Issue 39

S. Seitl et alii, Frattura ed Integrità Strutturale, 39 (2017) 110-117; DOI: 10.3221/IGF-ESIS.39.12 115 Based on the values of m avg no distinct difference can be observed between the 10-80% and 10-90% stress ratios. This might again be a consequence of the fact that the difference between 10-80% and 10-90% the stress ratios is small ( R 10-80 = 0.1250 and R 10-90 = 0.1111). On the other hand, the average value C avg is significantly greater for the 10-90% stress ratio compared to the 10-80% stress ratio. It can be concluded that for a fixed value of ∆ K , the crack propagation rate for the 10-90% is considerably faster. Figure 5 : (a) Paris-Erdogan law fitting curves from correlation of 3PBT data from VC under 10-70% and 10-75% stress ratios; (b) Paris-Erdogan law fitting curves from correlation of WST data from VC under 10-80% and 10-90% stress ratios Stress ratio Test Equation m .x+log( C ) m m avg C C avg 10-70% 1 1.7301 x - 0.4349 1.7301 2.0198 0.6473 0.6141 2.3094 x - 0.5433 2.3094 0.5808 2 3.2763 x - 1.2861 3.2763 3.9681 0.2763 0.2383 3.8338 x - 1.4086 3.8338 0.2445 4.7943 x - 1.6396 4.7943 0.1941 10-75% 1 4.2383 x - 1.065 4.2383 4.2299 0.3447 0.3558 3.9467 x - 1.0177 3.9467 0.3614 4.5047 x - 1.0792 4.5047 0.3613 Table 1 : 3PBT – Fitting curve equations and Paris-Erdogan law parameters. Stress ratio Test Equation m .x+log( C ) m m avg C C avg 10-80% 1 3.6086 x - 3.2615 3.6086 4.4102 0.0383 0.0344 4.2947 x - 3.3270 4.2947 0.0359 5.3274 x - 3.5448 5.3274 0.0289 10-90% 1 2.2933 x - 0.7533 2.2933 2.4518 0.4708 0.4748 2.6103 x - 0.7364 2.6103 0.4788 2 5.2891 x - 1.6165 5.2891 5.1182 0.1986 0.2000 5.0523 x - 1.5937 5.0523 0.2032 5.0132 x - 1.6181 5.0132 0.1983 Table 2 : WST – Fitting curve equations and Paris-Erdogan law parameters. -1,0 -0,8 -0,6 -0,4 -0,2 0,0 0,2 0,4 0,6 0,8 1,0 0,05 0,15 0,25 0,35 0,45 Crack propagation rate log(da/dN) [mm/cycle] Stress intensity factor log(∆K) [MPa.√m] 10-70 (1) 10-70 (2) 10-75 -3,5 -3 -2,5 -2 -1,5 -1 -0,5 -0,05 0 0,05 0,1 0,15 0,2 Crack propagation rate log(da/dN) [mm/cycle] Stress intensity factor log(∆K) [MPa.√m] 10-90 (1) 10-90 (2) 10-80