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Journal Article
Catalanotti, G., P. P. Camanho, J. Xavier, C. G. Dávila, and AT Marques. "Measurement of resistance curves in the longitudinal failure of composites using digital image correlation." Composites Science and Technology. 70 (2010): 1986-1993. Abstract
Catalanotti, C., J. Xavier, and P. P. Camanho. "Measurement of the compressive crack resistance curve of composites using the size effect law." Composites Part A: Applied Science and Manufacturing. 56 (2014): 300-307. Abstract
Catalanotti, G., and J. Xavier. "Measurement of the mode II intralaminar fracture toughness and R-curve of polymer composites using a modified Iosipescu specimen and the size effect law." Engineering Fracture Mechanics. 138 (2015): 202-214. AbstractWebsite

Abstract A modified Iosipescu specimen is proposed to measure the mode İI\} intralaminar fracture toughness and the corresponding crack resistance curve of fibre reinforced composites. Due to the impossibility of scaling the specimen, a modification of the classical size effect method is proposed. The calculation of the crack driving force curves is performed using the Finite Element Method. The classical Iosipescu shear feature was used and tests were coupled with digital image correlation to support the proposed approach. Experiments were performed on IM7/8552 material system and the R-curve was obtained. The steady-state value of the fracture toughness of the ply is found to be equal to R 0 ss = 34.4  kJ/m2.

Xavier, J., M. Oliveira, J. Morais, and J. Pinto. "Measurement of the shear properties of clear wood by the Arcan test." Holzforschung. 63 (2009): 217-225. Abstract
Xavier, J., A. M. R. Sousa, J. J. L. Morais, V. M. J. Filipe, and M. Vaz. "Measuring displacement fields by cross-correlation and a differential technique: experimental validation." Optical Engineering. 51 (2012): 043602. Abstract
Xavier, J., J. R. A. Fernandes, O. Frazão, and J. J. L. Morais. "Measuring mode I cohesive law of wood bonded joints based on digital image correlation and fibre Bragg grating sensors." Composite Structures. 121 (2015): 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.

Xavier, J., and F. Pierron. "Measuring orthotropic bending stiffness components of Pinus pinaster by the virtual fields method." The Journal of Strain Analysis for Engineering Design. 53 (2018): 556-565. AbstractWebsite

Orthotropic stiffness components of Pinus pinaster Ait. wood are simultaneously determined by means of a heterogeneous plate bending test. The proposed inverse identification approach couples full-field slope measurements provided by deflectometry with the virtual fields methods. Wooden plates oriented in the longitudinal–radial and longitudinal–tangential material planes were manufactured. A procedure was implemented to allow suitable specular reflective coating of the wooden plates, required in the deflectometry technique. Reconstructed curvature fields, applied load and plate dimensions were input in virtual fields methods for material parameter identification, assuming Kirchhoff–Love classical plate theory. Several virtual fields and load cases were analysed to address the identifiability of the method. The values of the orthotropic elastic constants obtained from the proposed approach were found in good agreement with regard to reference ones for the same species and determined from classical tensile, compression and shear mechanical tests.

Majano-Majano, Almudena, Antonio José Lara-Bocanegra, José Xavier, and José Morais. "Measuring the Cohesive Law in Mode I Loading of Eucalyptus globulus." Materials. 12 (2019). AbstractWebsite

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.

Silva, F. G. A., M. F. S. F. de Moura, N. Dourado, J. Xavier, F. A. M. Pereira, J. J. L. Morais, and M. I. R. Dias. "Mixed-mode I+II fracture characterization of human cortical bone using the Single Leg Bending test." Journal of the Mechanical Behavior of Biomedical Materials. 54 (2016): 72-81. AbstractWebsite

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.

de Moura, M. F. S. F., J. M. Q. Oliveira, J. J. L. Morais, and J. Xavier. "Mixed-mode {I/II} wood fracture characterization using the mixed-mode bending test." Engineering Fracture Mechanics. 77 (2010): 144-152. Abstract
Xavier, J., P. Monteiro, J. J. L. Morais, N. Dourado, and M. F. S. F. de Moura. "Moisture content effect on the fracture characterisation of Pinus pinaster under mode I." Journal of Materials Science. 49 (2014): 7371-7381. AbstractWebsite
Dourado, N., M. F. S. F. de Moura, J. Xavier, and F. A. M. Pereira. "A New Procedure for Mode I Fracture Characterization of Cement-Based Materials." Strain. 51 (2015): 483-491. AbstractWebsite

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–displacement curves was obtained, which validates the procedure.

Xavier, J., J. Morais, and F. Pereira. "Non-linear shear behaviour of bovine cortical bone by coupling the Arcan test with digital image correlation." Optics and Lasers in Engineering. 110 (2018): 462-470. AbstractWebsite

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.

