In Fatigue Analysis, Cycle Counting is the process of transforming a complex, “messy” history of stress or strain over time into a set of discrete, quantifiable cycles. Most real-world structures don’t experience simple, repetitive “up-and-down” loading (like a perfect sine or triangular wave). Instead, they are subjected variable vibrations. Fatigue laws, like the Palmgren-Miner Rule, require knowing exactly how many cycles occurred at specific stress (or strain) amplitudes to calculate the total damage. Cycle counting bridges that gap.
There are approximately 15 methods of cycle counting. The most common methods include: Rainflow, Level-Crossing, and Peak Counting. Because each method varies, their output may vary when analyzing the identical cycle histories.
To perform a fatigue life prediction, the process typically follows these steps: (1) Data Acquisition, (2) Cycle Counting, (3) Damage Calculation, and (4) Summation.
The tool below allows the user to input a stress or strain history and choose a cycle counting method. Upon calculation, it leads to the histogram of the analyzed results.