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Random Vibration Post-Processing

Question asked by 1-L5M1MV on Sep 11, 2009
Latest reply on Jan 25, 2010 by Joe Galliera

I have a quick question about interpreting the stress results of a Dynamic Random Vibration study.  The values are RMS Von Mises stresses, which (as far as my understanding goes) are equal to one standard deviation, assuming a normal (Gaussian) distribution.  So, when subjected to PSD acceleration, the stresses in each part have a 32% chance of exceeding the stresses shown.


The problem I'm having is determining a pass/fail criterion for this study.  Many of the studies I've seen claim to use the PSD curve (for a specific amount of time?), and then provide results in a damage or life plot.  I looked into using stresses created by the PSD curve and using them as inputs for a fatigue study, but it doesn't appear that SolidWorks has that capability.


I also tried assuming that 3*RMS stresses would ensure that stresses in the part would only have a 0.25% chance of exceeding the displayed RMS values (i.e.: the pass/fail limit is set to 1/3 of the material yield strength), but this seemed unrealistic.  The RMS stresses in many of the robust parts we studied were coming fairly close to the limit (1/3 Sy).


Can anyone give me some insight on interpreting these results?  For reference, I'm using PSD curves defined in MIL-STD-810G, Method 514.6C.