Fatigue Analysis

Service life analysis and damage calculation to estimate the fatigue process of monitored components.

The documentation of the corresponding PLC function blocks can be found here: FB_CMA_RainflowCounting, FB_CMA_MeanStressCorrection and FB_CMA_MinersRule

For the calculation of the Wöhler curve, the function F_CM_CalculateWoehlerCurve is executed on the basis of fictitious material parameters.

For more detailed explanations, refer to the Condition Monitoring documentation in the chapter Application Concepts, section Service Life Analysis and Damage Calculation.

Configuration options

• Number of Stress Range Bins: defines the number of bins for the stress level. The total number of bins is "nBins + 2"; the value must be at least one. The first bin of each row contains the stress levels that are less than or equal to the defined minimum; analogously, all values greater than the defined maximum fall into the last bin of each row.
• Minimum Stress Range: defines the lower limit of the stress level. All values that are less than or equal to this value are accumulated in a bin.
• Maximum Stress Range: defines the upper limit of the stress level. Values that exceed the maximum are counted in the last bin.
• Number of Mean Stress Bins: defines the number of bins for the mean values. The value must be at least one. Two separate bins are added in the first/last column of the Halfcycle Count Matrix, where mean values are kept that are less than or equal to or, respectively, greater than the defined limits.
• Minimum negative Mean Stress: defines the lower limit of the mean values. All values that are less than or equal to this value are accumulated in a bin.
• Maximum positive Mean Stress: defines the upper limit of the mean values. Values that exceed the maximum are counted in the last bin.
• Mean Stress Correction: defines the correction mode to be used. The correction according to Goodman and Gerber is available as well as the option not to make a correction.
• Use UTS Correction: if active, a UTS correction of the stress matrix is performed.
• UTS: defines the tensile strength of the monitored material.
• K1: defines the gradient of the Wöhler curve in the range N = 1..NC1.
• K2: defines the gradient of the Wöhler curve starting at N >= NC2.
• SRI: defines the "Stress Range Intercept".
• NC1: defines the transition point for the UTS correction.
• NC2: defines the transition point between K1 and K2.
• Woehler Curve: definition of the Wöhler curve.
• Additional Damage: defines the constant damage from the beginning. The total damage is thus calculated from the sum of fDamage and the accumulated damage with respect to the configured Wöhler curve.
• Additional Halfcycles: defines the initial value of the counted half cycles at the beginning. The total number of cycles is calculated from the sum of nCycles and the current number of input data.
• Input Length: defines the length of the input data array for block processing.

Output values

• Damage: indicates the calculated fatigue damage with respect to the defined Wöhler curve.
• HalfCycles: indicates the number of half cycles counted.
• Range Bins: output array of length "Number of Stress Range Bins" with summed half cycles along the middle stress.
• Mean Bins: output array of length "Number of Mean Stress Bins" with summed half cycles along the absolute stress.
• Cnt Results: specifies the number of output arrays calculated.
• New Result: is a Boolean value that indicates whether a new result was obtained in the current cycle.