Prove di flessione non tradizionali su acciai zincati. Caratterizzazione cinematica e statica del meccanismo ed identificazione dello stato di danneggiamento del rivestimenti

The aim of this work was the analysis of the hot dip zinc coated steel plates mechanical properties by means of a non-tradition bending test performed minimizing both the bending moment differences along the bending axis and the interactions between the clamping system and the specimen coating. A complete kinematic and static mechainism analysis was performed. All the kinematic and static variables were identified in order to completely characterise the specimen deformation mechanism and the stress level. Bending tests were performed both on non-coated and on hot dip zinc coated plates, correlating the measured varia bles (applied load and crosshead displacement) with the bending moment and the specimen bending angle. Tests are characterised by a good repeatability. Results show a crosshead displacement - load diagrams that depend on the main deformation mechanisms. Furthermore, the mechanical behaviour was influenced by the coating thickness. It can be seen throught the load values increase and the crosshead displacement - load diagram modification. For all the investigated coating conditions, radial cracks are observed. They initiate corresponding to the F phase and propagate up to the ζ-η interface. The coating thickness increase implies both an increase of the importance of the cracks in δ and ζ phases and the presence of cracks at ζ-δ interfaces. As a consequence, the increase of coating thickness implies an increase of the susceptibility to a coating-steel debonding damage mechanism, with a consequent loose of the coating adhesion and a decreasing of the capability of the zinc coating to improve the steel corrosion resistance.