Issue 30

A. Carofalo et alii, Frattura ed Integrità Strutturale, 30 (2014) 349-359; DOI: 10.3221/IGF-ESIS.30.42 354 damage is undoubtable, as testified by the generalized approach that has been proposed recently using experimental data of Waspaloy [19]. Anyway, the errors associated to measured strain and stress during test are so high that a notable scatter generally affects calculation of energy parameters. This observation is particularly true in large part of the test carried out in this work, where elastic behaviour is predominant and the loading and unloading curves are practically coincident. Nevertheless, hysteresis area reported in the previous tables can be correlated to the resulting stress range and a clear correlation exists in all the test conditions (Fig. 3a). On the other hand, it is not possible to use the values of hysteresis area as a damage indicator due to its low magnitude. From a practical point of view, the trends of hysteresis area against fatigue life that have an initial value higher than 0.5 mJ/mm 3 have been considered. Hysteresis area is practically constant or show limited variation up to failure (Fig. 3b). Therefore, the use of energy indicator related to hysteresis area to describe damage phenomena has a limited importance for the stress-strain level that is usually present in the working condition of an industrial component. Strain Range Cycles to failure Normalized Stress Range Stress Ratio Hysteresis Area Tangent Modulus Δε/Δε max N f /N max Δσ/Δσ max R = σ min /σ max H [mJ/mm 3 ] E T [N/mm 2 ] TIG-RT-1 0.767 0.0011 0.5352 -0.15 0.169 143012 TIG-RT-2 0.581 0.0203 0.7324 -1.18 0.217 222952 TIG-RT-3 0.795 0.0041 0.9081 -0.66 0.551 216812 TIG-RT-4 0.472 0.0157 0.5677 -0.20 0.042 211581 TIG-RT-5 0.473 0.0179 0.5664 -0.08 0.035 213285 TIG-RT-6 0.571 0.0617 0.6718 -3.94 0.702 217488 TIG-RT-7 0.472 0.0095 0.5389 -0.17 0.404 209687 TIG-RT-8 0.690 0.0084 0.8389 -0.57 0.144 213285 TIG-RT-9 0.795 0.0022 0.8065 -0.46 0.089 143342 TIG-RT-10 0.476 0.0328 0.5462 -0.16 0.162 203959 TIG-RT-11 0.584 0.0146 0.6691 -0.27 0.081 200947 TIG-RT-12 0.584 0.0105 0.6883 -0.34 0.125 205143 TIG-RT-13 0.804 0.0014 0.8598 -0.59 0.235 196114 TIG-RT-14 0.476 0.0308 0.5407 -0.11 0.087 203601 Table 4: TIG Welded Material – Room Temperature: fatigue test results. Strain Range Cycles to failure Normalized Stress Range Stress Ratio Hysteresis Area Tangent Modulus Δε/Δε max N f /N max Δσ/Δσ max R = σ min /σ max H [mJ/mm 3 ] E T [N/mm 2 ] TIG-538-3 0.686 0.0031 0.4097 -0.35 0.112 162957 TIG-538-4 0.660 0.1699 0.4905 -0.21 0.032 133696 TIG-538-5 0.675 0.0200 0.6552 -0.34 0.161 147811 TIG-538-6 0.801 0.0027 0.6730 -0.53 0.169 149473 TIG-538-8 0.516 0.0272 0.4562 -0.11 0.029 153746 TIG-538-9 0.660 0.0804 0.4764 -0.21 0.031 129936 TIG-538-11 0.794 0.0040 0.5328 -0.09 0.283 137832 TIG-538-12 0.574 0.0049 0.4525 -0.06 0.027 135120 TIG-538-13 0.551 1.0000 0.3246 0.16 0.092 131529 TIG-538-14 0.676 0.0160 0.4133 0.02 0.144 124787 TIG-538-16 0.780 0.0009 0.6105 -0.26 0.038 139634 TIG-538-17 0.789 0.0095 0.6203 -0.45 0.040 141017 TIG-538-18 0.684 0.0105 0.4146 0.07 0.046 103570 TIG-538-19 0.589 0.0240 0.5909 -0.18 0.081 131791 Table 5: TIG Welded Material – 538°C: fatigue test results.