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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
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Silva, Patrícia, Pedro Fernandes, José Sena-Cruz, José Xavier, Fernando Castro, Delfim Soares, and Vítor Carneiro. "Effects of different environmental conditions on the mechanical characteristics of a structural epoxy." Composites Part B: Engineering. 88 (2016): 55-63. AbstractWebsite

Abstract With the aim of characterising a commercially available epoxy adhesive used for fibre-reinforced polymers strengthening applications, when submitted to different environmental conditions, mainly thermal (TC), freeze–thaw (FT), and wet–dry (WD) cycles and immersion in pure (PW) and water with chlorides (CW) for periods of exposure that lasted up to 16 months, an experimental program was carried out. Several methodologies were used in its characterization, mainly the scanning electron microscope (SEM), dynamic mechanical analysis (DMA), standard tensile tests (STT) coupled with digital image correlation (DIC). In general the results revealed that the chemical composition was not affected by the environmental conditions. Nevertheless, it was verified through \{DMA\} and \{STT\} that the modulus of elasticity and tensile strength of the epoxy adhesive increased in the TC, while the specimens submitted to \{PW\} and \{CW\} faced a high degradation in terms of its mechanical properties. Eventually, the glass transition temperature (Tg) was not affected by the environmental conditions, apart from the specimens subjected to \{TC\} and FT, presenting a higher and lower Tg, respectively, when compared with the reference specimens.

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

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Silva, TEF, S. Gain, D. Pinto, A. M. P. de Jesus, J. Xavier, A. Reis, and P. A. R. Rosa. "Fracture characterization of a cast aluminum alloy aiming machining simulation." Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications. 233 (2019): 402-412. AbstractWebsite

Despite extensive research regarding metal cutting simulation, the current industrial practice very often relies on empirical data when it comes to tool design. In order accurately simulate the cutting process it is not only important to have robust numerical models that closely portray the phenomenon, but also to properly characterize the material taking into account the cutting conditions. The goal of this investigation focuses on the mechanical characterization of the cast aluminum alloy AlSi9Cu3 by conducting both compression and fracture tests. Due to its very good castability, machinability, and attractive mechanical properties, this alloy is widely used in casting industry for the manufacture of automotive components, among others. Besides the experimental characterization, a numerical methodology is proposed for the modeling of the cast alloy, making use of the Johnson–Cook constitutive material model, in Abaqus/CAE. The material model is calibrated based on compression tests at multiple conditions (quasi-static, incremental dynamic and high temperatures). The identified model is then validated by simulation of the ductile fracture tests of notched specimens. The obtained numerical results were consistent with the experimentally obtained, contributing to the validity of the presented characterization technique.

Silva, F. G. A., M. F. S. F. de Moura, N. Dourado, J. Xavier, F. A. M. Pereira, J. J. L. Morais, M. I. R. Dias, P. J. Lourenço, and F. M. Judas. "Fracture characterization of human cortical bone under mode II loading using the end-notched flexure test." Medical {&} Biological Engineering {&} Computing. 55 (2017): 1249-1260. AbstractWebsite

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.

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.

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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.

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.

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.

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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.

Pinto, V. C., T. Ramos, A. S. F. Alves, J. Xavier, P. J. Tavares, P. M. G. P. Moreira, and R. M. Guedes. "Dispersion and failure analysis of PLA, PLA/GNP and PLA/CNT-COOH biodegradable nanocomposites by SEM and DIC inspection." Engineering Failure Analysis. 71 (2017): 63-71. AbstractWebsite

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.

Pereira, J. C. R., A. M. P. de Jesus, J. Xavier, and A. A. Fernandes. "Ultra low-cycle fatigue behaviour of a structural steel." Engineering Structures. 60 (2014): 214-222. AbstractWebsite
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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.

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
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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.

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.

