Filipe Chaves - Profile on Academia.edu (original) (raw)

Papers by Filipe Chaves

Analele Universităţii "Dunărea de Jos" din Galaţi, Dec 29, 2023

The use of additive manufacturing (AM) has revolutionized the production of polymerbased material... more The use of additive manufacturing (AM) has revolutionized the production of polymerbased materials, offering a wide range of design possibilities and geometric complexity. However, due to the limitations of 3D printers to produce large parts, the parts often must be printed in several separate components and further joined together to obtain the final 3D-printed part. 3D printing can be used to produce only the most complex parts, which can be further combined with simple, non-printed parts from other materials to make the final product. One way to join 3D-printed part is an adhesive-bonded method. This paper focuses on the recent advances in adhesive bonding techniques for 3D-printed parts and explores various methods to enhance their mechanical performance. The benefits and limitations of each technique were discussed, and highlighted promising paths for future research. Finally, this paper provides a comprehensive overview of the current strategies to improve the mechanical performance of adhesive joints with AM-based adherents, offering guidance for the design and fabrication of high-performance structures in a range of applications. It was concluded that the configuration of the bonding area represents an essential parameter that directly influences the bonding strength and overall structural integrity of AM adhesive joints, and that the implementation of customized joint geometries can lead to a substantial enhancement in the joint strength of 3Dprinted parts. The incorporation of reinforcing materials, optimization of the printing parameters of adherents, pre and post-treatment methods show potential in enhancing the bonding strength of the 3D-printed joints. The synergistic integration of these cutting-edge technologies can yield mutual advantages that complement each other, ultimately resulting in an enhanced overall performance for AM parts.

Analele Universităţii "Dunărea de Jos" din Galaţi, Dec 15, 2022

Rapid prototyping (also known as additive manufacturing, AM) is a quickly developing process with... more Rapid prototyping (also known as additive manufacturing, AM) is a quickly developing process with increasing new applications in a large variety of industrial sectors (i.e., aerospace, automotive, medical, among others.) However, despite the great advantage of a decoupled price to part complexity of an AM fabricated structure, the material properties (largely governed by filament material and printing parameters) still present a significant limiting factor. In this context, the development of new filament materials for a wider range of applications has great potential. In this study, the influence of micro-scale filler reinforcement (powders), both natural (curauá) and synthetic (glass fibre), in the fabrication of an Acrylonitrile Butadiene Styrene (ABS) filament was evaluated. The filler was controlled by weight fraction (~1%) and the filament was fabricated via extrusion. A commercially available 3D printer was used to print tensile and flexural specimens for mechanical characterization as per ASTM standards. The fracture morphology was analysed after tensile testing via optical microscopy in order to evaluate the effect of the fillers on the material deposition and void formation. No significant variation in the tensile properties was reported, except for the strain at failure, while more significant flexural strength variation was observed as a function of filler material. The fillers presented a significant effect on the void density of the fractured surface. It was demonstrated that this simple fabrication technique can generate novel filament materials that may enhance the mechanical properties or widen the range of application (e.g., faster decomposition times in nature for singleuse plastics due to the hydrophilic nature of the natural filler and lower water absorption of the hydrophobic synthetic filler for marine environment applications).

The present work is dedicated to the development and design of a load jig inspired in the propose... more The present work is dedicated to the development and design of a load jig inspired in the proposed solution by Fernlund and Spelt in order to characterize fracture of bonded joints under mixed-mode I+II loading. The jig allows for easy alteration of the mode-mixity and permits covering the full range of mixed-mode I+II combinations. A data reduction scheme based on specimen compliance, beam theory and crack equivalent concept is proposed to overcome several difficulties inherent to the test analysis. The development was based in a design methodology using numerical validation based on experimental data obtained with a Dual Loading Frame from Virginia Tech. This methodology is presented and then validated with the experimental application of the jig. INTRODUCTION Bonded joints are being increasingly applied in structures involving risk, as is the case of the aeronautical, automotive, and civil infrastructure industries. The classical strength prediction based on stress or strain anal...

