acceleration of vibration

[toner5]

Hi,

I'm a stress engineer working in the transport aircraft industry. Usually I deal with static strength analysis. Though, we have had some projects lately dealing with avionics and avionics installations.

So, industry standard test documents (ie RTCA/D0-160D) require a 20g .011sec sawtooth-profile operational shock test as well as static crash safety criteria. For our general analysis of black-box support structure, we want to relate this shock test to static inertia loads to find the controlling conditon for analysis, not testing. I cannot seam to find any relation between the two searching the net and my old physics book. All I find is harmonic related.

Sadly, I cannot locate my eng vibration text.

Any assistance would be very helpful. Please consider this with a variable mass.

Thanks much,

tony

 

[tomirvine]

Here is an approach:

1. Assume that the structure behaves as a single-degree-of-freedom system.
2. Calculate or measure the natural frequency of the structure.
3. Estimate the damping.
4. Convert the shock pulse into a shock response spectrum, both in terms of acceleration and relative displacement responses.
5. The peak responses of the structural are then taken from the shock response spectra, as a function of the natural frequency.
6. Relate the peak acceleration and peak relative displacement values to some criteria limit, such as ultimate stress, fatigue, etc.

A good reference is:

D. Steinberg, Vibration Analysis for Electronic Equipment.

http://www.amazon.com/exec/obidos/ASIN/047137685X/vibrationdata-20/103-3228561-7171004

Tom Irvine

http://www.vibrationdata.com