Learning Forum

[Meisam Jalalvand]

I am setting a question for my 2nd yr Mech Eng students to show them the effect of combined bending moments on asymetic beams and show them how the results of a beam model is compared against solid brick elements and the theory. 

Solid elements give correct deflection and max stress but beam elements, when under combined stress, gives wrong max stress. With another colleague, we guess this is because the location the stress is taken from is wrong but not sure how to change the location of max stress in a beam element. This seems to be something the software should pick automatically. 

The questions is below. If you have any feedback or suggestion, we will apprecaite so we can find the same max stress from all three methods. 

The max stress of 534 MPa occurs at point B shown below. This is because this point has max distance from the neutral axis which is not completely aligned/perpendicular to the sides of the cross sectoin. 

It seems Ansys picks point A to report max stress. So, we found that if we pick point A, Ansys's max stress point is matching analytical method's prediction of stress of 347 MPa. But obviously this is value is not max stress. See belwo. Anysis beam element works fine if the cross section is not tilted and if the load is aligned with one of the sides. 

Any comment or advice will be apprecaite. 

 

[dlooman]

The beam "max combined stress" as described at the link below is the direct stress plus the largest of the four bending stress, sbz_top, sbz_bot, sby_top, sby_bot.  So in your case, it would be the stress at point A, not point B.  The name max combined stress is a little misleading.

 

Beam Tool (ansys.com)

[Meisam Jalalvand]

Thanks very much Dave! This is very helpful! I agree. 'Max' seems a bit misleading!