Issue 37

D. Angelova et alii, Frattura ed Integrità Strutturale, 37 (2016) 258-264; DOI: 10.3221/IGF-ESIS.37.34 263 one of type d 2 ) is plotted by dashed line in Fig. 4, too. In fact at corrosion condition da/dN increases, Figs. 4b, c; also the higher stress range plays the same role, leading to higher da/dN . As illustrated in Figs. 2b, 3a, 4, a reasonable agreement can be seen when comparing experimental da/dN and theoretical ones using the new analytical model M described by Eq. 1 and Tabs. 1, 2 (the case when many secondary cracks have initiated and influenced the growth of major crack). The proposed new model M is supported by the comparison of predicted N f,m , Eq. 2, and actual N f,exp fatigue lifetimes presented in Figs. 3b and 5. a b c Figure 4: Fatigue crack growth curves for Steel B: (a) air; (b) , (c) corrosion. C ONCLUSIONS hort fatigue crack behavior of two spring steels was investigated and analytically modeled: Steel EN10270-1SH/ DIN 17223C (Steel A) for own fatigue experiment; and BS250A53/DIN 55Si7 (Steel B) with already published fatigue data and for comparison with Steel A. Steel A is subjected to symmetric rotating bending fatigue in air, and Steel B - to fully reversed torsion fatigue in air and in corrosion environment. For Steel A two cases of loading are discussed, Δσ = 1200 MPa and Δσ = 1400 MPa. In both cases the major surface crack originates first and develops in three regimes of propagation: MSC, PSC, LC. The major crack at Δσ = 1400 MPa