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Banea M.D.,Institute Engineering Mecanica IDMEC
Assembly Automation | Year: 2012

Purpose - The purpose of this paper is to provide an insight into the techniques which are used and developed for adhesive bulk and joint specimens manufacturing. Design/methodology/approach - After a short introduction, the paper discusses various techniques for adhesive bulk and joint specimens manufacturing and highlights their advantages and limitations. A number of examples in the form of different bulk and joint specimens of different types of adhesives are used to show the methods for determining the adhesive's mechanical properties needed for design in adhesive technology. In order to predict the adhesive joint strength, the stress distribution and a suitable failure criterion are essential. If a continuum mechanics approach is used, the availability of the stress-strain curve of the adhesive is sufficient (the bulk tensile test or the TAST test is used). For fracture mechanics-based design, mode I and mode II toughness is needed (DCB and ENF tests are used). Finally, single lap joints (SLJs) are used to assess the adhesive's performance in a joint. Findings - Before an adhesive can be specified for an application, screening tests should be conducted in order to compare and evaluate the various adhesion parameters. Properties of adhesives can vary greatly and an appropriate selection is essential for a proper joint design. Thus, to determine the stresses and strains in adhesive joints in a variety of configurations, it is necessary to characterize the adhesive behaviour in order to know its mechanical properties. A great variety of test geometries and specimens are used to obtain adhesive properties. However, for manufacturing of adhesive bulk specimens and joints necessary for use in these tests, properly, moulds should be designed. Originality/value - The paper summarises the main methods of preparing adhesive bulk and joint specimens and the test methods for determining the mechanical properties needed for design in adhesive technology. Emphasis is given to the preparation of specimens of suitable quality for mechanical property determination and the moulds designed for this purpose. © 2012 Emerald Group Publishing Limited.

Banea M.D.,Institute Engineering Mecanica IDMEC | Da Silva L.F.M.,Universidadedo Porto
Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications | Year: 2010

The application of adhesively bonded joints in structural components made of composite materials for automotive industry applications has increased significantly in recent years and provides many benefits that will ultimately lead to lighter-weight vehicles, fuel savings, and reduced emissions. The principal benefits are design flexibility, opportunity for part consolidation, and joining of dissimilar materials. While much work has been conducted in adhesive bonding for the aerospace industry, the automotive industry does not currently have a full portfolio of processes and methods for evaluating candidate adhesives for use in bonding structural automotive components. Aerospace techniques and materials are not generally applicable, since the automotive industry must be more cognizant of cost and high volume production. In this article, the performances of two different adhesive types, an epoxy and a polyurethane, have been studied through bulk specimen and adhesive jointtests.Results showedthat the failure loads of both the bulk test and joint test specimens vary with temperature and this needs to be considered in any design procedure. Also, for the polyurethane adhesive, the single lap joint is sufficient to determine the adhesive shear strength.

Marques E.A.S.,Institute Engineering Mecanica IDMEC | Da Silva L.F.M.,University of Porto | Flaviani M.,University of Parma
Composites Part B: Engineering | Year: 2015

An important aerospace application of adhesives is in heat shields, bonded with room temperature vulcanizing silicone adhesive, which has high temperature resistance but low strength. Previous works proposed mixed adhesive joints as a solution and an investigation of this technique was performed. Three adhesive joint configurations were tested, including a mixed joint. The aim of the research was to simulate the load on a heat shield and predict the joint strength. Ceramic properties were obtained with an inverse method. There was a good agreement between experimental and numerical data, showing that this technique could be used for prediction and optimization. © 2015 Elsevier Ltd.

Banea M.D.,Institute Engineering Mecanica IDMEC | Da Silva L.F.M.,University of Porto | Campilho R.D.S.G.,University of Porto
International Journal of Adhesion and Adhesives | Year: 2011

Adhesives used in structural high temperature aerospace applications must operate in extreme environments. They need to exhibit high-temperature capabilities in order to maintain their mechanical properties and their structural integrity at the intended service temperature. One of the main problems caused by high temperature conditions is the fact that the adhesives have different mechanical properties with temperature. As is known, adhesive strength generally shows temperature dependence. Similarly, the fracture toughness is expected to show temperature dependence. In this work, the Double Cantilever Beam (DCB) test is analysed in order to evaluate the effect of the temperature on the adhesive mode I fracture toughness of a high temperature epoxy adhesive. Cohesive zone models, in which the failure behaviour is expressed by a bilinear tractionseparation law, have been used to define the adhesive behaviour and to predict the adhesive Pδ curves as a function of temperature. The simulation response for various temperatures matched the experimental results very well. The sensitivity of the various cohesive zone parameters in predicting the overall mechanical response as a function of temperature was examined as well for a deeper understanding of this predictive method. Also, issues of mesh sensitivity were explored to ensure that the results obtained were mesh independent. © 2011 Elsevier Ltd. All rights reserved.

Loureiro A.L.,Institute Engineering Mecanica IDMEC | Da Silva L.F.M.,University of Porto | Sato C.,Tokyo Institute of Technology | Figueiredo M.A.V.,University of Porto
Journal of Adhesion | Year: 2010

Adhesive bonding is increasingly being used in structural applications such as in automotive joints. The theoretical analyses and experimental data are generally for rigid and strong epoxy adhesives. Elastomeric adhesives such as polyurethanes are used in structural applications such as windshield bonding because they present important advantages in terms of damping, impact, fatigue, and safety which are critical factors in the automotive industry. However, there are other structural applications in the main body where polyurethanes may also be used. The main objective of the present project is to compare the behaviour of structural joints used in the automotive industry, such as single lap joints and T-joints made of rigid adhesives, and those made of elastic adhesives in terms of stiffness, strength, impact, damping, and fatigue. The elastomeric adhesive selected was a polyurethane from Sika (Sikaflex 256) and the structural adhesive selected was an epoxy from Huntsman (Araldite AV138/HV998). The shear strength of the polyurethane is approximately four times lower than that of the epoxy. However, the polyurethane shear failure strain is 330%, whereas that of the epoxy is only 6%. The benefits of using elastomeric adhesives in structural adhesive joints used in the automotive industry are described, especially in terms of ductility, impact, and fatigue. Copyright © Taylor & Francis Group, LLC.