Pereira, J. C. R., A. M. P. de Jesus, J. Xavier, and A. A. Fernandes. "ULCF assessment of X52 piping steel by means of cyclic bending tests." Journal of Constructional Steel Research. 138 (2017): 663-674. AbstractWebsite

Abstract Pipelines and piping components may experience large cyclic deformations during a reduced number of cycles (Ni = 1�100 cycles), when subjected to extreme cyclic loading events (e.g. hurricanes, support settlements, earthquakes). In accordance with these loading scenarios, a lateral movement can be applied to the pipeline inducing bending stresses that gradually promotes strain localization, due to progressive plastic instabilities (buckling), damage evolution and final failure. This work aims at characterizing ultra-low cycle fatigue (ULCF) behaviour of the \{X52\} piping steel under bending and local buckling state. An experimental program was carried out to derive \{ULCF\} data for smooth, notched and flat-grooved specimen geometries under cyclic bending. Furthermore, the small-scale tests were simulated in ABAQUS� with the objective of computing the parameters governing the fatigue damage models. The classical Coffin-Manson strain-life relation commonly used in the low cycle fatigue (LCF) regime is proposed to model the fatigue lives. In addition, the Xue model, particularly dependent of the monotonic fracture strain was also used for the prediction of the number of cycles until the crack initiation. The numerical data obtained with these models are compared, being achieved similar fatigue lives predictions for notched plane specimens. For the case of flat-grooved specimens which provides plain strain conditions, an overestimation from the Coffin-Manson relation was observed while the Xue model reproduces very good results for both specimens' series.

Pereira, J. C. R., A. M. P. de Jesus, J. Xavier, J. A. F. O. Correia, L. Susmel, and A. A. Fernandes. "Low and ultra-low-cycle fatigue behavior of X52 piping steel based on theory of critical distances." International Journal of Fatigue (2020): 105482. AbstractWebsite

The cyclic failure observed in structural components such as pipelines subjected to extreme loading conditions highlights some limitations concerning the application of existing fatigue damage models. The evaluation and prediction of this type of failure in these steel components under large-scale plastic yielding associated with high levels of stress triaxiality are not sufficiently known nor explored. This fatigue domain is conventionally called ultra-low-cycle fatigue (ULCF) and damage features are representative of both low-cycle fatigue (LCF) and monotonic ductile fracture. Thus, in order to understand the ULCF damage mechanisms both monotonic and LCF tests are required to get representative bounding damage information to model the material damage behaviour under such extreme loading conditions. This paper aims at exploring the Theory of Critical Distances (TCD) in the LCF and ULCF fatigue regimes, including the application of the point, line and area methods. The application of the TCD theories has not been explored so far in the ULCF fatigue regimes, despite its promising results in the LCF and high-cycle fatigue. An experimental program was carried out on several specimens’ geometries made of X52 piping steel. In detail, smooth plane specimens and notched plane specimens were cyclic loaded under tension/compression loading in order to obtain fatigue lives within the range of 101-104 cycles. In addition, cyclic bending tests on notched plane specimens were also incorporated in this study. Finite element simulations of all small-scale tests were conducted allowing to derive elastoplastic stress/strain fields along the potential crack paths. The numerical data were subjected to a post-processing in order to find characteristic lengths that can be treated as a fatigue property according to the TCD. A unified strain-life relation is proposed for the X52 piping steel together with a characteristic material length, consisting of a practical relation for pipeline strain-based design under extreme cyclic loading conditions.

Pereira, B., J. Xavier, F. Pereira, and J. Morais. "Identification of transverse elastic properties of the diaphysis of cortical bone." Journal of Mechanical Engineering and Biomechanics. 2 (2018): 50-55. AbstractWebsite
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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
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Morais, J. J. L., M. F. S. F. de Moura, F. A. M. Pereira, J. Xavier, N. Dourado, M. I. R. Dias, and J. M. T. Azevedo. "The double cantilever beam test applied to mode I fracture characterization of cortical bone tissue." Journal of the Mechanical Behavior of Biomedical Materials. 3 (2010): 446-453. Abstract

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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.

Majano-Majano, Almudena, Antonio José Lara-Bocanegra, José Xavier, and José Morais. "Experimental Evaluation of Mode II fracture Properties of Eucalyptus globulus L." Materials. 13 (2020). AbstractWebsite

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.

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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.

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Kuhn, P., H. Koerber, G. Catalanotti, and J. Xavier. "Intralaminar fracture toughness of UD glass fiber composite under high rate fiber tension and fiber compression loading." EPJ Web Conferences. 183 (2018): 02018. AbstractWebsite

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