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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.,Polytechnic Institute of Porto | Campilho R.D.S.G.,Polytechnic Institute of Porto
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.

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.

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.

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.

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