Este trabajo esta dedicado a la elaboracion y diseno de un aparato inspirado en la solucionpropue... more Este trabajo esta dedicado a la elaboracion y diseno de un aparato inspirado en la solucionpropuesta por Fernlund y Spelt para caracterizar la fractura de las uniones adhesivas bajoaplicaciones de cargas en modo mixto I + II . El aparato permite una facil variacion delmodo de mezcla y cubre todo el rango de combinaciones posibles (I y II).Ademas, se propone un procedimiento para tratamiento de datos en funcion del tamano degrieta, basado en la teoria de la viga y el concepto de grieta equivalente, superando variasdificultades inherentes a los ensayos realizados. El desarrollo se basa en una metodologiade diseno mediante la validacion numerica basada en datos experimentales obtenidos conun equipo de ensayo de doble accion en Virginia Tech. Esta metodologia se presenta acontinuacion, y esta validada con la aplicacion experimental del aparato.

Materialwissenschaft und Werkstofftechnik, 2011

Double cantilever beam (DCB) tests are common experiments in the field of adhesive fracture mecha... more Double cantilever beam (DCB) tests are common experiments in the field of adhesive fracture mechanics. During such an experiment, both the load and the crack length have to be monitored. Digital image processing techniques offer interesting possibilities in various fields of science. Automated analyses may significantly reduce the necessary manpower for certain cumbersome tasks. The analysis of large series of images may be done in less time, since automated image processing techniques are able to work efficiently and with constant quality 24h per day. In this work, a series of images obtained by a high-speed camera is analyzed in order to determine the crack growth behavior during a DCB test. The present work represents a contribution to the effort of automating the crack growth measurement, by proposing and comparing different automated techniques.

Mode II Fracture Toughness of a Brittle and a Ductile Adhesive as a Function of the Adhesive Thickness

The Journal of Adhesion, 2010

... 4 , 65 – 78 ( 1984 ). [CSA]; 3. Hart-Smith , LJ , Adhesive-bonded single-lap joints, NASA Con... more ... 4 , 65 – 78 ( 1984 ). [CSA]; 3. Hart-Smith , LJ , Adhesive-bonded single-lap joints, NASA Contract Report, Hampton, Virginia, NASA CR-112236 ( 1973 ). ... [Taylor & Francis Online], [Web of Science ®]; 6. da Silva , LFM , das Neves , PJC , Adams , RD , and Spelt , JK , Int. J. Adhes. ...

International Journal of Solids and Structures, 2011

The dual actuator load test was numerically analyzed in order to assess its adequacy for fracture... more The dual actuator load test was numerically analyzed in order to assess its adequacy for fracture characterization of bonded joints under different mixed-mode loading conditions. This test enables asymmetric loading of double cantilever beam specimens, thus providing a large range of mixed-mode combinations. A new data reduction scheme based on specimen compliance, beam theory and crack equivalent concept was proposed to overcome several difficulties inherent to the test. The method assumes that the dual actuator test can be viewed as a combination of the double cantilever beam and end loaded split tests, which are used for pure modes I and II fracture characterization, respectively. A numerical analysis including a cohesive mixed-mode damage model was performed considering different mixed-mode loading conditions to evaluate the test performance. Some conclusions were drawn about the advantages and drawbacks of the test.

Materialwissenschaft und Werkstofftechnik

Adhesively joints are increasingly being used in aerospace, automotive and maritime industries. T... more Adhesively joints are increasingly being used in aerospace, automotive and maritime industries. The use of this type of joining provides some advantages such as reduction in weight and cost. However, adhesive joints in transportation industry may be exposed to aggressive environments such as high humidity during their service life. A particular issue with the reliability of adhesive joints is the presence of cracks and flaws. Fracture mechanics tests for adhesive joints provide relevant mechanical properties to determine the adhesive toughness and play an important role in design process. This research aims to determine the fracture toughness of aluminum/adhesive/aluminum joints under pure mode I, pure mode II and mixed mode loadings. The fracture characterization of adhesively joints was performed when these specimens were submitted to mixed mode loadings and pure modes (shear and opening). The experimental tests Double Cantilever Beam (DCB) and End-Notched Flexure (ENF) were also done in order to assess the fracture toughness in Paiva for the help and advice while developing this thesis. A special thanks to Joana, Daniel and Rodrigo for the friendship and for being always by my side during this semester. And finally, all my family and friends for the support when I needed the most.

