Which stress (derived from Frequency Response Analysis) is relevant for fatigue life?

[fabs84]

Hi,
in the case of mechanical components which always work at high temperature (metal sheets) I calculate first the stress induced by thermal expansion (thermostructural analysis) and then the one induced by vibrations (frequency response analysis). Finally I use the Haigh Diagram to verify the fatigue failure: Mean stress is the Von Mises stress derived from thermostructural analysis, instead Range stress is the Max Principal stress derived from frequency response analsysis.

Is correct to consider Max Principal stress for the Range stress?
Both Von Mises and Max Principal are non-sinusoidal and vary in the period.

Best regards

 

[rb1957]

does seem odd to use principal for one and von Mises for the other.

why not the same for both ? i'd have a personal preference for principal, maybe run the calc with both as see the difference ?