Failure Criteria for Adhesive Bonds and their Relevance to Design: A Review

A unique, generally accepted, methodology to predict the failure conditions and load of adhesive bonds is still lacking. The primary distinction that needs to be done is between: i) rupture conditions, which inevitably involve material non-linearity; ii) design conditions, within linearity limits. Typically, the research is focussed on i), and this excludes the numerous solutions or numerical models based on linear elasticity. A first research line on bond failure relies on adhesive plasticity. Hart-Smith [1] obtained design charts admitting that at the ends of the overlap the adhesive yields plastically. Later, Crocombe and co-authors [2] assumed global yielding of the adhesive to be the key phenomenon. A second research line, appeared since early 1970‘s [3], is based on fracture mechanics; the related tests are focussed on the adhesive strength by using ad hoc specimens (double cantilever beam, end notched flexure). In a design perspective, the problem in applying fracture mechanics is that the existence of a crack must be assumed somehow. A synthesis of these two approaches, likely the most popular today, is given by damage mechanics, in particular by the cohesive zone used to describe the failure of the adhesive [4]. Clearly, all these methodologies require numerical modelling. On the other hand, in a simpler perspective oriented to joint design, criteria based on adhesive elastic stresses have been also proposed [5], to help dimensioning the joints. These are based on conventional stresses, for which a limit combination can be easily assessed experimentally, under both static and dynamic (impact) conditions. The proposed presentation aims at giving an overview of the available approaches, trying to identify merits, lacks and needs for future developments. [1] L.J. Hart-Smith, Tech. Rep. CR-112235,112236 (1973). [2] A.D. Crocombe, Int. J. Adhes. Adhes., 9, 145 (1989). [3] E.J. Ripling, S. Mostovoy, H.T. Corten., J. Adhesion, 3, 107 (1971). [4] J.W. Hutchinson, A.G. Evans, Acta Mater., 48, 125 (2000). [5] L. Goglio, M. Rossetto, E. Dragoni, Int. J. Adhes. Adhes., 28, 427 (2008)