Impact Loading of Single Lap Joints of Dissimilar Lightweight Adherends Bonded With a Crash-Resistant Epoxy Adhesive

Journal of Engineering Materials and Technology

The use of lightweight materials in the automotive industry for structural parts has been increas... more The use of lightweight materials in the automotive industry for structural parts has been increasing in recent years in order to reduce the overall vehicle's weight. New innovative lighter materials are being developed nowadays to accomplish that objective. In order to keep or even increase passenger's safety, structural parts made of these materials need to withstand static and impact loads within a range of different temperatures along the vehicle's life. The effect of these conditions when joining these dissimilar lighter materials is a critical issue to be considered when designing the car's body. In this paper, the strength under real car conditions of single lap joints (SLP) made of aluminum alloy (AA) bonded to carbon fiber reinforced polymer (CFRP) adherends was studied. A new crash-resistant epoxy adhesive was used to bond these lightweight materials and an extended characterization of its cohesive properties was carried out. The single lap joints were teste...

Application of adhesive bonding in PVC windows

Page 1. Resumo Os adesivos estruturais têm vindo a ser utilizados em muitas aplicações industriai... more Page 1. Resumo Os adesivos estruturais têm vindo a ser utilizados em muitas aplicações industriais ao longo das últimas décadas. Apesar da sua natureza tradicional, o sector da construção civil tem também utilizado adesivos estruturais. ...

A creative solution for rapid and inexpensive model-making in product design processes

Proceedings of the 5th International Conference on Advanced Research in Virtual and Rapid Prototyping, Leiria, Portugal, 28 September - 1 October, 2011, 2011

Preliminary finite element results

Adhesively bonded T-joints in polyvinyl chloride windows

Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications, 2008

The main objective of this study was to assess the applicability of adhesives to connect a transo... more The main objective of this study was to assess the applicability of adhesives to connect a transom to a polyvinyl chloride window frame. A modified methacrylate adhesive was selected and tested for its mechanical properties, environmental ageing, and glass transition temperature. Adhesively bonded T-joints were manufactured and tested, and compared with the conventional screw-fastened T-joints in terms of joint strength. The initial geometry of the adhesively bonded T-joints was optimized with a finite element analysis (FEA). Finally, the various manufacturing processes (welding, screw fastening, and adhesive, bonding) were compared in economical terms, which is a critical parameter for the industry. The joint strength results show that adhesively bonded joints perform as well or better than the conventional screw-fastened joints. The FEA indicates that further improvements are possible with little changes in the geometry. The adhesive bonding process is also attractive in economica...

Fracture toughness of a structural adhesive under mixed mode loadings

Materialwissenschaft und Werkstofftechnik, 2011

ABSTRACT This aim of this research was to determine the fracture toughness of steel/adhesive/stee... more ABSTRACT This aim of this research was to determine the fracture toughness of steel/adhesive/steel joints under mixed mode loadings. A structural and ductile epoxy adhesive was selected in this research. The experimental tests, i. e. Asymmetric Tapered Double Cantilever Beam (ATDCB), Single Leg Bending (SLB) and Asymmetric Double Cantilever Beam (ADCB), were realized to assess the fracture toughness in mixed mode. Experimental tests in pure mode I and II were also realized to complete the fracture envelope. In order to obtain the mode I critical energy release rates, GIc, the standard Double Cantilever Beam test was used, whilst the critical strain energy release rate in mode II, GIIc, was evaluated with the End Notched Flexure test. For various mixed mode tests, the critical strain energy release rate values were partitioned into mode I and mode II components. One of the main conclusions of the present work is that the introduction of a small amount of mode II loading (shear) in the joint results in a decrease of the total fracture energy, GT = GI + GII, when compared to the pure mode I fracture energy.

Fracture characterization of bonded joints using the dual actuator load apparatus

Journal of Adhesion Science and Technology, 2014

ABSTRACT Mixed-mode I + II fracture characterization tests of steel-bonded joints were carried ou... more ABSTRACT Mixed-mode I + II fracture characterization tests of steel-bonded joints were carried out with the dual actuator load apparatus using a previously developed data reduction scheme in order to obtain the fracture envelope. This test involves independent loading of the specimen arms of a clamped double cantilever beam, which allows for easy variation of the I + II mode mixity in fracture characterization through altering the applied displacement rates. Difficulties inherent to crack monitoring during its propagation and imperfections of initial crack manufacture are well managed with the proposed method. Three different cases corresponding to different mode mixities were tested. The experimental results revealed that a linear energetic criterion performs well in describing the fracture envelope of these bonded joints.

