Issue 37

D. Angelova et alii, Frattura ed Integrità Strutturale, 37 (2016) 258-264; DOI: 10.3221/IGF-ESIS.37.34 264 has initiated in an earlier stage than the secondary cracks and is well separated from them; it merges with only a couple of secondary cracks . At the same time the major crack at Δσ = 1200 MPa propagates at condition of interaction between and with many secondary cracks in its vicinity at no big difference between their initiation stages; it leads to exhaustion of local plasticity in PSC regime, crack merging (six secondary cracks merge with the major crack) and complete failure. For Steel B some fatigue tests data of major and secondary cracks propagation are studied in-air and corrosion environment, considering specific features of the three regimes of major crack growth: MSC, PSC, LC. For both steels short fatigue crack growth behaviour is modeled on the base of Hobson-Brown-Angelova, Akid-Murtaza- Angelova and Yordanova models. Three new versions of Yordanova model are proposed and approved at different conditions of loading, environment and specimen surface state; a special attention has been given to PSC regime of major crack propagation. The three proposed model versions are additionally supported by the comparison between the predicted and actual fatigue lifetimes. R EFERENCES [1] Miller, K. J., Metal Fatigue – Past, Current and Future. Proc. Inst. Mech. Engrs, London. (1991). [2] Suresh, S., Fatigue of Materials. Cambridge Univ. Press, Cambridge, UK, (1998). [3] Krupp, U., Fatigue Crack Propagation in Metals and Alloys, Wiley-VCH GmbH and co. KGaA. (2007) [4] Dowling ,N., Mechanical Behaviour of Materials, Prentice-Hall, New Jersey, USA, (2006). [5] Angelova D., Yordanova R., Nikolova L., Yankova Sv., Investigation on fatigue Behavior and Fatigue crack Growth of a Spring Steel. Part II: Mathematical description an Analyses, Scientific Proceedings, XXI, 2(139) (2013) 244-248. [6] Angelova, D., Yordanova, R., Lazarova, Ts., Yankova, Sv., On fatigue behavior of two spring steels. Part I: Wöhler curves and fractured surfaces, 20 th European Conference on Fracture, 30 th June – 04 th July, 2014, Trondheim, Norway. [7] Murtaza, G., Corrosion Fatigue Short Crack Growth Behaviour in a High Strength Steel. PhD thesis-University of Sheffield, (1992). [8] Miller, K. J., The two threshold of fatigue behaviour. Fatigue Fract. Engng Mater. Struct., 16 (1993) 931-939. [9] Hobson, P., Brown, M., de los Rios, E., Short fatigue cracks. In: EGP Publication 1, Mechanical Engineering Publications, London, (1986) 441-459. [10] Murtaza, G., Akid, R., Modelling short fatigue crack growth in a heat- treated low alloy steel. Int. J. Fatigue, 17 (1995) 207-214. [11] Angelova, D., Akid, R., A Note on Modelling Short Fatigue Crack Growth Behaviour, Fatigue & Fracture of Engineering Materials &Structures, 21 (1998) 771-779. [12] Yordanova, R., Modeling of fracture process in low-carbon 09Mn2 steel on the bases of short fatigue crack growth experiments. Comparative analyses on the fatigue behavior of other steels, PhD Thesis, University of Chemical Technology and Metallurgy, Bulgaria (2003). [13] Miller, K. J, Materials science perspective of metal fatigue resistance, Mater.Sci. Tech., 9 (1993) 453-462. [14] Navarro, A., de los Rios, E., Fatigue crack growth modelling by successive blocking of doslocations. Proc R. Soc. Lond. A, 437 (1992) 375-390.