M.f.s.f. de Moura | Faculdade de Engenharia da Universidade do Porto (original) (raw)

Papers by M.f.s.f. de Moura

$Research paper thumbnail of Mode II wood fracture characterization using the ELS test$

Engineering Fracture Mechanics, 2007

This paper describes experimental and numerical studies on the application of the end loaded spli... more This paper describes experimental and numerical studies on the application of the end loaded split test to mode II wood fracture characterization. A new data reduction scheme, based on the specimen compliance and on the equivalent crack concept, is proposed. The method presents three main advantages relatively to the classical methodologies: it does not require crack measurement during propagation; it

Materials Science …, 2010

This work reports on the experimental and numerical study of the bending behaviour of two-dimensi... more This work reports on the experimental and numerical study of the bending behaviour of two-dimensional adhesively-bonded scarf repairs of carbon-epoxy laminates, bonded with the ductile adhesive Araldite 2015 ®. Scarf angles varying from 2 to 45º were tested. The experimental work performed was used to validate a numerical Finite Element analysis using ABAQUS ® and a methodology developed by the authors to predict the strength of bonded assemblies. This methodology consists on replacing the adhesive layer by cohesive elements, including mixed-mode criteria to deal with the mixed-mode behaviour usually observed in structures. Trapezoidal laws in pure modes I and II were used to account for the ductility of the adhesive used. The cohesive laws in pure modes I and II were determined with Double Cantilever Beam and End-Notched Flexure tests, respectively, using an inverse method. Since in the experiments interlaminar and transverse intralaminar failures of the carbon-epoxy components also occurred in some regions, cohesive laws to simulate these failure modes were also obtained experimentally with a similar procedure. A good correlation with the experiments was found on the elastic stiffness, maximum load and failure mode of the repairs, showing that this methodology simulates accurately the mechanical behaviour of bonded assemblies.

$Research paper thumbnail of Pure mode II fracture characterization of composite bonded joints$

International Journal of Solids and Structures, 2009

A new data reduction scheme is proposed for measuring the critical fracture energy of adhesive jo... more A new data reduction scheme is proposed for measuring the critical fracture energy of adhesive joints under pure mode II loading using the End Notched Flexure test. The method is based on the crack equivalent concept and does not require crack length monitoring during propagation, which is very difficult to perform accurately in these tests. The proposed methodology also accounts for the energy dissipated at the Fracture Process Zone which is not negligible when ductile adhesives are used. Experimental tests and numerical analyses using a trapezoidal cohesive mixed-mode damage model demonstrated the good performance of the new method, namely when compared to classical data reduction schemes. An inverse method was used to determine the cohesive properties, fitting the numerical and experimental load-displacement curves. Excellent agreement between the numerical and experimental R-curves was achieved demonstrating the effectiveness of the proposed method.

Proceedings of the American …, 2001

The debonding of skin/stringer constructions is analyzed using a step-by-step simulation of mater... more The debonding of skin/stringer constructions is analyzed using a step-by-step simulation of material degradation based on strain softening decohesion elements and a ply degradation procedure. Decohesion elements with mixed-mode capability are placed at the interface between the skin and the flange to simulate the initiation and propagation of the delamination. In addition, the initiation and accumulation of fiber failure and matrix damage is modeled using Hashin-type failure criteria and their corresponding material degradation schedules. The debonding predictions using simplified three-dimensional models correlate well with test results.