Fracture Mechanics Tests in Adhesively Bonded Joints: A Literature Review

The Journal of Adhesion, 2013

ABSTRACT Fracture mechanics characterization tests for adhesive joints are analyzed and reviewed ... more ABSTRACT Fracture mechanics characterization tests for adhesive joints are analyzed and reviewed in order to understand their advantages and disadvantages. Data reduction techniques for analytical methods are summarized to understand the improvements implemented in each test. Numerical approaches are also used complementing tests information. Both linear and non-linear methods to obtain the fracture energy release rate are presented. Pure mode I and mode II tests are described. Simple mixed-mode tests, varying only the specimen geometry, with limited mode-mixity are also presented. Performing a wider mode-mixity range requires sophisticated apparatus that are studied in detail. There is no general agreement about the test suitability for mixed-mode fracture assessment of adhesive joints. A universal test that can easily be performed and give accurate results is essential to optimize the expensive testing at the design stage.

Mechanical characterization of a high elongation and high toughness epoxy adhesive

International Journal of Adhesion and Adhesives, 2013

ABSTRACT In this paper, a new epoxy adhesive has been mechanically characterized. The adhesive co... more ABSTRACT In this paper, a new epoxy adhesive has been mechanically characterized. The adhesive combines the properties of an epoxy adhesive and typical polyurethane (PU) adhesive, such as high elongation and high toughness. Experimental tests were performed to measure the tensile properties, shear properties, thermal properties and fracture properties. The tensile test shows high tensile strength and high elongation. The single lap joint (SLJ) test shows that the failure load is proportional to the overlap length for hard steel adherends. For the SLJs with mild steel adherends, the failure occurred due to adherend yielding. Impact tests were conducted using SLJ specimens and the results are consistent with the SLJ tested under static conditions. The Tg was obtained using a Dynamic Mechanical Analysis (DMA) type of test. The toughness in mode I was determined using the Double Cantilever Beam (DCB) test and the toughness in mode II using End Notched Flexure (ENF) test.

Numerical validation of a crack equivalent method for mixed-mode I+II fracture characterization of bonded joints

Engineering Fracture Mechanics, 2013

ABSTRACT The present work is dedicated to development of a crack equivalent data reduction scheme... more ABSTRACT The present work is dedicated to development of a crack equivalent data reduction scheme applied to the load jig previously developed by Fernlund and Spelt [1] in order to characterize fracture of bonded joints under mixed-mode I + II loading. The jig allows for easy alteration of the mode-mixity and permits covering the full range of mixed-mode I + II combinations. A data reduction scheme based on specimen compliance, beam theory and crack equivalent concept is proposed to overcome several difficulties inherent to the test analysis. The method assumes that the performed test can be viewed as a combination of the double cantilever beam and asymmetrically loaded end-notched flexure tests, which provide modes I and II fracture characterization, respectively. A numerical analysis including a cohesive mixed-mode I + II damage model was performed considering different mixed-mode loading conditions to validate the proposed data reduction scheme. Issues regarding self-similar crack growth and fracture process zone development are discussed. It was verified that the considered in-plane mix mode fracture criterion is well captured using the proposed data reduction scheme.

Computational Materials Science, 2011

Adhesive-bonding for the unions in structures is gaining momentum over welding, riveting and fast... more Adhesive-bonding for the unions in structures is gaining momentum over welding, riveting and fastening. It is vital for the design of bonded structures the availability of reliable damage models to predict their fracture behaviour. Cohesive Zone Models (CZM's) have been extensively used in the past, taking advantage of traction-separation laws between stresses and relative displacements to simulate crack growth along predefined paths. The eXtended Finite Element Method (XFEM) is a recent improvement of the Finite Element Method (FEM) that relies on damage laws based on the bulk strength of materials for damage initiation and strain for the assessment of failure, rather than the tipping tractions and tensile/shear relative displacements used for the CZM's. Compared to the FEM, XFEM excels in allowing discontinuities to grow within bulk solids along an arbitrary path. This work aims to assess the viability of the XFEM to predict the fracture behaviour of a thin layer of adhesive between stiff and compliant adherends. To build the XFEM damage laws, the fracture toughness in pure mode I (G Ic) and tensile cohesive strength (r 0 n) of the two adhesives were initially determined by Double-Cantilever Beam (DCB) and bulk tensile tests, respectively. Particular emphasis was given to G Ic , as this is the most influent parameter for the numerical predictions. The numerical simulations of the DCB tests with the proposed laws matched accurately the experimental load-displacement (P-d) curves, which validated the analysis procedure. The accuracy of the data reduction methods for calculation of G Ic was checked by comparison of the input values in the simulations with the results of G Ic calculations, with good results.