Arteiro, A., G. Catalanotti, J. Xavier, and P. P. Camanho. "Notched response of non-crimp fabric thin-ply laminates." Composites Science and Technology. 79 (2013): 97-114. Abstract
Arteiro, A., C. Catalanotti, J. Xavier, and P. P. Camanho. "Notched response of non-crimp fabric thin-ply laminates: analysis methods." Composites Science and Technology. 88 (2013): 165-171. Abstract
Xavier, J., S. Avril, F. Pierron, and J. Morais. "Novel experimental approach for longitudinal-radial stiffness characterisation of clear wood by a single test." Holzforschung. 61 (2007): 573-581. Abstract
Rodrigues, M. F., J. Correia, B. Pedrosa, A. de Jesus, B. Carvalho, C. Rebelo, J. Xavier, and R. Calçada. "Numerical analysis of a double shear standard bolted connection considering monotonic loadings." Engineering Structures and Technologies. 9 (2017): 183-194. AbstractWebsite

AbstractThe behaviour of standard boltedsteel connections submitted to monotonic loads, through the use of numerical models, is presented in the current paper.The bolted connections allow speed up constructive processes in an increasingly competitive and globalized world in which the costs are a decisive factor in the development of a project. The use of computational tools in the analysis of bolted connections becomes determinant, mainly for new solutions or solutions less explored in terms of design codes.Throughout the years, bolted connections have been suffering transformations resulting from research activities performed by many authors. Rivets have been replaced by bolts, the main achievement being the pre-stressed bolts. Methodologies based on finite element analyses were proposed for double shear bolted connection. The non-linear behaviour of these connections is investigated and their performances are compared. In the numerical modelling of the bolted connection, linear elastic and elastoplastic analyzes reveal that there are two slip levels associated with local non-linearities caused by the contact pairs, which vary with clamping stresses.

Xavier, J., A. Majano-Majano, and J. Fernandez-Cabo. "On the identifiability of stiffness components of clear wood from a 3D off-axes prismatic specimen: angle orientation and friction effects." European Journal of Wood and Wood Products. 74 (2016): 285-290. AbstractWebsite

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° and 9°, 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.

Pereira, João Luís, José Xavier, Bahman Ghiassi, José Lousada, and José Morais. "On the identification of earlywood and latewood radial elastic modulus of Pinus pinaster by digital image correlation: A parametric analysis." The Journal of Strain Analysis for Engineering Design. 53 (2018): 566-574. AbstractWebsite

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–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–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–strain curves are obtained and elastic properties are determined assuming the converged digital image correlation setting parameters.

Sampayo, L. M. C. M. V., P. M. F. Monteiro, J. A. F. O. Correia, J. M. C. Xavier, De A. M. P. Jesus, A. Fernandez-Canteli, and R. A. B. Calçada. "Probabilistic S-N Field Assessment for a Notched Plate Made of Puddle Iron From the Eiffel Bridge with an Elliptical Hole." Procedia Engineering. 114 (2015): 691-698. AbstractWebsite

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–N or Smith–Watson–Topper (SWT)–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.

Sousa, A. M. R., J. Xavier, J. J. L. Morais, V. M. J. Filipe, and M. Vaz. "Processing discontinuous displacement fields by a spatio-temporal derivative technique." Optics and Lasers in Engineering. 49 (2011): 1402-1412. Abstract
Lameiras, R., J. A. O. Barros, I. B. Valente, J. Xavier, and M. Azenha. "Pull-out behaviour of glass-fibre reinforced polymer perforated plate connectors embedded in concrete. Part II: Prediction of load carrying capacity." Construction and Building Materials. 169 (2018): 142-164. AbstractWebsite

Abstract The authors have recently proposed an innovative connector system that consists on a Glass Fibre Reinforced Polymer (GFRP) perforated plate that is embedded into Steel Fibre Reinforced Self-Compacting Concrete (SFRSCC) layers. The connection is strongly based in the mechanical interlock assured by the dowels originated from the \{SFRSCC\} passing through the holes opened on the \{GFRP\} plates. In this study, an analytical framework to evaluate the load capacity of the connections when loaded transversally was developed based on experimental pull-out tests presented in the companion paper (Part I). For a better understanding of the mechanical behaviour of the connections and to allow to make estimations of the load capacity of connection when it is conditioned by the rupture of the connector itself, pull-out pin-bearing tests with single-hole plates were executed to assess the effect of the type of \{GFRP\} on the strain distribution in the vicinity of the holes until the failure, as well as the estimated failure modes and load capacities of the connections.

Furtado, C., A. Arteiro, G. Catalanotti, J. Xavier, and P. P. Camanho. "Selective ply-level hybridisation for improved notched response of composite laminates." Composite Structures. 145 (2016): 1-14. AbstractWebsite

Abstract This work presents an experimental study on the effect of ply-level hybridisation on the tensile unnotched and notched response of composite laminates. In a first assessment, notched tests were performed on laminates with nominal ply thicknesses between 0.03 mm and 0.30 mm. From the understanding of the effect of ply thickness on the damage mechanisms that govern the notched response of laminates, the concept of ply-level hybridisation is introduced, which consists in combining plies of different grades. A uniform combination of thin and conventional plies resulted in a hybrid laminate with intermediate notched response. Selective hybridisation, where thin off-axis plies are combined with thicker 0° plies, resulted in a globally enhanced notched behaviour without compromising the unnotched and fatigue responses. This work clearly shows how ply-level hybridisation, when designed to trigger specific damage mechanisms, can be used to improve the notched response of composite laminates.

Ercin, G. H., P. P. Camanho, J. Xavier, G. Catalanotti, S. Mahdi, and P. Linde. "Size effects on the tensile and compressive failure of notched composite laminates." Composite Structures. 96 (2013): 736-744. Abstract
Xavier, J., A. M. P. de Jesus, J. J. L. Morais, and J. M. T. Pinto. "Stereovision measurements on evaluating the modulus of elasticity of wood by compression tests parallel to the grain." Construction and Building Materials. 26 (2012): 207-215. Abstract