Structural Composite Laminates

Research focus

The Peer review has evaluated this group as Good

This research topic concerns the study of structural composite laminates used in Civil Engineering mainly for structural reinforcement and retrofitting and advanced composite laminates mainly used in aerospace engineering. The research activity at DIS on the above subject started at the beginning of the 90’s. Among the various research activities on structural composite laminates carried out at Politecnico-DIS, the following topics are here mentioned and briefly described: (A) Interface models The behavior of interface surfaces is given in terms of cohesive law which relates displacement jump and cohesive tractions. Interface models range from linearized to finite kinematics, explore the different opening modes, account for anisotropy, rate dependency and dynamic behavior. These models have been mainly used for the simulation of delamination in layered composites in various situations, with reference to different composite materials. (B) Parameter identification A major obstacle in the use of cohesive interface models is the difficulty in correctly identifying model parameters. An extensive study of parameter identification techniques has been carried out, motivated mainly by the interface modelling. New procedures based on the use of Kalman filtering techniques have been proposed and applied to static and dynamic situations for rate independent and rate dependent interface models. (C) Advanced simulation tools for fracture processes The technology of interface elements has been used by modeling the interfaces explicitly ab initio, or developing self-adaptive techniques for the ad hoc insertion in 2D and 3D solid models discretized in initially coherent finite elements. Both the approaches require the development of special meshing or remeshing procedures. (D) Composites in Civil Engineering (durability and structural rehabilitation) This reseach topic deals with the mechanical behaviour of damaged steel structures repaired with FRP strips and the use of FRP (Fiber Reinforced Polymers) bars in concrete structures. In detail, reference is made to steel or cast iron structural elements damaged by fatigue or corrosion. Both large structures, such as rail or road bridges, and small structures, such as footbridges potentially of historical importance, are considered. The use of composite materials to reinforce these kinds of structures is currently under development and real cases of their application are limited. The potentiality of composite reinforcements for the repair of metallic structural elements has also been explored, and experimental and numerical research activity on both full and small scale elements has been performed. The experimental activity was devoted to the analysis of typical structural elements, even in full scale, reinforced and subjected to static or fatigue loading. The goal was to investigate the mechanical interaction between the materials under different loading conditions. In addition, the composite strips were pre-stressed in order to increase the effectiveness of the repair. Analytical and numerical models were developed to simulate the experimental tests and to predict stress distribution in the adhesive joint and fracture mechanics parameters at failure. Stressbased and energy-based failure criteria were defined consequently. Experiments were performed to asses the influence of cyclic (fatigue) and environmental loading on bond durability. Accordingly, a 51 set of standard reinforcement geometries representative of structural elements was pre-conditioned and then tested under tensile loading. The use of FRP bars in the world of construction is of particular interest in the case of structures located in aggressive environments. This is the case for marine structures or bridge slabs, repeatedly sprinkled with de-icing salts during winter. Internationally, there are several examples of concrete structures reinforced with FRP bars, among these, bridges were realised in Canada, USA and Germany. The construction of such structures led to development of design guidelines for the use of FRP bars by the ACI, the FIB and finally by the Italian National Research Council (CNR-DT 203/2006). Regarding such a recent and still developing technology, a variety of structural aspects need to be carefully investigated, as the behaviour of flexural elements, the shear strength, the fire resistance and the fatigue resistance of the bridge slabs. The low strength of the FRP bars, especially of GFRP (Glass FRP) bars, causes an increase of the displacements and of the width of fissures. In the case of bridge slabs, where the use of FRP bars is particularly suitable to replace the traditional steel bars, it is extremely important to analyze issues concerning the fatigue behaviour and the extreme conditions that take place in case of fire. To this end, an extensive experimental investigation and several numerical models are at the moment being studied.

Departments

Dipartimento di Ingegneria Strutturale (DIS)

Professors

Full Professors
Alberto Corigliano
Carlo Poggi
Associate Professors
Anna Pandolfi
Pierluigi Colombi
Assistant Professors
Valter Carvelli
Stefano Mariani