Analele Universităţii "Dunărea de Jos" din Galaţi, Dec 29, 2023

The use of additive manufacturing (AM) has revolutionized the production of polymerbased material... more The use of additive manufacturing (AM) has revolutionized the production of polymerbased materials, offering a wide range of design possibilities and geometric complexity. However, due to the limitations of 3D printers to produce large parts, the parts often must be printed in several separate components and further joined together to obtain the final 3D-printed part. 3D printing can be used to produce only the most complex parts, which can be further combined with simple, non-printed parts from other materials to make the final product. One way to join 3D-printed part is an adhesive-bonded method. This paper focuses on the recent advances in adhesive bonding techniques for 3D-printed parts and explores various methods to enhance their mechanical performance. The benefits and limitations of each technique were discussed, and highlighted promising paths for future research. Finally, this paper provides a comprehensive overview of the current strategies to improve the mechanical performance of adhesive joints with AM-based adherents, offering guidance for the design and fabrication of high-performance structures in a range of applications. It was concluded that the configuration of the bonding area represents an essential parameter that directly influences the bonding strength and overall structural integrity of AM adhesive joints, and that the implementation of customized joint geometries can lead to a substantial enhancement in the joint strength of 3Dprinted parts. The incorporation of reinforcing materials, optimization of the printing parameters of adherents, pre and post-treatment methods show potential in enhancing the bonding strength of the 3D-printed joints. The synergistic integration of these cutting-edge technologies can yield mutual advantages that complement each other, ultimately resulting in an enhanced overall performance for AM parts.

Analele Universităţii "Dunărea de Jos" din Galaţi, Dec 15, 2022

Rapid prototyping (also known as additive manufacturing, AM) is a quickly developing process with... more Rapid prototyping (also known as additive manufacturing, AM) is a quickly developing process with increasing new applications in a large variety of industrial sectors (i.e., aerospace, automotive, medical, among others.) However, despite the great advantage of a decoupled price to part complexity of an AM fabricated structure, the material properties (largely governed by filament material and printing parameters) still present a significant limiting factor. In this context, the development of new filament materials for a wider range of applications has great potential. In this study, the influence of micro-scale filler reinforcement (powders), both natural (curauá) and synthetic (glass fibre), in the fabrication of an Acrylonitrile Butadiene Styrene (ABS) filament was evaluated. The filler was controlled by weight fraction (~1%) and the filament was fabricated via extrusion. A commercially available 3D printer was used to print tensile and flexural specimens for mechanical characterization as per ASTM standards. The fracture morphology was analysed after tensile testing via optical microscopy in order to evaluate the effect of the fillers on the material deposition and void formation. No significant variation in the tensile properties was reported, except for the strain at failure, while more significant flexural strength variation was observed as a function of filler material. The fillers presented a significant effect on the void density of the fractured surface. It was demonstrated that this simple fabrication technique can generate novel filament materials that may enhance the mechanical properties or widen the range of application (e.g., faster decomposition times in nature for singleuse plastics due to the hydrophilic nature of the natural filler and lower water absorption of the hydrophobic synthetic filler for marine environment applications).

The present work is dedicated to the development and design of a load jig inspired in the propose... more The present work is dedicated to the development and design of a load jig inspired in the proposed solution by Fernlund and Spelt in order to characterize fracture of bonded joints under mixed-mode I+II loading. The jig allows for easy alteration of the mode-mixity and permits covering the full range of mixed-mode I+II combinations. A data reduction scheme based on specimen compliance, beam theory and crack equivalent concept is proposed to overcome several difficulties inherent to the test analysis. The development was based in a design methodology using numerical validation based on experimental data obtained with a Dual Loading Frame from Virginia Tech. This methodology is presented and then validated with the experimental application of the jig. INTRODUCTION Bonded joints are being increasingly applied in structures involving risk, as is the case of the aeronautical, automotive, and civil infrastructure industries. The classical strength prediction based on stress or strain anal...

