Editing Rainflow-counting algorithm (section)

{{Short description|Materials science algorithm}}
[[File:Rainflow counting vs stress-strain curve.svg|thumb|Rainflow counting identifies the closed cycles in a stress-strain curve]]

The '''rainflow-counting algorithm''' is used in calculating the [[fatigue (material)|fatigue]] life of a component in order to convert a loading sequence of varying [[stress (physics)|stress]] into a set of constant amplitude stress reversals with equivalent fatigue damage. The method successively extracts the smaller interruption cycles from a sequence, which models the material memory effect seen with stress-strain [[hysteresis]] cycles.<ref name="endo74">{{cite journal |first1=Tatsuo |last1=Endo |first2=Koichi |last2=Mitsunaga |first3=Kiyohum |last3=Takahashi |first4=Kakuichi |last4=Kobayashi |first5=Masanori |last5=Matsuishi |title=Damage evaluation of metals for random or varying loading—three aspects of rain flow method |journal=Mechanical Behavior of Materials |year=1974 |volume=1 |pages=371–380}}</ref> This simplification allows the number of cycles until failure of a component to be determined for each rainflow cycle using either [[Fatigue (material)#Miner's rule|Miner's rule]] to calculate the ''fatigue damage'', or in a [[crack growth equation]] to calculate the crack increments.<ref>{{cite journal |last1=Sunder |first1=R. |last2=Seetharam |first2=S. A. |last3=Bhaskaran |first3=T. A. |year=1984 |title=Cycle counting for fatigue crack growth analysis |journal=International Journal of Fatigue |volume=6 |number=3 |pages=147–156|doi=10.1016/0142-1123(84)90032-X }}</ref> Both methods give an estimate of the ''fatigue life'' of a component. In cases of multiaxial loading, [[critical plane analysis]] can be used together with rainflow counting to identify the uniaxial history associated with the plane that maximizes damage. The [[algorithm]] was developed by [[Tatsuo Endo (engineer)|Tatsuo Endo]] and M. Matsuishi in 1968.<ref name="matsuishi68">{{cite journal |last1=Matsuishi |first1=M. |last2=Endo |first2=T. |year=1968 |title=Fatigue of metals subjected to varying stress |journal=Japan Society of Mechanical Engineering}}</ref>

The rainflow method is compatible with the cycles obtained from examination of the  stress-strain hysteresis cycles. When a material is cyclically strained, a plot of stress against strain shows loops forming from the smaller interruption cycles. At the end of the smaller cycle, the material resumes the stress-strain path of the original cycle, as if the interruption had not occurred. The closed loops represent the energy dissipated by the material.<ref name="endo74"/>

[[File:Rainflow_fig1.PNG|thumb|right|Figure 1: Uniform alternating loading]]
[[File:Rainflow_fig2.PNG|thumb|right|Figure 2: Spectrum loading]]