Deformation and fracture of adhesive layers constrained by plastically-deforming adherends

The use of an embedded-process zone (EPZ) model to investigate the mode I c ohesive parameters for plastically-deforming, adhesively-bonded joints is d emonstrated in this paper. It is shown that for the particular systems inve stigated, the cohesive parameters are consistent with an adhesive layer def orming in accordance with its bulk constitutive properties (as constrained by the adherends). In other words, these systems provide examples where the cohesive tractions exerted by an adhesive layer can be calculated simply f rom considerations of the constrained deformation of the adhesive. Consiste nt with such calculations, the peak stress in the adhesive layer decreases as the level of the constraint decreases (either with an increase in the th ickness of the adhesive layer or with a decrease in the thickness of the ad herends). It is also shown that owing to a compensating effect in which the critical displacement for failure varies with the constraint, the energy a bsorbed by the adhesive layer (the 'intrinsic' toughness of the joint) is e ssentially independent of the geometry in these systems.