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  1. mechanicalFEA

    FFT and IFFT of PSD acceleration and stress

    http://www.ncode.com/fileadmin/mediapool/nCode/downloads/Whitepaper_nCode_frequency_domain_fatigue-Halfpenny.pdf
  2. mechanicalFEA

    FFT and IFFT of PSD acceleration and stress

    Sorry, Inverse fourier transformation? reading this paper 'a frequency domain approach for fatigue life estimation from finite element analysis' by Andrew Halfpenny (ncode) suggest that you can regenerate the time signal via an inverse fourier transformation assuming the PSD was created from...
  3. mechanicalFEA

    FFT and IFFT of PSD acceleration and stress

    Hello, given a test request which specifies a random vibration profile as a PSD and after running a simulation to get a PSD stress, is it possible to simply carry out inverse fft of the responce (nm^2)^2/Hz to get the stress in the time domain (nm^2/s) and then carry out rainflow counting to...
  4. mechanicalFEA

    element vs. nodal (stress)value's

    mesh check through, or mesh convergance is simply a plot of the rate of change of a parameter such as stress, strain or displacent with repect to a mesh larameter such as total number of nodes or elements. it shows how changing the mesh resolution impacts on the result. when there is little...
  5. mechanicalFEA

    Random Vibration cycles

    Hello, When calculating the number of cycles to failure during a random vibration test fatigue calculation based on minors cumulative damage, should you use the first resonant frequency, the frequency which has the larges mass participation or calculate the number of RMS zero crossing points...
  6. mechanicalFEA

    Random Vibration RMS Stress

    Thanks for your inputs, i understand the process to calculate percfent probability and life/cycles etc, after thinking about this i think its clear that FOS is simply calculated by adjusting time to failure, i.e a product must last a duration of a test say 1 hour 10000 cycles = FOS 1. To ensure...
  7. mechanicalFEA

    Random Vibration RMS Stress

    Hi all, Not sure if this is the best place for this post but here we go... How do I account for a factor of safety with RMS stresses abtained from an random vibration FEA analysis using an acceleration Vs frequency PSD excitation input. Is it a simple case of doubling the RMS stress value for...
  8. mechanicalFEA

    Half sine acceleration pulse FEA simuation.

    Greg, i assume the first mode is the mode with the lowest frequency? The displacement results i get from the modal analysis are not representative, nor the stress and strains. i thought modal analysis only tells the user how the part will behave, and at what frequencies are critical to...
  9. mechanicalFEA

    Half sine acceleration pulse FEA simuation.

    Cheers everyone for you responces greg, i have just done a quick modal analysis and found the first frquency to be 83.98Hz which i beleive to be very similar to the frequency of the input half sine wave. (83.333 Hz) Im new to frequency and modal analysis but have tons of experience with...
  10. mechanicalFEA

    Half sine acceleration pulse simulation

    Hello fellow engineers, I am doing some work for an automotive company and need to simulate one of their tests before i send the part of for pv testing, here is the test spec. Test Spec Half sin acceleration pulse. Duration = 6ms (0.006s) peak acceleration = 500ms^2 part to be orientated...
  11. mechanicalFEA

    Half sine acceleration pulse FEA simuation.

    Hello all, I wonder if anyone can help me with a simulation i am having problems with... here is the problem... A flat disc with a central mass is subjected to a shock test. The disk is fixed to a rig which subjects it to a half sine acceleration pulse which lasts for 6ms (0.006s) with a peak...

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