Rainflowmethode

Rainflow method

The rainflow method is a widely used technique in fatigue analysis for counting and characterizing cycle loads in a fluctuating stress or strain history. Developed by the American researcher Nigel E. Dowling in the 1970s, it provides a systematic approach to decompose complex load time histories into simple, individual load cycles, which are essential for predicting material fatigue life.

This method visualizes stress or strain data as a closed hysteresis loop array, allowing engineers to identify the number and size of stress cycles that contribute to fatigue damage. The process involves filtering the load history, then scanning through the data to identify local maxima and minima. These points are then grouped into load cycles based on specific rules, effectively "walking" the data like raindrops flowing down a surface, hence the name.

The rainflow counting procedure is favored because it accurately captures the effects of load reversals and variable amplitude loading conditions. It is compatible with existing fatigue life prediction models, such as S-N curves or strain-life equations, enabling more reliable assessments of component durability under complex loading scenarios.

This technique is extensively employed in fields such as aerospace, automotive, civil engineering, and materials science, where understanding and mitigating fatigue failure is critical. Its primary advantage is reducing complex load histories into a manageable set of representative cycles, simplifying fatigue analysis and ensuring safety and longevity of engineering structures and components.