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Recent content by gio1

  1. gio1

    accelerated vibration test

    Hi Greg I don't have information on the failure of the part, only measured acceleration data on it. The part has never failed in service but I'm trying to achieve a failure on rig through accelerated vibration testing, and I think that using an amplified random vibration based on a measured...
  2. gio1

    accelerated vibration test

    Hello I am planning an accelerated vibration test on a shaker rig, starting from time-history data of measured accelerations. My approach is as follows: - calculate gRMS of measured data - calculate gRMS of profile to be used on rig for a (say) 3x accelerated testing time, using Coffin-Manson...
  3. gio1

    frequency response FEA

    I tried, tried again and then again, but that plot never came back as it was yesterday. I think it was some bug that was affecting the session of the postprocessor I had open. Today (after a reboot) all plots had POSITIVE acceleration magnitude - as I would expect. I was slightly puzzled by...
  4. gio1

    frequency response FEA

    All I have done is choosing the nodal response result "acceleration" and picked a node. What I get is a graph with frequency (Hz) on the X axis and acceleration (mm/s2 - consistently with my units) on the Y axis. I can clearly locate the resonances, but the line goes into negative Y a few times...
  5. gio1

    frequency response FEA

    Hi I have carried out a FE frequency sweep analysis of an assembly using modal superimposition. The assembly is shaken using the same acceleration amplitude across a frequency range along one direction only. When plotting the response (acceleration) Vs frequency for several nodes there are...
  6. gio1

    crush analysis

    At the moment both ends are modelled in the same way, i.e. the only restraint is contact with friction. I will now try to clamp the non-impacted end as suggested by JulianHardy. I had also already planned to run the experiment quasi-statically, as suggested by VoyageofDiscovery. Of course will...
  7. gio1

    crush analysis

    Hello I am doing some dynamic analyses (with Abaqus/Explicit) to correlate the crushing of an extruded aluminum cylindrical tube with experimental results. The tube is mounted around a steel rod (assumed rigid) with no clearance. It is supported rigidly at one end and is impacted at the other...
  8. gio1

    fatigue calculations on shaft in torsion

    Correct me if I am wrong, but I think that sdra's approach is the same as using Von Mises as equivalent stress, as instead of multiplying the principal stress by sqrt(3) (to obtain Von Mises stress) he divides the endurance limit by the same number (1/sqrt(3)=0.577) so effectively the safety...
  9. gio1

    fatigue-sizing a shaft subject to torsion

    Sorry, I think the concentration factor in fatigue is Kf...
  10. gio1

    fatigue-sizing a shaft subject to torsion

    rb1957 Yes this topic has moved to the FEA section, sorry. Your point is interesting, if Petersen used max principal for Kt then it must apply for fatigue (Kt is the concentration factor for fatigue, right?) Thanks Gio1
  11. gio1

    fatigue calculations on shaft in torsion

    The stress cycle is a simple +/- 5 degrees reversed twist (pure torsion) applied on a cantilever shaft. Stresses are very easy to calculate and do not require FEA. Using Tresca as the equivalent fatigue stress (as feajob suggests) is the same as using max/min principal stresses because for pure...
  12. gio1

    fatigue calculations on shaft in torsion

    Note that for pure torsion sigma1=-sigma3, is my stress amplitude 2xsigma1 ?
  13. gio1

    fatigue calculations on shaft in torsion

    Hello Which equivalent stress should I use for fatigue calculations on a shaft subject to pure torsion? Von Mises and Maximum principal differ significantly in this case and give hugely different fatigue lifes. Thanks Gio1
  14. gio1

    fatigue-sizing a shaft subject to torsion

    Hello Which equivalent stress should I use for fatigue calculations on a shaft subject to pure torsion? Von Mises and Maximum principal differ significantly in this case and give hugely different fatigue lifes. Thanks Gio1
  15. gio1

    reaction consuming CO2

    I meant 2 LiOH + CO2 --> Li2CO3 + H2O My concern is that H2O (vapour) is being produced which could rise the pressure - is that true?
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