Rainflowcounting

Rainflow counting is a method used in fatigue analysis to extract meaningful stress-reversal information from a varying-load history. It converts a time history of stress or strain into a set of cycles, each defined by a range (the stress amplitude of the cycle) and a mean stress, enabling the application of S-N curves and cumulative-damage rules.

The basic idea is to identify turning points in the load history (peaks and valleys) and pair them to form closed stress-reversal cycles. A common implementation uses a stack-based procedure that processes the sequence of extrema and, according to a defined rule, extracts complete cycles while discarding partial ones at the ends. The result is a collection of cycles with associated ranges and mean stresses, which can be assembled into a histogram of cycle counts versus range.

Rainflow counting is widely used because it provides a physically interpretable measure of variable-amplitude loading, suitable for fatigue life estimation. It is often combined with Miner’s rule to accumulate damage from all counted cycles. Mean-stress effects can be incorporated through corrections such as Goodman or Gerber, or by using mean-stress-sensitive S-N curves. The method is applicable to random or complex loading histories and is routinely employed in automotive, aerospace, and mechanical design to predict remaining life or validate durability requirements.

Limitations include assumptions of linear elastic material behavior and the need for adequate sampling to capture reversals. Results can depend on data quality and preprocessing, such as filtering or detrending. While robust, rainflow counting is one component of a broader fatigue-analysis workflow.