$Research paper thumbnail of Mode-I interlaminar fracture of carbon/epoxy cross-ply composites$

Composites Science and Technology, 2002

Mode-I double-cantilever beam (DCB) tests were performed on carbon/epoxy [0 /90 ] 12 specimens. T... more Mode-I double-cantilever beam (DCB) tests were performed on carbon/epoxy [0 /90 ] 12 specimens. The starter crack was created at mid-thickness, between the 0 and 90 mid-layers. During the tests, however, the crack also propagated along the neighbouring 0 / 90 interface and within the 90 mid-layer. Nevertheless, the test results were apparently consistent with the assumptions of the corrected beam theory (CBT) that was used to obtain the interlaminar critical strain energy release rate, G Ic. The measured values were higher than those of unidirectional [0 ] 24 specimens, especially the final propagation values. A finite-element analysis confirmed the applicability of the CBT for interlaminar propagation along the two 0 /90 interfaces. The results also indicated that the intralaminar G Ic is significantly smaller than the interlaminar G Ic. This will prevent pure interlaminar propagation in multi-directional specimens with high interlaminar fracture toughness.

Composites Part A: Applied Science and Manufacturing, 2002

It is well known that composite laminates are easily damaged by low velocity impact. This event c... more It is well known that composite laminates are easily damaged by low velocity impact. This event causes internal delaminations that can drastically reduce the compressive strength of laminates. In this study, numerical and experimental analyses for predicting the damage in carbon±epoxy laminates, subjected to low velocity impact, were performed. Two different laminates 0 4 ; 90 4 s and 0 2 ;^45 2 ; 90 2 s were tested using a drop weight testing machine. Damage characterisation was carried out using X-rays radiography and the deply technique. The developed numerical model is based on a special shell ®nite element that guarantees interlaminar shear stresses continuity between different oriented layers, which was considered fundamental to predict delaminations. In order to predict the occurrence of matrix failure and the delaminated areas, a new failure criterion based on experimental observations and on other developed criteria, is included. A good agreement between experimental and numerical analysis for shape and orientation of delaminations was obtained. For delaminated areas, reasonable agreement was obtained.

Composites Part A: Applied Science and Manufacturing, 2011

Components in composite materials are progressively replacing metals for crashworthy applications... more Components in composite materials are progressively replacing metals for crashworthy applications in the automotive, railway and aeronautical industries. The numerical simulation of the crushing process for composite structures is a recent research area. Due to the complex mechanical behaviour of advanced composites, the capability of the existing analytical and numerical models to predict the crushing behaviour of composite materials is still limited. A numerical model for the crushing simulation of fibre-reinforced composite materials is proposed in this work. The progression of the main cracks is modelled using

International Journal of Solids and Structures, 2008

This work addresses both experimental and numerical analyses regarding the tensile behaviour of C... more This work addresses both experimental and numerical analyses regarding the tensile behaviour of CFRP single-strap repairs. Two fundamental geometrical parameters were studied: overlap length and patch thickness. The numerical model used ABAQUS ® software and a developed cohesive mixed-mode damage model adequate for ductile adhesives, and implemented within interface finite elements. Stress analyses and strength predictions were carried out. Experimental and numerical comparisons were performed on failure modes, failure load and equivalent stiffness of the repair. Good correlation was found between experimental and numerical results, showing that the proposed model can be successfully applied to bonded joints or repairs.

Este trabalho consiste num estudo experimental e numérico relativo ao comportamento de vigas de m... more Este trabalho consiste num estudo experimental e numérico relativo ao comportamento de vigas de madeira reparadas solicitadas à flexão em quatro pontos, inicialmente danificadas numa secção intermédia por esmagamento na zona de compressão. A reparação cons iste na remoção do material danificado e colagem de um remendo de carbono-epóxido para restituição da rigidez e resistência iniciais da viga. A an álise numérica pelo Método dos Elementos Finitos inclui modelos de dano coesivos para modelar a iniciação e propagação do dano no adesivo, interlaminar no remendo e no interior da madeira através de diferentes planos de propagação. A metodologia numérica proposta foi validada em termos de modo de rotura, rigidez inicial, e carga máxima suportada da viga sem dano, da viga danificada mas não reparada e da viga reparada com diferentes comprimentos de sobreposição do remendo. Os resultados obtidos mostraram que a metodologia proposta é adequada na simulação do comportamento destas reparações.

