Rainflow Cycle Counting Method
The Rainflow cycle counting method extracts the composition of a variable
amplitude load history. The software implements the method as follows:
Extract peaks and troughs from the load history.
Make the amplitudes of the first and last data
points the same by appending a data point if necessary.
Detect the highest peak and reorder the data such
that the highest peak becomes the first and last points.
Start counting the peaks as follows:
Consider the first four peaks and troughs
( 1, 2, 3, and 4). A Rainflow
cycle is
counted if the second segment is vertically shorter than the first and
the third segments (i.e. b is smaller than a and c).
If a cycle is counted, the program starts
from the beginning of the record ignoring peaks that have already been
counted. If no peak is counted, the program checks the next group of peaks
(peaks 2, 3, 4, and 5) and the process continues. At the end, each peak
and each trough corresponds to a Rainflow cycle.
Ignore and load cycles that are below the
percentage specified in the properties of the study.
Divide the alternating and mean stress ranges
into the number of bins specified in the properties of the study. You
can view the results by viewing the Rainflow
matrix chart.
Application of the Rainflow Cycle Counting Method
Fast Counting
Fast counting is used when the fatigue study refers to one static study
and has only one variable-amplitude event. In this case, the program extracts
bins directly from the original record. It then evaluates the damage resulting
from each bin at each node and calculates the accumulative damage.
Full Analysis
When multiple variable-amplitude events are used, the program calculates
the stresses at each point in time for each variable-amplitude record
at every node. At each node, the program combines the stresses and extracts
the Rainflow bins that are then used to evaluate the damage.
Full analysis is
also used when a variable amplitude record is associated with more than
one study with the different shifts or intervals.
Related Topics
Add
Events (Variable)
Fatigue
Analysis
Fatigue
Result Options
Performing
Fatigue Analysis