Issue 48

X.-g. Huang et alii, Frattura ed Integrità Strutturale, 48 (2019) 48 1 -490; DOI: 10.3221/IGF-ESIS.48.46 488 crack propagation is remarkable and the overall improvement effect of Zn exceeds that of Cr coating. Conversely, at high stress level, Cr coating has better effect because of its contribution to crack nucleation. C ONCLUSION n the present study, durability method to improve corrosion fatigue resistance of AH 32 steel in seawater are conducted by arc spraying Zn and Cr coatings. Pre-corrosion fatigue and corrosion fatigue tests are carried out to quantitatively determine the effect of coatings on corrosion fatigue behavior of AH 32 steel in seawater, and the mechanism of coating improving corrosion fatigue characteristics are investigated. The main results obtained can be concluded as follows: (1) Corrosion fatigue failure always initiates from corrosion defects at the surface of the specimen, because the stress concentration occurs at these corrosion defects, under cyclic loading, accelerates the nucleation of fatigue crack. The effect of corrosion in fatigue life of AH32 steel become more obvious at low stress level. The effect of loading frequency which determine the corrosion time at every cycle on corrosion fatigue life also cannot be ignored. (2) The results of corrosion fatigue and pre corrosion fatigue tests of Zn and Cr coated AH32 steel show that both Zn and Cr coating can greatly improve the corrosion fatigue of AH 32 steel, and the effect enhances with the decrease of stress. Cr coating on corrosion fatigue of AH 32 steel mainly reflects in extending the crack initiation life because of its better corrosion resistance. While the effect of Zn coating on corrosion fatigue of AH 32 steel mainly lies in not only inhibiting the initiation of corrosion fatigue but also restraining crack propagation as cathodic protection materials. To sun up, Cr coating has better durability effect than Zn coating at higher stress level, while Zn exceeds Cr at low stress level. A CKNOWLEDGMENTS he research work is supported by the National Natural Science Foundation of China (No.51404286), and the Fundamental Research Funds for the Central Universities of China (No.17CX02065). The authors are also grateful for the financial support from China Scholarship Council (No. 201806455016). R EFERENCES [1] Kjellander, S. L. (1972). Hull damage on large Swedish-built ships. Styrelsen for Teknisk Utveckling. Report No. 70- 1272/U981, Stockholem, Sweden. [2] Jordan C. R., and Cochran C. S. (1978). Further survey of in-service performance for structural details. SSC-272. [3] Folorunso O. M., Salau M. A., and Esezobor D . E. (2013). Offshore steel structures corrosion damage model. International Journal of Scientific & Engineering Research, 2(10), pp.1-6. [4] Melchers R. E. (2006). Recent progress in the modeling of corrosion of structural steel immersed in seawater. Journal of Infrastructure Systems, 12(3), pp.154-162. DOI: 10.1061/(ASCE)1076-0342(2006)12:3(154). [5] Melchers R. E. (1999). Corrosion uncertainty modeling for steel structures. Journal of Constructional Steel Research, 52, pp. 3-19. DOI: 10.1016/S0143-974X(99)00010-3. [6] Alamilla J. L., Espinosa-Medina M. A., and Sosa E. (2009). Modelling steel corrosion damage in soil environment. Corrosion Science, 51, pp. DOI: 2628-2638. 10.1016/j.corsci.2009.06.052. [7] Maeng W. Y., Kang Y. H., Nam T. W., Ohashi S., and Ishihara T. (1999). Synergistic interaction of fatigue and stress corrosion crack growth behavior in Alloy 600 in high temperature and high pressure water. Journal of Nuclear Materials, 275, pp. 194-200. DOI: 10.1016/S0022-3115(99)00114-2. [8] Pérez-Mora R., Palin-Luc T., Bathias C., and Paris P. C. (2015). Very high cycle fatigue of a high strength steel under sea water corrosion: A strong corrosion and mechanical damage coupling. International Journal of Fatigue, 74, pp.156-165. DOI: 10.1016/j.ijfatigue.2015.01.004. I T