Rainflow-counting algorithm

The rainflow-counting algorithm is used in calculating the fatigue life of a component in order to convert a loading sequence of varying stress into a set of constant amplitude stress reversals with equivalent fatigue damage.

[1] This simplification allows the number of cycles until failure of a component to be determined for each rainflow cycle using either Miner's rule to calculate the fatigue damage, or in a crack growth equation to calculate the crack increments.

[5] Igor Rychlik gave a mathematical definition for the rainflow counting method,[6] thus enabling closed-form computations from the statistical properties of the load signal.

All methods start with the process of eliminating non turning points from the sequence.

A completely closed set of rainflow cycles can be obtained for a repeated load sequence such as used in fatigue testing by starting at the largest peak and continue to the end and wrapping around to the beginning.

Rainflow counting identifies the closed cycles in a stress-strain curve
Figure 1: Uniform alternating loading
Figure 2: Spectrum loading
Rainflow counting using the four point method. Any pair of turning points B,C that lie between adjacent points A and D is a rainflow cycle. Count and eliminate the pair B,C and continue processing the sequence until no more cycles can be extracted.
Figure 3: Rainflow analysis for tensile peaks
Figure 4: Rainflow analysis for compressive valleys