Francesco Ascione

A computational mechanics model for joints subjected to hygrothermal aging is proposed. The formulation is based on an imperfect interface approach coupled with a damage evolution law, in which aging effects are introduced through time-dependent constitutive parameters governing interface stiffness, damage activation and viscous dissipation. The model is expressed in terms of internal state variables and derived within a thermodynamically consistent framework, ensuring a stable and robust numerical implementation. The governing equations are implemented in a finite element environment and validated by simulating tests on single-lap joints with different adhesives and conditioning media. Numerical results show excellent agreement with experimental load–displacement responses, demonstrating the capability of the model to predict aging-induced degradation mechanisms in bonded composite interfaces.

The bonding of steel/fiber-reinforced polymer (SRP/FRP) laminate strips to concrete/masonry elements has been found to be an effective and efficient technology for improving the elements’ strength and stiffness. However, premature laminate–substrate debonding is commonly observed in laboratory tests, which prevents the laminate from reaching its ultimate strength, and this creates uncertainty with respect to the level of strengthening that can be achieved. Therefore, for the safe and effective application of this technology, a close estimate of the debonding load is necessary. Towards this end, in this paper, a new, relatively simple, semi-analytic model is presented to determine the debonding load and the laminate stress and deformation, as well as the interfacial slip, for concrete substrates bonded to SRP/FRP and subjected to monotonic or cyclic loading. In the model, a bond-slip law with a linearly softening branch is combined with an elasto-plastic stress-strain relationship for SRP. The model results are compared with available experimental data from single-lap shear tests, with good agreement between them.

The use of the composite pultruded materials is increasing due to the particular characteristics of lightness, ease of installation, high corrosion resistance and, finally, lower maintenance costs. Even if the bolting technique is the most widely used, especially in the field of civil engineering re-adapting the rules valid for steel structures, thanks to several studies on adhesives, there is reason to believe that the best connection technique for pultruded profiles is gluing (the continuity of the fibers is guaranteed). Current applications involving such materials, strictly related to the field of civil engineering, include bridges, pedestrian and the motorway bridges, roof structures, helipads, solar charging stations, offshore structures, cooling towers and lockgates. In some of these structures, the system (composite material and resin) is in contact with water. Even if there are several studies on the durability of composite pultruded material, current literature referring to adhesives between pultruded adherents needs further investigation. Within this framework, the paper aims to investigate, from an experimental and numerical point of view, the effect of the hygrothermal ageing on both the fracture energy in mode II as well as the strength and stiffness of two commercial epoxy resins taking into account the further effect of the desorption. Finally, in view of a safe design of a bonded joint, limiting its behaviour to the elastic field only, a lower fracture energy value is presented in relation to the classical one.