What stress to use for fatigue analysis

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For fatigue analysis, the choice of stress values from finite element programs, such as von Mises, principal, or Tresca, depends on the material properties and loading conditions. Ductile materials typically utilize von Mises stress in conjunction with the material's S-N curve, while brittle materials or composites require different analysis approaches. The stress range calculation can vary; using principal stresses may involve determining the difference between σ11 from load case 1 and load case 2 or calculating the difference between σ11 and σ33 first. Understanding the material behavior under combined loading conditions is crucial for accurate fatigue analysis. Proper selection of stress values and calculation methods is essential for reliable results.
scootypuffsnr
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Hi,

I was wondering which stress values from a finite element program to use for fatigue analysis, (von mises, principal, tresca). I was leaning towards principal stresses but then would my stress range be σ11 from load case 1 (LC1) to σ11 of LC2, or would i need to do σ11-σ33 first and then would my stress range be (σ11-σ33) LC1 to (σ11-σ33) for LC2. Sorry I am a bit confused. Thank you
 
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It will largely depend on your material for analysis and loading conditions. Ductile materials with combined loading conditions (e.g. shear + tension) will tend to use Von Mises compared to the material's S-N curve. Brittle materials or composites will have very different analysis methods though...
 

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