Influence of the mechanical behaviour of different adhesives on an interference-fit cylindrical joint Giorgio Gallio a,n , Mariangela Lombardi a , Davide Rovarino b , Paolo Fino a , Laura Montanaro a a Politecnico di Torino, DISAT Department of Applied Science and Technology, INSTM RU Politecnico di Torino, Corso Duca degli Abruzzi 24,10129 Torino, Italy b MW Italia S.p.A., Via Pavia 72, Rivoli, Italy article info Article history: Accepted 5 August 2013 Available online 25 September 2013 Keywords: Interference fit Mechanical properties of adhesives Destructive testing Joint design abstract Hybrid adhesive joining techniques are often used in many industrial sectors to design lightweight structures. A hybrid adhesive joint results from the combination of adhesive bonding with other traditional joining methods such as welding and mechanical fastening, with the aim of combining the advantages of the different techniques and overcoming their drawbacks. This study focuses on the interference fitted/adhesive bonded joining technique. In this application, two cylindrical components are coupled together by inserting one into the other, after having placed an adhesive between them. Generally anaerobic acrylic adhesives, also known as “retaining compound” are used for this application. However the effect of the adhesive nature and of its mechanical and adhesive responses on the performance of the hybrid joint is still unclear. The aim of the present research is to improve the understanding of the behaviour of different adhesives, including rigid epoxies and flexible polyurethanes, in the presence of an interference-fit. Static strength of bonded and unbonded interference fit joints have been compared in order to investigate the role of the different adhesives. & 2013 Elsevier Ltd. All rights reserved. 1. Introduction In recent years, the use of adhesive bonding technology has greatly increased being a suitable technology able to bond dissimilar materials and often to guarantee an uniform stress distribution in the joint area [1–3]. However, the polymeric composition of adhesives implies durability issues, especially in harsh conditions (temperature and humidity). In order to overcome these problems, adhesive bonding can be used in combination with other traditional joining methods, such as mechanical fastening techniques (e.g. rivets or bolts) or welding techniques, generating a hybrid joint. In this way, hybrid adhesive joints should combine the advantages of the different techniques and, if possible, overcome their drawbacks [4]. This study focuses on the interference fitted/adhesive bonded hybrid joint. In this technique cylindrical assemblies are coupled together by inserting one part in another and by adding an adhesive between them. The hub–shaft geometry is usually exploited in technical literature in order to study this hybrid bonding technique [5–8], allowing to evaluate the contribution of both the techniques to the resultant resistance of the hybrid joint. Moreover, it is previously demonstrated that the behaviour of this hybrid joint can be also influenced by the assembling technique (press-fit or shrink fit), the type of sustained load, the fitted position and the interference level [5–11]. The acrylic anaerobic adhesives, commercially named “retain- ing compounds” [12], are usually exploited in the interference fitted/adhesive bonded hybrid joints [5–11], being possible in this configuration to exploit their curing technology based on a one component configuration on active metal surfaces. In this system, in fact, the presence of the interference contributes to guarantee the anaerobic polymerisation, protecting the curing layer of adhesive from the oxygen. Notwithstanding this, it is important to consider that in certain particular industrial applications other curing technologies could be more appropriate, especially when clearance zones are included in the joint design or different mechanical properties have to be matched. To the best of our knowledge, the effect of the adhesive nature and therefore of its mechanical and adhesive responses on the perfor- mance of the hybrid joint is still unclear. The adhesive nature and the curing technology could affect the performances of the interference joints. For this reason, in this study the behaviour of the principal families of structural adhesives, from a rigid epoxy to a more flexible polyurethane, will be evaluated in an interference fit joint. 2. Materials and methods 2.1. Design of the samples The role of the different adhesives in the interference fit joint was studied in a hub/shaft geometry. The hollow tubes and the Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/ijadhadh International Journal of Adhesion & Adhesives 0143-7496/$ - see front matter & 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ijadhadh.2013.09.021 n Corresponding author. Tel.: þ39 320 6016761; fax: þ39 011 090 6329. E-mail address: giorgio.gallio@polito.it (G. Gallio). International Journal of Adhesion & Adhesives 47 (2013) 63–68