pereira and Jos{\'e} Xavier and Bahman Ghiassi and Jos{\'e} Lousada and Morais, Jos{\'e}} } @article {Raposo20171086, title = {Characterization of the Tensile Mechanical Behavior of Wooden Construction on Materials from Historic Building}, journal = {Procedia Structural Integrity}, volume = {5}, number = {Supplement C}, year = {2017}, note = {

2nd International Conference on Structural Integrity, ICSI 2017, 4-7 September 2017, Funchal, Madeira, Portugal

}, pages = {1086-1091}, abstract = {

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.

}, keywords = {Digital Image Correlation, Historic buildings, Mechanical characterization, Rehabilitation, Wood structures}, issn = {2452-3216}, doi = {https://doi.org/10.1016/j.prostr.2017.07.083}, url = {http://www.sciencedirect.com/science/article/pii/S2452321617301944}, author = {P.C. Raposo and J. Martins and J.A.F.O. Correia and M.E. Salavessa and C. Reis and J.M.C. Xavier and A.M.P. de Jesus} } @article {Pereira2017210, title = {Direct and inverse methods applied to the determination of mode I cohesive law of bovine cortical bone using the DCB test}, journal = {International Journal of Solids and Structures}, volume = {128}, number = {Supplement C}, year = {2017}, note = {n/a}, pages = {210 - 220}, abstract = {

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.

}, keywords = {Bovine cortical bone, Cohesive law, Double cantilever beam test, Mode I}, doi = {https://doi.org/10.1016/j.ijsolstr.2017.08.028}, url = {http://www.sciencedirect.com/science/article/pii/S002076831730392X}, author = {F.A.M. Pereira and de M.F.S.F. Moura and N. Dourado and J.J.L. Morais and J. Xavier and M.I.R. Dias} } @article {Pinto201763, title = {Dispersion and failure analysis of PLA, PLA/GNP and PLA/CNT-COOH biodegradable nanocomposites by SEM and DIC inspection}, journal = {Engineering Failure Analysis}, volume = {71}, year = {2017}, note = {n/a}, pages = {63 - 71}, abstract = {

Biodegradable polymers such as PLA have been studied for medical applications, human ligament repair is one of such cases. However, these materials can be applied in other sectors as aerospace, aeronautics, automotive, food packaging. PLA presents a relatively brittle on the 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 moulding in a hot press, with small weight percentages of nanofillers added to the matrix. Nanocomposites dispersion was evaluated by SEM. Quasi static tensile tests were performed on a mechanical testing machine (Instron� ElectroPuls E1000) along with strain field measurements of specimens with centred crack with digital image correlation, revealing strain distribution along specimens.

}, keywords = {Composite(s), Failure analysis, Mechanical testing, Non-destructive testing, Static failure}, doi = {https://doi.org/10.1016/j.engfailanal.2016.06.009}, url = {http://www.sciencedirect.com/science/article/pii/S1350630716304745}, author = {V.C. Pinto and T. Ramos and A.S.F. Alves and J. Xavier and P.J. Tavares and P.M.G.P. Moreira and R.M. Guedes} } @article {Silva2017, title = {Fracture characterization of human cortical bone under mode II loading using the end-notched flexure test}, journal = {Medical {\&} Biological Engineering {\&} Computing}, volume = {55}, number = {8}, year = {2017}, note = {n/a}, pages = {1249-1260}, abstract = {

Fracture characterization of human cortical bone under mode II loading was analyzed using a miniaturized version of the end-notched flexure test. A data reduction scheme based on crack equivalent concept was employed to overcome uncertainties on crack length monitoring during the test. The crack tip shear displacement was experimentally measured using digital image correlation technique to determine the cohesive law that mimics bone fracture behavior under mode II loading. The developed procedure was validated by finite element analysis using cohesive zone modeling considering a trapezoidal with bilinear softening relationship. Experimental load-displacement curves, resistance curves and crack tip shear displacement versus applied displacement were used to validate the numerical procedure. The excellent agreement observed between the numerical and experimental results reveals the appropriateness of the proposed test and procedure to characterize human cortical bone fracture under mode II loading. The proposed methodology can be viewed as a novel valuable tool to be used in parametric and methodical clinical studies regarding features (e.g., age, diseases, drugs) influencing bone shear fracture under mode II loading.