Este trabajo esta dedicado a la elaboracion y diseno de un aparato inspirado en la solucionpropue... more Este trabajo esta dedicado a la elaboracion y diseno de un aparato inspirado en la solucionpropuesta por Fernlund y Spelt para caracterizar la fractura de las uniones adhesivas bajoaplicaciones de cargas en modo mixto I + II . El aparato permite una facil variacion delmodo de mezcla y cubre todo el rango de combinaciones posibles (I y II).Ademas, se propone un procedimiento para tratamiento de datos en funcion del tamano degrieta, basado en la teoria de la viga y el concepto de grieta equivalente, superando variasdificultades inherentes a los ensayos realizados. El desarrollo se basa en una metodologiade diseno mediante la validacion numerica basada en datos experimentales obtenidos conun equipo de ensayo de doble accion en Virginia Tech. Esta metodologia se presenta acontinuacion, y esta validada con la aplicacion experimental del aparato.

Materialwissenschaft und Werkstofftechnik, 2011

Double cantilever beam (DCB) tests are common experiments in the field of adhesive fracture mecha... more Double cantilever beam (DCB) tests are common experiments in the field of adhesive fracture mechanics. During such an experiment, both the load and the crack length have to be monitored. Digital image processing techniques offer interesting possibilities in various fields of science. Automated analyses may significantly reduce the necessary manpower for certain cumbersome tasks. The analysis of large series of images may be done in less time, since automated image processing techniques are able to work efficiently and with constant quality 24h per day. In this work, a series of images obtained by a high-speed camera is analyzed in order to determine the crack growth behavior during a DCB test. The present work represents a contribution to the effort of automating the crack growth measurement, by proposing and comparing different automated techniques.

Mode II Fracture Toughness of a Brittle and a Ductile Adhesive as a Function of the Adhesive Thickness

The Journal of Adhesion, 2010

... 4 , 65 – 78 ( 1984 ). [CSA]; 3. Hart-Smith , LJ , Adhesive-bonded single-lap joints, NASA Con... more ... 4 , 65 – 78 ( 1984 ). [CSA]; 3. Hart-Smith , LJ , Adhesive-bonded single-lap joints, NASA Contract Report, Hampton, Virginia, NASA CR-112236 ( 1973 ). ... [Taylor & Francis Online], [Web of Science ®]; 6. da Silva , LFM , das Neves , PJC , Adams , RD , and Spelt , JK , Int. J. Adhes. ...

International Journal of Solids and Structures, 2011

The dual actuator load test was numerically analyzed in order to assess its adequacy for fracture... more The dual actuator load test was numerically analyzed in order to assess its adequacy for fracture characterization of bonded joints under different mixed-mode loading conditions. This test enables asymmetric loading of double cantilever beam specimens, thus providing a large range of mixed-mode combinations. A new data reduction scheme based on specimen compliance, beam theory and crack equivalent concept was proposed to overcome several difficulties inherent to the test. The method assumes that the dual actuator test can be viewed as a combination of the double cantilever beam and end loaded split tests, which are used for pure modes I and II fracture characterization, respectively. A numerical analysis including a cohesive mixed-mode damage model was performed considering different mixed-mode loading conditions to evaluate the test performance. Some conclusions were drawn about the advantages and drawbacks of the test.

Materialwissenschaft und Werkstofftechnik

Adhesively joints are increasingly being used in aerospace, automotive and maritime industries. T... more Adhesively joints are increasingly being used in aerospace, automotive and maritime industries. The use of this type of joining provides some advantages such as reduction in weight and cost. However, adhesive joints in transportation industry may be exposed to aggressive environments such as high humidity during their service life. A particular issue with the reliability of adhesive joints is the presence of cracks and flaws. Fracture mechanics tests for adhesive joints provide relevant mechanical properties to determine the adhesive toughness and play an important role in design process. This research aims to determine the fracture toughness of aluminum/adhesive/aluminum joints under pure mode I, pure mode II and mixed mode loadings. The fracture characterization of adhesively joints was performed when these specimens were submitted to mixed mode loadings and pure modes (shear and opening). The experimental tests Double Cantilever Beam (DCB) and End-Notched Flexure (ENF) were also done in order to assess the fracture toughness in Paiva for the help and advice while developing this thesis. A special thanks to Joana, Daniel and Rodrigo for the friendship and for being always by my side during this semester. And finally, all my family and friends for the support when I needed the most.

