After running a Random vibration profile in a single axis the results are :

For a Stress plot

     Two options exist

               Show PSD Value

               RMS Value

1. When show PSD Value is ticked the results can be interpreted as follows:

     The stress is in Stress^2/Hz at a given frequency.

Eg Max PSD Value = 10 MPa^2/Hz,

     Frequency = 1000Hz

Stress^2 = 10 * 1000 = 10000,

Stress (RMS) = 100 Mpa  (one Sigma)

Peak Stress = 3*100 Mpa (3 sigma)

For RMS Value

When show PSD value is not ticked.

The Results shown are Stress (RMS)

What is this value? It is not the same as the RMS value calculated above.

Am inclinded to assume that it is the RMS value for the whole system.

Can anybody shed any light on this?