}, doi = {10.1007/s11517-016-1586-6}, url = {https://doi.org/10.1007/s11517-016-1586-6}, author = {F.G.A. Silva and de M.F.S.F. Moura and N. Dourado and J. Xavier and F.A.M. Pereira and J.J.L. Morais and M.I.R. Dias and P.J. Louren{\c c}o and F.M. Judas} } @article {Silva201672, title = {Mixed-mode I+II fracture characterization of human cortical bone using the Single Leg Bending test}, journal = {Journal of the Mechanical Behavior of Biomedical Materials}, volume = {54}, year = {2016}, note = {n/a}, pages = {72-81}, abstract = {

Abstract Mixed-mode I+II fracture characterization of human cortical bone was analyzed in this work. A miniaturized version of the Single Leg Bending test (SLB) was used owing to its simplicity. A power law criterion was verified to accurately describe the material fracture envelop under mixed-mode I+II loading. The crack tip opening displacements measured by digital image correlation were used in a direct method to determine the cohesive law mimicking fracture behavior of cortical bone. Cohesive zone modeling was used for the sake of validation. Several fracture quantities were compared with the experimental results and the good agreement observed proves the appropriateness of the proposed procedure for fracture characterization of human bone under mixed-mode I+II loading.

}, keywords = {Fracture characterization, Human cortical bone, Mixed-mode I+II, Single Leg Bending test}, issn = {1751-6161}, doi = {http://dx.doi.org/10.1016/j.jmbbm.2015.09.004}, url = {http://www.sciencedirect.com/science/article/pii/S175161611500332X}, author = {F.G.A. Silva and de M.F.S.F. Moura and N. Dourado and J. Xavier and F.A.M. Pereira and J.J.L. Morais and M.I.R. Dias} } @article {Xavier2016285, title = {On the identifiability of stiffness components of clear wood from a 3D off-axes prismatic specimen: angle orientation and friction effects}, journal = {European Journal of Wood and Wood Products}, volume = {74}, number = {3}, year = {2016}, note = {n/a}, pages = {285-290}, abstract = {

The robustness of the test method based on a single 3D off-axis prismatic specimen for the simultaneous identification of the orthotropic stiffness components of clear wood is addressed. In this method, the specimen is consecutively submitted to uniaxial compression tests along its three orthogonal axes. A data reduction based on anisotropic elasticity is applied to extract active material parameters from 3D full-field deformation measurements provided by stereo-correlation over adjacent faces. Two major limitations of this test method, directly affecting the parameter identification, are analysed and discussed: (1) off-axes angle orientation; (2) friction effects. A numerical study pointed out that radial and tangential rotations of about 29{\textdegree} and 9{\textdegree}, respectively, balances out the strain components in the specimen response. Moreover, friction can be reduced by using mass lubricant or soft material in the contact interface, realising transverse shear deformation.

}, doi = {10.1007/s00107-016-1032-3}, url = {http://dx.doi.org/10.1007/s00107-016-1032-3}, author = {J. Xavier and A. Majano-Majano and J. Fernandez-Cabo} } @article {Xavier201527, title = {Fracture behaviour of wood bonded joints under modes I and II by digital image correlation and fibre Bragg grating sensors}, journal = {Ci{\^e}ncia \& Tecnologia dos Materiais}, volume = {27}, number = {1}, year = {2015}, note = {

n/a

}, pages = {27-35}, abstract = {

Abstract Direct identification of cohesive laws in modes I and {\.I}I\} of wood bonded joints is addressed by the double cantilever beam (DCB) and end-notched flexure (ENF) tests, respectively. Moreover, the development and extension of fracture process zone (FPZ) ahead of the initial crack tip, is analysed by means of digital image correlation (DIC) and embedded fibre Bragg grating (FBG) sensors. From \{FBG\} spectral response, the spectrum geometric mean is determined and the strain induced by wavelength variation employed to identify the initial and final stages of the FPZ. These stages are used to consistently define the cohesive laws in both modes I and II. Resistance-curves are determined from the compliance-based beam method (CBBM). Besides, the crack tip opening displacements (CTOD) are determined by post-processing displacement field provided by \{DIC\} around the initial crack tip. The strain energy release rate as a function of the \{CTOD\} are then determined for both mode I and mode II. The respective cohesive laws are reconstructed by numerical approximation and differentiation. It is concluded that the proposed data reduction scheme is effective to determine both the \{FPZ\} development phase and the corresponding cohesive laws of wood bonded joints in both mode I and mode II.

