## General Mechanical

• emoshe
Subscriber

I am trying to run a nonlinear buckling analysis with multi linear isotropic hardening. The loading is just mechanical. The boundary conditions are supposed to simulate clamped-clamped. When I tried using fix supports at the ends of the columns, I kept on getting errors. So I had to treat it as one end with a fixed support and one where there is free displacement movement along the length of the column, to represent a vertical moving roller. Force is applied at the roller end. When I run the simulation, the solutions I am asking for always have red thunderbolts to the left side. How do I get rid of these? I have screenshots attached below; let me know if more are necessary. Also, from researching eigenvalue buckling analysis, I noticed that it gives higher buckling loads than actual buckling loads. I read that the rankine gordon equation, from my understanding, can get closer to experimental data. Is there a way to implement rankine gordon into ANSYS?

• 1shan
Ansys Employee
The red thunderbolt is because the solver is encountering an error. You can find the error under solver output(click on solution information). A structure can become unstable when a load reaches its buckling value or when nonlinear material becomes unstable.Instability problems usually pose convergence difficulties and therefore require the application of special nonlinear techniques. Have a look at - 8.11. Unstable Structures and 8.12. Guidelines for Nonlinear Analysis. Now when you apply a increasing axial axial force, the solver will fail to converge as the load deflection curve approaches a zero value as the structure starts buckling. Load corresponding to this state will be the buckling load. Now, in your case either the load has reached the buckling load or the solver has failed to converge before that. You can check this by observing the slope of load deflection curve. Instead of an axial force you can also insert an axial displacement. In this method the solver doesn't fail to converge. You can see the load increasing, reaching a maxima and then decreasing. Have a look at this
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Also euler and rankin gordon are analytical equations based on certain assumptions that don't consider material/geometric non linearities, geometric imperfections and load pertrubations which are accurately captured by a full nonlinear analysis and will give you the closest results to the experimental data.

Regards Ishan.