Impact Loading of Single Lap Joints of Dissimilar Lightweight Adherends Bonded With a Crash-Resistant Epoxy Adhesive

Journal of Engineering Materials and Technology

The use of lightweight materials in the automotive industry for structural parts has been increas... more The use of lightweight materials in the automotive industry for structural parts has been increasing in recent years in order to reduce the overall vehicle's weight. New innovative lighter materials are being developed nowadays to accomplish that objective. In order to keep or even increase passenger's safety, structural parts made of these materials need to withstand static and impact loads within a range of different temperatures along the vehicle's life. The effect of these conditions when joining these dissimilar lighter materials is a critical issue to be considered when designing the car's body. In this paper, the strength under real car conditions of single lap joints (SLP) made of aluminum alloy (AA) bonded to carbon fiber reinforced polymer (CFRP) adherends was studied. A new crash-resistant epoxy adhesive was used to bond these lightweight materials and an extended characterization of its cohesive properties was carried out. The single lap joints were teste...

Application of adhesive bonding in PVC windows

Page 1. Resumo Os adesivos estruturais têm vindo a ser utilizados em muitas aplicações industriai... more Page 1. Resumo Os adesivos estruturais têm vindo a ser utilizados em muitas aplicações industriais ao longo das últimas décadas. Apesar da sua natureza tradicional, o sector da construção civil tem também utilizado adesivos estruturais. ...

A creative solution for rapid and inexpensive model-making in product design processes

Proceedings of the 5th International Conference on Advanced Research in Virtual and Rapid Prototyping, Leiria, Portugal, 28 September - 1 October, 2011, 2011

Preliminary finite element results

Adhesively bonded T-joints in polyvinyl chloride windows

Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications, 2008

The main objective of this study was to assess the applicability of adhesives to connect a transo... more The main objective of this study was to assess the applicability of adhesives to connect a transom to a polyvinyl chloride window frame. A modified methacrylate adhesive was selected and tested for its mechanical properties, environmental ageing, and glass transition temperature. Adhesively bonded T-joints were manufactured and tested, and compared with the conventional screw-fastened T-joints in terms of joint strength. The initial geometry of the adhesively bonded T-joints was optimized with a finite element analysis (FEA). Finally, the various manufacturing processes (welding, screw fastening, and adhesive, bonding) were compared in economical terms, which is a critical parameter for the industry. The joint strength results show that adhesively bonded joints perform as well or better than the conventional screw-fastened joints. The FEA indicates that further improvements are possible with little changes in the geometry. The adhesive bonding process is also attractive in economica...

Fracture toughness of a structural adhesive under mixed mode loadings

Materialwissenschaft und Werkstofftechnik, 2011

ABSTRACT This aim of this research was to determine the fracture toughness of steel/adhesive/stee... more ABSTRACT This aim of this research was to determine the fracture toughness of steel/adhesive/steel joints under mixed mode loadings. A structural and ductile epoxy adhesive was selected in this research. The experimental tests, i. e. Asymmetric Tapered Double Cantilever Beam (ATDCB), Single Leg Bending (SLB) and Asymmetric Double Cantilever Beam (ADCB), were realized to assess the fracture toughness in mixed mode. Experimental tests in pure mode I and II were also realized to complete the fracture envelope. In order to obtain the mode I critical energy release rates, GIc, the standard Double Cantilever Beam test was used, whilst the critical strain energy release rate in mode II, GIIc, was evaluated with the End Notched Flexure test. For various mixed mode tests, the critical strain energy release rate values were partitioned into mode I and mode II components. One of the main conclusions of the present work is that the introduction of a small amount of mode II loading (shear) in the joint results in a decrease of the total fracture energy, GT = GI + GII, when compared to the pure mode I fracture energy.

Fracture characterization of bonded joints using the dual actuator load apparatus

Journal of Adhesion Science and Technology, 2014

ABSTRACT Mixed-mode I + II fracture characterization tests of steel-bonded joints were carried ou... more ABSTRACT Mixed-mode I + II fracture characterization tests of steel-bonded joints were carried out with the dual actuator load apparatus using a previously developed data reduction scheme in order to obtain the fracture envelope. This test involves independent loading of the specimen arms of a clamped double cantilever beam, which allows for easy variation of the I + II mode mixity in fracture characterization through altering the applied displacement rates. Difficulties inherent to crack monitoring during its propagation and imperfections of initial crack manufacture are well managed with the proposed method. Three different cases corresponding to different mode mixities were tested. The experimental results revealed that a linear energetic criterion performs well in describing the fracture envelope of these bonded joints.

