Issue 30

A. Carofalo et alii, Frattura ed Integrità Strutturale, 30 (2014) 349-359; DOI: 10.3221/IGF-ESIS.30.42 353 Low-Cycle Fatigue test Relevant data about the fatigue tests are resumed in Tab. 2-5 for each test condition. All the data are normalized with respect to a reference value corresponding to the maximum one. Failure is identified by a decay of 10 % of the maximum stress with respect to the stabilized cycle. Specimens that reached the run-out level of 10 5 cycles are marked in bold to indicate that the test was completed in load control up to failure. In the same tables, several indicators are reported, referred to the stabilized cycle, which is generally identified as the half-life cycle. In particular, the stress range, stress ratio R, tangent elastic modulus E T and the amount of the hysteresis area H have been calculated and showed. 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 ] MB-RT-1 0.984 0.0037 1.0000 -0.86 1.536 214109 MB-RT-2 0.879 0.0045 0.9798 -0.74 0.886 218793 MB-RT-3 0.771 0.0093 0.8824 -0.66 0.329 212641 MB-RT-4 0.686 0.0136 0.8408 -0.64 0.151 224218 MB-RT-5 0.581 0.0310 0.7667 -0.97 0.040 235026 MB-RT-6 0.795 0.0077 0.9620 -0.97 0.549 229147 MB-RT-8 0.790 0.0087 0.9492 -0.84 0.500 226862 MB-RT-9 0.562 0.0223 0.7410 -0.40 0.035 226357 MB-RT-10 0.564 0.1611 0.7563 -1.64 0.015 228901 MB-RT-11 0.602 0.0180 0.7832 -0.54 0.051 231935 MB-RT-13 0.461 0.0621 0.6062 -0.48 0.009 232259 MB-RT-14 0.460 0.0436 0.5952 -0.28 0.012 230506 MB-RT-15 0.459 0.0562 0.6050 -0.61 0.053 231954 MB-RT-16 0.460 0.0432 0.5511 -0.24 0.026 216363 Table 2: Base 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 ] MB-538-1 0.789 0.3191 0.5377 -0.36 0.051 118358 MB-538-3 0.697 0.4474 0.4091 -0.11 0.024 106123 MB-538-4 0.785 0.4518 0.4354 0.00 0.291 114078 MB-538-5 1.000 0.0040 0.6852 -0.52 0.392 123529 MB-538-6 0.880 0.0102 0.6565 0.56 0.065 129012 MB-538-8 0.890 0.0127 0.6001 -0.37 0.231 131086 MB-538-9 0.950 0.0030 0.7795 -0.80 0.378 154759 MB-538-10 0.786 0.0526 0.5511 -0.13 0.405 160511 MB-538-11 0.973 0.0396 0.6375 -0.40 0.179 100070 MB-538-12 0.895 0.1313 0.5450 -0.40 0.464 132828 MB-538-13 0.898 0.1002 0.5622 -0.37 0.190 101577 MB-538-14 0.786 0.3942 0.4440 -0.14 0.023 103100 MB-538-16 0.981 0.0034 0.6944 -0.31 0.153 115671 Table 3: Base Material – 538°C: fatigue test results. The application of load cycle in strain control originates non-linear phenomenon within the material. The applied work can be divided in potential and dissipated energy and several predictive models based on macroscopic energy approaches have been developed to evaluate fatigue damage. The importance of considering energy parameters to describe fatigue