Issue 9

C. M. Sonsino, Frattura ed Integrità Strutturale, 9 (2009) 3-12; DOI: 10.3221/IGF-ESIS.09.01 6 calculated for the reference radius r ref = 1.00 mm, Fig. 9, according to von Mises, the FAT value 225 MPa, which is a principal stress, was transformed into a von Mises stress of 200 MPa [6], Tab. 1. This table contains also allowable values for the reference radius r ref = 0.05 mm to be applied for thin sheets with t  5mm. Figure 8 : Results presented by load ranges versus fatigue life. Figure 9 : Principle of applying reference radii. All given allowable stress ranges  loc are in MPa for N = 2  10 6 , R = 0.5 , P s = 97.7% ; k = 3.0 , N k = 1  10 7 , k* = 22.0 , k‘ = 5.0 r ref [mm] 1.00 1.00 0.05 0.05 Hypothesis PSH von Mises PSH von Mises Steel 225 200 630 560 Aluminium 71 63 180 160 Magnesium 28 25 71 63 Table 1 : FAT-values according to the notch stress concept for different reference radii and strength hypotheses (PSH: Principal stress hypothesis). With regard to cumulative damage, Fig. 10, the fatigue life assessment for spectrum loading was carried out according to the Palmgren-Miner Rule keeping the slope k’ = k after the knee point [7] and using the allowable damage sum D al = 0.5 [8] . For the crack propagation calculations, the Paris-Erdogan curve for steel in salt water with R = 0 and P s = 50 %, Fig. 11 , was used.