Fracture Mechanics Tests in Adhesively Bonded Joints: A Literature Review

The Journal of Adhesion, 2013

ABSTRACT Fracture mechanics characterization tests for adhesive joints are analyzed and reviewed ... more ABSTRACT Fracture mechanics characterization tests for adhesive joints are analyzed and reviewed in order to understand their advantages and disadvantages. Data reduction techniques for analytical methods are summarized to understand the improvements implemented in each test. Numerical approaches are also used complementing tests information. Both linear and non-linear methods to obtain the fracture energy release rate are presented. Pure mode I and mode II tests are described. Simple mixed-mode tests, varying only the specimen geometry, with limited mode-mixity are also presented. Performing a wider mode-mixity range requires sophisticated apparatus that are studied in detail. There is no general agreement about the test suitability for mixed-mode fracture assessment of adhesive joints. A universal test that can easily be performed and give accurate results is essential to optimize the expensive testing at the design stage.

Mechanical characterization of a high elongation and high toughness epoxy adhesive

International Journal of Adhesion and Adhesives, 2013

ABSTRACT In this paper, a new epoxy adhesive has been mechanically characterized. The adhesive co... more ABSTRACT In this paper, a new epoxy adhesive has been mechanically characterized. The adhesive combines the properties of an epoxy adhesive and typical polyurethane (PU) adhesive, such as high elongation and high toughness. Experimental tests were performed to measure the tensile properties, shear properties, thermal properties and fracture properties. The tensile test shows high tensile strength and high elongation. The single lap joint (SLJ) test shows that the failure load is proportional to the overlap length for hard steel adherends. For the SLJs with mild steel adherends, the failure occurred due to adherend yielding. Impact tests were conducted using SLJ specimens and the results are consistent with the SLJ tested under static conditions. The Tg was obtained using a Dynamic Mechanical Analysis (DMA) type of test. The toughness in mode I was determined using the Double Cantilever Beam (DCB) test and the toughness in mode II using End Notched Flexure (ENF) test.

Numerical validation of a crack equivalent method for mixed-mode I+II fracture characterization of bonded joints

Engineering Fracture Mechanics, 2013

ABSTRACT The present work is dedicated to development of a crack equivalent data reduction scheme... more ABSTRACT The present work is dedicated to development of a crack equivalent data reduction scheme applied to the load jig previously developed by Fernlund and Spelt [1] in order to characterize fracture of bonded joints under mixed-mode I + II loading. The jig allows for easy alteration of the mode-mixity and permits covering the full range of mixed-mode I + II combinations. A data reduction scheme based on specimen compliance, beam theory and crack equivalent concept is proposed to overcome several difficulties inherent to the test analysis. The method assumes that the performed test can be viewed as a combination of the double cantilever beam and asymmetrically loaded end-notched flexure tests, which provide modes I and II fracture characterization, respectively. A numerical analysis including a cohesive mixed-mode I + II damage model was performed considering different mixed-mode loading conditions to validate the proposed data reduction scheme. Issues regarding self-similar crack growth and fracture process zone development are discussed. It was verified that the considered in-plane mix mode fracture criterion is well captured using the proposed data reduction scheme.

Computational Materials Science, 2011

Adhesive-bonding for the unions in structures is gaining momentum over welding, riveting and fast... more Adhesive-bonding for the unions in structures is gaining momentum over welding, riveting and fastening. It is vital for the design of bonded structures the availability of reliable damage models to predict their fracture behaviour. Cohesive Zone Models (CZM's) have been extensively used in the past, taking advantage of traction-separation laws between stresses and relative displacements to simulate crack growth along predefined paths. The eXtended Finite Element Method (XFEM) is a recent improvement of the Finite Element Method (FEM) that relies on damage laws based on the bulk strength of materials for damage initiation and strain for the assessment of failure, rather than the tipping tractions and tensile/shear relative displacements used for the CZM's. Compared to the FEM, XFEM excels in allowing discontinuities to grow within bulk solids along an arbitrary path. This work aims to assess the viability of the XFEM to predict the fracture behaviour of a thin layer of adhesive between stiff and compliant adherends. To build the XFEM damage laws, the fracture toughness in pure mode I (G Ic) and tensile cohesive strength (r 0 n) of the two adhesives were initially determined by Double-Cantilever Beam (DCB) and bulk tensile tests, respectively. Particular emphasis was given to G Ic , as this is the most influent parameter for the numerical predictions. The numerical simulations of the DCB tests with the proposed laws matched accurately the experimental load-displacement (P-d) curves, which validated the analysis procedure. The accuracy of the data reduction methods for calculation of G Ic was checked by comparison of the input values in the simulations with the results of G Ic calculations, with good results.