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Adaptive analysis | Fatigue Analysis

Fatigue Analysis

LUSAS performs fatigue calculations on the results of a linear finite element stress analysis using the total life approach. The fatigue life may be expressed in terms of the damage that is done to the structure by a prescribed loading sequence or as the number of repeats of the sequence that will cause failure of the structure. Contour plots illustrating the fatigue life of every part of the structure can be generated.

Fatigue Calculations

Fatigue calculations of the life of a structure or component are defined and calculated using the following data:

  • S-N Curves
    The S-N curve is used to calculate the number of cycles to failure for each loadcase. Minerís rule is used to combine the damage for each loadcase to give the total damage to the structure for the specified loading sequence. Log values are used because of the large variation in magnitude of the input data. The curve is considered linear in the log-log domain.

  • Fatigue Spectra
    A loading spectrum defining the loading sequence in terms of a series of loadcases, each of which has an associated load factor and number of cycles.
  • Fatigue loadcases
    Fatigue results are configured using a Fatigue loadcase, which allows previously defined S-N curves and fatigue spectra to be combined. The results entity specified is used to calculate the fatigue life.

Fatigue Results

Results from the fatigue calculations may be viewed using any of the standard LUSAS results processing methods. Fatigue results come from any chosen component of stress, as specified in the Fatigue loadcase.

Results may be visualised in two ways:

  • Loglife This is the log10 of the life expectancy of the structure subject to the level of loading measured in the number of cycles to failure.

  • Damage The amount of damage that a material sustains under fatigue loading. A value of unity represents failure.

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Any modelling and analysis capabilities described on this page are dependent upon the LUSAS software product and version in use.