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Variable Amplitude Multiaxial Strain-Life Technical Background

Fatigue occurs on the surface where one of the principal stresses is usually zero. As a result, multiaxial fatigue problems are usually biaxial in nature. Here we have assumed that the stress normal to the free surface is zero in all the calculations. Any stress concentration effects must be included in the input loading data.

Multiaxial Fatigue Calculators are used for constant amplitude loading where the largest cycle is assumed to do all of the fatigue damage. The Multiaxial Fatigue Analyzer counts cycles and sums fatigue damage for all cycles. Both use the same cyclic plasticity models. More damage models are available with the Multiaxial Fatigue Calculators. Fatigue Analyzers have the ability to read data from files.

Variable amplitude multiaxial strain life analysis can be summarized as a series of steps:

  • define applied stresses or strains
  • select material properties
  • correct material properties for surface finish
  • compute local stresses and strains
  • identify cycles
  • compute fatigue damage for each cycle
  • search for possible failure planes

Go to the Constant Amplitude Technical Background section for a more complete description of the basic fatigue variables.

Go to the Multiaxial Strain-Life Technical Background section for a more complete description of the various damage models used in multiaxial fatigue analysis.

Go to the Variable Amplitude Technical Background section for a more complete description of variable amplitude fatigue analysis.