Fatigue Analysis
Fatigue Analysis is intended for solutions to structures in a large number of loading cycles.
Transient analysis is not effective in such cases since the elapsed time is generally very high and fatigue effects manifest over many loading cycles.
In OptiStruct, both Uniaxial and Multiaxial Fatigue Analysis can be conducted.
Fatigue Support
**Modal Superposition is fatigue analysis performed based on stresses recovered from a flex H3D file sourced from a multibody analysis. The ASSIGN,H3DMBD entry can be used to identify the flex H3D file, and modal participation factors are assigned to obtain the corresponding stresses for the fatigue calculation. For more information, refer to Recover MBD Analysis Results and Fatigue Analysis Setup.
*An additional option to fatigue damage calculation, is the Pseudo damage method. This is supported only for Static SN and Static EN approaches (both uniaxial and multiaxial methods). For more information, refer to Pseudo Damage Method.
Vibration Fatigue Solution  Solution  Example Applications 

Random  Fatigue analysis based on Random Response Analysis 

SineSweep  Fatigue analysis based on a sinesweep test based on Frequency Response Analysis. 

SineonRandom  Superposition of multiple sinetones with background random noise 

Sinesweep on Random  For each damage calculation event, superposition of a single sinetone (representing the sweep) on the background random noise. Damage is then added up across the entire sweep to calculate final damage. 

Multiple sinetones  Superposition of multiple sinetones (without random vibration) 