Wood Science and Technology

An experimental and numerical study on mode II fracture behaviour of European beech (Fagus sylvat... more An experimental and numerical study on mode II fracture behaviour of European beech (Fagus sylvatica L.) in the RL and TL crack propagation systems is performed. It is a hardwood species that has attracted increasing interest for structural use in Europe in recent years. Three-point end notched flexure tests are performed. The R-curves of both crack propagation systems are obtained, from which the critical strain energy release rate (GIIc) is derived by applying the compliance-based beam method. This data reduction scheme avoids crack length monitoring during its propagation, which is an advantage in wood. Using a direct method, the shear traction‐separation laws in mode II loading are determined. Full field displacements around the crack tip are monitored by 3D digital image correlation technique, and the crack tip shear displacements are analysed. The proposed method is numerically validated by finite element analysis. Cohesive zone models are developed implementing a shear tracti...

Este trabalho apresenta um estudo numérico relativo à resistência residual de reparações adesivas... more Este trabalho apresenta um estudo numérico relativo à resistência residual de reparações adesivas por sobreposição simples, de laminados de carbonoepóxido. É utilizado o Método dos Elementos Finitos em conjunto com um modelo de dano coesivo em modo misto, baseado no uso indirecto da Mecânica da Fractura, para simular numericamente a iniciação e propagação do dano nas reparações. O modelo numérico é aplicado na identificação das alterações geométricas que maximizam a resistência residual das reparações sujeitas a solicitações de tracção, compressão e flexão.

In this work a numerical study has been performed to verify the adequacy of the End Notched Flexu... more In this work a numerical study has been performed to verify the adequacy of the End Notched Flexure (ENF) test to determine the fracture toughness under mode II loading of cortical bovine bone tissue. In this work a detailed numerical analysis using the finite element method and a cohesive damage model was performed in order to optimize the specimen geometry when applied to bone fracture characterization under mode II loading. A data reduction scheme based on specimen compliance and crack equivalent concept was used to overcome the difficulties inherent to crack monitoring during its growth. It was verified that a judicious selection of the geometry allows a rigorous estimation of toughness in mode II.

Construction and Building Materials, 2018

This study analyses a common L-shape configuration formed by wood members and a thick metal plate... more This study analyses a common L-shape configuration formed by wood members and a thick metal plate, duly fastened with steel dowels. Four connecting arrangements were experimentally tested, considering different values of space between dowels and distance to the boundary edge, which allowed measuring the initial stiffness and moment-carrying capacity. A three-dimensional finite element model, including a trapezoidal bilinear cohesive law, was developed to reproduce mixed-mode loading through cohesive zone modelling. Very satisfactory agreements between numerical predictions and experimental results were registered, regarding the full-extension of the load-displacement curves and damage profiles of the joints. In light of these, the model was applied in a larger range of possible combinations of distances to get global trends of the initial stiffness and moment-carrying capacity of these joints.

International Journal of Mechanical Sciences, 2018

This study presents two alternative methods to determine the cohesive law of bovine cortical bone... more 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.

Composite Structures, 2018

This paper presents experimental and numerical results on a repaired mortar beam under bending wi... more This paper presents experimental and numerical results on a repaired mortar beam under bending with thin bonded carbon-epoxy patches. The influence of the patch length on the stiffness and ultimate load was analysed, comparatively to undamaged and damaged beam configurations. Numerical analyses were executed employing a developed mixed-mode I + II cohesive damage model with realistic parameters obtained experimentally in previous studies. Accurate predictions of damage propagation in bulk mortar and within adhesive were accomplished for homothetic structures with different sizes. Stress profiles were obtained along both adhesive interface and in mortar to assess the failure modes observed experimentally. Important conclusions have been drawn about appropriate strategies to be followed in order to guarantee remarkable recover of initial stiffness and strength on damaged mortar beams submitted to bending.