Marques E.A.S.,Institute Engineering Mecanica IDMEC | Da Silva L.F.M.,University of Porto | Banea M.D.,Institute Engineering Mecanica IDMEC | Carbas R.J.C.,Institute Engineering Mecanica IDMEC
Journal of Adhesion | Year: 2015

This work presents a review of several investigations on the topic of adhesive bonding at high and low temperatures. Durability and strength at extreme temperatures have always been a major limitation of adhesives that, given their polymeric nature, exhibit substantial degradation at temperatures where other structural materials (such as metals for example) have minute changes in mechanical properties. However, due to the inherent advantages of bonding, there is a large and continued effort aiming to improve the temperature resistance of adhesive joints, and this effort has been spread among the various topics that are discussed in this review. These topics include adhesive shrinkage and thermal expansion, adhesive properties, joint geometry optimization, and design techniques, among others. The findings of these research efforts have all found use in practical applications, helping to solve complex problems in a variety of high-tech industries where there is a constant need to produce light and strong components that can withstand large temperature gradients. Therefore, the final sections of this work include a discussion on two specific application areas that demonstrate the strict demands that extreme temperature use imposes on adhesive joints and the methods used to improve their performance. © 2015 Copyright © Taylor & Francis Group, LLC.

Banea M.D.,Institute Engineering Mecanica IDMEC | De Sousa F.S.M.,Institute Engineering Mecanica IDMEC | Da Silva L.F.M.,University of Porto | Campilho R.D.S.G.,University of Porto | De Pereira A.M.B.,University of Aveiro
Journal of Adhesion Science and Technology | Year: 2011

The variation of the mechanical properties of adhesives with temperature and strain rate is one of the most important factors to consider when designing a bonded joint due to the polymeric nature of adhesives. It is well known that adhesive strength generally shows temperature dependence. Moreover, in many structural applications, the applied loads can be dynamic and the design of the joint requires the knowledge of the high loading rate mechanical behaviour of the adhesive. In this study, the combined effect of the temperature and test speed on the tensile properties of a high temperature epoxy adhesive was investigated. Tensile tests were performed at three different test speeds and various temperatures (room temperature (RT) and high temperatures (100, 125 and 150°C)). The glass transition temperature (T g) of the epoxy adhesive investigated is approximately 155°C. The ultimate tensile stress decreased linearly with temperature (T) while increased logarithmically with the loading rate, which is in the accord with the Airing's molecular activation model. © 2011 Koninklijke Brill NV, Leiden.

Da Silva L.F.M.,University of Porto | De Magalhaes F.A.C.R.G.,University of Porto | Chaves F.J.P.,Institute Engineering Mecanica IDMEC | De Moura M.F.S.F.,University of Porto
Journal of Adhesion | Year: 2010

The main goal of this study was to evaluate the effect of the thickness and type of adhesive on the Mode II toughness of an adhesive joint. Two different adhesives were used, Araldite® AV138/HV998 which is brittle and Araldite 2015 which is ductile. The end notched flexure (ENF) test was used to determine the Mode II fracture toughness because it is commonly known to be the easiest and widely used to characterize Mode II fracture. The ENF test consists of a three-point bending test on a notched specimen which induces a shear crack propagation through the bondline. The main conclusion is that the energy release rate for AV138 does not vary with the adhesive thickness whereas for Araldite 2015, the fracture toughness in Mode II increases with the adhesive thickness. This can be explained by the adhesive plasticity at the end of the crack tip. Copyright © Taylor & Francis Group, LLC.

Da Silva L.F.M.,University of Porto | Esteves V.H.C.,University of Porto | Chaves F.J.P.,Institute Engineering MecAnica IDMEC
Materialwissenschaft und Werkstofftechnik | Year: 2011

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, G T = GI+ GII, when compared to the pure mode I fracture energy. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Marques E.A.S.,Institute Engineering MecAnica IDMEC | Magalhaes D.N.M.,University of Porto | Da Silva L.F.M.,University of Porto
Materialwissenschaft und Werkstofftechnik | Year: 2011

Adhesive bonding is extensively used in aerospace applications. Some of the most important aerospace applications are in heat shields intended to protect metallic structures from extreme heat. Many heat shields are bonded with RTV silicone based adhesives, which have excellent resistance to high temperature but very low strength. This work proposes and studies three alternative configurations to these adhesive layers. One configuration with RTV silicone only (RTV106), one with only a high temperature epoxy (XN1244) and finally another configuration introducing both adhesives in the same joint (mixed joint). Experimental specimens and a testing device intended to simulate the loads on an actual heat shield were manufactured. These specimens were subjected to loading and tested until failure at both low and high temperatures. It was demonstrated that while the RTV silicone joints lose strength at 100°C, the epoxy and mixed joints are able to retain most of their strength. The mixed joint is also able to withstand large values of displacement at relatively high forces, indicating excellent capabilities at absorbing directed energy. The improvements and advantages deriving from the use of these alternative configurations are described and compared. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Loading Institute Engineering Mecanica IDMEC collaborators
Loading Institute Engineering Mecanica IDMEC collaborators