PSI - Issue 10

Alk. Apostolopoulos et al. / Procedia Structural Integrity 10 (2018) 49–58 Alk. Apostolopoulos and T. Matikas / Structural Integrity Procedia 00 (2018) 000 – 000

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The corrosion due to chlorides causes pitting along the specimen and non-uniform damage to the external geometry of the surface. This fact leads to buckling phenomena behavior of corroded bars under cyclic loads. Fractographic analysis carried out using a scanning electron microscope (SEM) in order to find the fatigue crack initiation sites and crack propagation form on the rebars. With SEM and EDX a research was conducted on specimens before and after various levels of salt spray corrosion. In both non corroded and corroded specimens of rebars with A, B class of duc tility, areas of MnS compounds were identified with the coexistence of other voids. This coexistence constitutes regions with degradation of consistency of steel material. Figs.3, 5 show the above observations. According to Avci et al. (2013), during the manufacturing of carbon steel, in metallurgical processes, manganese is introduced into Fe in order to scavenge the undesirable S impurities. Sulfur impurities are prone to forming FeS inclusions, which give rise to serious problems. Τ he presence of MnS phases and FeS in steel rebar make the material highly susceptible to corrosion (and localized corrosion phenomena) due to the presence of chloride ions (Wranglen (1969, 1974); Apo stolopoulos et al. (2016)).

Fig 3. B500B, Φ 12 non corroded, under LCF ±2.50%, strain controlled with 6 Φ free length. (a) Presents crack initiation from the boundary of the fracture surface towards the interior but also along the outer surface; (b) Zoom in.

Fig 4. B500B, Φ 12. 45 days corroded, under LCF ±2.50%, strain controlled with 6 Φ free length. (a) Indentation which moves in depth; (b) The effect of dissolved MnS compounds and oxides (Si, Fe) inside the steel bar.

Fig 5. B500B, Φ 12 90 days corroded, under LCF ±2.50%, strain controlled with 6 Φ free length. Crack appearance (a) grown near the perimeter but not in the outer surface (b) and other cracks starting from outside surface (the perimeter).