}, keywords = {Adhesion, Digital Image Correlation, fibre Bragg grating sensors., Joints/joining, Mechanical testing, Wood}, doi = {http://dx.doi.org/10.1016/j.ctmat.2015.06.001}, url = {http://www.sciencedirect.com/science/article/pii/S0870831215000439}, author = {J. Xavier and J.R.A. Fernandes and J.J.L. Morais and O. Fraz{\~a}o} } @article {Xavier201583, title = {Measuring mode I cohesive law of wood bonded joints based on digital image correlation and fibre Bragg grating sensors}, journal = {Composite Structures}, volume = {121}, year = {2015}, note = {

n/a

}, pages = {83-89}, abstract = {

Abstract This work addresses the experimental identification of mode I cohesive law of wood bonded joints. The approach combines the double cantilever beam (DCB) test with both digital image correlation (DIC) and embedded fibre Bragg grating (FBG) sensors. The spectrum geometric mean of the \{FBG\} reflected spectral response was determined, and the wavelength evolution was used to define the fracture process zone (FPZ) development phase. This evaluation allowed a consistent selection of experimental range of over which the identification procedure of mode I cohesive law is build up. Mode I crack length, Resistance-curve and cohesive law parameters are characterised and discussed. The strain energy release rate (GI) is determined from the P�d curve by the compliance-based beam method (CBBM). The crack tip opening displacement (wI) is determined by post-processing displacements measured by DIC. The cohesive law in mode I (sI�wI) is then obtained by numerical differentiation of the GI�wI relationship.

}, keywords = {Adhesion, Joints/joining, Mechanical testing, Wood}, doi = {http://dx.doi.org/10.1016/j.compstruct.2014.11.017}, author = {J. Xavier and J.R.A. Fernandes and O. Fraz{\~a}o and J.J.L. Morais} } @article {FernandezCabo2015, title = {Assessment of wire-frame analysis models of a historical planked timber arch}, journal = {Proceedings of the Institution of Civil Engineers - Structures and Buildings}, volume = {168}, number = {9}, year = {2015}, note = {n/a}, pages = {680-694}, abstract = {n/a}, doi = {10.1680/jstbu.14.00049}, url = {http://www.icevirtuallibrary.com/doi/abs/10.1680/jstbu.14.00049}, author = {J.L. Fern{\'a}ndez-Cabo and R. Widmann and M. Arce-Blanco and R. Crocetti and J. Xavier and A. Majano-Majano} } @article {Pinto2015635, title = {Comparative Failure Analysis of PLA, PLA/GNP and PLA/CNT-COOH Biodegradable Nanocomposites thin Films}, journal = {Procedia Engineering}, volume = {114}, year = {2015}, note = {

{\.I}CSI\} 2015 The 1st International Conference on Structural Integrity Funchal, Madeira, Portugal 1st to 4th September, 2015

}, pages = {635-642}, abstract = {

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{\texttrademark} ElectroPuls E1000) along with failure analysis of specimens with centered crack with digital image correlation, revealing strain distribution along specimens.

}, keywords = {biodegradable nanocomposites, Biodegradable polymers, CNT-COOH, DIC, FTM, GNP, mechanical failure, PLA}, doi = {http://dx.doi.org/10.1016/j.proeng.2015.08.004}, url = {http://www.sciencedirect.com/science/article/pii/S1877705815016434}, author = {V.C. Pinto and Tiago Ramos and Sofia Alves and J. Xavier and Paulo Tavares and P.M.G.P. Moreira and Rui Miranda Guedes} } @article {Xavier201512, title = {Determining mode I cohesive law of Pinus pinaster by coupling double cantilever beam test with digital image correlation}, journal = {Fracture and Structural Integrity}, volume = {31}, year = {2015}, note = {n/a}, pages = {13-22}, abstract = {

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.

