vibration test with payload

Hi,

I have got a question regarding a vibration tests. A system which has during normal operarion a payload has to perform a vibration test. As usual the normal operation time, at a defined vibation level, is reduced using the fourth power law resulting in short test time at higher vibration levels. My questions are as follows :
1). Has the test at the higher vibration levels, with a shorter test time, the same payload as the system during normal operation ?
2). Are there laws to determine the payload at the higher levels with shorter test time. Were are these equations defined.

I would be gratefull for answers solving my problem.

 

[vanstoja]

I'm not familiar with the so-called 4th power law between test time and whatever (vibration level, stress level, cumulative damage, etc.). What is this 4th power law and where does it come from? There is a classic book by Fackler,W.C.(1972), "Equivalence Techniques for Vibration Testing", SVM-9, The Shock and Vibration Information Center, US Navy Research Lab which has separate chapters on Cumulative Damage, Magnitude and Interaction Equivalences.
For cumulative damage equivalence, equation 3.12 gives:
V_2=V_1*t_R^(1/b) where
V's = Response acceleration amplitudes
t_R = Original time/ Sought time
b = Slope of the Stress-Cycle (S-N) curve
This is indicated to be for Sinusoidal Dwell equivalence.
If damping is involved then the numerator of the above equation becomes (n-1) "where n may vary from 2 to 8 , with 2.4 being the preferred value for structural materials when the stress levels are no more than 80% of the endurance stress."
Figure 3-2 shows that the steeper S-N curve slope b is for "permanent deficiency" whereas the shallower slope a is called "operational deficiency". I read that to mean that b means dead, kaput, etc. whereas a means functionally impaired.
Now, where does your 4th power rule fit into this convention?