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  1. dampit

    Vibration Fatigue

    Vibration fatigue - There are several methods. The simple approach is to generate SN data under Narrow band random condition - i.e generate a Srms vs. Cycle curve. Simply, predict a PSD using a analysis method, calculate the RMS and look up cycle to failure on your RMS Stress vs. cycles to...
  2. dampit

    Multi DOF spec question

    In the aerospace world, we would run a qual-test 600 sec per axis. This usually is adequate unless the failure mode can't be excited in a single axis. Most large shaker tables can be turned over on their sides to excite the x or y direction as well as vertical z-dir. But, there are such things...
  3. dampit

    Constant Displacement v. Grms

    For Sinusodal motion ONLY G = Acceleration in g-units D=inches peak to peak (Double-Amplitude) F=Frequency in Hz G=0.0511 F^2 D Note: Convert this to Grms by Grms = 0.7071 G Grms=(0.0511 / 0.7071) F^2 D = 0.072 F^2 D Converserly, d0 = Peak Displacement = 9.8 G / F^2 (Zero to Peak...
  4. dampit

    random vibration analysis

    RMS Response = sqrt(pi/2 * fn/zeta * PSD), Schiff D. - "Dynamic Analysis and Failure Modes of Simple Structures"
  5. dampit

    Vibration Engineer

    A must for structural engineers is Blevins: Formulas for Natural Frequencies and Mode Shapes, Roarks-Formalus for Stress and Strain, Thomson - Theory of Vibration, Crandalls - Random Vibration, Bendat and Piersol - Random Data, and of course The Shock and Vibration Handbook.
  6. dampit

    Spectrum Analysis; Need help to define the PSD frequency table

    First, do a sine sweep and find the resonant frequencies. 1st Bending mode will be about 6.3 times lower than 2nd bending mode, 3rd will be 17x higher than 1st-B. In a cantilever beam, the response near the tip will be mostly mode 1, but near the root you should see other modes or near the...

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