}, doi = {http://dx.doi.org/10.3221/IGF-ESIS.31.02}, url = {http://www.fracturae.com/index.php/fis/article/view/IGF-ESIS.31.02}, author = {J. Xavier and Oliveira, M. and J.J.L. Morais and de M.F.S.F. Moura} } @article {Silva2015, title = {Fracture Characterization of Human Cortical Bone Under Mode I Loading}, journal = {Journal of Biomechanical Engineering}, volume = {137}, number = {12}, year = {2015}, note = {n/a}, pages = {121004-121004}, publisher = {ASME}, abstract = {

A miniaturized version of the double cantilever beam (DCB) test is used to determine the fracture energy in human cortical bone under pure mode I loading. An equivalent crack length based data-reduction scheme is used with remarkable advantages relative to classical methods. Digital image correlation (DIC) technique is employed to determine crack opening displacement at the crack tip being correlated with the evolution of fracture energy. A method is presented to obtain the cohesive law (trapezoidal bilinear softening) mimicking the mechanical behavior observed in bone. Cohesive zone modeling (CZM) (finite-element method) was performed to validate the procedure showing excellent agreement.

}, doi = {10.1115/1.4031846}, url = {http://dx.doi.org/10.1115/1.4031846}, author = {F. Silva and M. de Moura and N. Dourado and J. Xavier and Pereira, F. and Morais, J and Dias, M. and P. Louren{\c c}o and F. Judas} } @article {Dourado2015483, title = {A New Procedure for Mode I Fracture Characterization of Cement-Based Materials}, journal = {Strain}, volume = {51}, number = {6}, year = {2015}, note = {n/a}, pages = {483-491}, abstract = {

Fracture characterization under mode I loading of a cement-based material using the single-edge-notched beam loaded in tree-point-bending was performed. A new method based on beam theory and crack equivalent concept is proposed to evaluate the Resistance-curve, which is essential to determine fracture toughness with accuracy. The method considers the existence of a stress relief region in the vicinity of the crack, dispensing crack length monitoring during experiments. A numerical validation was performed by finite element analysis considering a bilinear cohesive damage model. Experimental tests were performed in order to validate the numerical procedure. Digital image correlation technique was used to measure the specimen displacement with accuracy and without interference. Excellent agreement between numerical and experimental load{\textendash}displacement curves was obtained, which validates the procedure.

}, keywords = {cement-based materials, cohesive zone modelling, fracture toughness, mode I loading, single-edge-notched test}, doi = {10.1111/str.12165}, url = {http://dx.doi.org/10.1111/str.12165}, author = {N. Dourado and de M.F.S.F. Moura and J. Xavier and F.A.M. Pereira} } @article {Sampayo2015691, title = {Probabilistic S-N Field Assessment for a Notched Plate Made of Puddle Iron From the Eiffel Bridge with an Elliptical Hole}, journal = {Procedia Engineering}, volume = {114}, year = {2015}, note = {

{\.I}CSI\} 2015 The 1st International Conference on Structural Integrity Funchal, Madeira, Portugal 1st to 4th September, 2015

}, pages = {691-698}, abstract = {

Abstract Probabilistic fatigue models are required to account conveniently for several sources of uncertainty arising in the prediction procedures for structural details, such as the scatter in material behaviour. In this paper, a procedure to derive probabilistic S-N fields for structural details [1] is applied to a notched geometry with elliptic central hole made of puddle iron from the Eiffel bridge, based on the local approaches supported by the probabilistic ɛa{\textendash}N or Smith{\textendash}Watson{\textendash}Topper (SWT){\textendash}N fields [1,2]. This procedure suggests an extension of the fatigue crack propagation model proposed by Noroozi et al. [3,4] to structural details, in order to cover both the fatigue crack initiation and fatigue crack propagation, based on local strain approaches to fatigue. Both fatigue crack initiation and fatigue crack propagation mechanisms are accounted for in the proposed approach. The numerical results are compared with available experimental S-N fatigue data for the notched plate under consideration.

