Issue 43

P. Zampieri et alii, Frattura ed Integrità Strutturale, 43 (2018) 90-96; DOI: 10.3221/IGF-ESIS.43.06 91 seawater like offshore structures and pipelines [6]. Typically to study the interaction of corrosion and fatigue, it is used a model of pre-corroded samples and then the cyclic loads are applied to them. There are few cases where electrochemical and mechanical stresses act at the same time. Fatigue crack initiation and growth from artificial pits was modelled by Rokhlin et al. [7] . The authors find good agreement with the experimental data: they described fatigue crack initiation and growth from pits and obtained the relationship between reduction of fatigue life and artificial pits size. Other studies focused the attention on the pits shape characterization [8, 9]. Shan-hua Xu et al. [10] estimated the effects of corrosion pits on the fatigue life of steel plates. They defined three different pit shapes and concluded that corrosion causes a significant decrease in fatigue life as the pit depth increases and the surface roughness is a crucial factor to assess the fatigue strength. They also found that the start of the crack could trigger from a single pit or by the interaction and coalescence of multiple pits. Similar studies were conducted also by Acuna et al. [11] and by Kondo et al. [12]. Some researches were proposed as regards the fatigue corrosion interactions in steel bridges. The proposed approaches for corrosion fatigue life assessment are based on the use of S-N curves and cumulative damage laws. Sharifi et al. [13] studied the notch factor in steel bridges due to corrosion and proposed two functions which could represent fatigue notch factor in terms of average corrosion penetration and time of weathering exposure to compare it with the one obtained for various classes of structural detail as classified in BS 5400. They concluded that the fatigue notch factor could well quantified the effect of corrosion on the fatigue life of steel bridge members. Aim of this paper is to investigate the influence of the corrosive phenomenon on the fatigue strength of a friction type joint made of high strength preloaded bolts (M12 class 10.9). To work out these analyses the fatigue behavior of virgin bolted joints (without any degradation effect) and the behavior of the same joints, (having the same geometric and material properties) after corrosion effects were compared. To make so, an accelerated corrosion process was carried out on a lot of n. 10 specimens. At the end of the procedure, it was possible to perform fatigue tests (R=0) to plot the S-N fatigue curve of uncorroded and corroded specimens. Figure 1 : Geometry of the bolted joints.