International Journal of Adhesion & Adhesives 22 (2002) 273–282 Investigating the effect of spew and chamfer size on the stresses in metal/plastics adhesive joints Giovanni Belingardi, Luca Goglio*, Andrea Tarditi Dipartimento di Meccanica, Politecnico di Torino, Corso Duca degli Abruzzi, 24, 10129 Torino, Italy Accepted 4 December 2001 Abstract Regarding the optimisation of adhesive lap joints, several authors have proposed the use of adhesive spews (i.e. shoulders of adhesive connecting the unloaded ends of the adherends) and of chamfers at the ends of the adherends to reduce stress concentrations. Considering a hybrid joint between steel and FRP, this paper analyses in detail the effect of such solutions on the stress field, in order to identify the optimal condition and to assess design rules. It has been found that spew and chamfer angles of about 451 are sufficient to obtain a considerable reduction of the stress peaks. r 2002 Elsevier Science Ltd. All rights reserved. Keywords: B. Plastics; C. Finite element stress analysis; E. Joint design; Optimisation 1. Introduction The simplest and most popular solution for adhesively bonding two sheets is the single-lap joint. From the structural viewpoint, this is characterised by two harmful features: (a) the offset of the two sheets causes a bending action in the joint, adding additional stress components; (b) the stress distribution in the lap is not constant and displays peaks at its ends. After the simplified solution of Volkersen [1] (developed for riveted joints but applicable also to bonds) and the more complete study of Goland and Reissner [2] (which accounted for the peel stress) much effort has been spent over six decades to determine the stress field and to obtain the ‘‘optimal’’ design of the joint. The analytical approach has been progressively refined until recent times [3–7]. In general terms it makes use of the plate theory to model the sheets while some simplified assumption is made for the adhesive layer behaviour. The analysis is bidimensional, since it involves a strip of unit width in transverse direction, assuming plane strain conditions. Volkersen [3] im- proved his previous work by including the peeling stress and assuming a relationship between shearing strain and displacement more correct than that of Goland and Reissner. Segerlind [4] pointed out that as the lap length increases the stresses are in general reduced, but the stress peaks at the lap ends are more marked. Conversely, in case of short lap length the stresses are everywhere higher but more uniform. Renton and Vinson [5] developed an analytical solution for the case of an adhesive joint of orthotropic plates. Ojalvo and Eidinoff [6] accounted for the variation of the stresses through the adhesive thickness and investigated on the adhesive layer thickness effect. Bigwood and Crocombe [7] developed an analytical solution capable to describe not only simple lap joints but also more complicated geometries. Structural optimisation of the joint tries to modify the geometry of the adhesive layer and also of the adherend parts, with the scope of reducing the intensity of the stress peaks and therefore increase the strength of the joint. This approach has been made possible by the numerical analysis to treat cases with geometrical features that are beyond the analytical approach, such as fillets introduced at the ends of the overlap zone. This line of research has been explored over the last two decades [8–14], accounting also for the non-linearities occurring during collapse (material inelasticity, large displacements). The effects occurring at the ends of the overlap are extensively discussed in [8], on the basis of previous papers of Adams and co-workers. Dorn and Weiping Liu [10] performed a number of FEM analysis and some experimental measurements in order to study *Corresponding author. Tel.: +39-011-564-6934; fax: +39-011-564- 6999. E-mail address: goglio@polito.it (L. Goglio). 0143-7496/02/$ - see front matter r 2002 Elsevier Science Ltd. All rights reserved. PII:S0143-7496(02)00004-0