}, keywords = {Fatigue, Finite Element Modelling., Local approach, Probabilistic approach}, issn = {1877-7058}, doi = {http://dx.doi.org/10.1016/j.proeng.2015.08.011}, url = {http://www.sciencedirect.com/science/article/pii/S1877705815016501}, author = {L.M.C.M.V. Sampayo and P.M.F. Monteiro and J.A.F.O. Correia and J.M.C. Xavier and A.M.P. De Jesus and A. Fernandez-Canteli and R.A.B. Cal{\c c}ada} } @article {Silva201454, title = {Determination of cohesive laws in wood bonded joints under mode II loading using the ENF test}, journal = {International Journal of Adhesion and Adhesives}, volume = {51}, year = {2014}, note = {

n/a

}, pages = {54-61}, abstract = {

n/a

}, keywords = {Bonded joints, Cohesive laws, Digital Image Correlation, End notched flexure (ENF), Wood}, doi = {http://dx.doi.org/10.1016/j.ijadhadh.2014.02.007}, url = {http://dx.doi.org/10.1016/j.ijadhadh.2014.02.007}, author = {F.G.A. Silva and J.J.L. Morais and N. Dourado and J. Xavier and F.A.M. Pereira and de M.F.S.F. Moura} } @article {Pereira2014107, title = {Assessing wood quality by spatial variation of elastic properties within the stem: Case study of Pinus pinaster in the transverse plane}, journal = {Canadian Journal of Forest Research}, volume = {44}, number = {2}, year = {2014}, note = {n/a}, pages = {107-117}, abstract = {n/a}, author = {J. Pereira and J. Xavier and Morais, J and J. Lousada} } @article {Xavier2014109, title = {Determining mode {\.I}I\} cohesive law of Pinus pinaster by combining the end-notched flexure test with digital image correlation}, journal = {Construction and Building Materials}, volume = {71}, year = {2014}, note = {n/a}, pages = {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 {\.I}I\} loading. The strain energy release rate in mode {\.I}I\} (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 {\.I}I\} (wII). Using a direct method, the cohesive law in mode {\.I}I\} (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.

}, keywords = {Cohesive law, Digital Image Correlation, End-notched flexure test, Wood}, doi = {http://dx.doi.org/10.1016/j.conbuildmat.2014.08.021}, author = {J. Xavier and Oliveira, M. and J.J.L. Morais and de M.F.S.F. Moura} } @article {Xavier2014929, title = {Direct Evaluation of Cohesive Law in Mode I of Pinus pinaster by Digital Image Correlation}, journal = {Experimental Mechanics}, volume = {54}, number = {5}, year = {2014}, note = {n/a}, pages = {829-840}, abstract = {n/a}, keywords = {Cohesive law, Digital Image Correlation, Double cantilever beam test, Mode I fracture mechanics, Wood}, doi = {10.1007/s11340-013-9838-y}, url = {http://dx.doi.org/10.1007/s11340-013-9838-y}, author = {J. Xavier and Oliveira, M. and P. Monteiro and J.J.L. Morais and Moura, M.F.S.F.} } @article {Xavier20147371, title = {Moisture content effect on the fracture characterisation of Pinus pinaster under mode I}, journal = {Journal of Materials Science}, volume = {49}, number = {21}, year = {2014}, note = {n/a}, pages = {7371-7381}, publisher = {Springer US}, abstract = {n/a}, issn = {0022-2461}, doi = {10.1007/s10853-014-8375-0}, url = {http://dx.doi.org/10.1007/s10853-014-8375-0}, author = {J. Xavier and P. Monteiro and J.J.L. Morais and N. Dourado and de M.F.S.F. Moura} } @article {Fernandes2013269, title = {Determination of cohesive laws of composite bonded joints under mode II loading}, journal = {Composites Part B: Engineering}, volume = {52}, year = {2013}, note = {

