Keywords: adhesive joints, cohesive fracture, radius of curvature, fibre reinforced polymer, finite element method.

Today, in the field of civil engineering, the use of adhesive joints has been principally related to the need for reinforcing pre-existing straight structures made of concrete or masonry using fibre reinforced polymers (FRP). The case of a curved reinforcement element is a problem still to be assessed. The main scope of this paper is to study the behaviour, up to failure, of a curved adhesive joint and to understand in which way the joint behaviour is affected by the geometrical, mechanical and physical properties of the adherents and adhesive, with particular regard to the geometric curvature.

Recent research work has shown that some parameters play a relevant role, as well as the joint configuration (the thickness of the adhesive layer, the length of the bonding area, the radius of curvature, etc.), the mechanical properties of adherents (bending, axial and shear stiffness) and last but not least the environmental conditions (temperature, moisture etc.). The additional presence of shear and flexural stresses, also mobilised by the radius of curvature, even if less relevant with respect to the axial stresses justifies the interest towards more refined approaches which account for mixed mode I/II fracture.

Within this research field, the paper develops a wide numerical analysis of the behaviour of a generic curved adhesive joint showing the influence of the radius of curvature, relative to adherents and adhesive, in terms of fracture energy absorbed.

With this aim a mechanical model has been realised, by means of the finite element method, that accounts for the radius of curvature, the shear deformability as well as the coupling effects between axial and shear/flexural behaviour.

Several numerical tests have been conducted. These are relative to the case of the restoration of a pre-existing concrete beam by using a FRP system. Schematically the problem is represented by single lap joints, where the first adherent is made of concrete (support), while the second one is made of FRP (reinforcement). The results have highlighted a different effect of the radius of curvature if the external load provokes a tensile or compressive normal stress inside the adhesive. In the details, in the first case the aforementioned effect is absent for any load level; in the second one it is observed that a beneficial effect, in the sense of a delay in the energy absorption occurs as the radius of curvature decreases.

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