Experimental and numerical study on bond behavior in composite materials and strengthening systems

The mechanism of stress transfer across different materials bonded each other is one of the most discussed topic in research field. Different approaches can be used in order to study this topic: analytical approach, experimental approach and numerical approach. In this thesis these approaches are applied in order to study the bonding mechanism in various engineering field. In the first part, the attention is focused on adhesive joints for mechanical application in which aluminum, GFRP and glass materials are used. Two experimental campaigns are performed in order to evaluate the mechanical performances of double-lap joints using different type of adhesives and adherends. The influence of temperature on joint performances is also studied and results show the strong influence of this parameter on the mechanical strength of the adhesive joint. In a third experimental study, the mechanical performance of the adhesive joints in a steel-glass connection is investigated. The aim of part is to verify the applicability of the adhesive bonds on a tensegrity floor; that is a hybrid system characterized by a particular steel-glass adhesive junction that permits an effective cooperation between the two structural elements (a glass panel and a steel subframe). Experimental tests on hybrid system are performed with a stepwise cyclic loading and a numerical validation of the whole system is done through a Finite Element Model of the tested samples. The second part of the dissertation is focused on new strengthening systems for civil application. In the last few decades, the construction industry has had a rapid expansion of interest regarding strengthening and retrofitting of existing reinforced concrete (RC) and masonry structures. In fact, new strengthening systems for existing structures were investigated e optimized in terms of efficiency, easy application, durability and cost. Externally bonded composite materials, FRP (Fiber Reinforced Polymer) and FRCM (Fabric Reinforced Cementitious System), are studied in this section. The bond behavior between composite system and concrete substrate is investigated. An experimental campaign on strengthened beams with FRP (carbon sheet fibers) and FRCM (PBO fabric) applied at different environmental conditions are conducted in order to study the durability problems. Results, in term of force-displacement curve, are interpreted with an analytical approach. Finally, numerical models on FRCM system are carried out in order to develop a tool aimed to the optimization of the system. Augmented-FEs are implemented in numerical codes and used for 2D and 3D models. Tensile behavior of FRCM coupon is numerically simulated in all three stages of its characteristic behavior. Results of this study show a good agreement with experimental ones. The last part is focused on developing a new cohesive law, calibrated on experimental results, for 3D models of FRCM system. Parametric studies are conducted and then the proposed approach is validated by modeling different test setup.