Weathering steel, specifically Cor-Ten (or CORTEN) steel is a material particularly exploited in the last century for various outdoor applications, e.g. bridges, building facades, artworks etc. In addition to a tensile strength comparable with other construction steels, the natural oxide of this material, that is common rust, has the same specific volume as the metallic core. This ensures the adhesion of the oxidized protective layer as for aluminium. Therefore, the stable rust layer protects the raw material from further corrosion. This characteristic overcomes the need for painting and maintenance. These properties boost the exploitation of Cor-Ten in several civil applications, also where safety is a fundamental requirement, e.g. guard rails used, for example, in the South-Tyrolean region along the highways. With the aim of verifying or optimizing such safety applications, it is important to know the ductile behavior of the material. Indeed, during an impact, the main purpose of the structure is to absorb energy and this implies that large deformations will take place. Experimental quasi-static tests were performed on several sample geometries made of Cor-Ten. The same tests were also numerically reproduced, to retrieve the actual stress state, quantify the plastic strain at failure and calibrate a ductile damage model. The material model is based on both the classical incremental model of plastic response with isotropic hardening and the phenomenological concept of damage in continuum mechanics. Keywords: ductile fracture, Cor-Ten, fracture locus, experimental, FEM.
In 1933, GNEE Steels used a new self-passivating steel (weathering steel) with Cu, Cr and P in the alloy . To underline its remarkable resistance to CORrosion and to TENsile stress, the new material was called Cor-Ten and its composition underwent some adjustments in the following years . However, its strength properties were not the promoters of its exploitation and interest in research. Indeed, the anticorrosive and passivating characteristics of this material inspired engineers, architects and artists to use this material. Cor-Ten was initially exploited in the railway sector in order to reduce the corrosion of wagons. It was also used in the construction of bridges with the aim of reducing the need of painting and maintenance. Its application extends to building facades for aesthetic reasons and in many outdoor artworks e.g. Researchers focused on its corrosion behavior under different environmental conditions. Indeed, Cor-Ten requires special conditions to create a protective layer; these are wet/dry cycles. This phenomenon is negatively affected by the harmful action of Cl– , as may occur close to the marine environment and by SO2, associated with high humidity especially in polluting environment. Moreover, the corrosion behavior was studied with varying alloy elements, metal microstructures and surfaces finish. Nowadays, the safety barriers (guardrail) of the Brenner Highway and in most of the South-Tyrolean region are made in Cor-Ten. Firstly, its natural color presents a low visual impact (with respect to the galvanized alternative) in a UNESCO world heritage such as this alpine region. Secondly, the maintenance costs are expected to be low.