Issue 30

A. Carofalo et alii, Frattura ed Integrità Strutturale, 30 (2014) 349-359; DOI: 10.3221/IGF-ESIS.30.42

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 H [mJ/mm 3 ]

Tangent Modulus

[N/mm 2 ]

Δε/Δε max

N f

/N max

Δσ/Δσ max

R = σ min

/σ max

E T

0.984 0.879 0.771 0.686 0.581 0.795 0.790 0.562 0.564 0.602 0.461 0.460 0.459 0.460 0.789 0.697 0.785 1.000 0.880 0.890 0.950 0.786 0.973 0.895 0.898 0.786 0.981

MB-RT-1 MB-RT-2 MB-RT-3 MB-RT-4 MB-RT-5 MB-RT-6 MB-RT-8 MB-RT-9 MB-RT-10 MB-RT-11 MB-RT-13 MB-RT-14 MB-RT-15 MB-RT-16 MB-538-1 MB-538-3 MB-538-4 MB-538-5 MB-538-6 MB-538-8 MB-538-9 MB-538-10 MB-538-11 MB-538-12 MB-538-13 MB-538-14 MB-538-16

0.0037 0.0045 0.0093 0.0136 0.0310 0.0077 0.0087 0.0223 0.1611 0.0180 0.0621 0.0436 0.0562 0.0432 0.3191 0.4474 0.4518 0.0040 0.0102 0.0127 0.0030 0.0526 0.0396 0.1313 0.1002 0.3942 0.0034

1.0000 0.9798 0.8824 0.8408 0.7667 0.9620 0.9492 0.7410 0.7563 0.7832 0.6062 0.5952 0.6050 0.5511 0.5377 0.4091 0.4354 0.6852 0.6565 0.6001 0.7795 0.5511 0.6375 0.5450 0.5622 0.4440 0.6944

-0.86 -0.74 -0.66 -0.64 -0.97 -0.97 -0.84 -0.40 -1.64 -0.54 -0.48 -0.28 -0.61 -0.24 -0.36 -0.11 0.00 -0.52 0.56 -0.37 -0.80 -0.13 -0.40 -0.40 -0.37 -0.14 -0.31

1.536 0.886 0.329 0.151 0.040 0.549 0.500 0.035 0.015 0.051 0.009 0.012 0.053 0.026 0.051 0.024 0.291 0.392 0.065 0.231 0.378 0.405 0.179 0.464 0.190 0.023 0.153

214109 218793 212641 224218 235026 229147 226862 226357 228901 231935 232259 230506 231954 216363 118358 106123 114078 123529 129012 131086 154759 160511 100070 132828 101577 103100 115671

Table 2: Base Material – Room Temperature: fatigue test results.

Strain Range

Cycles to failure

Normalized Stress Range

Stress Ratio

Hysteresis Area H [mJ/mm 3 ]

Tangent Modulus

[N/mm 2 ]

Δε/Δε max

N f

/N max

Δσ/Δσ max

R = σ min

/σ max

E T

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

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