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cyclic loads on a beam

cyclic loads on a beam

cyclic loads on a beam

(OP)
If a beam is to be subjected to a load of, say 20 kN, in a series of 5 cycles, is it sufficient to use a pseudo time-dependent load of the form below,


  ¦
  ¦  /\    /\
  ¦ /  \  /  \   and so on, until 5 cycles
  ¦/ \/    \

OR, loads of +20kN must be followed by -20 kN for 5 cycles,

OR, one has to actually use a displacement-controlled strategy with positive and negative prescribed displacements at the loaded points in the form of,

+5 mm (assuming this would result in a total reaction load of 20 kN), followed by -5 mm,

OR, none of the above is right/appropriate? Any suggestions is highly appreciated.

azmi ibrahim
azmi@civil.engr.itm.edu.my

I'm always keen to learn more to advance
myself in areas that I'm interested in.

RE: cyclic loads on a beam

Your question is not clear.1.Does the load varies from +20KN to -20KN ?if yes,it is correct to  apply the load directly or by giving proper displacement so that the load varies from +20KN to -20kn in each cycle

GoodWishes

RE: cyclic loads on a beam

I, too, do not understand your question. If you already know that 20 kN delivers 5mm displacement and visa versa, then what are you looking for in your FEA? What does 5 cycles have to do with it? If you are looking for stress to evaluate ultra-low cycle fatigue, then wouldn't either input would give you the same answer?

RE: cyclic loads on a beam

If you exibhit yielding in the material then you will notice a differnce with each cycle.  You need to use a plastic material model that captures the bauschinger effect.

If it is not plastic then it will not matter if you have one or 5 cycles.

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