International Journal of Solids and Structures, 2017

Direct and inverse methods applied to the determination of mode I cohesive law of bovine cortical... more Direct and inverse methods applied to the determination of mode I cohesive law of bovine cortical bone using the DCB test,

International Journal of Adhesion and Adhesives, 2012

A simple procedure to measure the cohesive laws of bonded joints under mode I loading using the d... more A simple procedure to measure the cohesive laws of bonded joints under mode I loading using the double cantilever beam test is proposed. The method only requires recording the applied loaddisplacement data and measuring the crack opening displacement at its tip in the course of the experimental test. The strain energy release rate is obtained by a procedure involving the Timoshenko beam theory, the specimen's compliance and the crack equivalent concept. Following the proposed approach the influence of the fracture process zone is taken into account which is fundamental for an accurate estimation of the failure process details. The cohesive law is obtained by differentiation of the strain energy release rate as a function of the crack opening displacement. The model was validated numerically considering three representative cohesive laws. Numerical simulations using finite element analysis including cohesive zone modeling were performed. The good agreement between the inputted and resulting laws for all the cases considered validates the model. An experimental confirmation was also performed by comparing the numerical and experimental load-displacement curves. The numerical load-displacement curves were obtained by adjusting typical cohesive laws to the ones measured experimentally following the proposed approach and using finite element analysis including cohesive zone modeling. Once again, good agreement was obtained in the comparisons thus demonstrating the good performance of the proposed methodology.

International Journal of Adhesion and Adhesives, 2010

The widespread employment of carbon-epoxy laminates in high responsibility and severely loaded ap... more The widespread employment of carbon-epoxy laminates in high responsibility and severely loaded applications introduces an issue regarding their handling after damage. Repair of these structures should be evaluated, instead of their disposal, for cost saving and ecological purposes. Under this perspective, the availability of efficient repair methods is essential to restore the strength of the structure. The development and validation of accurate predictive tools for the repairs behaviour are also extremely important, allowing the reduction of costs and time associated to extensive test programmes. Comparing with strap repairs, scarf repairs have the advantages of a higher efficiency and the absence of aerodynamic disturbance. This work reports on a numerical study of the tensile behaviour of three-dimensional scarf repairs in carbon-epoxy structures, using a ductile adhesive (Araldite s 2015). The finite elements analysis was performed in ABAQUS s and Cohesive Zone Modelling was used for the simulation of damage onset and growth in the adhesive layer. Trapezoidal cohesive laws in each pure mode were used to account for the ductility of the specific adhesive mentioned. A parametric study was performed on the repair width and scarf angle. The use of over-laminating plies covering the repaired region at the outer or both repair surfaces was also tested as an attempt to increase the repairs efficiency. The obtained results allowed the proposal of design principles for repairing composite structures.

$Research paper thumbnail of Mode I fracture characterization of human bone using the DCB test$

International Journal of Structural Integrity, 2015

Fracture characterization of human cortical bone under pure mode I loading is performed in this w... more Fracture characterization of human cortical bone under pure mode I loading is performed in this work. A miniaturized version of the double cantilever test (DCB) test was used for the experimental tests. A data reduction scheme based on crack equivalent concept and Timoshenko beam theory is proposed to overcome difficulties inherent to crack length monitoring during the test. The application of the method propitiates an easy determination of the Resistance-curves that allow defining the fracture energy under mode I loading from the plateau region. The average value of fracture energy was subsequently used in a numerical analysis with element method involving cohesive zone modelling. The aim is to validate the proposed test and procedure concerning fracture characterization of human cortical bone under pure mode I loading. A bilinear cohesive zone model was used to simulate damage initiation and growth. The cohesive parameters were determined by an inverse procedure involving the fitting of numerical and experimental load-displacement curves. The excellent agreement obtained reveals that the proposed test and associated methodology is quite effective concerning fracture characterization of human cortical bone under pure mode I loading.