cyclic loads on a beam

[4n4s4n1s]

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,<br><br><br>&nbsp;&nbsp;¦<br>&nbsp;&nbsp;¦&nbsp;&nbsp;/\&nbsp;&nbsp;&nbsp;&nbsp;/\<br>&nbsp;&nbsp;¦ /&nbsp;&nbsp;\&nbsp;&nbsp;/&nbsp;&nbsp;\&nbsp;&nbsp;&nbsp;and so on, until 5 cycles<br>&nbsp;&nbsp;¦/ \/&nbsp;&nbsp;&nbsp;&nbsp;\<br><br>OR, loads of +20kN must be followed by -20 kN for 5 cycles,<br><br>OR, one has to actually use a displacement-controlled strategy with positive and negative prescribed displacements at the loaded points in the form of,<br><br>+5 mm (assuming this would result in a total reaction load of 20 kN), followed by -5 mm,<br><br>OR, none of the above is right/appropriate? Any suggestions is highly appreciated. <p>azmi ibrahim<br><a href=mailto:azmi@civil.engr.itm.edu.my>azmi@civil.engr.itm.edu.my</a><br><a href= > </a><br>I'm always keen to learn more to advance<br>
myself in areas that I'm interested in.

 

[brc01]

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

 

[DarrellW]

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?

 

[FeaGuru]

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.