Fatigue & Fracture Workbench
Define the load cycle, then explore mean stress, cumulative damage and stress intensity.
Mean stress · Miner · K / ΔK ↓Illustrative sinusoid only. Not measured test data or a specified loading waveform.
The definitions behind the numbers.
The load range is twice the amplitude. The ratio depends on the signed maximum load; it is not amplitude divided by mean.
R = Fmin / Fmax (Fmax ≠ 0)Fmean = (Fmax + Fmin) / 2Fa = (Fmax − Fmin) / 2ΔF = Fmax − Fmin = 2FaFmax = Fmean + FaFmin = Fmean − FaCan I use an all-compressive cycle?
Yes. With tension positive, an all-compressive cycle has negative Fmax and Fmin, with Fmax ≥ Fmin. For example, Fmax = −2 kN and Fmin = −10 kN give R = 5. A ratio greater than one is not automatically invalid.
Why is an input rejected?
Non-finite values, negative amplitudes, Fmin greater than Fmax, or a zero maximum in maximum-plus-ratio mode are rejected. A zero maximum is allowed in the other input definitions; the ratio is then undefined.
What happens if I change the unit or definition?
Changing the force unit converts the input forces and preserves the physical load. R is dimensionless. Switching definitions preserves the current valid cycle. Invalid inputs must be corrected before changing the definition or unit.
Go beyond the load cycle.
Independent, optional calculations. Inputs below are not automatically linked to the force cycle above. Example material values are illustrative, not a material database.
Mean-stress correction · Goodman / Soderberg
Result
Uniaxial screening only. Negative mean stress receives no benefit. Enter fatigue strength for your target life, surface, environment and reliability. No cycles-to-failure prediction. Corrected amplitude = Sa / (1 − max(Sm,0)/S), where S is Su or Sy.
Method and sourceCumulative damage · Palmgren–Miner
Result
D = Σ(n/N). Sequence effects and interactions are ignored. D=1 is a model threshold, not a guaranteed failure point; 1/D is total repetitions of the entered block from zero damage, not remaining service life.
Method and sourceMode I stress intensity · Kmax / ΔK
Result
K = Yσ√(πa). Supply a and Y from a matching geometry solution; Y=1 is an example, not an inferred factor. Tensile extrema only. No plasticity, crack closure, KIc validity or crack-growth life assessment.
Method and sourceThese tools do not approve a component for service. Use qualified material data and independent engineering review. Convert ksi√in ↔ MPa√m and other units.