n/a

}, pages = {269-274}, abstract = {

n/a

}, doi = {10.1016/j.compositesb.2013.04.007}, author = {R.M.R.P. Fernandes and J.A.G. Chousal and de M.F.S.F. Moura and J. Xavier} } @article {Xavier2013423, title = {Characterisation of the bending stiffness components of MDF panels from full-field slope measurements}, journal = {Wood Science and Technology}, volume = {47}, number = {2}, year = {2013}, note = {n/a}, pages = {423-441}, abstract = {n/a}, doi = {10.1007/s00226-012-0507-6}, author = {J. Xavier and U. Belini and F. Pierron and Morais, J and J. Lousada and M. Tomazello} } @article {Dias2013646, title = {Cohesive laws of composite bonded joints under mode I loading}, journal = {Composite Structures}, volume = {106}, year = {2013}, note = {n/a}, pages = {646-652}, abstract = {n/a}, doi = {10.1016/j.compstruct.2013.07.027}, author = {G.F. Dias and de M.F.S.F. Moura and J.A.G. Chousal and J. Xavier} } @article {Fernandes201371, title = {Comparison between neural networks and partial least squares for intra-growth ring wood density measurement with hyperspectral imaging}, journal = {Computers and Electronics in Agriculture}, volume = {94}, year = {2013}, note = {n/a}, pages = {71-81}, abstract = {n/a}, doi = {10.1016/j.compag.2013.03.010}, author = {Fernandes, A. and J. Lousada and Morais, J and J. Xavier and J. Pereira and P. Melo-Pinto} } @article {Silva2013Holz, title = {Determination of cohesive laws in wood bonded joints under mode I loading using the DCB test.}, journal = {Holzforschung}, volume = {67}, number = {8}, year = {2013}, note = {n/a}, pages = {835-959}, abstract = {n/a}, doi = {http://dx.doi.org/10.1515/hf-2013-0012}, url = {http://www.degruyter.com/view/j/hfsg.2013.67.issue-8/hf-2013-0012/hf-2013-0012.xml}, author = {F. Silva and J. Xavier and F.A.M. Pereira and Morais, J and N. Dourado and de M.F.S.F. Moura} } @article {Fernandes201359, title = {Measurement of intra-ring wood density by means of imaging VIS/NIR spectroscopy (hyperspectral imaging)}, journal = {Holzforschung}, volume = {67}, number = {1}, year = {2013}, note = {n/a}, pages = {59-65}, abstract = {n/a}, doi = {10.1515/hf-2011-0258}, author = {Fernandes, A. and J. Lousada and Morais, J and J. Xavier and J. Periera and P. Melo-Pinto} } @article {Ercin2013736, title = {Size effects on the tensile and compressive failure of notched composite laminates}, journal = {Composite Structures}, volume = {96}, year = {2013}, note = {n/a}, pages = {736-744}, abstract = {n/a}, doi = {10.1016/j.compstruct.2012.10.004}, author = {G.H. {Ercin} and P.P. Camanho and J. Xavier and G. Catalanotti and S. Mahdi and P. Linde} } @article {Xavier2012043602, title = {Measuring displacement fields by cross-correlation and a differential technique: experimental validation}, journal = {Optical Engineering}, volume = {51}, year = {2012}, note = {n/a}, pages = {043602}, abstract = {n/a}, doi = {10.1117/1.OE.51.4.043602}, author = {J. Xavier and A.M.R. Sousa and J.J.L. Morais and V.M.J. Filipe and M. Vaz} } @article {Xavier2012207, title = {Stereovision measurements on evaluating the modulus of elasticity of wood by compression tests parallel to the grain}, journal = {Construction and Building Materials}, volume = {26}, number = {1}, year = {2012}, note = {n/a}, pages = {207-215}, abstract = {n/a}, doi = {10.1016/j.conbuildmat.2011.06.012}, author = {J. Xavier and A.M.P. de Jesus and J.J.L. Morais and J.M.T. Pinto} } @article {Sousa201187, title = {Cross-correlation and differential technique combination to determine displacement fields}, journal = {Strain}, volume = {47}, number = {s2}, year = {2011}, note = {

