Issue 37

D. Angelova et alii, Frattura ed Integrità Strutturale, 37 (2016) 249-257; DOI: 10.3221/IGF-ESIS.37.33 256 (a) (b) Figure 6 : Presentation "Crack length, a - Numbers of cycles, N ": (a) Streel A, Specimen 7 (Δσ =1200 MPa) and Specimen 9 (Δσ =1400 MPa); (b) Steel B, Specimen sets tested in-air and corrosion environment. C ONCLUSIONS atigue behavior of two different spring steels was investigated: 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 corrosion environment. The presentation of the plotted Wöhler curves of both steels show that loading, surface condition and environmental factors are ones of the most influential factors. In Steel A for one of the highest stress range (Δσ = 1200 MPa) and at rough specimen surface, the surface short-fatigue-cracks development and observed microstructures show initiating, propagating and interaction between major and many secondary cracks in its vicinity, leading to exhaustion of local plasticity, crack merging and complete failure. In Steel B a similar situation can be observed only in corrosion environment and above certain high stress range (Δτ = 817 MPa). All this should be taken into consideration at choosing steels for different applications under fatigue conditions. A CKNOWLEDGEMENTS his study was supported by the Scientific Research Center at UCTM – Sofia, Bulgaria. F T