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A number in parentheses indicates the year of last reapproval. This standard does not intend to recommend a particularmethod. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use. Referenced Documents2.
NOTE 1—In spectrum loading, definition of cycle varies with thecounting method used. NOTE 3—In constant amplitude loading, a cycle is equal to tworeversals. Also known as variable amplitudeloading or irregular loading. Current edition approved June 1, Published June Originallyapproved in DOI: The reference load may be identical to the mean load of thehistory, but this is not required.
Significance and Use4. The definition of a cyclevaries with the method of cycle counting. These practices coverthe procedures used to obtain cycle counts by various methods,including level-crossing counting, peak counting, simple-rangecounting, range-pair counting, and rainflow counting.
Cyclecounts can be made for time histories of force, stress, strain,torque, acceleration, deflection, or other loading parameters ofinterest. Procedures for Cycle Counting5. One count is recorded each time the positive slopedportion of the load exceeds a preset level above the referenceload, and each time the negative sloped portion of the loadexceeds a preset level below the reference load.
Reference loadcrossings are counted on the positive sloped portion of theloading history. It makes no difference whether positive ornegative slope crossings are counted. The distinction is madeonly to reduce the total number of events by a factor of two.
This may beaccomplished by filtering small load excursions prior to cyclecounting. A second method is to make no counts at thereference load and to specify that only one count be madebetween successive crossings of a secondary lower levelassociated with each level above the reference load, or asecondary higher level associated with each level below thereference load. Avariation of the second method is to use the same secondarylevel for all counting levels above the reference load, andanother for all levels below the reference load.
In this case thelevels are generally not evenly spaced. Reversal points are assumedto occur halfway between levels.
This process is illustrated byFig. Note that once this most damaging cycle count isobtained, the cycles could be applied in any desired order, andthis order could have a secondary effect on the amount ofdamage.
Other methods of deriving a cycle count from thelevel-crossings count could be used. Peaks above the referenceload level are counted, and valleys below the reference loadlevel are counted, as shown in Fig.
Results for peaks andvalleys are usually reported separately. A variation of thismethod is to count all peaks and valleys without regard to thereference load. Instead of counting all peaks andvalleys, only the largest peak or valley between two successivemean crossings is counted as shown in Fig.
This process is illustrated by Fig. Note that oncethis most damaging cycle count is obtained, the cycles could beapplied in any desired order, and this order could have asecondary effect on the amount of damage. Alternate methodsof deriving a cycle count, such as randomly selecting pairs ofpeaks and valleys, are sometimes used.
The method is illustrated in Fig. Positive ranges, negative ranges, or both, may be counted withthis method. If only positive or only negative ranges arecounted, then each is counted as one cycle. If both positive andnegative ranges are counted, then each is counted as one-halfcycle. Ranges smaller than a chosen value are usually elimi-nated before counting. For theexample of Fig. If the load history begins and ends with itsmaximum peak, or with its minimum valley, all of these giveidentical counts.
In other cases, the counts are similar, but notgenerally identical. Three methods in this class are definedhere: range-pair counting, rainflow counting, and a simplifiedmethod for repeating histories. When the meanvalue is ignored, they are one-parameter methods, as aresimple-range counting, peak counting, etc.
Rules for this method are asfollows If out of data, go to Step 5. Formranges X and Y using the three most recent peaks and valleysthat have not been discarded. Count A-B asonecycle and discard points A and B. See Fig. Note that acycle is formed by pairing range A-B and a portion of rangeB-C. Count E-F asonecycle and discard points E and F. Count C-D as onecycle and discard points C and D. Count H-I asonecycle and discard points H and I. See the table in Fig. If out of data, go to Step 6.
Ycontains S, that is,point A. Ycontains S, that is, pointB. Count E-F as one cycleand discard points E and F. Note that a cycle isformed by pairing range E-F and a portion of range F-G. Count C-D as one-half cycle and discard point C. Note that a cycleis formed by pairing range E-F and a portion of range F-G.
Count A-B as one cycleand discard points A and B. Count H-C as one cycleand discard points H and C. Count D-G as one cycleand discard points D and G.