n/a

}, pages = {87-98}, abstract = {

n/a

}, doi = {10.1111/j.1475-1305.2010.00740.x}, author = {A.M.R. Sousa and J. Xavier and M. Vaz and J.J.L. Morais and V.M.J. Filipe} } @article {Xavier20112881, title = {Measurement of mode I and mode II fracture properties of wood-bonded joints}, journal = {Journal of Adhesion Science and Technology}, volume = {25}, number = {20}, year = {2011}, note = {n/a}, pages = {2881-2895}, abstract = {n/a}, author = {J. Xavier and Morais, J and N. Dourado and de M.F.S.F. Moura} } @article {Sousa20111402, title = {Processing discontinuous displacement fields by a spatio-temporal derivative technique}, journal = {Optics and Lasers in Engineering}, volume = {49}, number = {12}, year = {2011}, note = {n/a}, pages = {1402-1412}, abstract = {n/a}, doi = {10.1016/j.optlaseng.2011.07.007}, author = {A.M.R. Sousa and J. Xavier and J.J.L. Morais and V.M.J. Filipe and M. Vaz} } @article {Morais2010446, title = {The double cantilever beam test applied to mode I fracture characterization of cortical bone tissue}, journal = {Journal of the Mechanical Behavior of Biomedical Materials}, volume = {3}, number = {6}, year = {2010}, note = {

n/a

}, pages = {446-453}, abstract = {

n/a

}, doi = {doi:10.1016/j.jmbbm.2010.04.001}, author = {J.J.L. Morais and de M.F.S.F. Moura and F.A.M. Pereira and J. Xavier and N. Dourado and M.I.R. Dias and J.M.T. Azevedo} } @article {Catalanotti2010, title = {Measurement of resistance curves in the longitudinal failure of composites using digital image correlation}, journal = {Composites Science and Technology}, volume = {70}, number = {13}, year = {2010}, note = {n/a}, pages = {1986-1993}, abstract = {n/a}, doi = {doi:10.1016/j.compscitech.2010.07.022}, author = {G. Catalanotti and P.P. Camanho and J. Xavier and C.G. D{\'a}vila and Marques, AT} } @article {Moura2010144, title = {Mixed-mode {I/II} wood fracture characterization using the mixed-mode bending test}, journal = {Engineering Fracture Mechanics}, volume = {77}, number = {1}, year = {2010}, note = {n/a}, pages = {144-152}, abstract = {n/a}, doi = {10.1016/j.engfracmech.2009.09.014}, author = {de M.F.S.F. Moura and J.M.Q. Oliveira and J.J.L. Morais and J. Xavier} } @article {Xavier2009217, title = {Measurement of the shear properties of clear wood by the Arcan test}, journal = {Holzforschung}, volume = {63}, number = {2}, year = {2009}, note = {n/a}, pages = {217-225}, abstract = {n/a}, doi = {10.1515/HF.2009.034}, author = {J. Xavier and Oliveira, M. and Morais, J and Pinto, J.} } @article {Xavier2009b, title = {Variation of transverse and shear stiffness properties of wood in a tree}, journal = {Composites Part A: Applied Science and Manufacturing}, volume = {40}, number = {12}, year = {2009}, note = {n/a}, pages = {1953-1960}, abstract = {n/a}, doi = {10.1016/j.compositesa.2009.09.023}, author = {J. Xavier and S. Avril and F. Pierron and Morais, J} } @article {Xavier2007, title = {Novel experimental approach for longitudinal-radial stiffness characterisation of clear wood by a single test}, journal = {Holzforschung}, volume = {61}, number = {5}, year = {2007}, note = {n/a}, pages = {573-581}, abstract = {n/a}, doi = {10.1515/HF.2007.083}, author = {J. Xavier and S. Avril and F. Pierron and Morais, J} } @article {Xavier2004, title = {A comparison between the Iosipescu and off-axis shear test methods for the characterization of {\i}t Pinus pinaster Ait.}, journal = {Composites Part A: Applied Science and Manufacturing}, volume = {35}, number = {7-8}, year = {2004}, note = {

n/a

}, pages = {827-840}, abstract = {

n/a

}, doi = {doi:10.1016/j.compositesa.2004.01.013}, author = {J.C. Xavier and N.M. Garrido and Oliveira, M. and J.L. Morais and P.P. Camanho and F. Pierron} }